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Corrective lens. A corrective lens is a transmissive optical device that is worn on the eye to improve visual perception. The most common use is to treat refractive errors: myopia, hypermetropia, astigmatism, and presbyopia. Glasses or "spectacles" are worn on the face a short distance in front of the eye.
Abbe number. In optics and lens design, the Abbe number, also known as the V-number or constringence of a transparent material, is an approximate measure of the material's dispersion (change of refractive index versus wavelength), with high values of V indicating low dispersion. It is named after Ernst Abbe (1840–1905), the German physicist ...
In order to see a clear image, the eye must focus rays of light on to the light-sensing part of the eye - the retina, which is located in the back of the eye.This focusing - called refraction - is performed mainly by the cornea and the lens, which are located at the front of the eye, the anterior segment.
Eyeglass prescription. Using a phoropter to determine a prescription for eyeglasses. An eyeglass prescription is an order written by an eyewear prescriber, such as an optometrist, that specifies the value of all parameters the prescriber has deemed necessary to construct and/or dispense corrective lenses appropriate for a patient.
In optics, the Abbe sine condition is a condition that must be fulfilled by a lens or other optical system in order for it to produce sharp images of off-axis as well as on-axis objects. It was formulated by Ernst Abbe in the context of microscopes. [ 1] The Abbe sine condition says that. the sine of the object-space angle should be ...
A corrective lens can be used to correct hyperopia by imaging an object at the typical near point distance D onto a virtual image at the patient's actual near point, at distance NP. [2] From the thin lens formula, the required lens will have optical power P given by [3] [4]. The calculation can be further improved by taking into account the ...
Vertex distance is the distance between the back surface of a corrective lens, i.e. glasses (spectacles) or contact lenses, and the front of the cornea. Increasing or decreasing the vertex distance changes the optical properties of the system, by moving the focal point forward or backward, effectively changing the power of the lens relative to ...
While moving the streak or spot of light through the pupil across the retina, the examiner observes the relative movement of the reflex or manually places lenses over the eye (using a phoropter or trial frame and trial lenses) to "neutralize" the reflex. [2] Static retinoscopy is a type of retinoscopy used in determining a patient's refractive ...