In Vivo Study of the Long Term Structural Changes Induced by Macular Argon Laser.

PURPOSE: To assess the long-term structural changes induced by macular argon laser using en face optical coherence tomography (OCT).

MATERIALS AND METHODS: We reviewed the charts and OCT pictures of patients who had undergone macular laser for diabetic macular edema at least four years ago. Clinical parameters were recorded for each eye, including laser settings. We obtained En face pictures, that were flattened at the RPE (retinal pigment epithelium) plane. We then measured the retinal surface covered by laser marks and the maximal diameter of the largest identified lesion at this plane.  The most superficial level of neurosensory retinal damage as well as the total retinal thickness at this location were measured from the RPE. We also measured the distance between the RPE and the deeper plane at which laser marks were detected.

RESULTS: 21 eyes of 16-patients were analyzed. The mean age (±SD) was 61.7 ± 15.5 years. Patients had undergone macular laser 6.5 ± 2.8 years prior to entering our study.  In 16 eyes the most superficial laser marks were detected at the inner plexiform/inner nuclear layers. The level of neurosensory retinal damage was 159 ± 48 microns over the RPE (62.6 ± 18.3% of the retinal thickness). The deepest level at which laser marks were retrieved was 125 ± 110 microns below the RPE.  The growth of laser marks was correlated to time (Pearson's correlation coefficient = 0.23; p = 0.1).

CONCLUSIONS: Argon laser marks gradually expand in the horizontal and vertical axes. The damage induced by argon laser in the neurosensory retina often reaches inner layers.