Ocular dominance

Ocular dominance, sometimes called eye preference or eyedness, is the tendency to prefer visual input from one eye to the other. It is somewhat analogous to the laterality of right- or left-handedness; however, the side of the dominant eye and the dominant hand do not always match. This is because both hemispheres control both eyes, but each one takes charge of a different half of the field of vision, and therefore a different half of both retinas (See Optic Tract for more details). There is thus no direct analogy between "handedness" and "eyedness" as lateral phenomena.

Approximately two-thirds of the population is right-eye dominant and one-third left-eye dominant; however in a small portion of the population neither eye is dominant. Dominance does appear to change depending upon direction of gaze due to image size changes on the retinas. There also appears to be a higher prevalence of left-eye dominance in those with Williams–Beuren syndrome, and possibly in migraine sufferers as well. Eye dominance has been categorized as "weak" or "strong"; highly profound cases are sometimes caused by amblyopia or strabismus.

In those with anisometropic myopia (i.e. different amounts of nearsightedness between the two eyes), the dominant eye has typically been found to be the one with more myopia. As far as regards subjects with normal binocular vision, the widespread notion that the individual's better-sighted eye would tend to be the dominant eye has been challenged as lacking empirical basis.

Importance

In normal binocular vision there is an effect of parallax, and therefore the dominant eye is the one that is primarily relied on for precise positional information. This may be extremely important in sports which require aim, such as archery, darts or shooting sports. Ocular dominance and dominant hand should be ideally the same.

It has been asserted that cross-dominance (in which the dominant eye is on one side and the dominant hand is on the other) is advantageous in sports requiring side-on stances (e.g. baseball, cricket, golf); however, studies within the last 20 years have shown this not to be the case. In a 1998 study of professional baseball players, hand–ocular dominance patterns did not show an effect on batting average or ERA. Similarly, in 2005, a South African study found that "cricketers were not more likely to have crossed dominance" than the normal population.

Ocular dominance is an important consideration in predicting patient satisfaction with monovision correction in cataract surgery refractive surgery, also laser eye surgery, and contact lens wear.

Determination

A person's dominant eye "is determined by subjective alignment of two objects presented at a stereodisparity far beyond Panum's area". There are a number of ways to do this:

1. The Miles test. The observer extends both arms, brings both hands together to create a small opening, then with both eyes open views a distant object through the opening. The observer then alternates closing the eyes or slowly draws opening back to the head to determine which eye is viewing the object (i.e. the dominant eye).
2. The Porta test. The observer extends one arm, then with both eyes open aligns the thumb or index finger with a distant object. The observer then alternates closing the eyes or slowly draws the thumb/finger back to the head to determine which eye is viewing the object (i.e. the dominant eye).
3. The Dolman method, also known as the hole-in-the-card test. The subject is given a card with a small hole in the middle, instructed to hold it with both hands, then instructed to view a distant object through the hole with both eyes open. The observer then alternates closing the eyes or slowly draws the opening back to the head to determine which eye is viewing the object (i.e. the dominant eye).
4. The convergence near-point test. The subject fixates an object that is moved toward the nose until divergence of one eye occurs (i.e. the non-dominant eye). It is an objective test of ocular dominance.
5. Certain stereograms.
6. The pinhole test.
7. The ring test.
8. Lens fogging technique. The subject fixates a distant object with both eyes open and appropriate correction in place. A +2.00 or +2.50 lens is alternately introduced in front of each eye, which blurs the distant object. The subject is then asked to state in which eye is the blur more noticeable. This is the dominant eye.
9. A dichoptic motion coherence threshold test yields a quantified indication of ocular dominance.
10. The Spinning Dancer optical illusion may also reveal the same result as these other determinants.

Forced choice tests of dominance, such as the Dolman method, allow only a right or left eye result.

Treatment

It is possible to change eye dominance by actively suppressing the visual field of the dominant eye. This is achieved with an eye patch bandage that covers the dominant eye, with adhesive tape around the patch perimeter.

Another form of treatment is laser eye surgery.

The eye patch does not need to be black to blot out all light, and the dominant eye does not need to stay closed. The eye patch simply presents the dominant eye with a static unchanging visual field containing nothing of visual importance, and the brain is forced to rely on the suppressed eye for visual information.

The experience does cause irritation and frustration for the eye patch wearer since their visual capabilities for comprehension will be reduced until the brain starts to adapt to not being able to use the dominant eye.

See also

• Ocular dominance column
• Right- and left-hand traffic