Refraction and muscular imbalance, as simplified through the use of the ski-optometer

by Daniel Woolf

Heterophoria

This is the condition in which both eyes keep looking straight at the same object so long as both see it; but as soon as one eye is excluded from vision (as by a screen) that eye deviates. This is then a tendency of deviation which is strong enough to become manifest when either eye is covered, but which is abolished or overcome by the compelling impulse of binocular fixation as soon as both eyes are used for seeing. A heterophoria thus produces a maximum deviation. The deviation is also said to be latent, since it is absent under ordinary conditions and is brought to light only under special conditions. A common though improper term for heterophoria is “insufficiency.”