Evaluation of the effect of panretinal photocoagulation to retinal nerve fiber layer thickness in patients with proliferative diabetic retinopathy

Aim: To analyze the effects of panretinal photocoagulation on retinal nerve fiber layer thickness in diabetic patients.Methods: Patients with treatment naive diabetic retinopathy who underwent panretinal photocoagulation (PRP) comprised the study group .In all cases best corrected visual acuity(BCVA) and intraocular pressure were measured prior to treatment. Macula and peripapillary area were examined with optic coherence tomography. After completion ofPRP; measurements were repeated at the third and sixth month visits. BCVA , intraocular pressure, central macula thickness, retinal nerve fiber layer thickness were evaluated during the follow-up. Age-matched patients without DM compared the control group for comparing the prelaser retinal nerve and macula thickness. Variance analysis was used to compare thedifferences through the follow-up.Results: 58 eyes of 16 female and 14 men with an average age of 52,3 ± 6,4 (32-66) were the study group. All cases completed 6 months of follow-up. While visual acuity of 54 (93%)eyes was maintained or improved, 4 (7%) of the eyes experienced visual decrease during the follow-up period. At baseline and during the follow-up period there was no statistically significant difference in terms of intraocular pressure(p=0,774). No significant difference was detected between the initial retinal nerve fiber layer thickness of the control and study group (p=0,654).Mean retinal nerve fiber layer thickness was measured 108,5 µm initially, 115,8 µm at third month and 103 µm at sixth month in the study group. Difference between initial RNFLT and third month RNFLT was found +7.3 µm and considered statistically significant (p<0.05). Difference between initial RNFLT and sixth month RNFLT was found ? 5.5 µm and this reduction was statistically significant (p<0.05). RNLFT difference between third and sixmonth was ? 12.8 µm and this difference was statistically significant (p<0.05).Conclusion: Although there was no significant difference between RNFLT of study and control group at the baseline , increase in third month RNFLT may suggets intraretinal 4inflammation caused by laser photocoagulation due to cytokine release in the retina, increased capillary permeability and ensuing axonal edema.Significant RNLFT decrease at the sixth month could be explained with axonal loss due to direct or indirect effect of laser. Superiority of this study compared to previous studys is the utilization of SD-OCT instead of time-domain OCT as SD-OCT retinal imaging systems can analyze retina with higher resolution and field more detail.Key Words: Diabetic retinopathy, Panretinal photocoagulation, Retinal nerve fiber layer thickness , SD-OCT