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Among the numerous diseases of the cornea, there are many which change its normal form; this results in the production of distorted or even completely blurred retinal images, and accordingly vision suffers. Now there is a group of alterations in the form of the cornea, of which the bad effects upon vision may be removed by the use of glasses; these are cases of regular astigmatism.... The matter begins to be more difficult when we deal with the alteration in the form of the cornea known as keratoconus [which causes irregular astigmatism].
The results of optical correction are, however, entirely unsatisfactory in cases in which defects of vision are due to irregular corneal astigmatism. Donders recommended the correction of such cases by stenopaeic glasses. He and his pupil, von Wijngarden, demonstrated that the improvement of [near] vision resulting from the use of stenopaeic glasses was often really astonishing, and that
Fick AE. A Contact Lens. Arch Ophthalmol. 1997;115(1):120-121. doi:10.1001/archopht.1997.01100150122024