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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 ...
S2=vertex of the second optical surface; SH=distance from the vertex of the first optical surface to the primary principal plane; S′H′=distance from the vertex of the second optical surface to the secondary principal plane; SF=distance from the surface of the first optical surface to the front focal point, called the front focal distance; S ...
Back vertex distance BVP: Back vertex power CD: Centration distance C/D: Cup–disc ratio CF: Count fingers vision – state distance c/o or c.o. Complains of CT: Cover test c/u: Check up CW: Close work Δ: Prism dioptre D: Dioptres DC: Dioptres cylinder DNA: Did not attend DOB: Date of birth DS: Dioptres sphere DV: Distance vision DVD ...
BVD Back vertex distance is the distance between the back of the spectacle lens and the front of the cornea (the front surface of the eye). This is significant in higher prescriptions (usually beyond ±4.00D) as slight changes in the vertex distance for in this range can cause a power to be delivered to the eye other than what was prescribed.
An f-number conversion chart has been added by the user. At the same time, there were a number of aperture numbering systems designed with the goal of making exposure times vary in direct or inverse proportion with the aperture, rather than with the square of the f-number or inverse square of the apertal ratio or intensity ratio.
The aim of an accurate intraocular lens power calculation is to provide an intraocular lens (IOL) that fits the specific needs and desires of the individual patient. The development of better instrumentation for measuring the eye's axial length (AL) and the use of more precise mathematical formulas to perform the appropriate calculations have significantly improved the accuracy with which the ...
Positive signs indicate distances to the right of the corresponding vertex, and negative to the left. [4] For a thin lens in air, the principal planes both lie at the location of the lens. The point where they cross the optical axis is sometimes misleadingly called the optical centre of the lens. For a real lens the principal planes do not ...
The sign convention for the optical radius of curvature is as follows: If the vertex lies to the left of the center of curvature, the radius of curvature is positive. If the vertex lies to the right of the center of curvature, the radius of curvature is negative. Thus when viewing a biconvex lens from the side, the left surface radius of ...