عینک eyewear

A 5-Minute Safety Training Aid

You are driving on a dark twolane road. An on coming vehicle’s high beams suddenly appear. The vehicle flashes past and for the next few seconds, you’re blind. You’ve just experienced a common hazard known as night blindness.

Night blindness occurs when the eye is accustomed to low levels of light and the light intensity
suddenly rises. The eyes adjust to the new light level by contracting the pupils, but if that level of intensity is only momentary, then the eyes have to readjust to the lower level again by dilating the pupil.

While the eyes make these adjustments, there are several seconds that the vision is impaired.

During the day about 85 percent of the information we need to drive is visual, but at night this changes. Without enough light, we lose much of our contrast sensitivity (the ability to distinguish objects from the background) and peripheral vision (the ability to recognize objects at the edges of our visual field).

At night, headlights limit our visual range to the area they illuminate, only 250 to 350 feet of the road ahead.

At sixty miles per hour a car will cover 350 feet in four seconds. Therefore, slower driving speeds will allow you more time to spot a hazard and respond in a crisis.
With this in mind, pedestrians should wear light-colored clothing or put reflective tape on their clothes to make themselves more visible in the darkness.

If a driver turns his or her head from side to side, it will help make up for the lost side vision that occurs at night.

Also, if the driver must wear glasses to drive, frames that have thin sidepieces should be selected, since wide sidepieces will hinder side vision.

In addition to the problems listed above, there is the fact that as we age the lenses of our eyes become yellowed and we need more light to see. Most of us begin to notice this in our 40’s. By the age of 65 we need 2.5 times the light that we needed when we were 20 to see the same level of detail. For this reason, older persons should drive slower when they find it necessary to drive at night. Whatever your age, precautions must be taken to avoid accidents.

The following traffic safety do's and don’ts may help.

Do eResearch by Navid Ajamin -- spring 2013
+ Drive within the range of your headlights, not by what you think you see beyond your headlights.• + Adjust your rear view mirror to the “night” setting to dim headlight glare coming from behind. When the glare is gone, readjust to the “day” setting.
+ Focus your eyes on the right edge of the pavement to avoid being blinded by oncoming headlights.• + Clean your headlights.
+ Clean your windshield (inside and out).

+ Keep your eyes moving between the road and the rear and side-view mirrors.
+ Use your high beams when you can.• Take off sunglasses at dusk.
+ Turn your head from side to side to increase your peripheral vision.

+ Dim your instrument lights to reduce brightness when you look at them.

Don’t
• Drive faster than sixty-five miles per hour at night, slower on winding roads.• Put dark aftermarket tinting film on windows and windshields.
• Depend on fog or parking lights when driving at dusk or dawn.• Keep your high beams on when another vehicle approaches.
• Exceed the speed for driving conditions at night in rain, snow or fog.• Turn your interior lights on while driving your vehicle.
• Wear sunglasses at night.• Stare into your side-view mirrors as cars pass from behind.
• Use any type of medication that may change your night vision or cause drowsiness.[1]

Night blindness doesn’t mean you are completely unable to see at night, but that your vision is poorer then. It is not a disease in itself, but instead is a symptom of some other type of vision problem.

In some cases, being very nearsighted (myopic) can make it hard to see at night or in low light.

Certain cells in the eye’s retina are responsible for allowing you to see in dim light. If these cells are affected by a disease or condition, night blindness occurs.

Some of the eye conditions that can cause night blindness include:

• Nearsightedness (seeing well up close but not far away)
• Glaucoma (a disease of the optic nerve connecting the eye to the brain)
• Medicine for glaucoma that constricts (narrows) the pupil
• Cataracts (cloudiness of the eye’s naturally clear lens)
• Diabetes (uncontrolled blood sugar levels)
• Retinitis pigmentosa (an eye disease that causes blindness)
• Too little Vitamin A
• Keratoconus (having a cornea that is very steeply curved)

Is bumping and tripping through your darkened house normal or a symptom of something else?

