In full-field electroretinography, the negative deflection (a-wave) and the positive deflection (b-wave) of the bright-flash response are generated respectively by which retinal structures?

• A Retinal pigment epithelium, then photoreceptors
• B Retinal ganglion cells, then amacrine cells
• C Muller cells, then photoreceptors
• D Photoreceptors, then bipolar and Muller cells ✓

Explanation

The a-wave reflects hyperpolarisation of photoreceptors (rods and cones) and therefore indicates their integrity. The b-wave arises indirectly from activity of ON-bipolar cells with a contribution from Muller cells, so it reflects inner retinal function. This distinction localises disease: in retinitis pigmentosa both waves are extinguished, whereas in central retinal artery occlusion the b-wave is lost while the a-wave may persist initially because the photoreceptor supply comes from the choroid.

Reference: Khurana, Comprehensive Ophthalmology, 7th ed.

High-yield for: NEET PGINI-CETNExTFMGEUSMLEPLABMRCP

Written and medically reviewed by the StethoPrep medical team.