I'd suggest looking up Bells Palsy, our boxer had this when we first got him. It presents as an eye irritation and then moves to what looks like a cataract if not treated.

I don't know of any rat specific eye diseases. Any trouble with the eyes has always been due to an eye injury.

Thank you for replying. This is exactly what the specialist said. Our pet was however never injured that we know of, or never had an irritation which troubled her. The Specialist said that it is congenital and if either of her parents had diabetes, and it developed into cataracts, the cataracts (although a recessive gene) can more than likely appear early on in one or more in a litter.