Scleral cataracts in cats? Any information or experience is appreciated.?

About a year ago I noticed that my 17 year old Maine Coon's eye was cloudier than the other. At his 6 months checkup he was diagnosed as having what the vet called a scleral cataract. He asked about his night vision, and said that over time it would decrease but indicated it wasn't serious. Our cat is now noticeably having problems seeing at night, and the cloudiness seems to have increased. He is extremely healthy, very strong, and a little overweight (we manage it). Other than a little arthritis which we manage with Cosequin, he has no other health issues. Senior blood panel is done once a year. I'm worried he will become completely blind and wonder if this is something that can be treated before it progresses? His next appointment is in 2 weeks, so I want to be prepared with information. I can't seem to find anything on the internet specifically about this.