Making your website accessible to users with disabilities is the right thing to do. In more than one way optimizing for visually-impaired overlap with several good SEO practices such as using image alternative text, proper structure of headings, usage of page titles, form labels and more. The proposed new standard for Section 508 is expected to require conformance to the W3C Web Content Accessibility Guidelines (WCAG) 2.0 Level AA so test your website for conformance with these standards.