عینک eyewear

Cataract surgery is a procedure to remove the lens of the eye and, in most cases, replace it with an artificial lens. A cataract causes the lens to become cloudy when it is typically clear. Cataracts can eventually affect vision. Cataract surgery is performed by an eye doctor, also called an ophthalmologist.

Cataract surgery replaces the cloudy lens inside the eye with an artificial lens. Cataracts are common as you age, and surgery is usually safe and effective. Depending on your replacement lens, you may need glasses after cataract surgery.

It's normal to have:

• grittiness
• watering
• blurred vision
• double vision
• a red or bloodshot eye

These side effects usually improve within a few days, but it can take 4 to 6 weeks to recover fully.

For the first few weeks after surgery:

Do:

• use your eye drops as instructed
• take it easy for the first 2 to 3 days
• use your eye shield at night for at least a week
• take painkillers if you need to
• bathe or shower yourself as usual
• wear your eye shield when washing your hair
• read, watch TV and use a computer
• use your shield, old glasses or sunglasses outdoors
• avoid swimming for 4 to 6 weeks

What should you not do after a cataract operation?

Don't:

• do not rub your eyes.
• do not allow soap or shampoo to get into your eye.
• do not drive until you get the all-clear from your doctor.
• do not do any strenuous exercise or housework.
• do not wear eye make-up for at least 4 weeks.
• do not fly without seeking advice from your doctor.

Which glasses are best after cataract surgery?

Polarized lenses – Shop for cataract surgery sunglasses with polarized lenses, which reduce glare and are especially good for driving, says Dr. Khan. “They're going to give you a crisper image, and that comes in handy any time clarity of vision is important,” she says.

Who needs glasses after cataract surgery?

The lens is a curved piece of clear tissue in your eye. Situated behind your pupil, it changes the way light enters your eye and helps you focus your vision at different distances.

Cataract surgery involves replacing the lens in your eye with an artificial replacement called an intraocular lens (IOL). Whether you’ll need glasses after cataract surgery largely depends on what type of IOL you get.

There are many IOL options. Take the time to talk with your eye surgeon beforehand so that you make the choice that’s right for you

The main types of IOLs include:

• Monofocal: Monofocal IOLs are the most common, and also the only IOL that is usually covered by Medicaid and private health insurance. They focus at only one distance, either close, far, or intermediate range. Most people get them for distance vision.
• Multifocal: Multifocal IOLs provide both distant and near focus at the same time. They contain different zones, shaped like concentric rings, that allow you to focus on objects far away as well as objects close up.
• Extended depth of focus: Extended depth of focus IOLs have only one corrective zone. This zone is stretched to allow distance and intermediate vision.
• Accommodative: Accommodative IOLs change shape like your eye’s natural lens to allow you to focus at different distances.
• Toric: Toric IOLs correct astigmatism, a vision issue that’s caused by an irregularly shaped cornea.
• Light-adjustable lens (LAL): This newer type of IOL is the only one that can be customized after surgery. Adjustments are done through a series of office-based light treatment procedures.

How long should you wait before getting new prescription glasses after cataract surgery?

It’s important to wait for your eyes to fully heal and your vision to stabilize before getting a new prescription. Eye doctors often recommend waiting around 6 weeks after your surgery before having your eyes tested and getting new glasses.

Are there any signs that indicate you need new glasses?

It’s typical to have some blurriness and trouble seeing for a few days after cataract surgery. If you notice persistent changes to your vision, you may need to change your prescription.

Some vision changes you might notice include:

• blurry vision
• squinting a lot
• tired eyes
• frequent headaches
• light sensitivity

How do you know which glasses are right for you?

After you’ve healed from your cataract surgery, your eye doctor will perform an updated refraction to determine which eyeglass prescription is best for you. It’s most common that people who undergo cataract surgery will need reading glasses after their vision has stabilized.

CME (Cystoid macular edema) is the most frequent complication after an uncomplicated cataract surgery.

What are the negatives of cataract surgery?

Is there a downside to having cataract surgery? While generally safe and effective, cataract surgery carries risks like any surgery, including infection, swelling, and vision issues. However, serious complications are rare.

Reference:

• healthline.com/health/eye-health/glasses-after-cataract-surgery#when-glasses-are-needed
• glaucoma.org/articles/premium-intraocular-lenses-iols-for-patients-with-glaucoma
• practiceplusgroup.com/knowledge-hub/risks-benefits-cataract-surgery
• eyewiki.org/Cataract_Surgery_Complications
• nhs.uk/conditions/cataract-surgery/recovery

See also:

• Recovery - Cataract surgery
• What food not to eat after cataract surgery?
• How many days rest is required after cataract surgery?
• What are red flags after cataract surgery?

What are betamethasone eye drops used for? [1]

Betamethasone eye drops are used to treat short-term inflammatory eye conditions. They are usually prescribed by an eye specialist. They contain a corticosteroid (sometimes called a 'steroid') which helps relieve inflammation, redness and irritation.

Betamethasone Drops contain Betamethasone Sodium Phosphate which belongs to a group of medicines called corticosteroids. These are used to relieve redness and swelling. Betamethasone Drops are used to treat redness and swelling of the eyes, nose and ears.[2]

What is betamethasone and neomycin eye drop used for?

This medicine is used to reduce inflammation (redness, soreness and itching) of the eye when there may also be a risk for bacterial infection.[3]

What is betamethasone made of?

The formula for betamethasone acetate is C24H31FO6 and it has a molecular weight of 434.50. Chemically, it is 9-Fluoro-11β,17,21-trihydroxy-16β-methylpregna-1,4-diene-3,20 dione 21-acetate.[5]

• قطره چشم بتامتازون (Betamethasone Eye Drops) یک داروی ضد التهابی است که به دسته داروهای کورتیکواستروئید تعلق دارد.
• این دارو برای کاهش التهاب، قرمزی، درد، خارش، سوزش و تورم چشم‌ها تجویز می‌شود.
• بتامتازون چشمی با سرکوب سیستم ایمنی و کاهش تولید موادی که موجب التهاب می‌شوند، علائم را تسکین می‌دهد.
• بتامتازون برای درمان علائم شبیه سرماخوردگی ناشی از آلرژی‌ها در چشم‌، ورم (التهاب) داخل بینی و قرمزی و تحریک در چشم‌ها، گوش‌ و بینی استفاده می‌شود. بتامتازون نوعی داروی کورتیکواستروئیدی است که فقط با نسخه پزشک در دسترس است و برای بزرگسالان، کودکان و نوزادان بالای یک ماه توصیه می‌شود.
• قطره بتامتازون چشمی برای کنترل التهابات چشمی ناشی از آلرژی، عفونت‌ها و پس از اعمال جراحی چشم مانند لیزیک تجویز می‌شود و قرمزی، خارش و ناراحتی در چشم را کاهش و علائم ناشی از بیماری‌های التهابی را تسکین می‌دهد. از عوارض جانبی این دارو می‌توان به سوزش موقت، تاری دید و احتمال افزایش فشار داخل چشم اشاره کرد.
• قطره بتامتازون برای خارش چشم به عنوان کورتیکواستروئید عمل می‌کند و علائم خارش، قرمزی و سوزش چشم‌ها را تسکین می‌دهد. استفاده از قطره بتامتازون برای خارش چشم به این صورت است که پزشک توصیه می‌کند که معمولا بایستی ۱ یا ۲ قطره در چشم مبتلا بریزید.

