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On‐eye power characteristics of soft contact lenses
Author(s) -
Plainis Sotiris,
Charman W. N.
Publication year - 1997
Publication title -
ophthalmic and physiological optics
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 1.147
H-Index - 66
eISSN - 1475-1313
pISSN - 0275-5408
DOI - 10.1046/j.1475-1313.1997.97807272.x
Subject(s) - keratometer , lens (geology) , contact lens , cornea , optics , refraction , optometry , refractive error , power (physics) , optical power , corneal topography , ophthalmology , materials science , visual acuity , physics , medicine , laser , quantum mechanics
The power effect of a soft contact lens on the eye is a function of its off‐eye power, the manner in which the lens flexes on the eye, lens hydration changes and the cornea. The innovative aspect of the present study was the employment of a high‐illumination keratometer (Carl Zeiss Jena) which allowed us to obtain front and back surface keratometric readings when single‐vision lenses were in position on the eye. The on‐eye power of the lens could then be calculated from these readings, with the assumption that the centre thickness and refractive index of the lens corresponded to those in vitro . The estimates of the on‐eye powers agreed closely with the results indicated by over‐refraction and showed that all the lenses used closely conformed to the corneal shape and the tear lens formed was of minimal power (≤0.25 D). Moreover, comparison of in‐vitro with on‐eye power estimates indicated that the positive single vision lenses lost power on the eye (mean difference −0.38 D), while the negative ones maintained their power (mean difference −0.02 D). The findings of the present study appeared to be in agreement with the predictions of most of the flexure models developed in the past.