Oscar may not have been properly groomed at all before he came to you. One of my cats sheds in chunks, especially around her back end. She's nearly 17 but has been like this all her life as she's not a natural groomer, and doesn't like being brushed by us.
We pretty much have to force her down to get through her coat which is fairly traumatic all around, but if we didn't do this occasionally, she would matt up horribly.
If Oscar doesn't/won't groom himself you'll want to start gentle grooming as a regular treatment for him, and get some good tools to do the job.
I like the Mikki range, (from ebay and amazon as well as most pet suppliers) especially the matt breakers of which I have two - one left and one right handed - you swap the blades so even a wriggly cat cat be groomed on both sides without being turned around. These pull out the undercoat, effectively thinning the fur out without pulling or tugging, so even if there are clumps he shouldn't experience any discomfort while being groomed. Set down some Dreamies in front of him to distract him and he'll soon come to appreciate your grooming sessions as a good thing.
Good grooming prevents/reduces the occurence of furballs too, so it is healthier for a high dependency cat like Oscar to get used to being properly brushed, especially this time of year. It will also keep you house cleaner and save you picking up vomited furballs for the rest of the Spring
I'd also check his back claws aren't overgrown, if he's pulling clumps out by scratching he could be doing damage to the skin beneath too. As he's a fairly sedentary cat, as all blind cats tend to be, his back claws won't get any natural filing and he may not know how to bite his nails down (as most cats do when their claws become annoyingly long until they start to lose their teeth, anyway)
Thirdly, check his flea control is working. Excessive scratching is sometime (not always) as sign that either he has a minor infestation, or a flea allergy which can present after one single flea bite and doesn't necessarily mean he has fleas.
We're very, very good at flea treatment on here because we've all, without exception, had trouble with them in the past and occasionally still struggle to contain the little blighters, so no shame attached.
Our resident professional cat groomer is Gill(Ambercat) from whom I learned everything I know about cat hair and it's removal, except what it tastes like in your dinner.
Have a read of some of her posts, she knows her stuff.
