Pterygia are more common on the nasal side of the cornea than the temporal side—15 times more likely, to be precise. But researchers aren’t quite sure why. One hypothesis suggests the blood vessels that create this disorder grow inward because of a phenomenon known as the peripheral light focusing effect (PLF). This describes a process in which ultraviolet (UV) light passes obliquely through the temporal cornea and is concentrated on tissue near the nasal side of the cornea, causing damage there.
However, new research presented on Wednesday at ARVO 2019 in Vancouver seems to bust that myth. The researchers believe total UV irradiation in the nasal limbus is not greater than in the temporal limbus. The team created a corneal model using custom software and the corneal surface and UV refractive index data from a previous study to simulate the impact of the UV across the cornea.
The study “essentially rules out a PLF effect theory for pterygia formation,” explains Joseph Shovlin, OD, of Northeastern Eye Institute in Scranton, PA.
The researchers offer an alternative explanation: that temporal-to-nasal flow of tears over the UV exposed cornea causes accumulation of toxins on the nasal limbus.
“If this theory is correct, additional ocular surface disorders may be explained by the temporal to nasal tear flow dynamics to facilitate drainage to the punctal area,” adds Dr. Shovlin.
|King-Smith P, Mauger T, Begley C, Tankam P. Does the peripheral light focusing effect explain the strong nasal location preference of pterygia? ARVO 2019. Abstract 4701-B0264.|