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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.
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). These prisms force ...
Exotropia is a form of strabismus where the eyes are deviated outward, causing crossed diplopia and loss of binocular vision. Learn about the signs, symptoms, causes, and treatment options for exotropia, such as glasses, patching, exercises, surgery, and vision therapy.
Exophoria is a tendency of the eyes to deviate outward, usually mild and with fusion possible. It can be caused by refractive errors, divergence excess, or convergence insufficiency, and is common in infancy and childhood.
From left to right: an accommodative fixation stick, a vertical prism bar, and a horizontal prism bar. The PFR involves placing a prism bar in front of an eye. In a patient with BSV, a natural shift of the eye occurs. When measuring horizontal fusion ranges, base in prisms assess fusional divergence while base out prisms assess fusional ...
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.
A cover test or cover-uncover test is an eye examination to measure ocular deviation. Learn about the alternating and unilateral cover tests, the fixation targets, the characteristics of strabismus and the practical application of the test.