No blanket ban on any disabilities. Assessed on an individual basis. Woudl depend on level of disability, age and circumstances of child etc,
No one Official will admit to this, but it WILL be considered as a disadvantage, as are other things that deviate from a placing social workers idea of an ideal family. This is true of any disability, being older or youger than average, being single or white or gay/lesbian etc. So you are in good company!!
This means you will have to compensate for this by being wiling to take an low demand child ( unless you are high demand for another reason, such as being the ethnic mix that is in demand in your area. Or Muslim, as there is a shortage). So you probably won't get a a healthy baby or toddler. You might find an agency willing to asses you, but you are unlikely to get one placed as you will almost always lose out to a family not affected by disability.
I know a couple where she was Able bodied and he used a wheelchair. They were approved but then never had a child placed as they were always in competition with other couples. Eventually they adopted 2 cchildren from abroad.
As you may know, many children awaiting adoption who have visual impairments also have other conditions, such a learning difficulties, so you woudl need to look into this .
You might want to approach any voluntary adoption agencies which cover you area, as well as local authorities. Voluntary agencies often are better at assessing and supporting slightly out of the ordinary families.
Good luck