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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, orthoptists, and optometrists in order to measure the vertical and horizontal deviation and includes both manifest and latent components. [ 1 ]
This test is performed on patients suspected to have small angle deviations of less than 10 prism dioptres, a microtropia, that may or may not have been observed on cover test because of subtle eye movements. The test determines whether the patient has bifoveal fixation or monofixation despite their eyes seeming straight. [2]
Prism correction is commonly specified in prism dioptres, a unit of angular measurement that is loosely related to the dioptre. Prism dioptres are represented by the Greek symbol delta (Δ) in superscript. A prism of power 1 Δ would produce 1 unit of displacement for an object held 100 units from the prism. [2]
Visual acuity with Near chart without correctors Visual acuity with eye chart at Near 15.7 inches (400 mm) and without (sc: Latin sine correctore) correctors (spectacles); Ncc is with (cc: Latin cum correctore) correctors. See Visual_acuity#Legal_definitions: VA OS Left visual acuity VA OD Right visual acuity VDU Visual display unit VF Visual field
This may represent a single-vision lens prescription to improve near work, or the reading portion of a bifocal lens. OD is an abbreviation for oculus dexter, Latin for right eye from the patient's point of view. Oculus means eye. OS is an abbreviation for oculus sinister, Latin for left eye from the patient's point of view.
A familiar dispersive prism. An optical prism is a transparent optical element with flat, polished surfaces that are designed to refract light. At least one surface must be angled — elements with two parallel surfaces are not prisms. The most familiar type of optical prism is the triangular prism, which has a triangular base and rectangular ...
An example of the Landolt C eye chart (also known as the Japanese eye chart). Numerous types of eye charts exist and are used in various situations. For example, the Snellen chart is designed for use at 6 meters or 20 feet, and is thus appropriate for testing distance vision, while the ETDRS chart is designed for use at 4 meters. [16]
The Krimsky test is essentially the Hirschberg test, but with prisms employed to quantitate deviation of ocular misalignment by determining how much prism is required to centre the reflex. [2] The Krimsky test is advisably used for patients with tropias, but not with phorias.