Should Vision in Both Eyes Be The Same?

Should Vision in Both Eyes Be The Same?

by Brian Chou, OD, FAAO, FSLS

  • August 15, 2020

Should vision in both eyes be the same?  Symmetry is common in nature.  For example, your arms and legs are probably the same approximate length.  And a butterfly’s wing pattern is similar between the two sides.  The short answer is probably, but not always.

Unaided Vision is Often Similar

In most cases, you expect similar natural vision between the two eyes.  If you wear eyeglasses, the lenses are usually similar in power.  It is uncommon for children to have a sizeable difference – or anisometropia – between the two eyes.  Only about 2-4% of U.S. children have anisometropia.  But that figure increases 10-fold in those over age 75.  The older you get, the more common it is for the two eyes to focus differently.  In part, this is because eye disease is more common, including cataracts and retinal disorders, which can impact eyesight in one eye more than another.

Aided Vision is Also Often Similar

With the best eyeglasses or contact lenses, the resulting corrected vision is also usually similar between the two eyes.  Yet it is also common for unequal vision between the two eyes.

Under most cases, your eye doctor will try to bring out the maximal vision possible out of eye, whether through glasses and/or contact lenses.  Even so, there may be differences.  The goal is not necessarily to get equal vision.  For example, if you are nearsighted but have an unequal amount of astigmatism, contact lenses that only address nearsightedness will result in some visual asymmetry between the two eyes.  In other instances, certain eye conditions create an asymmetry even with the best-corrected vision, including amblyopia, keratoconus, scars of the cornea, cataracts, and retinal disorders.

Asymmetric Vision Sometimes is Purposely Targeted

Especially over age 40, your eye doctor may deliberately introduce a visual asymmetry to help with your close-up vision, whether using contact lenses, refractive eye surgery, and sometimes with glasses.  This is referred to as monovision, where the dominant eye is targeted with distance vision, and the non-dominant eye is targeted with near vision.  Monovision does not always work, but roughly two-thirds of those that give it a try accept it.

Unhealthy to Continually Compare Eyes

Eye doctors often observe patients comparing vision between each eye, even without prompting.  There is a role and time for doing this, but without the proper understanding, doing this can create an unhealthy obsessive-compulsive habit.  As you can expect, it is natural and normal to keep both eyes open simultaneously.  After all, you do not listen by obstructing one ear, or smell by blocking one nostril.

Compulsively comparing vision between the eyes is more common among engineer-types after getting new contact lenses or right after LASIK eye surgery.  Generally, this continued comparison does not help facilitate adapting to natural binocular vision, especially when there is an expected difference.  In extreme situations, doctors purposely prescribe glasses or contact lenses to blur up the “good” eye so that it is more similar to the “bad” eye.  But most commonly, you can avoid maladaptive and compulsive comparison by realizing that each eye is has the maximal vision.  In these situations, it is worth referencing Theodore Roosevelt’s quote: “Comparison is the thief of joy.”

If you wish to know if your unequal vision is normal or not, request an appointment at ReVision Optometry.