Knapp's Rule states that lenses placed at the anterior focal point of the eye, generally 15 mm in front of the eye, will create similarly sized images on the retina, whenever the disparity between the two eyes is due to a difference in axial length of the eyes.[1]
When a refractive error is corrected with spectacle lenses, the retinal images change size. It is magnified with convex lenses and minified with concave lenses. One difficulty, then, in prescribing glasses to an individual with a disparity in refractive error between the two eyes is that a disparity in image size between the two eyes may be created.
There is some controversy as to the soundness of Knapp's Rule.[2]
References
edit- ^ Heczko, Joshua; Sierpina, David (2018-03-01). "Rapid neuroadaptation to surgically-induced aniseikonia in a 17-year-old patient with high preoperative anisometropia: A case report". American Journal of Ophthalmology Case Reports. 9: 75–76. doi:10.1016/j.ajoc.2018.01.021. ISSN 2451-9936. PMC 5861630. PMID 29577095.
- ^ Kushner, Burton J. (January 2008). "Causes and Prevention of Diplopia After Refractive Surgery". American Orthoptic Journal. 58 (1): 39–44. doi:10.3368/aoj.58.1.39. ISSN 0065-955X.
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