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Given that an observer has a certain fixation disparity and suffers from eye strain, one may consider some of the following ways of remediation. Eye glasses with an included prism power is the optical method to reduce a fixation disparity. Different procedures have been proposed to determine the required amount of prism for the individual.
The prismatic lenses of the belay glasses are arranged so as to bend light from above through total internal reflection into the observer's eye, allowing the belayer to observe the climber while maintaining a comfortable head/neck position. The design based on the eyeglasses frame provides for a split field of vision:
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]
These special types of glasses are magnifiers, meaning they help people see things (most often text) up close, explains Tal Raviv, M.D., founder and medical director of Eye Center of New York ...
In the MKH method, this alleged misalignment is assessed by the Polatest apparatus and subsequently the patient is instructed to use prism glasses in daily life to correct for the alleged misalignment, with the prism glasses made according to the Polatest results. The MKH method claims to reduce eye strain-related symptoms.
Prism spectacles with a single prism perform a relative displacement of the two eyes, thereby correcting eso-, exo, hyper- or hypotropia. In contrast, spectacles with prisms of equal power for both eyes, called yoked prisms (also: conjugate prisms, ambient lenses or performance glasses) shift the visual field of both eyes to the same extent. [5]