It is a requirement that all government related websites meet section 508 accessibility guidelines, and your business website should as well. Accessibility is a right, not a privilege.
Common visual problems are due to cataracts, glaucoma, age-related macular degeneration, corneal opacity, diabetic retinopathy, childhood blindness, trachoma and onchocerclasis.
Since people with visual disabilities can’t actually view your website they need to utilize assistive technologies(AT). A common screen reader for windows is JAWS (not the shark). JAWS is an acronym for Job Access with Speech. JAWS used a virtual cursor when interacting with web content.