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The prism cover test (PCT) is an objective method to measure ocular misalignment or deviation of the eye. It involves using prism bars, occluder, and targets to neutralise the deviation and record the angle and base of the prism.
A fixation disparity is not constant within a certain observer, but can vary depending on the viewing conditions. If test prisms with increasing amount are placed in front of the observer’s eyes, the fixation disparity changes in the eso direction with base-in prisms and in the exo direction with base-out prisms (Fig. 3).
Prentice's rule is a formula to calculate the amount of prism correction in a lens based on decentration and lens power. It can be used for prescribing, tolerance control, or determining unprescribed prism in eyeglasses.
The Maddox rod test is a subjective method to measure horizontal and vertical deviations of the eyes, using a red line and a white light. The double Maddox rod test can also assess torsion and cyclotropias, by comparing the angles of two red lines.
Convergence insufficiency is a binocular vision disorder that affects the ability of the eyes to turn towards each other. It can cause symptoms such as double vision, eye strain, headache, and difficulty reading. Learn about the diagnosis, treatment, and prevalence of convergence insufficiency.
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 in the presence of increasing vergence demands.
The patient is asked to fixate on a target while the examiner places a 4 prism dioptre base-out prism over the patient's eye, observing the response of the fellow eye. [ 1 ] The target is a single isolated distance target of approximately 1-2 lines better than best corrected acuity at distance.
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