This is a real-world medical entrance exam question, please give the true answer based on the question and selection. Topic name: Diagnosis and Treatment of Retina, Subject name: Ophthalmology
A 35-year-old insulin dependent Diabetes Mellitus (iddm) patient on insulin for the past 10 years. He complains of gradually progressive painless loss of vision. Most likely he has: 
Select and explain. 
A. Cataract, B. Vitreous haemorrhage, C. Total rhegmatogenous retinal detachment, D. Tractional retinal detachment not involving the macula
A: Cataract
Answer: A: Cataract 
Explanation: Cataract - pre senile cataract, so is likely possibility here and is answer of choice. Vitreous hamorrhage would be sudden and more so in proliferative diabetic retinopathyso excluded. Total rhegmatogenous retinal detachment would be sudden so excluded. Tractional retinal detachment not involving the macula - at periphery this won't cause loss of vision so should not be the answer here.