Vision Testing: How Eye Diagnostics Are Performed

A vision test at the ophthalmologist consists of several simple steps. First you read the symbols on a chart, then the doctor measures refraction and checks near vision. Let's break down what eye diagnostics consists of and what the numbers in the report mean.

What a vision test includes

A vision test includes several steps. Each eye is checked separately, and the results are recorded separately.

• visual acuity testing — reading the symbols on a chart from a distance;
• near vision testing — reading a card from approximately 36 cm;
• objective determination of refraction — refractometry and skiascopy;
• a repeat check with glasses or contact lenses, if the person has them.

What it looks like: you sit five meters from the chart, both eyes open, one covered with a palm, a sheet of paper, or an occluder. No preparation is needed, and the procedure is painless.

The eye doctor's charts and visual acuity testing: how visual acuity is determined

In ophthalmology, visual acuity testing (visometry) is the measurement of visual acuity, that is, the eye's ability to perceive two points separately at a minimal distance. In CIS countries it is expressed in fractions of a unit and checked using the Sivtsev or Golovin chart from five meters: 0.1 — only the top row is visible; 1.0 — the tenth line is read from five meters with each eye.

If the symbols in the top row cannot be named from five meters, the person is moved closer to the chart every 0.5 meters and the calculation is done using the formula V = d / D, where d is the testing distance and D is the distance from which a normal eye sees that row. For vision below 0.1, Polyak optotypes are used; in children, the Orlova chart is used.

In English-speaking countries, the Snellen chart is used and a fraction is written: 20/20 (6/6) is normal, while 20/40 (6/12) means that the line you read from 20 feet would be read by a person with normal vision from 40 feet. Instead of letters, there may be numbers and pictures — for those who cannot read, especially children. One or two mistakes in the smallest line do not prevent the result from being counted for that line.

Instrument-based and computer-based vision diagnostics

Instrument-based vision diagnostics relies on objective methods: refractometry, in which refraction is measured with a special device, and skiascopy — observing the movement of a light spot in the illuminated pupil while rotating an ophthalmoscopic mirror. They show refraction regardless of the person's responses, which is valuable in expert assessment and when examining very young children.

Some Snellen charts are video monitors with letters or pictures. Home tests on a screen, in apps, and on the internet became part of telemedicine during the pandemic, and their accuracy turned out to be close to that of in-office testing.

Vision testing in children

Children are given vision tests as screening: in young children, vision problems can often be corrected or improved, while undetected and untreated problems lead to permanent vision damage.

A child's vision can be checked without letters: the Orlova chart is used in children; for those who cannot read, numbers, lines, or pictures are used. And if a small child does not know numbers, refraction is determined objectively — by refractometry or skiascopy.

How to understand the results and when testing is needed

The report will contain the lines OD (right eye), OS (left eye), and OU (both eyes). An example record for myopia: OD 0.4 with correction −1.75 D — with a diverging lens of −1.75 diopters, the right eye sees the tenth line. Degrees of myopia: mild — up to −3 D, moderate — from −3 to −6 D, high — over −6 D. For hyperopia: mild — up to +2 D, moderate — from +2 to +5 D, high — over +5 D. Values in a prescription are multiples of 0.25 D.

An abnormal result means that glasses or lenses are needed, or that there is an eye condition requiring further evaluation by a doctor. Vision testing is performed as part of a routine examination, especially if vision has changed. There are no risks associated with visual acuity testing.

Vision testing by itself is not a reason to call an ambulance. The numbers 103 and 112 are for conditions that threaten life: severe injury, stroke, heart attack.

This material is for reference: it explains how eye diagnostics are performed but does not replace a doctor's consultation.

This content is for reference and does not replace a doctor's consultation. Medical disclaimer