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The prism cover test ( PCT) is an objective measurement and the gold standard in measuring strabismus, i.e. ocular misalignment, or a deviation of the eye. [1] It is used by ophthalmologists and orthoptists in order to measure the vertical and horizontal deviation and includes both manifest and latent components. [1]
Exophoria. Exophoria is a form of heterophoria in which there is a tendency of the eyes to deviate outward. [ 1] During examination, when the eyes are dissociated, the visual axes will appear to diverge away from one another. [ 2] The axis deviation in exophoria is usually mild compared with that of exotropia .
Convergence insufficiencyis a sensory and neuromuscular anomaly of the binocular visionsystem, characterized by a reduced ability of the eyesto turn towards each other, or sustain convergence. Symptoms. [edit] The symptoms and signs associated with convergence insufficiency are related to prolonged, visually demanding, near-centered tasks. They ...
A prism of power 1 Δ would produce 1 unit of displacement for an object held 100 units from the prism. Thus a prism of 1 Δ would produce 1 cm visible displacement at 100 cm, or 1 metre. This can be represented mathematically as: = where is the amount of prism correction in prism dioptres, and is the angle of deviation of the light.
Maddox rod. 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 ...
Fixation disparity. Fixation disparity is a tendency of the eyes to drift in the direction of the heterophoria. While the heterophoria refers to a fusion-free vergence state, the fixation disparity refers to a small misalignment of the visual axes when both eyes are open in an observer with normal fusion and binocular vision. [1]
In crystallography, the monoclinic crystal system is one of the seven crystal systems. A crystal system is described by three vectors. In the monoclinic system, the crystal is described by vectors of unequal lengths, as in the orthorhombic system. They form a parallelogram prism. Hence two pairs of vectors are perpendicular (meet at right ...
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 ...