• قبل از مصرف هر دارویی به موارد منع مصرف آن توجه داشته باشید و اگر بیماری خاصی دارید به پزشک اطلاع دهید. موارد احتیاط و منع مصرف قطره بتامتازون شامل موارد زیر است:

• حساسیت
• در صورت وجود عفونت‌های ویروسی، باکتریایی یا قارچی در چشم
• افراد با اختلالات سیستم ایمنی
• سابقه گلوکوم
• دوران بارداری و شیردهی با تجویز و مشورت پزشک

• در صورت فراموشی مصرف قطره بتامتازون چه کنیم؟

  اگر یک نوبت مصرف را فراموش کردید، به محض یادآوری، آن را مصرف کنید، مگر اینکه زمان نوبت بعدی رسیده باشد.

What is ofloxacin betamethasone eye drops for? [4]

Betamethasone + Ofloxacin is used to treat bacterial infections and inflammation of the eye/ear.

• Do not skip any doses and finish the full course of treatment even if you feel better.
• Stopping it early may make the infection come back and harder to treat.
• Do not touch the tip to any surface to avoid contamination.

نکاتی که قبل از مصرف قطره چشمی بتامتازون باید در نظر گرفته شود

• بعضی داروها را نمی‌توان در بعضی از شرایط تجویز نمود و بعضی داروها نیز در صورتی که نیاز به درمان تکمیلی باشد تجویز می‌گردد. بنابراین بهتر است که قبل از مصرف این قطره ، پزشکتان از موارد زیر مطلع باشد:
• در صورتی که تاکنون به قطره‌های چشمی حساسیت داشته‌اید.
• در صورتی که فکر می‌کنید دچار عفونت چشمی شده‌اید.
• در صورتی که از لنزهای تماسی چشم استفاده می‌کنید.
• در صورت حاملگی و یا در صورتی که به نوزاد خود شیر می‌دهید.
• اگر از سایر داروها استفاده می‌کنید. این داروها شامل تمام داروهای در دسترس است، چه برایتان تجویز شده است و چه بدن تجویز پزشک آن را مصرف می کنید نظیر داروهای گیاهی و داروهای مکمل.

What does betamethasone do to the eye? [3]

Betamethasone may cause your vision to be temporarily blurred. If affected, do not drive or take part in any activity in which you need to see clearly. Other side effects include any of the following: drooping of the eyelid, dilation of the pupil, and swelling or redness of the outer surface of the eye.

This medicine may also cause certain reactions such as irritation, tingling or stinging sensation, and itching.
These reactions may not appear until some time after you have started using the drops or ointment.

Some side effects may need immediate medical help.Alert your doctor quickly if you experience any of the following:

• Clouding of the eye lens
• Pain in the eyes, blurred vision that does not improve after a few minutes.

Do not use Betamethasone Drops if you are: [2]

• allergic (hypersensitive) to Betamethasone Sodium Phosphate or to any of the other ingredients of this medicine.

Do not use in your eyes if you:

• have a viral infection of the eye
• have a fungal infection of the eye
• have tuberculosis of the eye
• have an eye infection that is producing pus
• suffer from raised pressure in your eye(s) (glaucoma)
• suffer from herpes in your eye(s)
• have undiagnosed red eye(s)
• are wearing soft contact lenses. These should be removed whilst you are using Betamethasone Drops.

بهترین زمان مصرف قطره بتامتازون بستگی به نوع مشکل و دستور پزشک دارد. به‌طور کلی، توصیه می‌شود که این قطره‌ها در زمان‌های مشخصی از روز استفاده شوند تا اثربخشی آن‌ها بیشتر شود. برای درمان التهاب یا علائم آلرژیک، معمولا بهتر است قطره‌ها در زمان‌هایی استفاده شوند که علائم بیشتر باشند، برای مثال صبح‌ها وشب‌ها.

Reference:

1. patient.info/medicine/betamethasone-eye-drops-betnesol-vistamethasone
2. medicines.org.uk/emc/product/3395/pil#gref
3. mims.com/singapore/drug/info/betamethasone/patientmedicine/betamethasone%2B-%2Bophthalmic#
4. 1mg.com/generics/betamethasone-ofloxacin-400531
5. accessdata.fda.gov/drugsatfda_docs/label/2008/014602s047lbl.pdf

The anterior segment of the eye is composed of the conjunctiva, cornea, anterior chamber, and iris. Behind the iris, actually visible through the pupil, lies the lens. The ciliary body is a doughnut shaped muscle behind the base of the iris that functions in accommodation and secretes the aqueous.

Anterior segment optical coherence tomography (AS‐OCT) has become one of the cornerstones of non‐contact imaging modalities for assessing such structures as the cornea, anterior chamber angle, aqueous outflow pathway, sclera, and ocular surface structures.

(A) AS-OCT image captures the anterior segment region of the eye, including cornea, iris, ciliary body and lens. (B) Open angle. (C) Angle- closure.

What does anterior eye mean?

The word anterior means front, and the anterior chamber is named after its location at the front of your eye. It holds a clear fluid called aqueous humor. While this small chamber and the clear liquid inside it might not seem all that important, it's actually a critical structure and plays a key role in your vision.

• قدامی (anterior) == جلویی، پیشین ( پیش یعنی جلو )
• خلفی (posterior) == عقبی، پسین ( پس یعنی عقب )

What does the anterior chamber do?

The structure of your eyes is a key part of how they work, and the anterior chamber is one of the most important structures.

If you’ve ever used a magnifying lens, you know that the distance between what you’re looking at, the lens and your eye all have to be just right to get the sharpest view. It’s the same for your eyes. Your corneas must be the right distance from your lens and retina.

This is why the anterior chamber is so important. The fluid inside the anterior chamber creates internal pressure (intraocular pressure) that keeps your eyeball “inflated.” That’s how the cornea stays at the right distance to do its part in focusing light.

How aqueous humor travels through the anterior chamber?

When everything is working as it should, the parts of your eye work together to maintain the right balance of aqueous humor in your anterior chamber. This fluid does more than provide internal pressure so that your eyeball keeps its shape. It also carries oxygen and nutrients, and plays a part in your eye’s immune defenses. The fluid in the anterior chamber contributes to the pressure in your eye. Too much or too little pressure may lead to eye damage.

Here’s how the aqueous humor gets to and leaves your anterior chamber:

• Your ciliary body makes aqueous humor.
• It flows into your posterior chamber. This is a small, fluid-filled space behind your iris.
• The fluid flows through your pupil, which opens to your anterior chamber.
• Most of the aqueous humor exits your anterior chamber through the drainage angle. This is near the outer rim of your anterior chamber, where your iris and the outer wall (sclera) of your eye meet.
• The fluid goes into a drainage network called the trabecular meshwork.

Eventually, the aqueous humor moves into the veins in your sclera where it merges with your blood.

The anterior segment or anterior cavity is the front third of the eye that includes the structures in front of the vitreous humour: the cornea, iris, ciliary body, and lens.

Within the anterior segment are two fluid-filled spaces:

1. the anterior chamber between the posterior surface of the cornea (i.e. the corneal endothelium) and the iris.
2. the posterior chamber between the iris and the front face of the vitreous.

Aqueous humour fills these spaces within the anterior segment and provides nutrients to the surrounding structures.

Some ophthalmologists and optometrists specialize in the treatment and management of anterior segment disorders and diseases.

