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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.
Esotropia is a condition in which one or both eyes deviate inward, causing a cross-eyed appearance. It can be constant or intermittent, and has different types and causes, such as hyperopia, congenital, or accommodative factors.
Heterophoria is an eye condition where the eyes are not straight at rest position, but can be aligned by fusion. Learn about the types, signs, symptoms, causes, diagnosis and treatment of heterophoria.
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.
Esophoria is an eye condition involving inward deviation of the eye, usually due to extra-ocular muscle imbalance. It is a type of heterophoria and can be caused by refractive errors, divergence insufficiency or convergence excess.
The strength of the prism is increased until the streak of the light passes through the centre of the prism, as the strength of the prism indicates the amount of deviation present. The Maddox rod is a handheld instrument composed of red parallel plano convex cylinder lens , which refracts light rays so that a point source of light is seen as a ...