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The most common application for this is the treatment of strabismus. By moving the image in front of the deviated eye, double vision can be avoided and comfortable binocular vision can be achieved. Other applications include yoked prism where the image is shifted an equal amount in each eye.
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. It is used by ophthalmologists and orthoptists in order to measure the vertical and horizontal deviation and includes both manifest and latent components. [1]
A cover test or cover-uncover test is an objective determination of the presence and amount of ocular deviation. It is typically performed by orthoptists, ophthalmologists and optometrists during eye examinations . The two primary types of cover tests are: the unilateral cover test (or the cover-uncover test).
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.
Other lower-order aberrations are non- visually significant aberrations known as first order aberrations, such as prisms and zero-order aberrations (piston). Low order aberrations account for approximately 90% of the overall wave aberration in the eye.
Treating a case of unsatisfactory alignment often involves prisms, botulinum toxin injections, or more surgery. The likelihood that the eyes will stay misaligned over the longer term is higher if the patient is able to achieve some degree of binocular fusion after surgery than if not.
The entire process of Subjective Refraction involves the patient fixating at the Snellen Chart, whilst the clinician presents a variety of lenses and alters the power of the lenses in the trial frames according to the patient's subjective responses regarding improvements to their vision.
The Four Prism Dioptre Reflex Test (also known as the 4 PRT, or 4 Prism Dioptre Base-out Test) is an objective, non-dissociative test used to prove the alignment of both eyes (i.e. the presence of binocular single vision) by assessing motor fusion.
Visual or vision impairment ( VI or VIP) is the partial or total inability of visual perception. In the absence of treatment such as corrective eyewear, assistive devices, and medical treatment – visual impairment may cause the individual difficulties with normal daily tasks including reading and walking. [6]
A logMAR chart (Logarithm of the Minimum Angle of Resolution) is a chart consisting of rows of letters that is used by ophthalmologists, orthoptists, optometrists, and vision scientists to estimate visual acuity.