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Visual Function Tests
High YieldAssessment of visual acuity, contrast sensitivity, and color vision
Visual acuity is the vital sign of ophthalmology, but a Snellen line alone misses contrast loss, colour deficits, and near-vision dysfunction that profoundly affect daily life. ETDRS LogMAR is the research gold standard — know why it supersedes Snellen and when to deploy contrast and colour testing. This section covers six core assessments that quantify the full breadth of visual function.
Key Points
- ETDRS/LogMAR is the gold standard for VA in clinical trials — each letter = 0.02 logMAR; 5 letters per line with equal spacing (geometric progression)
- Snellen chart limitations: unequal letter difficulty, variable letters per line, non-linear scale — but remains most widely used in clinical practice
- Contrast sensitivity (Pelli-Robson) detects subtle visual dysfunction missed by high-contrast VA — reduced in early cataract, glaucoma, optic neuritis, MS
- Ishihara detects red-green colour deficiency (protan/deutan) only — cannot detect tritan (blue-yellow) defects; use D-15 or anomaloscope for complete assessment
- Near vision testing assesses reading acuity and presbyopia — add trial lenses starting at +1.00 D for patients ≥40 years
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