Three chambers of fluid:

• The Anterior chamber (between cornea and iris)
• The Posterior chamber (between iris, zonule fibers and lens)
• The Vitreous chamber (between the lens and the retina).

Diagram of anterior segment of a human eye (horizontal section of the right eye)
1. Lens, 2. Zonule of Zinn or ciliary zonule, 3. Posterior chamber 4. Anterior chamber 5. Aqueous humour flow; 6. Pupil, 7. Corneosclera 8. Cornea, 9. Trabecular meshwork and Schlemm's canal. 10. Corneal limbus 11. Sclera; 12. Conjunctiva, 13. Uvea 14. Iris, 15. Ciliary body.

Reference:

• catalyzex.com/paper/angle-closure-detection-in-anterior-segment
• my.clevelandclinic.org/health/body/anterior-chamber
• aao.org/education/image/anterior-segment-anatomy-2
• en.wikipedia.org/wiki/Anterior_segment_of_eyeball
• tandfonline.com/doi/full/10.1111/cxo.12869
• ncbi.nlm.nih.gov/books/NBK11534
• know-the-eye.com

The normal oculocephalic reflex, also known as the Doll's Eye Reflex, is a neurological response that occurs when an individual's head is turned quickly in one direction. In this reflex, the eyes move in the opposite direction of the head movement, which is essential for maintaining stable visual fixation on a target. For instance, when the head is turned to the right, the eyes should move to the left to counteract the head's motion, allowing the person to maintain a clear and stable view of the environment.

This reflex is a crucial part of our everyday activities and plays a fundamental role in spatial orientation and balance. It is also vital for activities that require tracking objects or staying focused on a specific point while in motion.

A healthy and intact oculocephalic reflex is a normal response that helps ensure proper coordination between head and eye movements, contributing to overall neurological health and function. When assessing patients, medical professionals look for the presence of a normal oculocephalic reflex to determine the integrity of brainstem function and to rule out potential neurological issues.

What is the Oculocephalic Reflex and how do you use it?

This reflex is brainstem mediated and keeps the eyes looking straight ahead when the head is turned, in an unconscious patient. It’s a test to use on the unconscious patient to see if the brainstem is intact.

The best way to remember this is by thinking of doll’s eyes. It is in fact called the doll’s eye reflex. The old dolls used to have the eyes painted on, so that when you turned the head, the eyes moved with the head. This would indicate that the brainstem was not intact. The more modern dolls have eyes that move back towards the centre, when the head is turned.

The reflex is mediated by three cranial nerves VIII, III and VI.

When the head is turned to one side, the semicircular canals pick up this movement and send a signal via CN VIII to the medial vestibular nucleus, which then sends a signal via the ipsilateral CNIII to the medial rectus muscle and via the contralateral CNVI to the lateral rectus muscle. So when the head is turned to one side, the eyes move in the opposite direction to face the centre.

The way to perform this test in the unconscious patient, is to hold the head(assuming no cervical injury), with eyes held open. The head is turned rapidly to one side. The eyes will move in a smooth motion to the centre, i.e.., looking forward. If they do not and continue to look sideways; it indicates that the brainstem is not intact ie., a possible poor outcome.

Checking for oculocephalic reflex:

Hold her eyelids open with the thumb and index finger of one hand so you can watch her eyes. Briskly but gently rotate her head from side to side and assess her eye movements. A normal response is for the eyes to move in the direction opposite the head movement, such as looking left as you turn her head to the right.

What does a positive oculocephalic reflex mean?

A positive doll's eye reflex (eyes move in opposite direction of head movement) indicates an intact brainstem. A negative doll's eye reflex (eyes remain midline or move in same direction of head movement) indicates severe brain stem dysfunction. These results only apply to patients who are comotose.

What is the Oculocephalic deviation?

Oculocephalic Reflex or the Doll's Eyes Phenomenon. Sometimes a person has a reflex deviation of the apples of the eye to one side. This anomaly, which occurs when the patient tries to turn their head vertically or horizontally, is called an oculocephalic reflex.

In which patient is oculocephalic reflex testing contraindicated?

Contraindications to the test include rupture of the tympanic membrane. Drugs including sedatives, aminoglycoside antibiotics, tricyclic antidepressants, and some antiseizure agents can diminish the oculocephalic and vestibulo-ocular reflexes.

What nerve is tested in the oculocephalic reflex?

The oculocephalic reflex (doll's eyes reflex) is an application of the vestibular-ocular reflex (VOR) used for neurologic examination of cranial nerves 3, 6, and 8, the reflex arc including brainstem nuclei, and overall gross brainstem function.

When does the doll's eye reflex disappear?

age 11.5 weeks

Conclusions: The oculocephalic reflex is suppressed in the vast majority of normal infants by age 11.5 weeks. The disappearance of the reflex occurs gradually and longitudinally and is part of the normal maturation of the visual system. eResearch by Navid Ajamin -- winter 2024

What causes a doll's eye reflex?

Oculocephalic reflex is caused by quickly turning and briefly holding the patient's head to the right, then to the left, and unbending and bending the neck. In this case, the eyes deviate in the opposite direction (for example, when turning the head to the left, the eyes deviate to the right).

Video:

• Doll's eye reflex
• Oculocephalic Reflex
• Doll's eye reflex in comatose patient
• Doll’sEyeReflex / Vestibulo Ocular reflex
• Oculocephalic Reflex Testing During Brain Death

Reference:

• ophthalmologybreakingnews.com/the-dolls-eye-reflex--exploring-a-vital-neurological-assessment
• journals.lww.com/nursing/citation/2005/06000/checking_for_oculocephalic_reflex.16.aspx
• sciencedirect.com/topics/medicine-and-dentistry/caloric-reflex-test
• nursingcenter.com/ncblog/october-2022/dolls-eyes
• lonestarneurology.net/blog/oculocephalic-reflex
• resus.com.au/the-oculocephalic-reflex
• pubmed.ncbi.nlm.nih.gov/31869180
• pubmed.ncbi.nlm.nih.gov/20450249

See also:

• Oculocephalic and oculovestibular reflexes
• Unilateral loss of oculocephalic response in a patient with hemispheric cerebral hemorrhage

Double vision is usually a temporary issue, but it can also be a sign of more serious health conditions. Health conditions that affect your eyes are the most common diplopia causes.

symptoms and Causes of Diplopia

Diplopia can occur in various forms and is categorized into several types based on different factors. Here are some of the different types of diplopia:

1. Monocular Diplopia:
This type of diplopia occurs when the double vision is present in one eye only. Double vision in one eye typically suggests a problem within the eye itself rather than an issue with the alignment of the eyes. Causes may include astigmatism, cataracts, corneal irregularities, or abnormalities in the lens.

2. Binocular Diplopia:
Binocular diplopia refers to double vision that occurs when both eyes are open. Double vision in both eyes is usually due to misalignment or coordination problems between the two eyes, resulting in the images from each eye not merging properly in the brain. Binocular diplopia can be caused by various conditions such as cranial nerve palsies, muscle weaknesses, strabismus (misalignment of the eyes), or nerve disorders.

3. Horizontal Diplopia:
Horizontal diplopia is characterized by double vision horizontally, where the two images appear side by side. It is often associated with muscle imbalances or weaknesses in the muscles responsible for horizontal eye movement, such as the lateral rectus and medial rectus muscles.

