Health requirements differ for pre- and post-employment members and incumbent firefighters

Within NFPA 1582, Standard on Comprehensive Occupational Medical Program for Fire Departments, there are 13 essential job tasks firefighters must be able to perform to become a firefighter. Certain pre-existing health conditions, such as monocular vision (a.k.a. vision in only one eye), use of a hearing aid, and a history of seizures, prevent pre-employment members from becoming a firefighter. Meanwhile, incumbent firefighters who develop one of these conditions may remain on the job. Should there be a different set of health requirements for pre-employment members and incumbent firefighters? Should incumbent firefighters be expected to meet the same standards of employment...