What is induced astigmatism?

What can cause induced astigmatism?

Some conditions and issues that can cause astigmatism include:

• Eye injuries.
• Keratoconus.
• Complications after eye surgery.

Surgically Induced Astigmatism (SIA)

Surgically induced astigmatism (SIA) is defined as the difference between the postoperative and preoperative astigmatism, which is a form of astigmatism related to the process of healing and scar reshuffling that takes place at the surgical incision. The presence of corneal astigmatism may lead to suboptimum refractive outcomes and patient dissatisfaction after cataract surgery. Considering this, controlling surgically induced astigmatism (SIA) during cataract surgery plays a significant role in this surgery to reduce astigmatism to emmetropia, improve uncorrected visual acuity, and thereby increase patient satisfaction.

To optimize visual performance with intraocular lens (IOLs), SIA should be one of the factors taken into account for IOL power selection. Nowadays, with the improvement of people’s living standards and the extension of working age, the demand for eye use is increasing. When people develop cataracts or presbyopia, they expect to achieve good vision both in the far and near distances with spectacle independence after surgery. Cataract surgery has evolved from vision restoration surgery to a refractive procedure.

Can phone worsen astigmatism?

Overuse of Electronic Devices: The excessive use of smartphones, tablets, computers, and other electronic devices could lead to astigmatism, as well as dry eye. Improper Light Levels: Watching TV or using electronic screens in the dark can cause eye strain and eye fatigue and possibly be a cause for astigmatism.

The symptoms of Induced Astigmatism is same as the regular astigmatism, but it is caused by LASIK complications. Symptoms of induced astigmatism include blurred vision, double vision and ghost images. The surgery permanently changes the shape of the cornea, although It is unusual, but possible and a botched LASIK procedure can cause it.

Induced astigmatism is astigmatism that is present after laser eye surgery but wasn't there before. It could be an increase of existing astigmatism, or new astigmatism along a different axis. This term should not be confused with irregular astigmatism.

Reasons

• It probably due to a poor quality ablation and did not deliver the correct amount of laser energy to the correct places on the cornea.
• Flap complications or other complications causing scarring may result in induced astigmatism.

What is the difference between induced astigmatism and irregular astigmatism?

Sometimes these phrases are used in a confusing way. In the context of laser eye surgery complications patients, both kinds of astigmatism are "induced", that is, caused by surgery, but there is a huge difference between "simple" astigmatism, which is a type of refractive error and can normally be fully corrected with glasses or contact lenses, and irregular astigmatism, which is a broader term encompassing curvature irregularities on the surface of the cornea that are NOT correctible with glasses or soft contact lenses.

What causes induced astigmatism?

If there are no overt complications during or after surgery, induced astigmatism is probably due to a poor quality ablation, that is a laser treatment that for some reason did not deliver the correct amount of energy to the correct places on the cornea. In rare cases this could be because of failure on the surgeon's part to programme in the appropriate amount of correction; in other cases it may be a problem with the fluence or delivery of the laser energy.

Laser eye surgery complications, particularly flap complications or other complications causing scarring, may result in induced astigmatism.

Topography of the OS showing irregular astigmatism.

What are the results to the patient?

Astigmatism is a refractive error and it causes distorted vision. Normally it should be correctible with glasses or soft contact lenses, so the result for the patient (absent other complications) should merely be that s/he must continue to wear glasses or contact lenses.

How is it diagnosed? eResearch by Navid Ajamin -- summer 2013

With a standard refraction examination (the "better 1 or better 2?" variety).

How is it treated?

With glasses or contact lenses.[1]

Irregular astigmatism is a type of eye disorder in which the surface of the cornea is marred by peaks, ridges, valleys, and other abnormal shapes. When the cornea is not uniformly smooth, light cannot be collected and focused onto the lens properly. A person with mild irregular astigmatism may have slightly blurry or distorted vision, while a severe case can cause multiple images to appear in each eye that are disorienting and sometimes debilitating. The condition is generally more difficult to treat than other types of astigmatism.

The underlying causes of irregular astigmatism are not always easy to determine, and many possible problems may lead to the disorder. Some people have irregular astigmatism from birth due to genetic factors. Others develop problems later in life due to eye injuries or severe infections. In some cases, surgery to correct regular astigmatism or another eye disorder also can lead to accidental damage to the surface of the cornea.

A person who has irregular astigmatism typically has trouble focusing on both close- and far-range objects. The condition is often worse in one eye than the other, and holding one eye closed may help to temporarily see better. If the cornea is seriously malformed, light may be refracted in such a way that the same image appears multiple times on different places on the lens, causing double or triple vision in a single eye. Vision problems can in turn lead to such symptoms as headaches, nausea, and balance issues.[2]

Look at this picture from a few different distances:

People without astigmatism will see all the lines correctly: the same thickness with exactly the same spacing between them. If you suffer from astigmatism, you will see something like two triangles having a peak in the middle of the drawing. As you rotate your head from side to side, so the triangles rotate together with you because astigmatism shows itself within a certain angle.

Healthy eyes will see all the lines at the same thickness, while people suffering from astigmatism will see some lines thicker and darker than others. Try to rotate your head for this graphic!

People who suffer from astigmatism can often see an indistinct object more clearly when they rotate their head, or face their head downwards, looking up at the same time.

Oblique astigmatism is an aberration of off-axis rays that causes radial and tangential lines in the object plane to focus sharply at different distances in the image space.

Reference:

• njcponline.com
• howtoimproveeyesight.com
• isegeek.com/what-is-irregular-astigmatism.htm
• lasermyeye.org/patients/learning/inducedastig.html
• my.clevelandclinic.org/health/diseases/8576-astigmatism
• researchgate.net/figure/Overall-mean-surgically-induced-astigmatism
• eyewiki.org/Astigmatism_Correction_at_the_Time_of_Cataract_Surgery
• doughertylaservision.com/vision-blog/how-to-successfully-live-with-astigmatism
• semanticscholar.org/paper/Effect-of-axis-orientation-on-visual-performance-in-Kobashi-Kamiya
• dovepress.com/long-term-evaluation-of-surgically-induced-astigmatism-and-corneal-hig-peer-reviewed
• touchophthalmology.com/refractive-surgery/journal-articles/how-to-get-accuracy-in-intraocular-lens-calculation

See Also:

• Physiology of Astigmatism -- eyewiki.aao.org
• Induced astigmatism after cataract surgery -- saoptometrist.co.za
• Solutions for Surgically Induced Astigmatism -- crstodayeurope.com/articles
• Irregular astigmatism induced by annular tinted contact lenses -- ncbi.nlm.nih.gov