A 59-year-old women with no previous history of diabetes mellitus was admitted in diabetic ketoacidosis. Ultrasonic biometry was used to measure axial vitreous length during therapy. Vitreous length increased from 14.09 mm shortly after admission to 14.26 mm (p less than 0.05) when the episode of diabetic ketoacidosis cleared. An interesting finding was the presence of a horseshoe-shaped retinal tear after the patient was discharged. Severe dehydration with resultant shrinkage of the vitreous compartment may provide sufficient vitreoretinal traction to cause a retinal tear. In addition, an estimate of volume change showed a comparable decrease in vitreous volume seen with therapy using osmotic agents measured in rabbits.