Structure of the Eye


All about eyesight

The 20/20, is a term one would have heard so many times when it comes to discussing eyesight. What exactly is a 20/20 vision? The clarity of one’s vision is usually tested at a primary level using a Snellen eye chart. The standard method of reading the chart is from a distance of 20 feet. A 20/20 vision indicates that the person can read the chart from a distance of 20 feet and this is what is visible to a person with normal Eye Sight from 20 feet away. The same can also be termed as 6/6 vision when the distance is calculated in meters. Though 20/20 is labeled as the perfect vision one can have eyesight which is above that. The maximum clarity till recently was thought to be vision which is 20/10 but most recent studies have shown eyesight better than 20/8. There are birds such as hawks and owls which have visions that are much sharper than humans. Birds like hawks are said to have a vision which is 20/2.

There are many who do not have the so called perfect 20/20 vision which is considered most favorable by physicians. People suffer from many an eye problem like near-sightedness, far sightedness and complications such as astigmatism. 20/20 cannot be said to be the perfect eyesight but just a measure that is considered normal. It actually is only a way of denoting the vision acuity from a particular distance. It is only a basic measure of vision. But there are various other factors that affect the visual ability of a person like the side or peripheral vision, perception of depth, coordination of the eyes, the ability to focus and the color vision. All these factors together contribute to the actual visual ability of an individual.

Persons suffering from many vision problems can get the same corrected by the use of glasses or contact lenses. Some people also suffer from eye diseases which can be treated with ocular medication. A comprehensive eye examination can determine the exact problem and the necessary treatment option can be adopted. A very popular way of treating many an eye problem today is the Lasik surgery. The laser surgery is very effective and has proved beneficial to many and a large number of those who suffered from vision complications have been blessed with a 20/20 vision and Lasik surgery has proved to be beneficial and a boon to many.

Eye Care & Vision Problems : How to Get Rid of Bloodshot Eyes

Snellen Eye Chart

All of us would be familiar with the Snellen eye chart. It is the chart used to test the clarity of your vision when you visit an eye specialist. The chart gets its name from Herman Snellen, a Dutch ophthalmologist, who was instrumental in preparing the chart way back in 1862.

The chart has eleven lines in all and the first line has just one alphabet which is very large in size. In the lines below the number of alphabets increases and at the same time the size of the alphabets decreases. The test is taken in a way where one eye is covered and the person is told to read out the alphabets. The visual acuity is determined depending upon the smallest alphabet that the person is able to read. The other eye is tested in the same fashion. The alphabets shown on the Snellen Eye Chart are known as optotypes. The letters are not printed in an ordinary manner but the length, width and height do have some geometrical implications.

The customary Snellen chart has only the following 10 alphabets C, D, E, F, L, N, O, P, T, Z. The chart that is wall mounted is inexpensive and is generally used for a preliminary examination of the eye. The Visual acuity is determined by a formula which is:

Distance from where the test is conducted/ distance where the smallest optotype recognized subtends at an angle of 5 arcminutes. The chart is placed at a standard distance of 20 feet in most countries for the test. The chart also has certain specifications, it should be made on non-reflective material, it should have a matte finish, should be made of durable plastic and also the standard size is 22”*11”.

The Snellen eye chart also has its variations i.e. for illiterate persons and for young children who do not know how to read. For the illiterate, the chart has the alphabet E written in various directions and the ones for young children have symbols on it. The Snellen eye chart has also been a subject for a lot of criticism. Many are of the opinion that patients might memorize the chart and this would end up in a wrong result. Also after testing one eye they may be able to memorize it because of which the other eye may seem perfect. But even with all the criticism the chart has been in use all these years. Even with so much progress made in the field of medicine, the Snellen Eye Chart is the primary test one has to go through which speaks volumes about it.

Eye Test

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Color Blindness Test

A simple test to determine whether you are color blind, known as the Ishihara Color Blindness Test.

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Retina and Vision

Vision loss is one of the greatest losses that one can suffer. Retinal damage is one of the leading causes of vision loss. The retina is a tissue that is multi layered and which is present at the rear of the eye. It is about 0.5mm in thickness. The Retina can be affected with various kinds of problems and the treatment varies depending upon the nature of the problem. Retinal surgery comes as a boon to many who are bordering on losing their precious vision. But this does not necessarily mean that every patient’s original vision would be restored. Some would have to bear with the loss of partial vision for life.

Researchers are also contemplating and studying retinal transplant as an option to restore lost vision. Studies have shown encouraging results and this could soon be a reality. Electronic retinas have also been considered and researchers are trying out the benefits of this type of retina to help patients get better vision. Retina is a nerve tissue and damage to the retina can lead to many eye problems. Macular degeneration and Retinitis Pigmentosa are common age related problems. This can lead to blindness if not treated in time. Degenerative diseases are not the only ones that affect the retina and thereby vision. The retina can also be affected due to malnutrition. A lack of Vitamin A in ones diet can at a later stage be the cause for nightblindness.

The retina can be said to be a very crucial part of the eye and any sort of problem with the retina can lead to vision loss if not treated on time. Surgery can help patients with retinal problems and this can help in slowing down the Vision loss process. The retina is quite vulnerable to damage by the free radicals. Diseases that affect the retina are supposed to be the leading cause of loss of vision. The rods and cones which help in sensing the light get affected and this in turn makes the patient unable to see.

Millions of patients the world over are affected by retinal problems. Over the years the damage that is inflicted upon the retina is unfathomable. This leads to many a problem at a later stage and finally ends up in Vision loss. The eyes have to taken care of well for it has to last a lifetime and an eye specialist needs to be consulted regularly so as to arrest any problem at the earliest.

Eye Health & Optometry – How to Prevent Blindness