The misalignment of ocular components and ocular monochromatic aberrations

Abstract

In this thesis, a theoretical method was developed to calculate the tilt and decentration of the crystalline lens from various possible reference axes in the human eye based on the misalignments of Purkinje images. The derivation was based on the Gullstrand-Emsley eye model utilizing the equivalent mirror theorem in the paraxial region.

A Purkinje image photographing system was developed to measure various misalignment parameters in the left eyes of twenty-one subjects. These factors included: 1) angle alphas defined both by aligning Purkinje image I and IV and by aligning Purkinje image I and III, 2) lens tilt and decentration with respect to the aligned Purkinje image I and IV, the pupillary axis and the line of sight, 3) the decentration of the pupil from the aligned Purkinje image I and IV. The measurement results explain the inconsistent results of current angle alpha measurements when compared to the traditional accepted value. Human eye lens tilt and decentration were measured for the first time. The pupil centration measurement revealed a special reference - the coaxially sighted corneal reflex axis - to represent the traditionally defined visual axis. A general trend of the misalignment of the 21 eyes measured was found.

An automated two-dimensional semi-Maxwellian view ocular aberration measurement system was developed for the first time. An effective and flexible wavefront aberration reconstruction procedure was also developed to reconstruct wavefront aberration reconstruction procedure was also developed to reconstruct wavefront aberration from measured ray aberration data. Pilot measurement of four eyes under natural pupil condition, with the center of the natural pupil as the reference, proved the effectiveness of both the system and the wavefront reconstruction method.

Using the coaxially sighted cornea reflex as the reference, wavefront aberrations of the left eyes of twenty-one emmetropic subjects were reconstructed from the measured ray aberration data. These data were also converted to wavefront aberrations using the geometrical center of the pupil as the reference. The average of the wavefront aberration o f the twenty-one eyes measured showed mainly primary symmetrical aberrations.

Finally, the symmetrical component and the symmetrical component of the mean squared wavefront aberration of each eye were calculated and used to correlate with each misalignment parameter measured. There is no significant correlation between either aberration component and the misalignment of the ocular structures in the twenty-one eyes studied.