I'm sure each state is different as to what is determined to be a disability. Just for ref., here is Ohio's list of impairments:
An individual qualifies for a ?Removable Placard for Persons with Disabilities? if that disability limits or impairs the ability to walk as determined by a physician or chiropractor (O.R.C. 4503.44). Attach the physician or chiropractor?s letter or prescription stating the physical disability. The disability must meet at least one of the following criteria:
SECTION A:
Indicate in the box(es) provided to the left of each of the 7 qualifications which one(s) of the qualifications you meet with an X.
1. Cannot walk two hundred feet without stopping to rest;
2. Cannot walk without the use of, or assistance from, a brace, cane, crutch, another person, prosthetic device,
wheelchair, or other assistive device;
3. Is restricted by a lung disease to such an extent that the person?s forced (respiratory) expiratory volume for one
second, when measured by spirometry, is less than one liter, or the arterial oxygen tension is less than sixty
millimeters of mercury on room air at rest;
4. Uses portable oxygen;
5. Has a cardiac condition to the extent that the person?s functional limitations are classified in severity as Class III
or Class IV according to standards set by the American Heart Association;
6. Is severely limited in the ability to walk due to an arthritic, neurological, or orthopedic condition;
7. Is blind.
WHAT IS YOUR SPECIFIC DISABLING CONDITION?