Calcified silicone lenses may be associated with asteroid hyalosis

"The problem of dystrophic calcification of IOLs has been described in association with some hydrophilic acrylic designs including cases in which the deposits were observed on the surfaces of the lenses, and cases in which the deposits were observed within the substance of the lenses. In 2004, however, there have been two reports of dystrophic calcification of silicone IOLs," Dr. Werner said.

She reported three such cases; another case was reported in Austria. Dr. Werner is assistant professor, John A. Moran Eye Center, University of Utah, Salt Lake City.

Deposits found In the three cases that Dr. Werner observed, the deposits were seen only in the area of the YAG laser capsulotomy, but in the Austrian case the deposits were also seen on the periphery of the optic covered by the posterior capsule.

Dr. Werner and her colleagues also analyzed a fourth case of dystrophic calcification of a silicone IOL in which the diabetic patient had bilateral asteroid hyalosis. The patient had undergone cataract surgery in 1994 on the left eye, which had a three-piece silicone lens implanted. She then underwent cataract surgery of the right eye in 1995 and received a three-piece hydrophobic acrylic IOL. She underwent YAG laser capsulotomy of the left eye in 1996 for possible posterior capsule opacification; however, there was increasing opacification within the area of the capsulotomy over the ensuing years. The right eye had no opacification, according to Dr. Werner.

"The surface analysis of the first of the silicone plate IOLs confirmed the presence of calcium and phosphate within the deposits. The second silicone-plate IOL had more deposits on the surface of the lens, and surface analysis confirmed the presence of calcium and phosphate in the deposits. The third silicone-plate IOL had deposits that could be extensively removed from the lens surface by YAG laser application; calcium and phosphate were also detected within the few deposits on the lens. In the three-piece silicone IOL, the deposits were similar to those of the other lenses and calcium and phosphate were also confirmed within the deposits," Dr. Werner reported.

Regarding asteroid bodies, the composition, origin, and mode of formation are controversial. She pointed out that some investigators have reported lipid-containing calcium compounds, and other studies suggested against a lipid character.

"What is certain is that asteroid bodies represent a continuous supply of calcium or they are an indicator of a continuous supply of calcium to the vitreous," she stated.

Dr. Werner also noted that YAG laser capsulotomy, which allows direct contact between the posterior surface of the IOL and the vitreous, accelerated the process of calcium precipitation-at least in two of the cases.