A patient's unaided visual acuity improves from 6/36 to 6/9 when he looks through a pinhole disc. The most likely explanation is:

• A Macular pathology
• B Media opacity involving the entire crystalline lens
• C Optic neuropathy
• D Refractive error ✓

Explanation

A pinhole allows only narrow paraxial rays through, reducing the blur circle produced by any refractive error, so acuity improves markedly when poor vision has a refractive cause. Organic lesions of the retina or optic nerve produce a genuine reduction in retinal function that no aperture overcomes. A diffuse cataract also fails to improve, although a small central opacity may paradoxically worsen behind a pinhole. This cheap bedside test therefore separates optical from organic causes of visual loss.

Reference: Parsons' Diseases of the Eye, 23rd ed.

High-yield for: NEET PGINI-CETNExTFMGEUSMLEPLABMRCP

Written and medically reviewed by the StethoPrep medical team.