It’s most outward feature is a font size and color contract toolbar that helps users more easily read your content. But it also does a lot of behind-the-scenes work like adding skip-to-content links, implementing an outline to the link :focus state for better keyboard navigation, utilizing longdesc for images and a whole lot more. Each feature can be turned on or off through a settings page.
The ADA requires that title II entities (State and local governments) and title III entities (businesses and nonprofit organizations that serve the public) communicate effectively with people who have communication disabilities. The goal is to ensure that communication with people with these disabilities is equally effective as communication with people without disabilities.
Both sites include hidden same-page links at the top of the page for skipping to particular content. The CDC site includes five of these links, roughly corresponding with each of the landmark regions. These links become visible when keyboard users tab into the page. These links may ultimately be unnecessary if browsers support navigation by headings or landmarks. Screen readers already provide this support, but until browsers do so natively, non-mousers with eyesight can benefit from skip links like the ones on these government sites.

A language picker at the top of the page. When users select a new language, the page is reloaded with all text translated. The lang attribute on the element also changes to reflect the new language, so screen readers will pronounce the text correctly. This is a very cool feature, and makes the site accessible to millions of people who would otherwise be excluded due to language. However, it's a little buggy. Selecting some of the languages (e.g., " Slovenčina") does not result in translated text on the home page, but does result in a changed lang attribute, so screen readers that support the selected language will pronounce the English text using the new language's speech engine, which is not likely to be intelligible.
The ADA requires that title II entities (State and local governments) and title III entities (businesses and nonprofit organizations that serve the public) communicate effectively with people who have communication disabilities. The goal is to ensure that communication with people with these disabilities is equally effective as communication with people without disabilities.
Luckily, the international nonprofit World Wide Web Consortium (W3C) brings together smart people who develop open standards to ensure the long-term growth of the Web. They produce recommendations for making websites fair and equally accessible for the highest number of people possible. Their Web Content Accessibility Guidelines (WCAG) 2.1 offer clear guidance for web developers to achieve ADA compliance.
State and local governments: in determining whether a particular aid or service would result in undue financial and administrative burdens, a title II entity should take into consideration the cost of the particular aid or service in light of all resources available to fund the program, service, or activity and the effect on other expenses or operations. The decision that a particular aid or service would result in an undue burden must be made by a high level official, no lower than a Department head, and must include a written statement of the reasons for reaching that conclusion.
You can test specific themes for compliance with these guidelines using a tool such as the WAVE Web Accessibility tool.  For sites that require 100% compliance, we recommend testing your theme of choice using the demo page for the theme, for example Twenty Fourteen. We also recommend using Header Text (displaying the Site Title), rather than a Header Image, as some themes will not provide AltText and therefore generate an error in the accessibility tool when a Header Image is set.
The guidelines are broken down by four main principles: perceivable, operable, understandable, and robust. Under each principle, there are guidelines that provide specific goals a website should work toward. Under each guideline, there are testable success criteria. Those criteria are graded A, AA, or AAA. This grade shows the level of conformity to accessibility, AAA being the highest. The law only requires A and AA guidelines to be met.
Enough Time: Users have sufficient time to read and use the website’s content. If part of the website has a time limit, users are able to turn off the time limit, or they can adjust or extend it to at least ten times the default limit (unless the time limit is essential to the website’s functionality, such as auction websites like eBay). Content that moves, blinks, or automatically updates can be paused or stopped unless it’s essential to the website’s functionality.

For people who are blind, have vision loss, or are deaf-blind, this includes providing a qualified reader; information in large print, Braille, or electronically for use with a computer screen-reading program; or an audio recording of printed information. A “qualified” reader means someone who is able to read effectively, accurately, and impartially, using any necessary specialized vocabulary.

Why was Amazon sued to begin with? Believe it or not, it was the Kindle converter for documents. Amazon has developed its own converter (MobiPocket) to digitize all the documents, books, and magazines that are shown on Kindle. But the problem is that Amazon’s converter was making it difficult for people with disabilities to access any items other than super basic documents.

This guidance document is not intended to be a final agency action, has no legally binding effect, and may be rescinded or modified in the Department's complete discretion, in accordance with applicable laws. The Department's guidance documents, including this guidance, do not establish legally enforceable responsibilities beyond what is required by the terms of the applicable statutes, regulations, or binding judicial precedent.
I should mention one caveat to all of this. Businesses that are required to comply but don't have the ability to bring their websites into compliance can provide an accessible alternative to provide the same information, goods, and services that they provide online, like a staffed phone line. The trick, however, is that this option has to provide at least equal access, including in terms of hours of operation. And, as we know, the internet is around 24/7, so good luck with that. 

Thanks for writing. While I’m not a lawyer I believe if your physical practice is ADA exempt your web presence, as an extension of that physical business would maintain the same exemption status. If you’d like to be absolutely certain I’d confer with an ADA lawyer (email us, questions at yokoco dot com if you need a referral) but I don’t believe you have reason to worry.
Until the ADA is updated to address the special case of website accessibility, or the Department of Justice releases its website accessibility regulations, complying with WCAG 2.0 Level AA is the best way to ensure that people with disabilities have equal access to your website. The overview below is a great starting point about meeting the WCAG 2.0 Level AA recommendations.

Craig facilitates the execution of each project from start to finish, helping you convey your vision and bring it to life. Craig’s primary objective is to make certain that all of your needs are addressed throughout the project, from detailed technical specifications to assisting with collecting assets. This allows the staff of Quantum Dynamix to focus on what they do best; creating innovative work that meets your objectives.
Eric Kazda is a leading expert in the interactive development industry with over fifteen years of experience. With a mastery of critical development technologies, Eric has crafted innovative award-winning work for clients both large and small. Coupling this knowledge with a real world understanding of usability and technological feasibility, his work is developed to be accessible by every user.

In an August 2016 case involving the University of California Berkeley, the DOJ ruled that the public university was in violation of ADA Title II (similar to Title III but it instead applies to government organizations) because their YouTube channel’s videos didn’t include captions for hearing impaired visitors. The DOJ found this to violate the ADA as deaf users did not have equal access to the online content.

An example is Patagonia Works, Inc. which had a complaint for a permanent injunction filed against it in the United States District Court stating, Under Section 302(b)(1) of Title III of the ADA, it is unlawful discrimination to deny individuals with disabilities an opportunity to participate in or benefit from the goods, services, facilities, privileges, advantages or accommodations, which is equal to the opportunities afforded to other individuals. 42 U.S.C. 12182 (b)(1)(A)(ii). Below is a summary of what the lawyers asked the court for.
President George H.W. Bush signed the Americans with Disabilities Act into law July 26, 1990. The ADA prohibits discrimination of people with disabilities and guarantees the same opportunities as everyone else. These opportunities include employment possibilities, purchasing of goods and services and the ability to participate in State and local government programs.