Standardized digital imaging technique aims to increase understanding of intralenticular glistenings

October 1, 2008

A technique for obtaining digital photographs under standardized conditions was developed as the foundation for scientific assessment of IOL glistening size and severity, which ultimately will be used to investigate visual impact.

Key Points

Researchers developing a method for standardized digital photographic analysis of intralenticular glistenings believe it represents an important step forward in the scientific assessment of this IOL complication and its visual significance.

"We are all familiar with glistenings in IOL material," said Dr. Trattler, a private practitioner in Miami and a volunteer assistant professor at Bascom Palmer Eye Institute, University of Miami Miller School of Medicine. "However, their prevalence, severity, and visual significance with respect to effects on visual acuity, contrast sensitivity, and/or dysphotopsias remain controversial because no consistent standard exists for the in vivo evaluation or photographic capture of these microvacuoles.

According to current concepts, IOL glistenings are thought to represent water bubbles (microvacuoles) in the lens material that arise because temperature changes allow water to collect within the gaps formed by nonhomogenous polymerization. The microvacuoles are visible because of their different refractive index relative to the lens material. Development of glistenings has been more common in injection-molded IOLs compared with lathe-cut implants because the former manufacturing process may cause more gaps to form.

Magnification

So far, a slit-lamp magnification of 20 to 30× has worked best for the photography. Recording one image for each patient with a magnification of 10 to 12× appears helpful for calibration because it allows for visualization of the entire pupil and may allow correlation to white-to-white dimensions.

Broad tangential illumination was needed for maximum vacuole visibility. Light is set to enter the eye from the temporal side to minimize shadowing from the nose. A slit size of 2 mm provides the best depth of field.

The camera is focused on the bulk of material at the center of the lens and set to capture the central 4 mm of the IOL diameter. Color photography was found to be better than black-and-white because it provided better contrast. A high-definition camera, at least 5 megapixel, was needed for good-quality images.

Glistenings grading scale

The investigators also have devised a grading system by which the severity of the glistenings is scored on a scale of 1 to 4 using digital image processing software that factors in the number and size of the microvacuoles in a central 2- × 2-mm region.

Randall J. Olson, MD, the John A. Moran Presidential Professor and chairman, Department of Ophthalmology and Visual Sciences, University of Utah, Salt Lake City, is collaborating on the project. He has conducted previous research on glistening in various IOL materials and was instrumental in developing the glistenings grading scale.

"The clinical impact of glistenings is still controversial largely because large-scale studies have not been completed," he said.

"What we do know is they correlate with loss of high-frequency contrast sensitivity and have been shown to get worse with time, at least over the first 3 years [Waite A, Faulkner N, Olson RJ. Glistenings in the single-piece, hydrophobic, acrylic intraocular lenses. Am J Ophthalmol. 2007;144:143-144]."

He continued: "They are so common they deserve a more thorough analysis to determine also if they do not cause light scattering glare disability and if severe glistenings could decrease visual acuity to a significant degree, as has been suggested but not clearly documented to date."

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