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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.
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.
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 is an objective determination of the presence and amount of ocular deviation, such as strabismus or phoria. It involves covering and uncovering one eye while observing the movement of the other eye with a fixation target at different distances.
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.
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.
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.