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O. Touzeau, S.E. Scheer, C. Allouch, R. Kopito, V.M. Borderie, L. Laroche; Quantification of Enantiomorphism of Astigmatism . Invest. Ophthalmol. Vis. Sci. 2003;44(13):2544.
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© ARVO (1962-2015); The Authors (2016-present)
Purpose: To quantify enantiomorphism (mirror-image symmetry) of astigmatism Methods: Polar values (cylinder, axis) of regular astigmatism were transformed in rectangular coordinates (x,y). Left eye astigmatism and right eye perfect enantiomorphism astigmatism were expressed as points in a "dioptric plane". The distance between the two points was measured to quantify the enantiomorphism. The validity of the index was graphically verified using Holladay's graph. The index was tested in various clinical situations. Results: The value of the index is null only when both eyes present a perfect enantiomorphism: equal cylinders and mirror symmetry for both axes (sum of both axes equal 180°). Values of index differ significantly according to the etiologic group (idiopathic astigmatism: 0.72D, phacoemulsification: 1.41D, extracapsular cataract extraction: 2.88D, keratoconus: 4.56D, penetrating keratoplasties: 8.09D; p<0.001). Enantiomorphism decrease significantly with aging (0.62D in young patients versus 0.93D in older patients; p<0.001). Corneal astigmatism shows higher enantiomorphism than subjective astigmatism (0.70D versus 0.91D; p=0.02). Conclusions: Enantiomorphism of astigmatism can easily be quantified by an index calculated using cylinders and axes. Aging, anterior segment surgery and keratoconus decrease enantiomorphism of astigmatism.
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