In retinitis pigmentosa, which two ERG changes are commonly observed?

• A. Higher amplitude and faster implicit time
• B. Lower amplitude and delayed implicit time
• C. No changes
• D. Increased latency with normal amplitude

Answer: (B)

Retinitis pigmentosa causes progressive loss of photoreceptors, especially rods, so the overall electrical signal measured from the retina gets weaker and slower. An electroretinogram reflects both how strong the retinal response is (amplitude) and how quickly it occurs (implicit time). With fewer functioning photoreceptors, the ERG amplitude drops. At the same time, the remaining signaling becomes slower because the degenerating retina takes longer to respond, producing a longer implicit time. That combination—reduced amplitude with delayed implicit time—is characteristic of RP. It's also typical that rod-driven (scotopic) responses fail first, with cone responses affected later as the disease progresses.