Visual Acuity (Visus)
Visual acuity is the ability of the eye to distinguish fine details — measured by checking how small characters a person can recognize from a specified distance.
The most recognizable tool is the chart with rows of letters decreasing in size, but for children, charts with pictures, symbols, or the letter E oriented in different directions are also used — the child does not need to know the alphabet for the test to be valid. The result is recorded as a fraction, for example, 1.0 or 20/20, where the first number indicates the testing distance, and the second indicates the distance from which a person with normal vision recognizes the same character.
Two things are important to understand. First: visual acuity is tested separately for each eye, with the other one covered. Binocular testing would show the result of the better eye and overlook issues in the weaker one — exactly the mechanism by which aniseikonia and amblyopia can remain unnoticed.
Second: visual acuity is just one of the parameters of vision. A child may have normal acuity in both eyes while still having difficulty maintaining eye convergence while reading, smoothly tracking text, or judging distances. A good result from the chart does not exclude difficulties in other areas — and vice versa, it does not in itself constitute a diagnosis.
How does it work in ocu•vio?
Results from charts cannot be obtained at home, and ocu•vio does not attempt this — we do not measure how a child sees. Instead, we support daily viewing hygiene: regular breaks, changing distances, and a calmer rhythm of near work.
Frequently Asked Questions
Does a child need to know letters to test visual acuity?
No. Charts with pictures, symbols, or the letter E oriented in different directions are used, so the test is valid even for a child who does not yet know the alphabet.
Why is each eye tested separately?
Binocular testing would show the result of the better eye and overlook difficulties in the weaker one — this is the same mechanism by which differences in vision between eyes can remain unnoticed.
Does a good result from the chart mean everything is fine?
Not necessarily. Visual acuity is one of the parameters of vision. A child may have a normal result and still have difficulty maintaining eye convergence while reading, smoothly tracking text, or judging distances.
Related concepts
This dictionary entry serves an exclusively educational purpose. The ocu•vio platform is not a medical device as defined by legal regulations — it does not diagnose, treat, or correct vision defects or eye diseases. Digital missions and PDF materials serve a recreational and relaxing function, supporting daily digital hygiene and healthy screen habits. The content of the dictionary does not replace consultations with a specialist.
Source: editorial work of ocu•vio based on publicly available specialized literature.