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t = center thickness (in metres); n = refractive index; P = front base curve (in 1/metres); h = vertex distance (in metres); F = back vertex power (in 1/metres), (essentially, the prescription for the lens, quoted in diopters ). If the difference between the eyes is up to 3 diopters, iseikonic lenses can compensate.
Prentice's rule, named so after the optician Charles F. Prentice, is a formula used to determine the amount of induced prism in a lens: = where: P is the amount of prism correction (in prism dioptres) c is decentration (the distance between the pupil centre and the lens's optical centre, in millimetres)
assess alignment of both eyes. The Four Prism Dioptre Reflex Test (also known as the 4 PRT, or 4 Prism Dioptre Base-out Test) is an objective, non-dissociative test used to prove the alignment of both eyes (i.e. the presence of binocular single vision) by assessing motor fusion. [1] Through the use of a 4 dioptre base out prism, diplopia is ...
Esophoria is an eye condition involving inward deviation of the eye, usually due to extra-ocular muscle imbalance. It is a type of heterophoria. Cause. Causes include: Refractive errors; Divergence insufficiency; Convergence excess; this can be due to nerve, muscle, congenital or mechanical anomalies.
Ophthalmology. Esotropia is a form of strabismus in which one or both eyes turn inward. The condition can be constantly present, or occur intermittently, and can give the affected individual a "cross-eyed" appearance. [1] It is the opposite of exotropia and usually involves more severe axis deviation than esophoria.
The free-air correction is the amount that must be added to a measurement at height to correct it to the reference level: δ g F = 2 g R × h {\displaystyle \delta g_{F}={\frac {2g}{R}}\times h} Here we have assumed that measurements are made relatively close to the surface so that R does not vary significantly.
Neurology, ophthalmology. Diplopia is the simultaneous perception of two images of a single object that may be displaced horizontally or vertically in relation to each other. [1] Also called double vision, it is a loss of visual focus under regular conditions, and is often voluntary.
Vincenty's formulae are two related iterative methods used in geodesy to calculate the distance between two points on the surface of a spheroid, developed by Thaddeus Vincenty (1975a). They are based on the assumption that the figure of the Earth is an oblate spheroid , and hence are more accurate than methods that assume a spherical Earth ...
IOL calculation formulas differ in the way they calculate ELP. In the original theoretical formula the ELP is considered a constant value of 4 mm for every lens in every patient. Better results are obtained by relating the expected ELP to the axial length and corneal curvature.
Geodesists use the following formula to correct for velocity relative to Earth during a gravimetric run. a r = 2 Ω u cos ϕ + u 2 + v 2 R . {\displaystyle a_{r}=2\Omega u\cos \phi +{\frac {u^{2}+v^{2}}{R}}.}