Experimental investigation on mechanism of hydrophilic acrylic intraocular lens calcification.

PURPOSE: To construct a model simulating intraocular lens (IOL) opacification attributable to the formation of calcium phosphate deposits and to investigate the kinetics of deposit formation.
DESIGN: Prospective laboratory investigation.
SETTING: Department of Ophthalmology, Medical School and Department of Chemical Engineering, Laboratory of Inorganic and Analytical Chemistry, University of Patras, Greece. STUDY POPULATION: Three hydrophilic acrylic IOLs (26% water content) were placed inside a 10-mL double-walled thermostated reactor simulating the anterior chamber. Simulated aqueous humor was injected continuously into the reactor using a pump with variable speed. OBSERVATION PROCEDURES: The observation of IOLs was carried out in situ daily by optical microscopy. Scanning electron microscopy and energy-dispersive radiographic spectroscopy were used for the identification of the morphologic features and the composition of the deposits.
RESULTS: The lenses were removed and inspected 5, 9, and 12 months after the initiation of the experiment. Investigation showed deposits of calcium phosphate crystallites in the interior of opacified IOLs. However, these deposits were not observed on the surface of the IOLs.
CONCLUSIONS: In agreement with earlier reports by our group and in the literature, IOL opacification is the result of calcification. It is suggested that the surface hydroxyl groups of the polyacrylic polymeric components of the IOLs are capable of inducing surface nucleation and crystal growth of calcium phosphates. However, most important is the finding that the calcification of IOLs is initiated from their interior through the development of sufficiently high local supersaturation, realized through the diffusion of calcium and phosphate ions.