# Eye Test Source page: https://www.kudretgozistanbul.com/en/treatments/eye-test **Author:** Kudret Eye İstanbul | **Medical Approval:** Op. Dr. Mehmet Ali Özdil | **Date:** 2026-09-04 > **Summary:** Eye tests are short assessments, carried out by ophthalmologists during a comprehensive examination, that measure functions such as visual acuity, colour vision, the central and peripheral visual field and the accuracy of a prescription. Used together, they reveal refractive errors as well as the first signs of eye disease. ## Quick Facts - **Duration:** Usually 15-30 minutes, depending on the tests performed - **Age:** Can be done at any age, including children - **Prescription validity:** Usually two years --- ## Common Eye Tests ### Visual Acuity Test - Measures how clearly each eye sees at a set distance; the patient reads a chart of E letters or other symbols 6 metres away, one eye at a time, and the doctor records the smallest line seen. - Used in diagnosing myopia, hyperopia and astigmatism as well as macular degeneration, cataracts and glaucoma. - Result is a fraction: 6/6 means you read at 6 metres what a normal eye reads at 6 metres; 6/12 means a normal eye reads at 12 metres the line you can only read at 6. - Shows how much vision is lost, not why (prescription, cataract, macula or optic nerve). Falling acuity with an unchanged prescription points to the eye itself; a difference between the eyes in children is the first sign of lazy eye, visible only when each eye is measured on its own. ### Colour Blindness Test - Red-green colour blindness (daltonism) is the most common type. - **Ishihara test:** dot-pattern plates (pseudoisochromatic) with numbers or letters that colour-blind people see differently or not at all. - **Anomaloscope:** not a screening test but an advanced diagnostic test; the person matches a red-green light mixture to a yellow light, showing type and degree. - **Lantern test:** coloured lights to assess colour discrimination. - Done in a well-lit room, each eye separately. - Congenital colour blindness stays the same for life; acquired loss in an adult, especially red-green, can be an early sign of optic nerve disease. Required for certification in aviation, driving, seafaring and electrical work; early diagnosis in children matters for schooling. - It is permanent, but special glasses or contact lenses can improve colour perception. ### Amsler Grid Test - A grid of straight lines, one eye at a time, detecting bent lines or distorted, blurred or dark areas that point to the macula (for example macular degeneration). With both eyes open, the healthy eye hides the change. - Can be done at home by people with or at risk of macular disease; catching a new distortion early matters in wet age-related macular degeneration. ### Visual Field Test - Maps how much of the visual field is seen, with a special device; used for glaucoma, retinitis pigmentosa and brain tumours. - Peripheral loss can go unnoticed for years while central vision stays sharp. - Cornerstone of glaucoma diagnosis and follow-up: eye pressure shows risk, OCT shows structural thinning, the field shows the real loss; repeated tests show whether treatment has stopped it. - Loss on the same side in both eyes points to the visual pathways or brain. A certain field width is required for a driving licence and some occupations. ### Duochrome Test - Letters on red and green backgrounds, one eye at a time, to check whether the prescription focuses exactly on the retina. - Red focuses slightly behind the retina, green slightly in front. Sharper on red means slight under-correction; sharper on green means slight over-correction. - Fine-tunes the final quarter of a dioptre, not a disease test; works in colour-blind people too. ### Device Measurements Eye pressure, corneal thickness and map, retinal layers and corneal cell count are measured by devices, because conditions like raised pressure or a thinning macula give no symptoms. Not every test is done at every examination: symptoms, age and first findings decide which are added. ## Understanding Your Prescription - **Sphere (SPH):** main correction for short- or long-sightedness; minus (−) for difficulty seeing far, plus (+) for near; larger number means stronger prescription. - **Cylinder (CYL):** astigmatism correction; blank means none. - **Axis:** direction of astigmatism, an angle between 0 and 180 degrees. - **Addition (ADD):** extra near power, usually needed after 40, added on top of the distance prescription and usually equal in both eyes. - **Prism:** helps the eyes align; only for double vision or squint, blank on most prescriptions. ## Prices The price varies with the tests performed. --- ## Frequently Asked Questions **Q: What diseases do eye tests diagnose?** A: Myopia, hyperopia, astigmatism, colour blindness, glaucoma, cataracts, macular degeneration, retinitis pigmentosa and brain tumours. **Q: How is a colour blindness test performed?** A: Usually with Ishihara plates carrying numbers or patterns in different colours. **Q: What is the Duochrome test?** A: A test of colour aberration in the eye: the patient says on which background, red or green, the letters look sharper. **Q: How long does an eye test take?** A: Usually 15-30 minutes, depending on the tests. **Q: Can eye tests be done on children?** A: Yes, at any age, using methods suitable for children. **Q: How should I prepare?** A: Remove contact lenses as your doctor instructs, and rest your eyes beforehand.