Purpose: The aim of our study was to compare the level of Endothelin 1 in plasma and vitreous between type 1 and type 2 diabetes mellitus and control group and understand its role in diabetic retinopathy. 

Design: Prospective randomized case control study. 

Methods: This study was conducted on three groups. 
Group 1 were type I diabetic patients; Group 2 were type II diabetics and group 3 were controls (complete healthy non-diabetic individuals).  Full ophthalmological examination was done to all our cases. Endothelin level in vitreous and plasma was estimated together with glycated haemoglobin HbA1c and other parameters were estimated in all patients and controls. Results: Plasma Endothelin 1 level was significantly elevated in diabetics compared to controls (normal subjects). Vitreous endothelin 1 was significantly lower in diabetics compared to controls. There was a positive correlation between glycated hemoglobin HbA1C and serum Endothelin-1 ET-1 level in both type 1 and 2 diabetes mellitus. Endothelin 1 level is elevated in poorly controlled diabetic patients. 

Conclusion: Endothelin-1 plays an important role in mediating retinal changes in diabetics.