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A COMPARISON OF THE ERRORS ARISING FROM THREE METHODS OF PHAKOMETRIC COMPUTATION

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Abstract

Phakometric determination of the crystalline lens surface powers traditionally requires measurement of Purkinje images I, III and IV which are formed by reflection at the anterior corneal surface, the anterior lens surface and the posterior lens surface, respectively1-3. In this case, any discrepancies between refractive error and lens power are taken up by a calculated axial length3. An alternative method has been described which uses only Purkinje images I and III4. Here, any discrepancies between refractive error and an ultrasonically determined axial length are taken up by the posterior lens power3. Both methods suffer from difficulties encountered measuring Purkinje image III due to its poor quality coupled with the fact that it is positioned in the vitreous chamber whereas the other images fall approximately in the iris plane5. A further technique has therefore been developed which uses only Purkinje images I and IV6. Now, any discrepancies between refractive error and an ultrasonically determined axial length are taken up by the anterior lens surface power. The present study aims to compare the errors arising from all three methods of phakometric computation.

© 1993 Optical Society of America

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