GB1239620A - - Google Patents

Abstract

1,239,620. Ophthalmic lenses. SOC DES LUNETIERS. Oct. 28, 1968 [Oct. 30, 1967; July 26, 1968], No. 51043/68. Heading G2J. If an eye 1, Fig. 1, looking at an object at infinity along the optical axis 3 of an ophthalmic lens 2 finds that the correction for ametropia is perfect and the lens 2 forms an image at R o , in the absence of eye 1, then when the eye 1 rotates about its centre of rotation O through an angle U the image of an object at infinity should be formed by lens 2 at a point R on sphere 5 centred at O and passing through R o , but in practice a spherical surfaced lens 2 forms a sagittal focus at S and tangential focus at T with the circle of least confusion at I. Accordingly the present lens has a surface shaped to eliminate or reduce the astigmatism TS and/or the field curvature I R particularly in the case of high power toric lenses such as those having a power greater than 12 D required in aphakia. This is achieved by taking a circle, passing through H and having a radius of approximately 27 or 28 mm, and evaluating along the two principal meridians the distances required from points on the circle K, G, etc. to the corrected lens surface and tabulating them as a function of angle U. For a progressive foci lens the correcting surface is evaluated along the vertical meridian on the basis of an object distance which gets progressively less as the eye looks downwardly, or for a lens of two or three focal lengths it is evaluated for the appropriate two or three object distances such as infinity, intermediate and reading distances.