Considerations in Contact Lens Use Under Adverse Conditions Proceedings of a Symposium (1991) / Chapter Skim
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Vision Performance With Contact Lenses
Vision Performance With Contact Lenses
Pages 135-141
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From page 135... ...
VISUAL ACUITY MEASURES - Let us begin by considering various characteristic of contact lenses that might contribute to changes in visual acuity. Although aberrations are the primary concern, residual astigmatism, which is probably the more important aspect of contact lenses, must also be considered.
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From page 136... ...
Recently, some people have tried to measure the same kind of function but by using the more traditional visual acuity testing procedures namely, modified Snellen-type testing charts. The information obtained from these tests is in traditional terms that can be understood a little more readily than some of the results from psychophysical testing methods.
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From page 137... ...
Untrained operators can conduct the test fairly easily, and the results can be interpreted fairly simply. ACUITY CHANGES Guillon and co-workers measured visual acuity changes in a group of subjects first with spectacle correction and then with contact lens correction.
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From page 138... ...
A careful review of the literature reveals that from one study to the next there can be just about any conclusion one wants regarding the effects of contact lenses on acuity. The more recent studies show that contrast sensi
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From page 139... ...
When there is a "significant" difference between the two types of corrections contact lenses and spectacles it can usually be attributed to the fact that there was residual astigmatism present when the subjects were wearing contact lenses. I think that the result is very meaningful, however, in terms of what results might be anticipated with contact lenses worn by military personnel.
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From page 140... ...
RESIDUAL ASTIGMATISM Residual astigmatism which remains when the contact lens is in place, is a very real problem with regard to fitting military personnel with contact lenses. The task is to fit a group of subjects with an unknown distribution of refractive errors, and without knowing precisely the incidence of astigmatism.
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From page 141... ...
For an individual who has a certain amount of asi~gmai~sm, it cannot always be predicted what type of lens will produce the best visual acuity for that person. In conclusion, the military's policy toward contact lenses cannot really restrict the lens type to soft contact lenses and expect to provide an optimal correction for the majority of potential pilots.
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