I am glad you are checking his blood sugar yourself. That is the key to keeping diabetes under control IMO. Since you can check his BG yourself, hopefully your vet will let you up is dosage a little more quickly. It takes about 3- 4 days for the body to adjust to a new dose, then the dosage can be adjusted.
If he possibly has Cushings, that can make regulation difficult. Did you get the links I sent you last night? There is information about diabetes and Cushings. Unfortunately, sometimes they occur together.
I forgot to ask you what type of insulin you are using.
Eye drops really won't help prevent blindness. Getting him regulated quickly and keeping his diabetes under control is the key. Has your vet checked his eyes? Cataracts can form almost immediately. I have known cases where blindness was the first symptom the owner noticed when her dog became diabetic.
Pets with Diabetes - Petdiabetes.org: Cataracts and Dry Eye
Lady does have dry eye, another side effect of diabetes. It's very important for a diabetic dog to be under the care of an ophthalmologist. Lady gets a yearly checkup, but is prone to eye infections, uveitis and ulcers like all diabetics so we are usually in there more often.