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IMAGE FORMATION BY ASTIGMATIC LENSES
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amount anisometropia aperture axis direction B.A. line back surface back vertex power base curve beam best form blank centre of rotation CHAPTER chromatic aberration concave convergence convex cornea correcting lens crosslines crown glass curvature cylinder D.C. ax decentration deviation diagram diameter distance lens distant object edge equal Explain clearly Find focal length focal lines frame front surface fused bifocal give given hyperopia inches infra-red instrument lens measure lens surface light main lens marked meniscus lens metre myopia negative lens neutralising ophthalmic optical centre optician oval parallel perpendicular placed plane plano portion positive lenses prescription principal meridians principal powers prism dioptres prismatic effect produced radius refractive index retina right eye rimless scale segment spectacle glass spectacle lenses sph.-cyl sphere spherical aberration spherical lens spherometer surface powers thickness thin lens tool toric form toric lens toric surface transposition trial ultra-violet vision