Download PDF by W.A. Douthwaite, MSc PhD FBCO DCLP (Auth.): Contact Lens Optics and Lens Design

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

ISBN-10: 0750688793

ISBN-13: 9780750688796

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Extra info for Contact Lens Optics and Lens Design

Sample text

Anisometropia is more likely to be axial than refractive and the foregoing indicates unfortunately that the fundamentals have not yet been unequivocally resolved. The only thing that can be stated with some certainty is that, if an anisometrope has comfortable binocular vision with a spectacle correction, she or he can expect to encounter adaptation problems when transferring to contact lenses. A study by Winn et al. (1986) has concluded that all anisometropes are better corrected by contact lenses if the aim is to minimize aniseikonic effects.

1 Refractive anisometropia In refractive anisometropia the uncorrected retinal image size will be the same in the two eyes. Positive correcting lenses will magnify, and negative 22 Anisometropia correcting lenses will minify, the retinal image. Thus correcting lenses will induce an image size disparity which may result in binocular vision problems. A pair of contact lenses will induce a much smaller change than a pair of spectacle lenses. Therefore a contact lens correction appears to be the more satisfactory of the two alternatives.

00 D. 5. The uncorrected basic retinal image size is determined by the axial length of the eye. The longer eye produces a larger retinal image. 6. Positive spectacle lenses increase the retinal image size. Negative lenses decrease the retinal image size. The effect is more pronounced with large vertex distances. 7. In axial ametropia, the increase in retinal image size due to a positive spectacle lens produces an image which is still smaller than that of an emmetropic eye. Corrected axial myopes possess retinal image sizes which are larger than those of the emmetrope.

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Contact Lens Optics and Lens Design by W.A. Douthwaite, MSc PhD FBCO DCLP (Auth.)

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