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By moving the image in front of the deviated eye, double vision can be avoided and comfortable binocular vision can be achieved. Other applications include yoked prism where the image is shifted an equal amount in each eye.
Also called double vision, it is a loss of visual focus under regular conditions, and is often voluntary. However, when occurring involuntarily, it results from impaired function of the extraocular muscles, where both eyes are still functional, but they cannot turn to target the desired object. [2]
In some cases, convergence insufficiency can be the underlying cause of difficulty learning to read. As a result of the eyes not converging on the same point for sustained periods of time when reading, words can appear blurry or double because the brain is receiving two different images.
When one eye turns inward, outward, upward, or downward, two different pictures are sent to the brain. Thus, the brain can no longer fuse the two images coming from the two eyes. This causes loss of depth perception and binocular vision. The term is from Greek exo meaning "outward" and trope meaning "a turning".
For mild conditions, prism glasses can be prescribed to correct specific types of double vision. In more extreme cases, additional intervention such as botulinum toxin injection and strabismus surgery, might be required to rebalance the actions of the extraocular muscles. [5]
In a person with normal ocular alignment the light reflex lies slightly nasal from the center of the cornea (approximately 11 prism diopters—or 0.5mm from the pupillary axis), as a result of the cornea acting as a temporally-turned convex mirror to the observer.
A corrective lens is a transmissive optical device that is worn on the eye to improve visual perception. The most common use is to treat refractive errors: myopia, hypermetropia, astigmatism, and presbyopia. Glasses or "spectacles" are worn on the face a short distance in front of the eye.
Chromatic correction of visible and near infrared wavelengths. Horizontal axis shows degree of aberration, 0 is no aberration. Lenses: 1: simple, 2: achromatic doublet, 3: apochromatic and 4: superachromat.
In several cases of double vision, once the underlying cyclotropia was identified, the condition was solved by surgical cyclotropia correction. Conversely, artificially causing cyclotropia in cats leads to reduced vision acuity, resulting in a defect similar to strabismic amblyopia.
Other lower-order aberrations are non- visually significant aberrations known as first order aberrations, such as prisms and zero-order aberrations (piston). Low order aberrations account for approximately 90% of the overall wave aberration in the eye.