Final answer:
Convergence using vergence facility is measured by assessing the accommodation-convergence reflex, where the medial recti muscles and the oculomotor nerve work together to maintain clear vision at varying distances.
Step-by-step explanation:
To measure convergence using vergence facility, you would assess the speed and ease with which the eyes can shift focus between distant and near targets. This test identifies the ability to move the eyes from divergence (looking at a distant object) to convergence (looking at a closer object) and back. The procedure typically involves having the individual focus on a target as it moves closer to the face, which stimulates the accommodation-convergence reflex. The medial recti muscles of the eyes must contract to maintain single vision, a process known as convergence. Meanwhile, the oculomotor nerve adjusts the shape of the lens for focus, which is called accommodation. As a result, this coordination between eye muscle control and lens adjustment is crucial for maintaining clear vision at varying distances, and this ability can decrease with age, requiring corrective lenses. A common clinical method involves using a vergence facility flipper with lenses of different powers and asking the patient to report when two separate images converge into one or focus clearly while switching their gaze between the lenses.