Determining the zone of reflection for posterior corneal surface comparison phakometry

Author: Carkeet, Andrew

Source: Ophthalmic and Physiological Optics, Volume 29, Number 1, January 2009 , pp. 99-104(6)

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Abstract:

Although comparison phakometry has been used by a number of studies to measure posterior corneal shape, these studies have not calculated the size of the posterior corneal zones of reflection they assessed. This paper develops paraxial equations for calculating posterior corneal zones of reflection, based on standard keratometry equations and equivalent mirror theory. For targets used in previous studies, posterior corneal reflection zone sizes were calculated using paraxial equations and using exact ray tracing, assuming spherical and aspheric corneal surfaces. Paraxial methods and exact ray tracing methods give similar estimates for reflection zone sizes less than 2 mm, but for larger zone sizes ray tracing methods should be used.

Keywords: asphericity; comparison phakometry; exact ray tracing; paraxial optics; posterior cornea; zone size

Document Type: Technical note

DOI: http://dx.doi.org/10.1111/j.1475-1313.2008.00597.x

Publication date: 2009-01-01