Improvements to Phakometry Using Bessel Beams.

Abstract

The main problem with phakometry is the low visibility of the third Purkinje image. We built a phakometer using Bessel beams, which have properties of being resistant to diffraction and the potential for self-reconstruction. This instrument had lenticular images three times brighter than those of a conventional phakometer. To investigate Purkinje image brightness, accuracy, and repeatability of a "Bessel" phakometer compared with those of a conventional phakometer. Phakometers were developed with a telecentric imaging system focused at the pupil plane of the eye to capture anterior cornea, anterior lens (PIII), and posterior lens (PIV) Purkinje images. A Bessel beam was generated by a diode laser beam passing through a high-powered doublet with a central obstruction. Software was used to determine image sizes and estimate lens anterior and posterior surface radii of curvature (Ra, Rp), equivalent refractive index (RI), and equivalent power (F). The Bessel phakometer's accuracy was assessed using a model eye. Repeatability (interobserver and intraobserver) and Purkinje images brightnesses of Bessel and conventional phakometers were assessed with six participants. The lens parameters of the model eye determined by the Bessel phakometer were similar to those provided by the model eye's manufacturer with differences (manufacturer - Bessel) in Ra and Rp, RI, and F of +1.18 mm, 0.18 mm, +0.0053, and -0.55 D, respectively. The intraobserver repeatabilities for the Bessel and conventional phakometers were similar. The interobserver repeatabilities of Ra, Rp, and RI for the Bessel phakometer were almost half those (i.e., two times better) for the conventional phakometer. Brightnesses of PIII and PIV were approximately three times higher with the Bessel phakometer than with the conventional phakometer. The Bessel beam phakometer provided accurate estimates of lens parameters of a model eye and produced brighter Purkinje images and better interobserver repeatability than that of a conventional phakometer.