Impact of panretinal photocoagulation on optic nerve head parameters

Background: To investigate the impact of panretinal photocoagulation (PRP) on quantitative optic nerve head (ONH) assessment in patients with diabetic retinopathy. Methods: Eighty eyes of 80 diabetic patients who did not undergo PRP and 45 eyes of 45 subjects with diabetes who underwent PRP were enrolled in the prospective, cross-sectional study. Participants were evaluated by confocal scanning laser ophthalmoscopy (CSLO). The global values of ONH parameters were compared among the groups. Results: The eyes that had been treated with PRP had a significantly greater rim area (1.84 ± 0.45 vs. 1.68 ± 0.30 mm²), smaller cup/disc area ratio (0.14 ± 0.12 vs. 0.19 ± 0.12), smaller linear cup/disc ratio (0.34 ± 0.17 vs. 0.42 ± 0.14) and shallower cup depth (0.15 ± 0.09 vs. 0.18 ± 0.07 mm) than controls (p = 0.021, p = 0.019, p = 0.007, p = 0.04, respectively). On the other hand, PRP-treated eyes were found to have a significantly thinner mean peripapillary retinal nerve fibre layer compared with the eyes in the control group (0.21 ± 0.08 vs. 0.25 ± 0.09 mm; p = 0.029). Conclusions: These results suggest that the ONH morphology in eyes treated with PRP may be altered to mask glaucomatous cupping due to PRP itself. Therefore caution must be taken to interpret the CSLO parameters obtained from eyes that have been treated with PRP.