4. Vertical Diplopia:
Vertical diplopia involves double vision vertically, with the two images appearing one above the other. It is commonly associated with imbalances or weaknesses in the muscles responsible for vertical eye movement, such as the superior rectus and inferior rectus muscles. Conditions like thyroid eye disease or trauma to the eye muscles can lead to vertical diplopia.

5. Intermittent Diplopia:
Vertical diplopia involves double vision vertically, with the two images appearing one above the other. It is commonly associated with imbalances or weaknesses in the muscles responsible for vertical eye movement, such as the superior rectus and inferior rectus muscles. Conditions like thyroid eye disease or trauma to the eye muscles can lead to vertical diplopia.

6. Comitant Diplopia:
Comitant diplopia refers to double vision in which the separation between the two images remains constant, regardless of the direction of gaze. It suggests that the misalignment of the eyes is equal in all directions of gaze and typically points to a problem with the eye muscles or their control.

7. Incomitant Diplopia:
Incomitant diplopia occurs when the separation between the two images changes depending on the direction of gaze. The degree of misalignment varies, indicating an underlying condition affecting the extraocular muscles or nerves. Incomitant diplopia can be caused by conditions such as oculomotor nerve palsy, cranial nerve palsies, or orbital disorders.

This is when double vision occurs in only one eye. This means that the doubling does not go away even when you cover the other eye or look in different directions.

Lots of eye problems can cause double vision.

Anything that affects your brain, your eyes or the nerves and muscles that control them can lead to diplopia.

What are the causes?

1. Astigmatism. This is a condition where the front surface of the cornea is abnormally curved hence causing double vision.
2. Keratoconus. Keratoconus is a degenerative condition that causes the cornea to gradually become cone-shaped and thin.
3. Pterygium. This is thickening and hardening of the conjunctiva causing it to extend to the cornea and cause double vision.
4. Dry eyes.The eye dries out too quickly or does not produce enough tears.
5. Retinal abnormalities. For example, in macular degeneration, the centre of the field of vision gradually disappears, and if there’s swelling, double vision can occur in one eye.
6. Cataracts. Cataracts in the eyes can also cause diplopia in one eye.
7. Poorly-fitting glasses or contacts.
8. Migraines.
9. Abnormalities in your iris (the colored part of your eye).
10. Proptosis (bulging eyes).
11. Head injuries.
12. Cranial nerve issues.
13. Nearsightedness (myopia).
14. Farsightedness (hyperopia).

Diplopia risk factors

Anyone can experience double vision, but it’s most common in adults older than 60.

Having certain neurological or other health conditions can increase your risk, including:

• Myasthenia gravis.
• Vertigo.
• Brain aneurysms.
• Strokes.
• Diabetes (including diabetes-related retinopathy).
• Vitamin B1 deficiency.
• Thyroid disease.
• Multiple sclerosis (MS).

Reference:

• amblyoplay.com/what-is-diplopia-or-double-vision
• binettereyecentre.com.au/2019/09/20/what-causes-double-vision

Coma and astigmatism

Both image errors systemically appear on the regularly curved surfaces of spherical lenses and cannot be avoided in the first place. Coma is caused by obliquely inciding parallel rays of light on a spherical lens, astigmatism is caused by obliquely inciding diverging rays of light on the spherical surface.

Both errors can primarily be corrected by sophisticatedly combining several lenses and using aspheric lenses. The technical effort required for the correction is also reflected by the lens prices.

Coma (asymmetry error)

If a collimated ray ("parallel" light) incides on a lens not in parallel but at an angle to the optical axis, the ray will pass through the optic system in an unsymmetrical way due to different surface curvatures. In case of this imaging error, the rays are not bundled again in one image point. The focal points are therefore also not on the optical axis, but shifted towards the margin. In the image this error is visible as a drop-shaped, tail-like unilateral distortion of an image spot. The tail is always outwards in radial direction. Coma is caused by spherical aberration.

Assymetric error of lens (coma)

The user has the possibility to suppress this error by stopping down. The resulting artificial vignetting avoids rays inciding unsymmetrically on the lens close to the edge. Good lenses can avoid this error by means of a clever lens design.

Astigmatism (dotlessness)

If a diverging ray of light incides vertically on the lens surface and thus passes unsymmetrically to the optical axis, astigmatism occurs on spherical lens surfaces.

For easier examination, the inherently cone-shaped beam can be divided into two planes perpendicular to each other. (Both are approximately oriented towards the main beam which passes through the centre of the aperture, the meridional beam extends towards the optical axis, the sagittal beam is at right angles to it.

Meridional and sagittal ray

The reasons for astigmatism in case of oblique rays of light are the different local curvature radii of the latitudinal circles compared to the larger constant curvature radius of the meridional plane on the lens surface. The results are two different focal points and focal lengths for the different (meridional and sagittal) partial optical paths.

Creation of astigmatism

The image spot is no longer a dot, but reproduced in the form of two lines. It no longer seems to be sharp, but dotless. The camera image is not sharply focused for the viewer. This error can be suppressed by means of special lens types.

What causes coma in optics? eResearch by Navid Ajamin -- autumn 2024

Coma, so called because a point image is blurred into a comet shape, is produced when rays from an off-axis object point are imaged by different zones of the lens.

Coma is an aberration which causes rays from an off-axis point of light in the object plane to create a trailing "comet-like" blur directed away from the optic axis (for positive coma). A lens with considerable coma may produce a sharp image in the center of the field, but become increasingly blurred toward the edges. For a single lens, coma can be partially corrected by bending the lens. More complete correction can be achieved by using a combination of lenses symmetric about a central stop.

What are Aberrations of the Eye?

Described as small optical irregularities, aberrations are imperfections of the eye that result in light being unable to focus onto the retina effectively as well as defects in visual image. There are two types of aberrations; lower-order aberrations (0, 1st and 2nd order), and higher-order aberrations (3rd,4th…).

Higher Order Aberrations

Higher order aberrations (HOAs) of the eye are unable to be corrected by cylinder or spherical corrections and include spherical aberrations, coma and trefoil.

Coma Aberrations

Coma aberrations are caused when light rays from one edge of the pupil focuses before those from the opposing edge. Visually those with this type of aberration may experience smearing of an image so that images may appear to have a tail like a comet.

Trefoil Aberrations

Classed as a third order aberration, trefoil has a more minor affect on image quality compared to an equal amount of coma.

Spherical Aberrations

Spherical aberrations can cause halos surrounding point light sources and a reduction in contrast sensitivity.

It is thought that HOAs are responsible for individuals reporting complaints of glare, halos and reduction in contrast sensitivity following corneal refractive surgery. Approximately 90% of aberrations are caused by the cornea.

The eyes of young people tend to be less affected by higher order aberrations due to the partial compensation of aberration between the surface of the cornea and the internal optics. This mechanism has been found to work systematically for spherical aberrations and horizontal comas. As they are only affected by a small number of spherical aberrations and comas, young eyes are thought to approximate to an aplanatic optical system. However, as we age, more aberrations occur on average, specifically spherical aberrations as well as horizontal comas.

Lower Order Aberrations

Lower order aberrations include astigmatism, positive defocus (myopia), and negative defocus (hyperopia).

Astigmatism

Those with astigmatism have an eye that is shaped like a rugby ball than rather football. As a result, light tends to be focused at more than one place in the eye, causing blurry vision, eye strain and headaches. It is usually accompanied by short or long-sightedness.

