Hi, Welcome to JustAnswer. I am a licensed veterinarian and I'd be happy to assist you. There are two "diseases" that can cause this "film" that I think you are describing. One is nuclear sclerosis where the pupil gets an opaque appearance. This doesn't cause blindness, but can decrease vision. It really is a normal aging process, but in 10+ year old dogs. Your dog at 5.5 years is really too young for this. . .if she is really 5.5 years old!
The other problem is cataracts. These are blinding opacities of the lenses, and the most common cause is diabetes. There can be other causes, but sugar diabetes is the most common. Have you noticed if your dog is drinking more than normal, or producing more than normal urine?