According to Knapp's law, spectacle lenses are theoretically superior to contact lenses for minimizing aniseikonia in which type of anisometropia?

• A Refractive anisometropia
• B Both axial and refractive equally
• C Index anisometropia
• D Axial anisometropia ✓

Explanation

Knapp's law states that if a correcting lens is placed at the anterior focal point of the eye, axial anisometropia produces equal retinal image sizes regardless of the eye length difference, because the spectacle magnification compensates for the axial size difference. Hence spectacles are theoretically favoured in axial anisometropia while contact lenses suit refractive anisometropia. In clinical practice the effect often fails because the lens cannot sit exactly at the anterior focal point, but the theoretical statement tested here remains axial anisometropia.

Reference: Khurana Comprehensive Ophthalmology, 7th ed.

High-yield for: NEET PGINI-CETNExTFMGEUSMLEPLABMRCP

Written and medically reviewed by the StethoPrep medical team.