Download e-book for iPad: Contact Lens Optics and Lens Design by W.A. Douthwaite, MSc PhD FBCO DCLP (Auth.)


By W.A. Douthwaite, MSc PhD FBCO DCLP (Auth.)

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There are now examples of commercial soft lens products which are moulded either fully or partially hydrated. CIBA Vision’s daily disposable lens which is marketed under the name Focus Dailies is cast moulded in glass reusable moulds in a fully hydrated state. After casting, the lens is polymerized using ultraviolet light. The Johnson & Johnson Vision Care range of 58% water content hydrogel lenses are cast moulded in a partially hydrated state, a process described by the company as stabilized soft moulding.

48 D too negative. 10 The over-refraction. Point D is the place where the point image is formed after refraction at the first contact lens surface only refraction is of high power and the contact lens is a thick lens, with powerful surfaces. In the example illustrated above, we have a high plus spectacle lens at a finite vertex distance which serves to magnify the retinal image. When the contact lens returns with the correct BVP, much of this magnification is lost and the visual acuity may not be as good as that found at the time of the over-refraction.

In these circumstances the front surface radius will also alter and these induced changes may well affect the power of the contact lens. In order to investigate the consequence of power changes due to the lens bending on the eye we must make some assumptions about induced changes in the lens parameters. 13 constant. 125. 125. Baron (1975) suggested that a change in back surface radius will be accompanied by an almost equal change in the front surface radius. The most useful work on this subject was published by Bennett (1976) who assumed that the lens volume remained unchanged; there is no redistribution of lens thickness, with the lens front surface remaining spherical when resting on a spherical cornea.

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