Reference:

• vision-doctor.com/en/optical-errors/coma-and-astigmatism.html
• news-medical.net/health/What-are-Aberrations-of-the-Eye.aspx
• exposuretherapy.ca/photography-guide/lens-aberrations-and-distortion
• visiondirect.com.au/optical-centre/eye-care/what-causes-distorted-vision

See also: Combining coma with astigmatism can improve retinal image over astigmatism alone

What is retinoschisis?

Retinoschisis is a condition that happens when your retina divides into two or more layers. Schisis means a split or a cleft. Retinoschisis affects the light-sensing layer of your retina and the layer of cells that transmits signals to your brain through the optic nerve.

This division of the layers can affect how well you see. Splits can occur in the center of the retina but are more likely at the periphery (outer edges).

What are the signs and symptoms of retinoschisis?

You may have no symptoms of the disease. If you do, symptoms that may happen with juvenile X-linked retinoschisis include:

• Eyes that turn toward your nose (crossed eyes).
• Eyes that move uncontrollably from one side to the other (nystagmus).
• Loss of central (foveal) vision or side (peripheral) depending on where the split occurs.
• Having farsightedness.

If you’ve developed acquired retinoschisis, you might find that you can’t see clearly on either side (loss of peripheral vision). You may not have any symptoms at all.

If you have retinoschisis and it becomes severe, or you also have retinal detachment, you may notice:

• Floaters and flashers.
• Distorted images.
• Loss of central (foveal) vision or side (peripheral) depending on where the split occurs.

Are X-linked disorders male or female?

X-linked recessive diseases most often occur in males. Males have only one X chromosome. A single recessive gene on that X chromosome will cause the disease. The Y chromosome is the other half of the XY gene pair in the male.

Patterns of inheritance

Patterns of X-linked recessive inheritance in a royal family

In humans, inheritance of X-linked recessive traits follows a unique pattern made up of three points.

• The first is that affected fathers cannot pass X-linked recessive traits to their sons because fathers give Y chromosomes to their sons. This means that males affected by an X-linked recessive disorder inherited the responsible X chromosome from their mothers.
• Second, X-linked recessive traits are more commonly expressed in males than females.This is due to the fact that males possess only a single X chromosome, and therefore require only one mutated X in order to be affected. Women possess two X chromosomes, and thus must receive two of the mutated recessive X chromosomes (one from each parent). A popular example showing this pattern of inheritance is that of the descendants of Queen Victoria and the blood disease hemophilia.
• The last pattern seen is that X-linked recessive traits tend to skip generations, meaning that an affected grandfather will not have an affected son, but could have an affected grandson through his daughter. Explained further, all daughters of an affected man will obtain his mutated X, and will then be either carriers or affected themselves depending on the mother. The resulting sons will either have a 50% chance of being affected (mother is carrier), or 100% chance (mother is affected). It is because of these percentages that we see males more commonly affected than females.

X-Linked Retinoschisis (XLRS)

A rare disorder involving multiple structure of the eye characterized by reduced visual acuity in males due to juvenile macular degeneration. Clinical features such as vitreous hemorrhage, retinal detachment, and neovascular glaucoma can be observed in advanced stages.

X-linked Retinoschisis or X-Linked Juvenile Retinoschisis is a rare congenital disease of the retina caused by mutations in the RS1 gene, which encodes retinoschisis, a protein involved in intercellular adhesion and likely retinal cellular organization.

X-linked retinoschisis, with a prevalence of about 1 in 15,000 to 30,000, is one of the main causes of juvenile macular degeneration in males. It is characterized by symmetric bilateral macular involvement beginning in the first decade of life.

It is caused by a large variety of mutations in the RS1 gene on Xp22.1-p22.3, which encodes the protein retinoschisis. This protein is involved in intercellular adhesion and likely retinal cellular organization. X-linked retinoschisis is inherited in an X-linked manner with complete penetrance and variable expressivity.

Most affected individuals are males, as heterozygous females are rarely affected. However, retinoschisis has been reported in non-consanguinous females. The phenotype can be markedly variable even within the same genotype and can involve the peripheral retina.

Reference:

• educate.choroida.com/2023/02/03/x-linked-retinoschisis-genetics-and-management
• my.clevelandclinic.org/health/diseases/24310-retinoschisis
• fightingblindness.org/diseases/x-linked-retinoschisis-xlrs
• en.wikipedia.org/wiki/X-linked_recessive_inheritance
• medlineplus.gov/ency/article/002051.htm

A problem in any part of the eye can cause sudden blurry vision, but when present in only one eye, it may be a medical emergency. It should be evaluated and treated by a physician as soon as possible — to prevent permanent damage and vision loss.

Sudden blurry vision may be the body’s warning about a serious health problem. Prompt medical treatment can lead to the best possible outcome.

The following warning signs may be an indication of a serious eye problem. If you experience even one of these, seek emergency medical services immediately for evaluation and treatment:

• sudden unexplained change in your vision (e.g., blurred vision)
• eye pain
• eye injury
• signs of a stroke, such as a facial droop, one-sided weakness, or difficulty speaking
• marked vision impairment — especially if only in one eye
• loss of one aspect of the visual field
• sudden blurred vision secondary to a weakened immune system due to conditions like HIV or chemotherapy treatment

Reference: Sudden Blurry Vision: Potential Medical Emergency (assileye.com)

Preeclampsia and eclampsia are complications of pregnancy. The nurse plays a vital role in helping detect these conditions. Therefore, it’s important to know how to detect this condition in a pregnant patient.

The hormonal changes associated with pregnancy can impact a variety of things, including vision. In some cases, pregnant women may experience blurred vision as a result of high blood pressure. If vision loss is significant, this could be a sign of a serious health issue called preeclampsia. Typically occurring late in pregnancy, this condition can put both mother and child at serious risk if not treated. If you are pregnant and experiencing any significant vision problems, consult with your doctor immediately.

Blurred vision is the most common visual complaint. Focal or generalized arteriolar narrowing is the most common ocular finding in preeclampsia/eclampsia syndrome. Other ocular manifestations include photopsia, visual field defects, sudden inability to focus, and in severe cases, complete blindness.

The preeclampsia/eclampsia syndrome is a multisystem disorder that can include cardiovascular changes, hematologic abnormalities, hepatic and renal impairment, and neurologic or cerebral manifestations. It also can affect the eye and visual pathways. Visual symptoms concern up to 25% of patients with severe preeclampsia and 50% of patients with eclampsia. This review discusses the ophthalmic complications of preeclampsia/eclampsia with focus on the hypertensive retinopathy, exudative retinal detachment and cortical blindness.

How common is preeclampsia?

Preeclampsia is a condition unique to pregnancy that complicates between 5% and 8% of all births in the United States. It’s also the cause of about 15% of premature deliveries (delivery before 37 weeks of pregnancy) in the U.S.

Preeclampsia is a serious medical condition that can occur about midway through pregnancy (after 20 weeks). People with preeclampsia experience high blood pressure, protein in their pee, swelling, headaches and blurred vision. But you may have no symptoms.

Treatment is necessary to avoid life-threatening complications. It typically goes away after childbirth.

Preeclampsia is a serious blood pressure condition that develops during pregnancy. People with preeclampsia often have high blood pressure (hypertension) and high levels of protein in their urine (proteinuria). Preeclampsia usually develops after the 20th week of pregnancy.

