To study RNFL thickness in gestational diabetes mellitus based on OCT measurements. Methods: Case-control study with Inclusion criteria: 2groups of age 18-40yrs at 32-34weeks gestation Group 1: Healthy pregnant women Group 2: Pregnant women with GDM Exclusion Criteria: Preexisting hypertension/retinal diseases/renal disease/vascular disease/glaucoma/IOP>21mmHg/cataract/ refractive error correction more than or equal to +/-5D (spherical) or +/-3D (cylinder). Grouping-Study Design: more than 2 unrelated group study. Sample Size: n=182 Procedure: After detailed history taking &.written consent detailed ophthalmic examination is done Patients are classified into group1&2. Using CIRRUS HD OCT peripapillary RNFL is measured in superior, inferior, nasal and temporal fields. Results: Peripapillary RNFL showed significant thinning in GDM patients when compared to healthy pregnant female Conclusion: Peripapillary RNFL thinning in GDM patients measured in their third trimester suggest a neurodegenerative process preceding microvascular changes in gestational diabetes mellitus. The degree of retinal thinning at the level of macula correlated with the glycemic status of the patients. Thereby making it mandatory to carry out routine evaluation of retina with the help of OCT in all GDM patients to detect early neurodegenerative changes and to keep the blood glucose levels in normal range to prevent the occurrence of diabetic retinopathy.