Vision Recording and the Snellen Chart
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Direct answer
Distance visual acuity is recorded on the Snellen chart at six metres, one eye at a time, and expressed as a fraction: the numerator is the testing distance and the denominator is the smallest line the patient reads, so 6/6 is normal and 6/60 means the patient sees at six metres what a normal eye sees at sixty. Below 6/60, vision is recorded as counting fingers, hand movements, perception of light, or no perception of light. A pinhole test is performed whenever acuity is reduced: improvement with the pinhole indicates an uncorrected refractive error.
What you must remember
- Method: test at six metres with good illumination, occlude one eye completely without pressing it, record the smallest line read, and always note whether it is with or without glasses; never record vision with the patient squinting.
- Chart construction: each Snellen letter subtends five minutes of arc at its designated distance, with limb thickness of one minute; the standard lines run 6/60, 6/36, 6/24, 6/18, 6/12, 6/9, 6/6 and sometimes 6/5.
- Pinhole: a 1 to 1.5 mm pinhole improves vision in refractive error by blocking peripheral rays; little or no improvement suggests media opacity or retinal and optic nerve disease.
- Low vision recording: if the top line is not read, bring the chart closer and record it as the new fraction; then counting fingers at a stated distance, hand movements, perception of light with projection, and no perception of light.
- Near vision: recorded at 25 cm with the N notation chart; N5 to N6 reading is typical for a normal adult, and near recording is essential before prescribing for presbyopia.
- Children and special groups: use the illiterate E chart, Landolt broken ring, Lea symbols or matching cards; preferential looking tests estimate acuity in infants.
- Categories of impairment: WHO categories grade visual impairment from less than 6/18 down to blindness below 3/60 or a visual field within 10 degrees of fixation in the better eye, thresholds used with presenting vision in Indian surveys.
Common confusion
Students often treat the two numbers of the fraction as a ratio to be simplified — they are distances, and 6/60 must never be written as 0.1 in a case record. Another recurring error is recording vision through squinting or a pinhole without saying so; always label the finding as unaided, with glasses, or with pinhole. Finally, do not confuse perception of light with projection of light: an eye may perceive light yet fail to project it correctly when the retina is damaged, which carries a worse prognosis.
Exam-focused takeaway
In theory, vision recording is a favourite short note, often asked with visual impairment categories; prepare the fraction, the low-vision ladder and the pinhole logic. In viva and practicals, examiners expect you to record vision on a real patient fluently and in the correct order — distance, near, then pinhole — and to interpret what the numbers imply about cause. In the posting, make it an unbreakable habit: every eye examination begins with vision, every treatment note ends with vision, and your records will be judged on whether you recorded it before dilating or bandaging the eye.
Frequently asked questions
What does a recording of 6/36 mean?
The patient reads at six metres the line a normal eye can read at thirty-six metres; vision is subnormal and the next step is pinhole testing to look for a refractive cause.
Why does the pinhole improve vision in refractive error?
It permits only paraxial rays, which need less precise focusing, so optical blur from uncorrected myopia, hypermetropia or astigmatism is reduced.
How is vision recorded below 6/60?
By bringing the chart closer, then as counting fingers at a stated distance, hand movements, perception of light with its projection in four quadrants, and finally no perception of light.
At what distance is near vision routinely recorded?
At 25 centimetres using the near chart, with the result recorded in N notation; N5 to N6 is normal adult reading performance.
What vision defines blindness in programme terms?
Blindness is defined as presenting vision below 3/60 in the better eye or a visual field constricted to within 10 degrees of central fixation.
Why test each eye separately?
Because vision may differ markedly between the eyes, occlusion during testing prevents the better eye masking disease in the worse eye, which is the whole purpose of the record.