Preeclampsia can also affect other organs in your body and cause kidney and liver damage, brain injury and other serious side effects. It’s dangerous for both you and the developing fetus. Because of these risks, your healthcare provider will need to monitor your pregnancy closely and recommend treatment right away.

Preeclampsia Vision Changes

Preeclampsia is a hypertensive disorder affecting pregnant women, typically occurring after the 20th week of gestation.

In modern days, preeclampsia remains a leading cause of maternal and perinatal morbidity and mortality worldwide.

The most common symptoms include high blood pressure (hypertension) normally occurring in conjunction with proteinuria (presence of protein in the urine), signs of organ dysfunction, and preeclampsia vision changes.

The extended list of symptoms to look out for includes:

• High blood pressure
• Vision changes and disturbances
• Proteinuria (presence of protein in the urine)
• Excessive face & body swelling (edema)
• Persistent and severe headaches
• Pain or tenderness in the upper right side of the abdomen, just below the ribs
• Pain or tenderness in the shoulder
• Reduction in urine output (kidney dysfunction)
• Severe nausea and vomiting in the second half of pregnancy
• Shortness of breath

Another one of the prominent symptoms of preeclampsia is visual disturbances. They often occur during pregnancy and may persist postpartum.

The rise in blood pressure occurring with the condition affects organ systems, including the eyes. Which contributes to a range of visual difficulties. The fluctuations in vision can be alarming and significantly impact a woman's daily life, adding to the already substantial burden of this condition.

Preeclampsia vision changes commonly include blurry vision, light sensitivity (photophobia), and visual disturbances like seeing flashing lights or floaters.

Preeclampsia vision changes may indicate potential severe complications.

Eye problems are way easier to detect than high blood pressure. So they are quite often the reason a pregnant woman or new mom gets the diagnosis and receives timely medical care.

Blurry vision

The vascular changes and low blood flow to the eyes affect visual function. Blurry vision may occur as a result of changes in the cornea, lens, or retina, leading to a decrease in visual acuity and sharpness. Fluid retention and eye swelling may contribute to blurriness.

Photophobia

Photophobia, as a preeclampsia symptom, makes individuals highly sensitive to light. Thus causing discomfort and a strong aversion to bright light sources. It can further lead to eye strain, headaches, and visual disturbances, adding to the burden of preeclampsia vision changes.

Preeclampsia Flashes

Flashes of light are another ocular discomfort we commonly associate with preeclampsia vision changes. These flashes, often described as brief, bright flickers or streaks of light, can appear suddenly and sporadically in a woman's visual field. Their occurrence is a result of abnormal retinal stimulation, due to vascular alterations.

Preeclampsia Floaters

Preeclampsia floaters are dark spots or specks that appear to "float" in a person's visual field. The causes are tiny protein or cell aggregations in the vitreous humor (the gel-like substance that fills the eye). They may appear as small dots or cobweb-like shapes, often moving with eye movements. Preeclampsia floaters are indicative of abnormal blood flow in the retinal blood vessels.

Reference:

• pmc.ncbi.nlm.nih.gov/articles/PMC3729391
• bettervisionguide.com/9-causes-blurred-vision
• ophthalmology24.com/preeclampsia-vision-changes
• pampers.com/en-us/pregnancy/prenatal-health-and-wellness/article/preeclampsia

Blurry vision after eating occurs when a rapid increase in blood sugar levels causes the lens of the eye to swell. This changes the shape of the lens, thereby affecting your eyesight.[1]

Blurry Vision Causes [2]

The causes of blurred vision fall into four general categories:

Retinal. There's a problem with your retina, the structure at the back of your eye that senses light.

Clouding. The parts of your eye that light passes through to reach the retina are normally transparent. These include the cornea, lens, and jellylike substance that fills your eyeball, called the vitreous humor. If any of those things is clouded for some reason, your vision will be blurry.

Nerve issues. The path that carries messages from your eyes to your brain is disrupted in some way.

Refractive errors. These refer to problems in the way the light is focused on your retina.

Common signs and symptoms include:

• Blurred vision when looking at distant objects
• A constant need to strain eyes to look at far objects
• Headaches after long periods of reading or other visual activities

Reference:

1. verywellhealth.com/blurry-vision-after-eating-5118069
2. webmd.com/eye-health/why-is-my-vision-blurry

Myokymia (pronounced mai-ow-KAI-mee-uh) is the medical term for eye twitching. It’s a common problem experienced by almost everyone at some point in their lives.

During myokymia, tiny involuntary contractions occur in a muscle of one eyelid. This looks like a “twitch” from the outside. Eyelid spasms usually happen in the lower eyelid, but they can happen in the upper eyelid too.

Types of eyelid twitches

There are three common types of eye twitching: general eyelid spasm, essential blepharospasm and hemifacial spasm. The types are organized by the severity of the twitch and whether other areas of the face are affected.

Eye twitch or tic (general eyelid spasm)

When you think of an “eye twitch,” you’re probably picturing a general eyelid spasm. This is a slight, temporary pulsing or flickering of the eyelid.

General eye spasms are usually unilateral, meaning they only affect one eye at a time. However, it’s possible for both eyes to experience a general spasm. Depending on which eye muscle is affected, you may have under eye twitching or a twitch in the upper eyelid.

Fatigue, too much caffeine or physical or emotional stress usually cause a general eye spasm. It is common, does not affect vision and will likely go away on its own.

While eye spasms can be annoying, they’re almost never cause for concern. They can last anywhere from a few moments to several days and usually go away on their own. In rare situations, spasms can last for months or even longer.

Eye twitching is a movement or spasm of the eyelid or eye muscles that can't be controlled. There are different types of eye twitching. Each type of twitch has a different cause.

The most common type of eye twitching is called myokymia. This type of twitch or spasm is very common and happens to most people at some point. It can involve either the upper or lower eyelid, but usually only one eye at a time. The eye twitching can range from barely noticeable to irritating. The twitching usually goes away within a short time but could happen again over a few hours, days or longer.

Another type of eye twitching is known as benign essential blepharospasm. Benign essential blepharospasm starts out as increased blinking of both eyes and may lead to the eyelids being squeezed shut. This type of twitching is uncommon but can be extremely severe, affecting all aspects of life.

Hemifacial spasm is a type of twitching that involves muscles on one side of the face, including the eyelid. Twitching may start around your eye and then spread to other parts of the face.

Myokymia can occur as the result of certain aspects of your lifestyle or due to conditions that irritate your eyes. Irritants can also cause your eyes to twitch more often or for longer periods of time.

Potential causes of eye twitching include:

• Stress

• Anxiety

• Exercise

• Fatigue

• Caffeine use

• Certain medication, such as topiramate, clozapine, and flunarizine, though this is uncommon

• Dry eyes

• Eye strain

• Alcohol use

• An outdated vision prescription

• Tobacco use

• Poor diet

• Eye allergies

• Dehydration

An eye spasm is rarely the result of an underlying illness. However, it may be present alongside some other conditions, including:

• Brain damage caused by inflammation or stroke

• Parkinson’s disease

• Autoimmune disease, like multiple sclerosis (MS)

• Head trauma

• Brain tumor or lesion

These are very unlikely to cause eye twitching in the average person. Usually, if an underlying condition is to blame, there will be other symptoms present with the eye twitch.

