Supplemental Skills

At the assistant level color vision is a plate book and a pass/fail. At the technician level it is a small family of tests with different jobs, a set of conditions that decide whether the result means anything, and a report that names an axis rather than a verdict.

Congenital versus acquired is the question behind the test. Congenital red-green deficiency is X-linked, affects roughly 8% of males, is the same in both eyes, and does not change over a lifetime. An acquired defect is the opposite on every count: it can appear at any age, is frequently asymmetric, and evolves. That single contrast dictates technique — test each eye separately, with the patient's best correction in place — because binocular testing is exactly how an asymmetric acquired defect goes unnoticed.

Kollner's rule is the classic association: outer retinal and macular disease tends to produce blue-yellow defects, optic nerve disease tends to produce red-green defects. It is a rule of thumb with well-known exceptions — glaucoma and dominant optic atrophy often run the other way — but it is why the physician wants the axis and not merely a failure. It is also why a red-green defect in a patient on ethambutol is treated as a monitoring finding of consequence: ethambutol optic neuropathy classically shows reduced acuity and red-green loss, often before the patient complains, so color testing joins acuity and fields at every monitoring visit.