A 22-year-old man presents with progressive night blindness since adolescence and recent tunnel vision. Funduscopy reveals the classic triad of retinitis pigmentosa. The structure marked **A** in the diagram represents bone-spicule pigment clumps in the mid-peripheral retina. Which of the following best explains the pathophysiological basis for the appearance of these bone-spicule pigmentations?

Question

Accepted Answer

B. Intraretinal pigment migration from the retinal pigment epithelium around retinal vessels secondary to rod photoreceptor degeneration. ## Why option 1 is correct

The bone-spicule pigmentation pattern marked **A** in retinitis pigmentosa represents intraretinal pigment migration from the retinal pigment epithelium (RPE) around retinal vessels. This occurs as a secondary change following progressive rod photoreceptor degeneration. As rods die, the RPE loses its normal trophic support and undergoes migration, depositing pigment in a characteristic bone-spicule pattern in the mid-periphery. This is a hallmark finding of RP and reflects the underlying rod-cone dystrophy pathophysiology described in the AAO BCSC Section 12 and Berson et al. (1993).

## Why each distractor is wrong

- **Option 2**: While RPE changes do occur in RP, the bone-spicule appearance is not due to proliferation of RPE cells but rather migration of existing pigment from the RPE. Proliferation would produce a different clinical pattern.
- **Option 3**: Lipofuscin accumulation occurs in the RPE itself and is not the primary mechanism for bone-spicule pigmentation. Lipofuscin represents age-related RPE changes, not the specific pigment migration pattern of RP.
- **Option 4**: Melanin granules within photoreceptor outer segments do not produce the characteristic bone-spicule pattern. This option confuses the location and source of the pigmentation.

**High-Yield:** Bone-spicule pigmentation in RP = RPE pigment migration around vessels secondary to rod death, not primary RPE proliferation or photoreceptor melanin changes.

[cite: AAO BCSC Section 12: Retina and Vitreous; Berson et al. Arch Ophthalmol 1993]

Answer

A. Proliferation of retinal pigment epithelial cells in response to cone photoreceptor loss

Answer

C. Accumulation of melanin granules within the photoreceptor outer segments

Answer

D. Deposition of lipofuscin in the inner nuclear layer due to impaired phagocytosis

Explanation

Why option 1 is correct

Why each distractor is wrong

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