Reference:

• mayoclinic.org/symptoms/eye-twitching/basics/definition/sym-20050838
• allaboutvision.com/symptoms/eye-twitching/myokymia
• allaboutvision.com/en-au/conditions/eye-twitching

An accommodative spasm is a condition in which the eyes focus constantly or automatically. It can occur after an activity, like reading, in which a person is using their near vision. When a person is reading, the eye focuses on an object close to the face, such as a book or newspaper.[1]

Accommodative spasm is a condition in which the eye muscles automatically focus more than is necessary for a given stimulus. Symptoms include blurry vision, fluctuating vision, headaches/eyestrain, ineffective spectacle correction, and unstable responses during an eye exam.

Patients with accommodative spasm have a difficult time relaxing their focusing muscles when transitioning from near to far, so they may complain of blurred distance vision after a period of near work. This happens because their eyes are still focusing for their near vision task, even though they are now looking at a farther distance. After discontinuing the near work, the distance vision gradually improves as the eye muscles eventually relax and allow the distance to become clear.

Accommodative spasm is often seen in young patients and is most common for individuals who frequently perform extended near tasks such as staring at a computer screen, tablet or cell phone. Typically, this condition improves slowly with aging as the ability to focus up close gradually lessens.

Taking visual breaks is helpful to reduce the symptoms that occur with mild accommodative spasm. The general rule for visual breaks while performing computer and near work is 20/20/20: every 20 minutes, look 20 feet away, for 20 seconds to help reduce potential eyestrain. Visual breaks may not be enough to treat significant accommodative spasm and the doctor may prescribe bifocal, progressive, or antifatigue glasses. These lenses allow for patients to relax their eye muscles while doing near work so that when they then switch their focus to distance, vision remains clear. Please ask your doctor if you have any questions about this condition.[2]

The ability to accommodate requires a change in the dioptric power of the eye through the increase of lens thickness and curvature. This is achieved through the contraction of the ciliary muscle and relaxation of the lens zonules. These changes are necessary to view objects and images clearly at near. Accommodation testing offers the practitioner crucial information about a patient’s focusing capacity.

Accommodation decreases with increasing age and the loss of lens elasticity. Other causes of decreased accommodation can include head trauma, midbrain diseases and encephalitis. In pre-presbyopes, this is termed accommodative insufficiency. The exact underlying mechanism for accommodative insufficiency in healthy pre-presbyopic subjects is not well understood. However, evidence suggests the presence of an inhibitory accommodative control system regulated by the autonomic nervous system, specifically the sympathetic branch.

Accommodative dysfunction is a term that encompasses accommodative insufficiency, ill-sustained accommodation, accommodative excess and accommodative infacility. Of these subtypes, insufficient accommodation is the most commonly encountered condition, representing 55% to 84% of cases. It also accounts for the most common cause of asthenopia in children ages eight to 15, highlighting the importance of proper diagnosis and management.

Those with accommodative insufficiency often present with difficulty performing near tasks. Symptoms can include visual discomfort, eyestrain, fatigue, blurred vision, headache, diplopia and difficulty focusing from one distance to another. These can interfere with a student’s academic progress because avoiding work at near relieves the visual demand.

Accommodative insufficiency is often misdiagnosed in young children and must be differentiated from dyslexia or other binocular vision disorders.[4]

What glasses are good for accommodative spasms?

Visual breaks may not be enough to treat significant accommodative spasm and the doctor may prescribe bifocal, progressive, or antifatigue glasses. These lenses allow for patients to relax their eye muscles while doing near work so that when they then switch their focus to distance, vision remains clear.

Computer vision syndrome can be caused by intraocular etiologies like refractive error, accommodative spasm, binocular vision dysfunction or an extraocular etiology like ergonomics. Dry eye is the major contributing factor to computer vision syndrome.

A spasm of accommodation, also known as “pseudo-myopia,” occurs when the eyes lock their focus on a near object but then have difficulty releasing the focus to view distant objects. The reason this is considered a false myopia is because it involves the focusing mechanism of the lens and not the elongation of the eye, a characteristic of true myopia.

However, pseudo-myopia can be treated with vision therapy, assuming the accommodation spasm was the only culprit for blurry vision at a distance. If that is the case, after a successful vision therapy program, the patient may no longer need to wear prescription lenses for vision correction.

Reference:

1. texaschildrens.org/content/conditions/accommodative-spasm
2. familyeyemd.com/patient-education/accommodative-spasm
3. mycorneacare.com/glossary/computer-vision-syndrome
4. reviewofoptometry.com/article/accommodation-in-peril
5. optometrists.org/childrens-vision/guide-to-pediatric-eye-conditions/what-is-myopia/myopia-and-vision-therapy

What is anemia?

Anemia is a condition that results from the body not producing an adequate number of healthy red blood cells (RBC). It is the most common blood condition, affecting over 3 million people in the U.S.

Red blood cells and anemia

The main function of RBC is to carry oxygen from the lungs and deliver it to the body. Red blood cells also remove carbon dioxide from the body and carry it back to the lungs, where it is exhaled.

Healthy red blood cells are donut-shaped and flattened in the center without the hole in the middle. They have an iron-rich protein called hemoglobin inside them. This protein attaches to the oxygen from the lungs and allows the RBC to deliver the oxygen to the rest of the body.

When the body does not produce enough healthy red blood cells, as happens in anemia, not enough oxygen reaches the tissues, leading to many different symptoms.

Red blood cells are made in your bone marrow, the tissue inside your bones. They last 90 to 120 days, after which the body destroys them and signals for new ones to be made.

Adequate nutrition is important in making enough RBC. This includes having enough:

• Iron

• Folic acid

• Vitamin B12

This is why a poor diet or poor absorption of nutrients can impact the body’s ability to make RBC and may lead to anemia.

Test for anemia

Anemia is diagnosed with a blood test. A doctor will look at the values of hemoglobin to determine whether someone has the condition. Anemia is diagnosed when the blood shows a hemoglobin value that is:

• Less than 13.5 gm/dl in a man

• Less than 12.0 gm/dl in a woman

• Varies with age for children

What causes anemia?

Anemia occurs when the body does not produce enough healthy red blood cells. While Iron deficiency is the most common cause of anemia, it can occur due to many underlying causes and conditions.

Causes

Anemia has three major causes:

• Loss of blood

• Insufficient RBC production

• RBC destruction occurs at a higher-than-normal rate

How does anemia affect the eyes?

Anemia occurs when there is a deficiency of red blood cells, leading to decreased oxygen to the body, including the eyes. The whites of the eyes may develop a blue color, the inside of the lower eyelids may become pale, and the retina may become damaged due to a lack of oxygen and leaking blood vessels.

Certain types of anemia can cause specific changes in the eye, such as:

• Swelling in the retina (the light-sensitive tissue of the eye)

• Damage to the optic nerve (which carries messages from the eye to the brain)

• Blockage of the artery and veins that serve the retina (retinal artery occlusion and retinal vein occlusion)

Why is anemia common in girls?

Why Anemia Affects Teens and Young Women. Teen girls and young women are vulnerable because they lose blood (and iron) during menstruation, especially if their periods are heavy, Byrne said. Gynecologists define heavy periods as menstrual bleeding:

• Lasting more than seven days.
• With at least quarter-sized blood clots
• Needing period products (such as tampons) replaced one or more times per hour
• Requiring multiple pads to contain the blood
• Having to change pads or tampons overnight

Can a 17 year old have anemia?

