Just found this:
All colourpoint cats run a slightly higher risk of sight defects than full colour cats. This is because the enzyme that is needed to chemically produce pigment is faulty and doesn't work at body temperature. That same enzyme is also responsible for formation of the optic nerve in the foetus. Siamese cats have been found to have abnormally formed optic nerves, which is what can cause the tendency in that breed to be cross-eyed in those with a worse degree of optic nerve abnormality. The snow bengal colouring is caused by the same faulty enzyme. (Blue eyed cats are also at slightly higher risk of developing retinal atrophy and glaucoma due to the lack of pigment - again this is only a SLIGHT tendency.)
HOWEVER - this does not usually cause any noticeable problems with sight for the vast majority of colourpoint cats. At worst, it is usually a slight difference in depth perception, which is usually noticed by the individual having crossed eyes to compensate. It is very unusual for a colourpoint cat to have their sight affected in any noticeable way, as the brain learns to compensate when they first open their eyes and start to percieve the world.