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In a bifocal lens, this generally indicates what is to be placed in the top segment. NV is an abbreviation for near vision. This may represent a single-vision lens prescription to improve near work, or the reading portion of a bifocal lens. OD is an abbreviation for oculus dexter, Latin for right eye from the patient's point of view. Oculus ...
which is the ratio of the output beam width to the input beam width. Note the sign convention: a telescope with two convex lenses (f 1 > 0, f 2 > 0) produces a negative magnification, indicating an inverted image. A convex plus a concave lens (f 1 > 0 > f 2) produces a positive magnification and the
The phoropter measurement is made at a common vertex distance of 12 mm from the eye. The equivalent prescription at the patient's cornea (say, for a contact lens) can be calculated as follows (this example assumes a negative cylinder sign convention): Power 1 is the spherical value, and power 2 is the steeper power of the astigmatic axis:
Intra-ocular lens IOP: Intra-ocular pressure ISNT: Inferior, Superior, Nasal, Temporal rule used to assess optic disc appearance K: Keratometry OS oculus sinister (left eye) LHyperT or LHT: Left hypertropia LHypoT: Left hypotropia LO: Lenticular opacity L/R FD: L/R fixation disparity L/R: L hyperphoria Left ET: Left esotropia LVA: Low vision ...
Likewise, the magnification of a lens is given by = = where the negative sign is given, by convention, to indicate an upright object for positive values and an inverted object for negative values. Similar to mirrors, upright images produced by single lenses are virtual while inverted images are real.
1: Imaging by a lens with chromatic aberration. 2: A lens with less chromatic aberration. In optics, aberration is a property of optical systems, such as lenses and mirrors, that causes the image created by the optical system to not be a faithful reproduction of the object being observed. Aberrations cause the image formed by a lens to be ...
In a real optical system, the best optical quality is usually achieved where most rays of light are roughly normal (i.e., at a right angle) to the lens surface. In the case of an eyeglass lens, this means that the lens should be roughly shaped like a cup with the hollow side toward the eye, so most eyeglass lenses are menisci in shape.
Negative relative accommodation (NRA) was proposed by Joseph Kearney of Oxford University in 1967 as a measure of the maximum ability to relax accommodation while maintaining clear, single binocular vision. It is an indirect measurement of fusional vergence in binocular vision. [1]