OP1.3 | Visual Acuity, Colour Vision, Pinhole, Menace and Blink Reflex Testing — Summary & Reflection

KEY TAKEAWAYS

Key takeaways — VA, Colour Vision, Pinhole, Menace and Blink Reflex Testing:

• Snellen VA: VA = test distance / distance letter subtends 5 arcmin for normal eye. 6/6 = normal. Hierarchy below 6/60: CF at x m → HM → PL → PR → NPL. Test each eye separately; unaided AND corrected VA; start from the top.

• Pinhole test: improvement (≥2 lines) → refractive cause → prescribe; no improvement → organic cause → investigate. Dense cataract may not improve.

• Near VA: Jaeger (J) or N notation at 33 cm. N5 = normal.

• Ishihara plates: tests red-green colour deficiency (X-linked, ~8% males). 3 seconds per plate; daylight or colour-corrected light. Does NOT test blue-yellow defects.

• Menace reflex: afferent CN II, efferent CN VII. Absent normally until ~3 months in infants. Tests visual pathway + facial nerve.

• Blink (corneal) reflex: afferent CN V1 (nasociliary), efferent CN VII bilaterally. Direct + consensual response. Absent afferent (V1 lesion) → neither eye blinks when cornea stimulated on that side. Absent efferent (VII lesion) → ipsilateral blink absent, contralateral (consensual) preserved.

• Legal blindness (NPCBVI): VA <6/60 in better eye = blind for programme certification.

REFLECT

Reflect using Kolb's experiential learning cycle:

Concrete experience: You are posted at a Vision Centre in a rural PHC. A 65-year-old farmer presents with gradual visual deterioration in both eyes for 2 years. His unaided VA is 6/60 in the right eye and 6/36 in the left. With pinhole: RE 6/18, LE 6/12. He tells you he has been avoiding work in bright light.

Reflective observation: The pinhole improved VA in both eyes. Does this mean his problem is entirely refractive? What would the avoidance of bright light suggest to you (think: posterior subcapsular cataract causing glare)? Does pinhole improvement always exclude cataract?

Abstract conceptualisation: Cataract (particularly posterior subcapsular) can scatter light and cause glare without entirely eliminating pinhole improvement. A small central opacity may still allow enough improvement through the pinhole to look like a 'refractive' pattern. How would you modify your examination to distinguish cataract from pure refractive error?

Active experimentation: List the investigations you would add (red reflex, slit-lamp, fundoscopy) and how each would change your management decision in this farmer. What referral pathway exists under the NPCBVI for a patient with bilateral cataract and VA 6/60?