Glaucoma is a mysterious disease. Just last month, I considered why corneal biomechanical properties have such a strong influence on this optic neuropathy. Parapapillary atrophy (PPA), an atrophic region of absent retinal pigment epithelium adjacent to the optic nerve, is yet another mysterious risk factor for glaucoma and its progression. PPA is more prevalent in eyes with glaucoma (65%) than in normal eyes (~5%), although it often occurs in eyes with myopia. The presence of PPA indicates a greater likelihood that an eye will experience glaucoma progression, and even the area around the optic nerve with PPA indicates what region of visual field is more likely to experience progression. In fact, optic disc hemorrhages, one of the strongest signs of progression, typically fall within a region of preexisting PPA. So it sounds like PPA is closely associated with glaucoma right? Well… The story gets a little bit more complicated.
In the Ocular Hypertension Treatment Study, optic nerve photography was collected at baseline and during follow-up, so the investigators took a look at the presence of PPA and its enlargement over time and correlated that to the patients with ocular hypertension who converted to primary open-angle glaucoma during the study. They did not find much. Eyes with a larger region of PPA at baseline were no more likely to go on to develop glaucoma than those with a smaller region of PPA. For those who did develop glaucoma, an increase in PPA over time was not different than increases in PPA in patients who never developed glaucoma. How can PPA be associated with glaucoma progression but not with its development? It’s possible that ocular hypertension is a different disease, one that is more driven by eye pressure than by optic nerve local anatomy—but we simply do not know all of the answers.
A recent study in JAMA Ophthalmology adds a little more complexity to the picture. De Moares and colleagues looked at longitudinal data from the African Descent and Glaucoma Evaluation Study (ADAGES) to understand differences in PPA between those of African and European descent. In ocular hypertension, there was no difference between the relationship between PPA and progression between those of African or European descent, but in eyes with glaucoma, there was a stronger relationship between PPA and progression in those of European descent. And again, regardless of African or European descent, PPA progression was not associated with glaucoma progression.
So where are we with PPA and glaucoma? Scratching our heads. Parapillary papillary atrophy is associated with some form of stress in the optic nerve that in the right situation—perhaps in patients of European descent, perhaps in eyes with lower intraocular pressures, perhaps in eyes with preexisting damage— will lead to glaucoma progression. There are likely additional aspects to be elucidated. Until then, when we detect PPA, we can bring it in to the complex individualized risk algorithm known as the art of managing glaucoma.