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ophthalmic trial frame is used to hold lenses and other accessories during correction of refractive errors. Test of. Visual acuity. A trial frame is a tool used by ophthalmic professionals like ophthalmologists and optometrists. It is basically an adjustable spectacle frame with multiple cells, used to hold corrective lenses, and other ...
Its four symmetrical prisms allow visualisation of the iridocorneal angle in four quadrants of the eye simultaneously, and works well with a slit lamp. Most importantly, the size and shape of the instrument - a smaller front surface that rests on the cornea without requiring lubricating fluid, only the patient's tear film - allows for ...
The cause of astigmatism is unclear; however, it is believed to be partly related to genetic factors. [3] [4] The underlying mechanism involves an irregular curvature of the cornea and protective reaction changes in the lens of the eye, called lens astigmatism, that has the same mechanism as spasm of accommodation. [1] [3] Diagnosis is by an eye examination called autorefractor keratometry ...
Refractive index. A ray of light being refracted through a glass slab. In optics, the refractive index (or refraction index) of an optical medium is a dimensionless number that gives the indication of the light bending ability of that medium. Refraction of a light ray. The refractive index determines how much the path of light is bent, or ...
In statistics, Welch's t-test, or unequal variances t-test, is a two-sample location test which is used to test the (null) hypothesis that two populations have equal means. It is named for its creator, Bernard Lewis Welch, and is an adaptation of Student's t -test, [1] and is more reliable when the two samples have unequal variances and ...
Šidák correction for t-test. One of the application of Student's t-test is to test the location of one sequence of independent and identically distributed random variables. If we want to test the locations of multiple sequences of such variables, Šidák correction should be applied in order to calibrate the level of the Student's t-test.
The majority of autorefractors calculate the vision correction a patient needs (refraction) by using sensors that detect the reflections from a cone of infrared light. These reflections are used to determine the size and shape of a ring in the retina which is located in the posterior part of the eye. By measuring this zone, the autorefractor can determine when a patient's eye properly focuses ...
A refractometer is a laboratory or field device for the measurement of an index of refraction ( refractometry ). The index of refraction is calculated from the observed refraction angle using Snell's law. For mixtures, the index of refraction then allows the concentration to be determined using mixing rules such as the Gladstone–Dale relation ...