However, it is important to know that most common form of anemia in adolescents in the United States is iron deficiency anemia. This typically happens when a teen does not get enough iron in their diet. Other common reasons for teens be iron deficient include rapid growth spurts and onset of menstrual cycles for girls.

Eye symptoms of specific anemias

Some types of anemia cause specific changes in the eye. This can include swelling in the structures of the retina, including the macula, the blockage of blood vessels and damage to the optic nerve (which carries messages from the eye to the brain).

Some specific anemias that impact the eyes include:

Sickle cell anemia – People with sickle cell disease (SCD) have red blood cells shaped like a sickle. This causes the RBC to stick together and block blood flow to body parts such as the eyes. Blocked blood vessels cause pressure to build up, causing the vessels to burst and bleed resulting in retinal complications.

The white of the eyes can become yellowish if jaundice develops. Symptoms include sudden floaters, blurred vision, blind spots, light flashes, a dark curtain closing over vision and side vision loss.

Iron deficiency anemia – When severe, this can lead to blockage of the blood vessels, including central retinal vein occlusion and retinal artery occlusion. In addition, it may cause disc edema — swelling where the retina and optic nerve connect.

Vitamin B12 deficiency anemia – Also known as pernicious anemia, this condition can lead to optic neuropathy (damage to the optic nerve).

Thalassemia – This blood disorder is passed from parent to child and causes the body to make an insufficient amount of hemoglobin. It can cause complications in the retina and yellowing of the whites of the eye.

Hemolytic anemia – This blood disorder causes red blood cells to be destroyed faster than they are made. Certain medications, particularly the class of antibiotics known as cephalosporins, are the most common cause. In addition, infections such as malaria and HIV can lead to this type of anemia.

Can anemia cause blurry vision?

In most cases, people do not have many eye or vision symptoms from anemia unless it has begun to cause damage to the eye’s tissues. If anemia worsens, bleeding and swelling in the retina could lead to vision issues.

General symptoms of anemia

Anemia impacts every body system. The effects can be mild or severe, depending on the type of anemia.

General symptoms of anemia include:

• - Fatigue and weakness

• - Lightheadedness or headaches

• - Shortness of breath

• - Fast or irregular heartbeat

• - Throbbing sound in the ears

• - Cold hands or feet

• - Pain in the chest

If anemia becomes severe, symptoms can progress and include a pale undertone to the skin, brittle nails and mouth ulcers.

Managing anemia to protect vision

The type and severity of anemia you have will determine the treatment. Iron supplements and vitamins may be recommended to treat some mild types of anemia. Your doctor may also prescribe medicines that help your body produce more red blood cells. In addition, changes in diet to boost your iron levels can be beneficial.

Anemia can sometimes signal a more serious condition. A medical history, physical exam and laboratory tests may be required to detect underlying causes such as autoimmune diseases, bleeding in your stomach, inflammation from an infection, cancer or kidney disease.

If you are experiencing symptoms that may indicate anemia, schedule an appointment with your primary care provider. In addition, schedule a comprehensive eye exam to help ensure your eyes are healthy.

Reference:

• allaboutvision.com/conditions/related/anemia-effects-on-eyes
• cedars-sinai.org/blog/anemia-a-barrier-to-womens-health.html
• hopkinsmedicine.org/health/conditions-and-diseases/irondeficiency-anemia/symptoms-of-iron-deficiency-anemia-in-children

See also:

• Association between Refractive Errors and Anemia
• Association between Anemia and Myopia in Korean Adults

Lens aberration is a phenomenon that occurs when light rays passing through a lens do not converge at a single point, resulting in a distorted or imperfect image. It is caused by the limitations of the lens’s design and the way it interacts with light. There are several types of lens aberrations, each with its own unique characteristics and effects on the image.[1]

In optics, aberration is a property of optical systems, such as lenses, that causes light to be spread out over some region of space rather than focused to a point. Aberrations cause the image formed by a lens to be blurred or distorted, with the nature of the distortion depending on the type of aberration. Aberration can be defined as a departure of the performance of an optical system from the predictions of paraxial optics. In an imaging system, it occurs when light from one point of an object does not converge into (or does not diverge from) a single point after transmission through the system. Aberrations occur because the simple paraxial theory is not a completely accurate model of the effect of an optical system on light, rather than due to flaws in the optical elements.

An image-forming optical system with aberration will produce an image which is not sharp. Makers of optical instruments need to correct optical systems to compensate for aberration. Aberrations are particularly impactful in telescopes, where they can significantly degrade the quality of observed celestial objects. Understanding and correcting these optical imperfections are crucial for astronomers to achieve clear and accurate observations.[2] eResearch by Navid Ajamin -- autumn 2024

Minimizing Lens Aberrations [1]

Lens aberrations can be minimized by using high-quality lenses with advanced optical designs and specialized lens elements. Some techniques used to reduce aberrations include:

• Aspherical lens elements: These have non-spherical surfaces to correct for spherical aberration and coma.
• Apochromatic lenses: These use special glass types to minimize chromatic aberration.
• ED (Extra-low Dispersion) glass: Reduces chromatic aberration by using glass with low dispersion properties.
• Floating lens elements: These move within the lens barrel to correct for aberrations at different focusing distances.

Lens aberrations are inherent limitations of lenses, but they can be effectively minimized through careful lens design and the use of advanced optical technologies. Understanding the different types of aberrations and their effects on the image can help photographers and videographers select the appropriate lenses for their specific needs and achieve the desired image quality.

Types of Lens Aberrations [1]

Lens aberrations are imperfections in the way a lens focuses light. They can cause images to appear blurry, distorted, or have other defects. There are many different types of lens aberrations, but some of the most common include:

1. Spherical Aberration

Spherical aberration occurs when light rays that pass through the center of a lens are focused at a different point than light rays that pass through the edges of the lens. This can cause images to appear blurry or have a “soft” focus. Spherical aberration is most noticeable in wide-angle lenses.

2. Coma

Coma occurs when light rays that pass through the center of a lens are focused at a different point than light rays that pass through the edges of the lens, but in this case, the difference in focus is not symmetrical. This can cause images to appear to have comet-like tails. Coma is most noticeable in off-axis objects.

3. Astigmatism

Astigmatism occurs when the lens is not perfectly spherical, causing light rays to focus at different points depending on their orientation. This can cause images to appear blurry or have double vision. Astigmatism is most noticeable in objects that are at an angle to the camera.

4. Field Curvature

Field curvature occurs when the focal plane of a lens is not flat, but instead is curved. This can cause images to appear blurry at the edges, while the center of the image is in focus. Field curvature is most noticeable in wide-angle lenses.

5. Distortion

Distortion occurs when the magnification of a lens is not uniform across the image. This can cause straight lines to appear curved or bowed. Distortion is most noticeable in wide-angle lenses.

6. Chromatic Aberration

Chromatic aberration occurs when light of different colors is focused at different points. This can cause images to appear to have colored fringes around the edges of objects. Chromatic aberration is most noticeable in high-contrast images.

Lens aberrations are a common problem in photography, but they can be corrected using a variety of techniques. Some lenses are designed to minimize certain types of aberrations, and some cameras have built-in correction features. Additionally, software can be used to correct lens aberrations in post-processing.

Reference:

1. sathee.prutor.ai/article/physics/physics-aberration-of-lens/#lens-aberration
2. en.wikipedia.org/wiki/Optical_aberration
3. Lens Aberration Concepts (gsu.edu)
4. phillipreeve.net/blog/lens-aberrations-explained-part-1