Ocular dominance, or eye dominance, refers to the inclination to prefer one eye’s visual input compared to that of the other eye. It is also called “eyedness,” with the usage of this word similar to the utilization of “handedness.” About two-thirds of the general population has right eye dominance, while the remaining one-third has left eye dominance. Some people neither have left nor right ocular dominance.
The concept of handedness somewhat gives a clue on what ocular dominance is. In handedness, the right cerebral hemisphere controls the left hand, while the left cerebral hemisphere controls the right hand. Most people have left brain dominance and right handedness. The laterality of the dominant hand and the laterality of the dominant eye do not always coincide, because both left and right cerebral hemispheres control both eyes, but they take charge of different halves of both retinas. Dominance may change according to the gaze direction because it causes a change in the size of the retinal image.
Ocular dominance can be classified as weak or strong. Among people with very strong eye dominance, there is usually an underlying eye disease such as strabismus or amblyopia. In strabismus, the eyes are misaligned, such that at any particular instance, only one eye views the object of regard. The non-preferred or non-dominant eye often develops decreased visual acuity or amblyopia despite the absence of detectable disease.
In sports that require precision, such as darts, archery, and shooting, a person relies primarily on the dominant eye for the right aim. Cross-dominance, a phenomenon wherein the dominant hand is on the side opposite the dominant eye, is a factor that improves performance in sports such as golf, baseball, or cricket. There is, however, no definite evidence documented regarding this theory.
Tests for eye dominance include the Miles test, Porta test, Dolman method or the hole-in-the-card test, convergence near-point test, lens fogging technique, and camera test. The Dolman method is a forced choice test of dominance and only allows either a left eye or right eye result, which means that it does not effectively determine whether a person has non-dominance. An objective test of ocular dominance is the convergence near-point test, wherein the person being tested fixates his or her eyes on an object moving toward the nose until the non-dominant eye diverges. Knowing a person’s ocular dominance is important in contact lens calibration, refractive surgery, and cataract surgery, which aim for monovision correction.