THE VERTICAL prism vergences (variously called vertical fusional amplitudes and maximal vertical divergences) of most subjects are of the order of ±2.5 to ±3 Δ.1 With repeated or prolonged testing it may sometimes be possible to increase these limits a little.2 Ophthalmologists usually regard this range of vertical prism vergences as implying fixed limits in the ability of neuromuscular apparatus and the fusion powers of the two eyes to make vertical divergences. Hyperphorias are considered of real significance so far as their magnitudes encroach upon these limits of divergence. Yet, clinically speaking, if small hyperphorias were thought to be the cause of symptoms, they were corrected by prisms, even though the vertical prism vergences were equal and normal.
In this paper it will be shown that the eyes of most persons are capable of compensating for, or adapting to, much larger degrees of vertical divergence. With this adaptation
OGLE KN, deH. PRANGEN A. OBSERVATIONS ON VERTICAL DIVERGENCES AND HYPERPHORIAS. AMA Arch Ophthalmol. 1953;49(3):313-334. doi:10.1001/archopht.1953.00920020322009