The enigma of subnormal vision in persistent pupillary membrane.

Persistent pupillary membrane (PPM) is a common congenital anomaly of the eye, representing the remnants of tunica vasculosa lentis. It is often detected as an incidental finding upon examination. The presentation may vary from being an insignificant strand of iris to a hyperplastic dense membrane, with or without adhesions to the surrounding structures, which notably obscures the visual axis. When present as an isolated pathology, these patients are often asymptomatic. However, some patients with isolated PPM do present with poor visual acuity or subnormal quality of vision. The severity of their disability does not always correlate to the extent of the anomaly present in the eye. The rationale as to why only some patients with significant PPM experience this visual handicap while others don't is one of the baffling conundrums in ophthalmology at present. Hence, we attempt to elaborate on the possible mechanisms that explain the unpredictable and variable clinical manifestation of persistent pupillary membranes.