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Relaxation of accommodation can result in an increase in exophoria and a decrease in esophoria, leading to an inaccurate result. The examiner should check the function of the Maddox Wing Instrument before use; the septa can be easily bent, leading to the septa not covering the intended view.
If the patient saw a red line to the right and white light to the left, they are said to have esotropia or esophoria (uncrossed diplopia) in which base out (BO) prisms of increasing strength are used until the lines are superimposed.
The test is indicated with the use of a presence of a prism in individuals with a strabismus and fusion is considered present if 4 lights are maintained, with or without the use of a prism. The W4LT can also be indicated when aiding a person to develop and strengthen their fusional capacities.
If the eye was exotropic, covering the fixating eye will cause an inwards movement; and if esotropic, covering the fixating eye will cause an outwards movement. The alternating cover test, or cross cover test is used to detect total deviation (tropia + phoria).
Prentice's rule, named so after the optician Charles F. Prentice, is a formula used to determine the amount of induced prism in a lens: = where: P is the amount of prism correction (in prism dioptres) c is decentration (the distance between the pupil centre and the lens's optical centre, in millimetres)
Glasses, surgery [3] Frequency. ~2% (children) [3] Strabismus is a vision disorder in which the eyes do not properly align with each other when looking at an object. [2] The eye that is pointed at an object can alternate. [3] The condition may be present occasionally or constantly. [3]
Heterophoria is an eye condition in which the directions that the eyes are pointing at rest position, when not performing binocular fusion, are not the same as each other, or, "not straight". This condition can be esophoria, where the eyes tend to cross inward in the absence of fusion; exophoria, in which they diverge; or hyperphoria, in which ...
Treatment options for esotropia include glasses to correct refractive errors (see accommodative esotropia below), the use of prisms, orthoptic exercises, or eye muscle surgery. The term is from Greek eso meaning "inward" and trope meaning "a turning".
This is most commonly achieved through the use of Fresnel prisms. These slim flexible plastic prisms can be attached to the patient's glasses, or to plano glasses if the patient has no refractive error, and serve to compensate for the inward misalignment of the affected eye.
Based on prism-FD curves (Fig. 3b), one can find the aligning prism sP 0 that nullifies the naturally prevailing fixation disparity sFD 0. This test procedure is typically made in near vision of 40 cm, e.g. with the Mallett-unit, the Disparometer, or the Wesson card (see above).