Diagnostic test · Eye care
Eye power testing (refraction)
Eye power testing, called refraction, measures how each eye focuses and finds the lens power that gives you your clearest vision. It is how a glasses prescription is worked out. The test takes about 15 to 30 minutes; dilating drops are sometimes used and blur near vision for a few hours.
Medically reviewed by Dr. Meera Krishnan, MBBS, MS (Ophthalmology) —
At a glance
The essentials.
- Practice
- Eye care
- Type
- Diagnostic test
- Typical time
- 15 to 30 minutes
The full guide
What it is
Refraction is the measurement of the eye’s focusing power. An instrument gives a starting estimate, and the examiner then refines it lens by lens while you read a letter chart, until the combination that gives your clearest vision is found. The result is your glasses prescription.
Why an ophthalmologist may recommend it
Eye power testing is recommended for blurred vision at distance or near, headaches or eye strain with reading or screen work, and as part of a routine examination. A change in power can also be the reason an existing cataract is noticed, so the test is often read together with an examination of the eye.
How to prepare
Bring your current glasses, even if they feel wrong, and any previous prescriptions. If you wear contact lenses, ask the clinic whether to leave them out before the test. If dilating drops might be used, plan for someone else to drive you home.
Safety and limitations
Refraction is a low-risk test. A change of glasses corrects focus; it does not treat an eye disease. If the examination finds another cause for blurred vision, such as a cataract, the ophthalmologist explains the next steps. This website is not for emergencies; for sudden loss of vision, call 108 or go to the nearest emergency department.
Results and follow-up
The prescription is yours to keep and can be dispensed anywhere. The ophthalmologist tells you when the power should next be checked, based on your age, findings, and symptoms.
Sources
Before you come
What to bring and how to prepare
A short checklist to run through before your appointment. If anything here is unclear, call the clinic and ask.
- Bring your current glasses, even if they feel wrong, and any previous prescriptions.
- If you wear contact lenses, ask the clinic whether to leave them out before the test.
- If dilating drops might be used, plan for someone else to drive you home.
What happens
On the day.
What to expect from the moment you arrive to the moment you leave.
during
During the visit
you look into an instrument for the starting measurement, then read the chart through different lenses and say which of two choices looks clearer. There are no wrong answers; the test converges on the same result.
after
Afterwards
you receive the measured prescription, explained in plain terms. In some people, especially at a first assessment, drops are used to relax the eye’s focusing before measuring; these blur near vision for a few hours.
Before your appointment
Frequently asked questions
Practical answers about preparation, timing and what happens at the clinic.
How often should eye power be checked?
It depends on your age, your prescription, and any eye conditions. The ophthalmologist advises an interval at the visit; a noticeable change in vision is a reason to come back sooner.
Why are drops sometimes used before the test?
The eye’s own focusing can mask part of the true power, especially in younger patients. Drops relax that focusing so the measurement is accurate. They blur near vision for a few hours.
Will I be given my prescription?
Yes. The measured prescription is explained and given to you, and you can have glasses made wherever you choose.
Where this fits
Related care and consulting times.
The conditions this is used alongside, and when the consultant sees patients at the clinic.
Consultation hours
- Eye care
- Mon–Sat, 5:30 PM–8:30 PM.
Medically reviewed by Dr. Meera Krishnan, MBBS, MS (Ophthalmology) —
Appointments
Plan your visit.
Mon–Sat, 5:30 PM–8:30 PM.