Lack of retinal pigment causes visual impairment and underdeveloped fovea (central retina) in particular contributes to loss of acuity and nystagmus, again little to no melanin in iris also contributes to photophobia. The combination of eye differences also causes nystagmus which can also contribute to visual impairment.

It’s the abnormal development of the retina and abnormal patterns of nerve connections between the eye and the brain that cause vision problems. The presence of these eye problems defines the diagnosis of albinism - according to albinism.org

Lack of pigment causes extreme short sightedness

The optic nerve is underdeveloped too