Hi M., I'm a blind mother of 3 babies who all have different special needs. I worked for The Blind Children's learning Center in Tustin CA for about 5 years before I had my kids & I have some techniques that will help you & baby.
For motor skills, try putting things for him to grab just at the line between his fingers & his palm, let him grab them once, then again & let him hold the objectt. The action of grabbing will build his responses over time, & holding objects will increase his hand strength as well. You can also ly him on his back and gently move his legs in a bicycle kick motion to the tune of a nursery song; this will help his range of motion in his legs and help build up any lack in muscle tissue.
For his visual impairment, use toys that are noisy such as musical toys, rattles, & toys that vibrate. That way _if he can't see them he can still interact. Put these toys where he can feel them, & eventually reach for them himself. Vibrating toys are also great for stimulating Nerve endings in his hands and feet, but not more than about 3-5 minutes depending on the strength of the vibration.
Talk to him, about everything you are doing throuout his day, "Time for a Diaper Change, bath, feeding," or "Feel these Jammies, These are the ones you'll be wearing today," You get the idea. Take time to let him feel before you do things, for example the Jammies, or bath water.
watch him for signs of overstimulation especially in public places or when there's a lot of people or movement around him. But most of all, focus on his achievements & what he can do, more than what he can't. The other moms have posted great resources for early intervension & medical professionals but these are just a few things you can do on an everyday basis to help your sweet son grow to be a strong & healthy young man.
I hope these techniques help. Pleas contact me if you'd like I have lots of other ideas & other techniques that may be useful, I'm just trying not to write an ebook on your answer page. Best of luck & many blessings to you both. Stay strong & love love love that baby.
A.