Low Vision Assessment Step by Step: History, Charts, Contrast, Magnification and Rehabilitation
Last updated: November 2026
RPC Rounds for Optometrists · B.Optom study guide
Low vision care starts where glasses stop helping. The aim is not to restore sight but to help the person do the tasks that matter to them: reading, moving safely, recognising faces, working. A structured assessment finds out what they want to do, what vision they have, and which aids and strategies will work.
Definitions
- WHO (ICD-11): moderate visual impairment worse than 6/18 to 6/60; severe worse than 6/60 to 3/60; blindness worse than 3/60, or a field under 10° around fixation, in the better eye with presenting correction.
- In India, disability percentage for certification follows the RPwD Act 2016 assessment guidelines; see the disability certificate calculator.
1. Functional history
- Diagnosis and stability (macular degeneration, glaucoma, diabetic retinopathy, retinitis pigmentosa, albinism, optic atrophy).
- Goals: list specific tasks (reading newspaper print, mobile phone, medicine labels, cooking, writing, school board, mobility, work).
- Lighting and glare problems, falls, living situation, mood, hearing and dexterity (which affect the choice of aid).
2. Measuring vision
| Test | How |
|---|---|
| Distance acuity | LogMAR chart (Bailey-Lovie, ETDRS or Feinbloom) at a closer distance (for example 2 m or 1 m) and convert; record every letter read |
| Near acuity and reading speed | N-point or M-units at a measured distance; MNREAD or similar to find the critical print size |
| Contrast sensitivity | Pelli-Robson chart; low contrast predicts difficulty with faces, steps and mobility |
| Visual fields | Confrontation, Amsler grid for central scotomas, and perimetry; find eccentric viewing direction |
| Refraction | Careful retinoscopy and subjective with large steps (±1.00 D) and trial frame; even small changes can help |
| Glare and colour | Glare sensitivity; filters help albinism, cone dystrophy and RP |
3. Working out the magnification
- Distance: magnification ≈ acuity achieved ÷ acuity needed (6/60 to see 6/12 needs 5×).
- Near (Kestenbaum rule): starting add (D) = 1 ÷ distance visual acuity as a fraction (6/60 = 0.1, so +10.00 D). Then adjust with the near acuity and the target print size: required magnification = current near acuity ÷ target near acuity.
- Equivalent viewing power (EVP) lets you compare aids. Use the low vision aids calculator.
4. Low vision aids
| Aid | Advantages | Drawbacks |
|---|---|---|
| High-plus reading spectacles (microscopes) | Hands free, wide field for the power | Very short working distance (+10 D = 10 cm) |
| Hand magnifiers | Cheap, flexible distance | Need steady hands; small field at high power |
| Stand magnifiers | Fixed focus, good for tremor | Bulky; need an add or reading glasses for the image |
| Illuminated magnifiers | Light improves contrast | Battery or charging |
| Telescopes (Galilean, Keplerian) | Distance tasks: board, TV, signs | Narrow field; not for mobility; Keplerian brighter and wider but longer |
| Electronic magnifiers (CCTV, portable video magnifiers) | High magnification, contrast reversal, comfortable working distance | Cost |
| Smartphones and tablets | Zoom, contrast, text-to-speech, apps that read text | Training needed |
| Non-optical aids | Lighting, large print, high contrast markers, typoscopes, talking devices, white cane | Simple and very effective |
5. Rehabilitation
- Training in eccentric viewing for central scotomas, scanning for field loss, and correct use of each aid.
- Orientation and mobility training, daily living skills, and education support (large print books, Braille, screen readers).
- In India: disability certificate (UDID), concessions, and NGO and government rehabilitation services. Screen for depression and Charles Bonnet syndrome (visual hallucinations in sight loss), and reassure.
Practical pearls
- Start by asking "What is the one thing you most want to do again?" and build the assessment around that task.
- Good lighting is the cheapest and most powerful low vision aid: show the difference with a lamp at the visit.
- Let the patient try aids on their own reading material, such as their newspaper or phone, before prescribing.
Where students slip
- Measuring acuity only at 6 m and recording "counts fingers" when a closer logMAR test would give a usable number.
- Prescribing the strongest aid instead of the weakest that does the task.
- Forgetting that contrast and fields often limit function more than acuity.
Test yourself: flip cards
Quick quiz
Related: Low Vision Aids Calculator: Kestenbaum Rule and Magnification, Low Vision vs Legal Blindness in India (RPwD 2016), Visual Disability Certificate Calculator (India, RPwD Act), Living With Low Vision: Magnifiers, Lighting, Phone Tools and Support, 6/60, 6/18, 6/36 & 3/60 Vision Meaning: Legal Blindness in India (RPwD 2016). Back to the optometry curriculum.
Key sources
- World Health Organization. World report on vision. 2019
- Dickinson C. Low Vision: Principles and Practice. Butterworth-Heinemann; 1998
- Ministry of Social Justice and Empowerment, India. Guidelines for the assessment of visual impairment under the RPwD Act (as amended 2024)
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