I have heard (no first hand experience,) and it makes sense, that they are most spooky when loosing eyesight. They can see shapes and shadows and movement but not enough to be relaxed, almost like riding in dusky light. When they are completely blind they don't have that to be spooky about. They may listen more and be more sensitive but I haven't heard of more spooky though it is possible and depends on the environment too, and if riding depends on the rider (trust).
A lot of horses who lose eyesight are older and have more experience and less spooky naturally. Most horses adjust very well and most of those can still be ridden and do most normal things. You will need to adjust their environment and be careful not to change things on them and approach them correctly (don't sneak up etc). Some horses do not adjust and cannot handle it, or handle it but are miserable and unable to act the way they used to, these horses will need to be put down.