Optics: eye examining – vision testing and correcting – Spectacles and eyeglasses – Ophthalmic lenses or blanks
Patent
1995-09-27
1998-06-23
Sugarman, Scott J.
Optics: eye examining, vision testing and correcting
Spectacles and eyeglasses
Ophthalmic lenses or blanks
351160R, G02C 704
Patent
active
057710880
DESCRIPTION:
BRIEF SUMMARY
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to contact lens designed to accommodate and correct for the effects of presbyopia, myopia and hyperopia and, in particular, to such lenses which are provided with characteristics to compensate for defects associated with peripheral vision.
2. State of the Art
In the design of ophthalmic lenses, it is an aim that the optics of a lens used to correct vision ideally provide precise refractive correction and do not add to the natural aberrations within the eye. However, good vision is dependent upon several factors: visual acuity, contrast sensitivity, high defocus perception threshold, good visual performance (speed and accuracy of recognition), tolerance to illuminant intensity, and tolerance to illuminant color.
These are somewhat interdependent and all degrade with age.
Contact lenses provide an opportunity by which some of these effects are countered by appropriate optical design, since the lens and the eye are in close physical proximity, compared to spectacles, and optical alignment is consequently easier to achieve.
It is well known that visual performance is degraded by contrast and object size reduction and is generally improved by higher illuminant intensity. However, with age, the illuminant intensity becomes the most dominant factor with respect to visual performance. For instance, a work force in its early forties will require 50 to 100% higher lighting levels than a work force in its early twenties to do the same visual tasks at the same efficiency level. Further, the younger population is highly tolerant to varying light levels, and with age the population becomes very sensitive to light level. This is linked to the fact that younger people can operate effectively over the whole visible spectrum, while the vision of older people can be impaired severely at the blue end of the visible spectrum. Consequently, the older a person is the more sensitive to the spectral content of lighting he becomes. This aspect also varies greatly on an individual basis.
There is always, in the human eye, a certain degree of intrinsic spherical aberration. This is the primary cause of unwanted blur in the retinal image. This blur is due to rays which pass along the axis of the eye (paraxial rays) and which are focussed slightly behind the fovea, whereas rays which pass through the outer regions of the pupil are focussed in front of the fovea. In fact, at the outer limit set by the iris (peripheral rays), the focus is substantially myopic. Accordingly, there is always a part of the image received by the human eye that is blurred. The mechanics of the human eye and the function of the human brain, in general, compensate for this. With age, in particular, the degree of this lack of focal clarity increases to the point that the human eye and brain cannot accommodate for this and some means of focal correction is called for.
In addition to the above visual problems with the human eye, there are some further physical problems with the human eye. For example, the human eye mechanism is designed to operate internally as a sphere, with the surface of the cornea, onto which a contact lens is placed, also being spherical. As will be appreciated, this is not always the case. This lack of sphericity in the surface of the cornea can cause problems in the optical performance of the human eye, as well as in the fitting of contact lenses. Consequently, over the years the industry has disclosed a way of compensating for this by what has become commonly called a toric lens.
Specifically, toric contact lenses are contact lenses which are adapted to optically compensate for the non-sphericity of the cornea of the human eye. This can be done by building optical correction components into the back surface of the contact lens, that is the surface of the contact lens which is in contact with the cornea of the eye when fitted, or in the front surface of the contact lens.
One known approach for the design of contact lenses in an attempt to alleviate this prob
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Pilkington Barnes Hind Inc.
Sugarman Scott J.
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