If you aren’t sure whether you have night blindness, consider the following questions:

• Do you find yourself having trouble moving around your house at night, even with small night lights?
• Is driving at night becoming more difficult?
• Do you avoid going outside at night for fear of tripping?
• Do you have trouble recognizing people’s faces in darkened settings?
• Does it take your eyes a long time to adjust to light when coming in from the darkness?
• Similarly, does it take you a long time to adjust to seeing anything in a darkened room?

If you have any concerns about your ability to see in the dark or in dim light, speak with your ophthalmologist right away. Having a complete eye exam will help identify any condition affecting your vision.

Treating night blindness depends solely on its cause. If your refractive error is significant, getting a new prescription for your eyeglasses may be all you need for better vision in low light. In some cases, having cataracts removed can be illuminating as far as your vision is concerned. Your ophthalmologist can explain what is causing your night blindness and suggest how to brighten your outlook.[2]

Humans are not designed to be creatures of the night, so remember to respect the road and the darkness.

The Fédération Internationale de l'Automobile (FIA) created the Golden Rules for Road Safety as guidelines for drivers to keep themselves and other road users safer in transit. To start: Check your vision regularly, protect your eyes from glare and always wear your glasses on the road. The FIA also advises that motorists: [3]

• Always pay attention
• Obey the speed limit
• Buckle up
• Use a child safety seat
• Check their tyres
• Don't text and drive
• Stay bright in reflective gear
• Wear a helmet
• Stop when they're tired
• Watch out for pedestrians, especially kids
• Slow down for kids
• Never drink and drive

Reference:

1. tdi.texas.gov
2. aao.org/eye-health/news/shedding-light-on-night-blindness
3. essilor.com/ie-en/blog/your-life-and-your-eyes/cannot-see-when-driving-at-night

Night blindness is a type of vision impairment also known as nyctalopia. People with night blindness experience poor vision at night or in dimly lit environments.Historically, nyctalopia, also known as moonblink, was a temporary night blindness believed to be caused by sleeping in moonlight in the tropics.Although the term “night blindness” implies that you can’t see at night, this isn’t the case. You may just have more difficulty seeing or driving in darkness.

Night blindness is a heterogeneous group of ophthalmological disorders that results in a diminished ability to see under scotopic (dim light) conditions.

There are both acquired and congenital forms of night blindness.

• Acquired forms of night blindness include an insufficiency of vitamin A and paraneoplastic syndromes (melanoma-associated retinopathy and cancer-associated retinopathy).
• Congenital forms include both stationary (in which the severity remains relatively constant throughout life) and progressive (in which severity increases over time) forms of night blindness.
• Stationary forms can result from genetic mutations in rod photoreceptors or rod bipolar cells.
• Progressive forms include retinitis pigmentosa, choroideremia, and gyrate atrophy.

Some types of night blindness are treatable while other types aren’t. See your doctor to determine the underlying cause of your vision impairment. Once you know the cause of the problem, you can take steps to correct your vision.

nyctalopia is a type of vision impairment. People with night blindness experience poor vision at night or in dimly lit environments. It is not a disease in itself, but rather a symptom of an underlying problem, usually a retina problem.

Your vision relies on light coming through your eye, hitting the retina at the back of the eye, being transmitted through the optical nerve, and processed by the brain.

At night, your pupils will get larger to allow more light in. The rod cells on your retina will collect more light, as they are more photosensitive than the cone cells. Your optic nerve will take this mostly black-and-white image to your brain, where it is interpreted into your surroundings.

What Causes Night Blindness?
A number of eye conditions can cause night blindness, including:

1. Nearsightedness or blurred vision when looking at faraway objects.
2. Cataracts or clouding of the eye's lens.
3. Retinitis pigmentosa, which occurs when dark pigment collects in your retina and creates tunnel vision.
4. Vitamin A Deficiency
5. Zinc Deficiency
6. Dry Eyes
7. Diabetes

Are the Symptoms of Night Blindness?

To identify night blindness, the American Academy of Ophthalmology suggests that people consider the following questions:

• Is moving around the house in dim light a challenge?
• Is driving at night increasingly difficult?
• Is it tricky to recognize faces in dim light?
• Does it take an abnormally long time to adjust to a light room after being in the dark?
• Does it take a long time to see in a darkened room after being in the light?

