Which of the following is an orthograde degeneration etiology?

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

Answer: (A)

Orthograde (anterograde) degeneration moves away from the site of injury along the neural pathway, so degeneration starts where the damage occurs and then travels forward to downstream neurons. When the retina is directly damaged, as with panretinal photocoagulation (PRP), the injury can initiate degenerative changes that propagate along the visual pathway from the retina toward the brain. In this sense, PRP is an example of an orthograde degeneration etiology because the retinal insult is the starting point and the degeneration advances along the downstream neurons of the visual system.

In contrast, pituitary tumor–related problems typically produce retrograde transsynaptic degeneration, traveling back toward the retina after affecting the optic chiasm. NAION is ischemic damage to the optic nerve itself, also more consistent with retrograde changes toward the retina. Retinitis pigmentosa is a primary retinal degenerative disease that progresses within the retina rather than as a transsynaptic process along the visual pathway, so it doesn’t illustrate the orthograde transneuronal pattern in the same way.