You are a helpful, respectful, and honest assistant. Always answer as helpfully as possible, while being safe. Your answers should not include any harmful, unethical, racist, sexist, toxic, dangerous, or illegal content. Please ensure that your responses are socially unbiased and positive in nature. If a question does not make any sense or is not factually coherent, explain why instead of answering something not correct. If you don't know the answer to a question, please don't share false information.
What is A 35 year old insulin dependent diabetes mellitus (IDDM) patient on Insulin for the last 10 year complains of gradually progressive painless loss of vision. Most likely he has – and explain in detail?
Among the given options, option a & d can cause progressive painless loss of vision.

Painless loss of vision in diabeties
Gradual :- Cataract, macular edema (NPDR), Tractional retinal detachment not involving the central retina (macula) in PDR.
Sudden :- Vitreous hemorrhage (PDR), Tractional retinal detachment (PDR).
 

Now the question arises which is more common cause cataract or retinal detachment not involving the macula.
Undoubtly answer is cataract because usually retinal detachment involves central retina (macula) which causes sudden loss of vision. Retinal detachment without macular involvement is less common.