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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]
This x-intercept is also referred to as aligning prism or – in earlier times – as associated phoria when the subjective nonius method was used (sP 0) the slope of the curve near zero prism load; Fig. 3: Fixation disparity as a function of the forced vergence angle which is induced by base-in prisms and base-out prisms in front of the eyes ...
In studies that used standardized definitions of convergence insufficiency, investigators have reported a prevalence of 4.2–6% in school and clinic settings. The standard definition of convergence insufficiency is exophoria greater at near than at distance, a receded near point of convergence, and reduced convergence amplitudes at near. [4]
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 .
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 ...
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.
The prism fusion range ( PFR) or fusional vergence amplitude is a clinical eye test performed by orthoptists, optometrists, and ophthalmologists to assess motor fusion, specifically the extent to which a patient can maintain binocular single vision ( BSV) in the presence of increasing vergence demands. Motor fusion is largely accounted to ...
A cover test or cover-uncover test is an objective determination of the presence and amount of ocular deviation. It is typically performed by orthoptists, ophthalmologists and optometrists during eye examinations . The two primary types of cover tests are: the alternating cover test. the unilateral cover test (or the cover-uncover test).