The link for full information on registering as visually impaired is
http://www.rnib.org.uk/livingwithsightl ... _loss.aspxand the full criteria are in a further link on that page.
For registration, vision (in both eyes) has to be far below driving standard and is defined as the number of lines a person can read on the Snellen chart WITH any glasses or contact lenses, which is why so few KC people are registered (even though some have limited lens wear time, so are effectively partially sighted for at least part of every day). The only person who can do the registration is the consultant who can complete the necessary form if his patient satisfies the criteria.
For many people with KC, the condition stays mild or stabilises before it becomes a 'progressive, debilitating' condition so KC is no more 'discriminated against' in the Equality Act than the dozens of other eye conditions that people have, or the hundreds of potentially disabling diseases eg rheumatoid arthritis that also aren't automatically counted as 'disabilities' when they are first diagnosed. I don't know what the rationale was for selecting cancer, HIV, MS and registered visually impaired for special treatment under the Act, but any individual with whatever condition can be covered by the Act if their condition meets the 'substantial, long-term and adverse effects on everyday activities' definition.
As far as KC in the workplace is concerned, you kindly posted for me on this forum the transcript of an excellent talk we had from AFBP employment advisers about the help that is available (which doesn't depend on registration). That post was a year or two ago. I'll see if I can find the relevant thread when I have a moment.
Anne