Observations on the optical effects of a cataract

To describe and measure the optical effects seen by a person with a cataract and to use these observations to deduce physical changes in the crystalline lens caused by the cataract formation.

Humphrey Systems, Dublin, California, USA.

Caustic patterns created on the retina by a bright point source of white light as that source is viewed at various far-point distances ranging from the anterior focal point of the eye to +15.00 diopters were observed. The subtended retinal angle of a diffractive ring of light created by a small bright source of white light was observed and measured.

Three optical effects were seen and measured: multiple-image formation at certain far-point positions; a diffractive light ring surrounding small bright sources; a radial needle of bright light surrounding a small bright-white source. With a point source of light positioned at the anterior focal point of the eye, the Y sutures of the lens could be visualized. With the point source at other distances, characteristic caustic patterns could be visualized, allowing assessment of the lens' optical character. The subtended retinal angle of the diffractive ring was measured so the periodic lens structure could be evaluated.

The lens acted refractively as if it were divided into 3 elements with noncoincident optical axes. These 3 segments were associated with areas defined by the Y sutures, causing 3 images to be formed at certain distances. The caustic patterns indicate that each segment is slightly toroidal with axes at about 120 degrees apart combined with overcorrected spherical aberration. The period structure creating the diffractive ring had a period of 10 microns, approximately the width of a cortical lens cell, indicating that fluid between the cells likely creates a diffractive phase grating.