Introduction: Pan Retinal Photocoagulation (PRP) is considered as gold standard treatment of proliferative diabetic retinopathy (PDR). The study was designed to objectively evaluate PRP in this era of pharmacotherapy by analysing its effect on Retinal nerve fiber layer thickness (RNFLT). 

Aims: To evaluate effect PRP on RNFLT by Spectral Domain Optical Coherence Tomography and to compare RNFL loss with patients of nonproliferative diabetic retinoapathy (NPDR) and to correlate RNFL loss with number of PRP laser spots. 

Materials and methods: Average RNFLT was measured by Spectral Domain Optical Coherence Tomography in 26 patients (52 eyes) with bilateral PDR or very severe NPDR before and after 1 year of PRP (group A) and in 26 patients (52 eyes) with bilateral mild, moderate or severe NPDR initially and after 1 year (group B). Pre and Post PRP RNFLT of patients in group A were compared using paired t test. RNFL thinning was calculated by subtracting average

RNFLT at second visit 1 year apart from first visit in both groups. RNFL thinning in group A was compared with group B by unpaired t test. RNFL thinning in group A was correlated with number of PRP spots and Pearson correlation coefficient (r) was calculated. 

Results: There was significant difference between pre and post PRP RNFLT after 1 year (p value < 0.0001). RNFL thinning was significantly more in group A as compared to group B (p value < 0.0001). RNFL thinning in group A strongly correlated with number of PRP spots and the value of Pearson correlation coefficient (r) was 0.87 (p value < 0.0001). 

Conclusions: RNFL thinning occurs after PRP which can be detected as early as 1 year with SDOCT and RNFL thinning correlate with number of PRP spots.