FMCSRs and the Physical Qualification Standards
Where the rules live
49 CFR 391.41 states the physical qualification standards. Section 391.43 governs how the examination is performed and reported; 391.45 requires the driver to be examined and certified at least every 24 months; 391.46 permits certification of drivers with insulin-treated diabetes mellitus who meet specific criteria; 391.47 resolves conflicts between medical evaluations; 391.49 provides the Skill Performance Evaluation (SPE) certificate for drivers with limb impairment. Federal exemptions are separate administrative grants layered on top of these rules.
How to read a standard
Most standards are phrased as "no established medical history or clinical diagnosis of [condition] likely to interfere with the ability to operate a CMV safely." The diagnosis itself is not automatically disqualifying; what matters is the documented likelihood of impairment-syncope, dyspnea, collapse, or loss of consciousness or control. "Established" means documented, not merely reported by the driver. The standards address: loss of a limb; hand/finger and arm/foot/leg impairment; epilepsy or any condition likely to cause loss of consciousness or control; cardiovascular disease; respiratory dysfunction; hypertension; rheumatic, arthritic, orthopedic, muscular, neuromuscular, and vascular disease; diabetes requiring insulin; mental, nervous, organic, functional, or psychiatric disorders; current alcoholism; vision (20/40 in each eye separately, with or without correction; at least 70 degrees horizontal field in each eye; ability to recognize red, green, and amber); and hearing (forced whisper at 5 feet in the better ear, or audiometric average loss no greater than 40 dB at 500, 1000, and 2000 Hz).
Traps
Assuming a diagnosis alone disqualifies; assuming a disqualifying condition ends the CDL permanently (exemptions, SPE certificates, and 391.46 exist); applying newer clinical thresholds where FMCSA has its own; and forgetting that acuity must be met in each eye, not just binocularly.
Rule of thumb
Diagnosis is not disqualification; documented risk of impairment is.