A medical card is not issued on the basis of medical conditions, it's based on income guidelines. If you exceed the income guidelines for a medical card, you can appeal on "hardship grounds", which is where you can show that the additional medical costs you incur because of your illness/medical condition (not one from a specified list of conditions) will cause "undue hardship" to you and your family (e.g. by paying medical bills, you can't pay the rent).
There is also a long-term illness scheme which helps persons with specific medical conditions meet the cost of prescribed medication for that condition.
Link to HSE booklet on Medical Cards, etc [broken link removed]
Link to HSE Income Guidelines for Medical Card and GP Visit Card [broken link removed]
You need Adobe reader to read these documents