The Effect of Grid Laser Photocoagulation on Cone Photoreceptors

Abstract

Purpose: : To determine the effect of grid laser photocoagulation on cone photoreceptors.

Methods: : C57BL/6 mice were irradiated with diode laser photocoagulation using a 100 µm spot size and sufficient power to get a faint gray burn in a grid pattern with burns separated by one burn width. At various times after laser the generation of superoxide radicals in the retina was assessed by the level of fluorescence in retinal sections one hour after intravenous injection of hydroethidine (HDE) and oxidative damage was measured by staining for 4-hydroxy-2-nonenal (HNE). Cone cell density was measured by confocal microscopy of retinal flat mounts stained with rhodamine-conjugated peanut agglutinin (PNA).

Results: : Unexpectedly some cones at relatively low density survived within gray low-intensity laser burns and were eliminated by increasing the power to create dense white burns. Cone density was not reduced in regions adjacent to laser burns, but cone morphology and orientation was altered. There was increased fluorescence in the outer nuclear layer (ONL) overlying areas of grid laser photocoagulation after intravenous injection of HDE indicating increased generation of superoxide radicals, and increase staining for HNE suggesting oxidative damage.

Conclusions: : These data suggest that the morphology and orientation of cones adjacent to laser burns is altered which could be a source of distorted vision. Regions of grid laser had evidence of oxidative stress and damage, which could be a source of progressive damage.

Keywords: laser • oxidation/oxidative or free radical damage • retina