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The prism cover test ( PCT) is an objective measurement and the gold standard in measuring strabismus, i.e. ocular misalignment, or a deviation of the eye. [1] It is used by ophthalmologists and orthoptists in order to measure the vertical and horizontal deviation and includes both manifest and latent components. [1]
Through this test, suppression, microtropia, diplopia and manifest deviations can be noted. However this test should always be used in conjunction with other clinical tests, such as Worth 4 dot test, Cover test, Prism cover test and Maddox rod to come to a diagnosis.
In general, strabismus can be approached and treated with a variety of procedures. Depending on the individual case, treatment options include: Correction of refractive errors by glasses; Prism therapy (if tolerated, to manage diplopia) Vision Therapy; Patching (mainly to manage amblyopia in children and diplopia in adults) Botulinum toxin ...
Esotropias measuring more than 15 prism diopters (PD) and exotropias more than 20 PD that have not responded to refractive correction can be considered candidates for surgery. Techniques Disinserting the medial rectus muscle. The goal of strabismus surgery is to correct misalignment of the eyes.
The Maddox rod test can be used to subjectively detect and measure a latent, manifest, horizontal or vertical strabismus for near and distance. The test is based on the principle of diplopic projection.
When this muscle's function is diminished due to a fourth cranial nerve palsy, the affected eye will extort, deviate upward (hypertropia), and, to a smaller extent, drift inward. Treatment [ edit ] Congenital fourth cranial nerve palsy can be treated with strabismus surgery, where muscle attachment sites on the globe are modified to realign the ...
Prism correction is measured in prism dioptres. A prescription that specifies prism correction will also specify the "base". The base is the thickest part of the lens and is opposite from the apex. Light will be bent towards the base and the image will be shifted towards the apex.
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).
Aniseikonia can occur naturally or be induced by the correction of a refractive error, usually anisometropia (having significantly different refractive errors between each eye) or antimetropia (being myopic (nearsighted) in one eye and hyperopic (farsighted) in the other.)
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).