Health Blog

Saturday, 13 April 2013

Visual acuity, and definitions

Vision is the ability to see and distinguish between details. It is not the same as Visual acuity. Visual acuity refers to the strength of glasses or contact lenses and is measured in diopters.

You can also read about the peripheral and central vision

Eyesight is the Visual resolution, as it says on the LSP. Eyesight measured on an eye chart, which consists of the letters, there will be smaller, the farther down on the Board you look.

The measurement determines the smallest angle that can separate the two points. Commonly referred to eyesight in connection with fractional numbers or as decimal fractions.

Visual acuity, and definitions

With healthy eyes, you can see the smallest letters on the eye chart from six meters distance, which is equivalent to a Visual acuity of 6/6.

Visually impaired can be will at six metres distance see what a normally sighted people look at 18 meters distance, and Visual acuity is therefore 6/18.

As social blind  will only be able to recognize the large letters on the vision Board at six metres distance. This means that the first of six meters away can see what a normally sighted people looking at 60 meters distance, which is equivalent to a Visual acuity of 6/60.

Other factors affecting eyesight

There are factors other than distance between letters that have an influence on our eyesight.

Light also has an impact. A good lighting and a Blackboard with black letters on a white background gives the greatest possible contrast. Why should you measure of vision with the same lighting in all clinics.

You can also measure the contrast sensitivity, which means that you measure eyesight under different contrast ratio. It gives a good picture of the quality of vision.

Eye Chart

Contrast Sensitivity


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