Other symptoms may also occur with night blindness. The nature of these symptoms will depend on the underlying cause but may include:

• headaches
• eye pain
• nausea
• vomiting
• blurry, or cloudy vision
• sensitivity to light
• difficulty seeing into the distance

The sole symptom of night blindness is difficulty seeing in the dark. You're more likely to experience night blindness when your eyes transition from a bright environment to an area of low light, such as when you leave a sunny sidewalk to enter a dimly lit restaurant. You're likely to experience poor vision when driving due to the intermittent brightness of headlights and streetlights on the road.

How can I Prevent Night Blindness? eResearch by Navid Ajamin -- spring 2009

You can't prevent night blindness that's the result of birth defects or genetic conditions, such as Usher syndrome. You can, however, properly monitor your blood sugar level and eat a balanced diet to make night blindness less likely.

For many people around the world, night vision can be a problem. There are many root causes of night blindness, but the common symptom is the inability to see well or clearly at night.

Different causes of this condition will require different approaches to treatment. Getting regular eye exams to diagnose some issues before night blindness occurs can help to reduce your risk.

People with poor night vision typically are not able to see well in the dark. They are, however, able to see perfectly well during the day, even though transitions from bright environments to dim ones, such as when entering a darkened hall from the sunny outdoors, may be challenging.

One key to seeing at night is a healthy amount of rhodopsin, which is an eye pigment in the retina responsible for night vision. It is used specifically by the photoreceptor cone cells to perceive light, while the rods, on the other hand, are highly sensitive to darkness. Rhodopsin enables us to quickly adapt our vision from a dark room to a light room.

Vitamin A is an essential component of rhodopsin, so a deficiency in vitamin A can result in poor night vision. Though vitamin A deficiency is rare in industrial nations, there are other reasons vitamin A intake may be compromised, including:

• Iron deficiency can affect vitamin A uptake.
• Small-bowel bypass surgery may reduce vitamin A absorption.
• Excess alcohol consumption impairs absorption.
• Medications can affect fat absorption (Xenical) or cholesterol (statins).
• Low fat diets may be low in vitamin A.
• Zinc deficiency is associated with decreased release of vitamin A from the liver.
• Other conditions such as fibrosis, pancreatic insufficiency, and inflammatory bowel disease affect how vitamin A is utilized in the body.

For people whose night vision begins worsening due to other related eye conditions, the vision loss can occur very slowly over time. It can also occur quickly, depending on how acute the eye condition is, such as with untreated retinal bleeding. Cataracts, for example, tend to develop slowly, but for a smaller percentage of the population, they can evolve rapidly.

Symptoms vary (based on the individual) and can include any or all of the following:

• Weak vision in dim light
• Difficulty seeing during night driving
• Slow vision adaption between bright and dim light conditions (such as taking a longer time than other people to adjust to indoor lighting when coming from the bright outdoors)
• Fifty to seventy percent of people with night blindness also have nystagmus and strabismus, as well as low vision and myopia.

Only your doctor can provide an adequate diagnosis of any signs or symptoms, and whether they are night blindness symptoms, or symptoms of another disorder. The determination of the cause of night blindness should be fairly easy with a full, dilated exam and targeted tests, such as an optical coherence tomography scan (commonly known an OCT scan). This is particularly important so that the eye doctor has a history of test results with the patient.

If the night blindness is genetic, your doctor may administer a test called an electroretinogram, which determines the function of the retina and therefore its proper classification.

Reference:

• healthline.com/health/vision-night-blindness
• en.wikipedia.org/wiki/Nyctalopia
• nvisioncenters.com/education/night-blindness
• researchgate.net/publication/284826657_Night_Blindness
• lybrate.com/topic/night-blindness-causes-and-symptoms
• naturaleyecare.com/eye-conditions/night-blindness
• medicalnewstoday.com/articles/324004.php#what-are-the-symptoms

See also: Identifying a gene for canine night blindness