Contrast sensitivity and glare testing
- Examination
Some people read the chart well but see poorly in fog, at dusk or into headlights. Contrast and glare tests measure this everyday vision.
See it in 3D: Lens · Macula · Optic nerve
What it is
Contrast sensitivity is the ability to see objects that differ only slightly from their background, such as a kerb at dusk or a face in shadow. The Snellen chart uses black letters on white and misses this loss. Letter charts that fade in contrast at a fixed size (Pelli-Robson) and grating charts across several stripe widths measure it. Glare testing repeats acuity or contrast with a bright light shining towards the eye and shows how much scattered light, as from a cataract, degrades vision.
Normal values and scales
- Young adults score close to the top of the Pelli-Robson scale; scores fall with age, and a clear drop below age norms is a real deficit.
- Posterior subcapsular cataract and capsule opacification cause much more glare disability than chart acuity suggests.
- Contrast falls early in optic neuritis, glaucoma, diabetic retinopathy and macular degeneration, even with 6/6 acuity.
- After refractive surgery, some patients notice halos, night glare and reduced contrast.
- Low contrast sensitivity in older people is linked to falls and to difficulty driving.
How it is done
- Test with the patient's usual glasses, in standard room lighting, one eye at a time.
- Pelli-Robson chart: the patient reads groups of three letters that become fainter; the score is the faintest group read with at least two letters right.
- Grating charts: the patient reports the direction of stripes of different widths; the results form a contrast sensitivity curve.
- Glare: repeat acuity or contrast while a bright light source is directed towards the eye at set levels.
- Compare with the other eye and with normal values for age.
How to interpret it
- A patient with good chart acuity but disabling glare, trouble driving at night or in sunlight may still benefit from cataract surgery.
- In optic neuritis, contrast often stays reduced after acuity has recovered.
- Good lighting, high-contrast markings at home and anti-glare measures help patients whose deficit cannot be corrected.
Next step / Initial management
- Good acuity but disabling glare or night-driving problems: refer to ophthalmology; glare testing can support cataract surgery or capsulotomy.
- Glare and halos after refractive surgery: refer back to the surgeon.
- Reduced contrast with normal acuity and fundus: think of the optic nerve; check pupils for a relative afferent defect and colour vision.
- Older adult with falls and poor contrast: improve lighting and contrast at home, check glasses and consider low-vision referral.
Test yourself
Think of the answer, then tap the question to see it.
How does the Pelli-Robson chart differ from a Snellen chart?
Its letters keep the same size and become fainter, so it measures contrast rather than resolution.
A patient reads 6/9 but cannot drive into oncoming headlights. Which type of cataract is typical?
Posterior subcapsular cataract, which causes glare out of proportion to acuity.
Which optic nerve disease often leaves reduced contrast sensitivity after acuity recovers?
Optic neuritis.
Connections
See it in 3D3
The structures of Durgical's 3D anatomy where it is found.
Educational content; not a clinical guideline and no substitute for assessment by a health professional. For sudden visual loss, severe eye pain, a chemical burn or an eye injury, go to an emergency department at once.
Sources: Contrast Sensitivity (StatPearls Publishing (NCBI Bookshelf), 2023); Cataract (StatPearls Publishing (NCBI Bookshelf), 2024).
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Representative model, for educational purposes only.