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In geometry, a prism is a polyhedron comprising an n-sided polygon base, a second base which is a translated copy (rigidly moved without rotation) of the first, and n other faces, necessarily all parallelograms, joining corresponding sides of the two bases.
Vision therapy (VT), or behavioral optometry, is an umbrella term for alternative medicine treatments using eye exercises, based around the pseudoscientific claim that vision problems are the true underlying cause of learning difficulties, particularly in children. [1]
This table of bases gives the values of 0 to 1296 in bases 2 to 36, using A−Z for 10−35. "Base" (or "radix") is a term used in discussions of numeral systems which use place-value notation for representing numbers. Base 10 is in bold. All 10s are in italic
During an eye examination, the presence of suppression and the size and location of the suppression scotoma may be the Worth 4 dot test (a subjective test that is considered to be the most precise suppression test), or with other subjective tests such as the Bagolini striated lens test, or with objective tests such as the 4 prism base out test.
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]
For an abnormal result, based on where the light lands on the cornea, the examiner can detect if there is an exotropia (abnormal eye is turned out), esotropia (abnormal eye is turned in), hypertropia (abnormal eye higher than the normal one) or hypotropia (abnormal eye is lower than the normal one).
Dissociated vertical deviation (DVD) is an eye condition which occurs in association with a squint, typically infantile esotropia. The exact cause is unknown, although it is logical to assume it is from faulty innervation of eye muscles.
To perform the test you will need Bagolini Striated Glasses; Pen torch or a distant light source. Alternatively, trial frames and lenses or a lorgnette can be used. In some cases, the use of prisms is necessary to measure a deviation and test for the presence of binocular functions.