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Prism correction is measured in prism dioptres. A prescription that specifies prism correction will also specify the "base". The base is the thickest part of the lens and is opposite from the apex. Light will be bent towards the base and the image will be shifted towards the apex. In an eyeglass prescription, the base is typically specified as up, down, in, or out, but left and right are also ...
The Maddox rod test can be used to subjectively detect and measure a latent, manifest, horizontal or vertical strabismus for near and distance. The test is based on the principle of diplopic projection. [1] Dissociation of the deviation is brought about by presenting a red line image to one eye and a white light to the other, while prisms are used to superimpose these and effectively measure ...
Esophoria is an eye condition involving inward deviation of the eye, usually due to extra-ocular muscle imbalance. It is a type of heterophoria .
Anisometropia is caused by common refractive errors, such as astigmatism, far-sightedness, and myopia, in one eye. [6] Anisometropia is likely the result of both genetic and environmental influences. [7] Some studies suggest, in older adults, developing asymmetric cataracts may cause worsen anisometropia.
Heterophoria is an eye condition in which the directions that the eyes are pointing at rest position, when not performing binocular fusion, are not the same as each other, or, "not straight". This condition can be esophoria, where the eyes tend to cross inward in the absence of fusion; exophoria, in which they diverge; or hyperphoria, in which ...
The formula for vertex correction is , where F c is the power corrected for vertex distance, F is the original lens power, and x is the change in vertex distance in meters.
The cover test is used to determine both the type of ocular deviation and measure the amount of deviation. The two primary types of ocular deviations are the tropia and the phoria. A tropia is a misalignment of the two eyes when a patient is looking with both eyes uncovered. A phoria (or latent deviation) only appears when binocular viewing is broken and the two eyes are no longer looking at ...
Diagnosis of convergence insufficiency is made by an eye care professional skilled in binocular vision dysfunctions, such as an optometrist, opthomologist, or orthoptist to rule out any organic disease. Convergence insufficiency is characterized by one or more of the following diagnostic findings: patient symptoms, high exophoria at near, reduced accommodative convergence / accommodation ratio ...
Esotropia is a form of strabismus in which one or both eyes turn inward. The condition can be constantly present, or occur intermittently, and can give the affected individual a "cross-eyed" appearance. [1] It is the opposite of exotropia and usually involves more severe axis deviation than esophoria. Esotropia is sometimes erroneously called ...
A good procedure is a chart, analogous to the familiar Snellen visual acuity chart, in which one letter in each row differs in depth (front or behind) sequentially increasing in difficulty.