Which of the following is NOT considered an orthograde degeneration etiology of the optic nerve?

• A. PRP
• B. CRAO
• C. Pituitary tumor
• D. Retinitis pigmentosa

Answer: (C)

Orthograde degeneration travels from the retinal ganglion cells forward along the optic nerve toward the brain. When the retina or optic nerve itself is damaged, as in retinitis pigmentosa or after central retinal artery occlusion, the degeneration moves in that forward direction toward central visual structures. A lesion at the optic chiasm or beyond, such as a pituitary tumor compressing the chiasm, produces retrograde degeneration that travels back toward the retina, not forward toward the brain. Panretinal photocoagulation is a treatment for retinal ischemia and is not an etiologic cause of transneuronal degeneration along the optic pathway. Therefore, the condition that is not an orthograde degeneration etiology is the pituitary tumor, since it causes retrograde degeneration.