Visual Impairment In Primary And Secondary Intraocular Lens Calcification Dependent On Calcium Phosphate Levels

The aim of the study was to assess the quantity of calcium phosphates in primary and secondary intraocular lens calcification and investigate its influence on straylight and light loss as a measure of optical impairment. A novel method for quantifying calcium phosphates in hydrophilic intraocular lenses was employed for this purpose.

Intraocular lens calcification is a rare but serious complication of cataract surgery, where calcium phosphate crystals form on the lens surface and within the polymer.
Two types of calcification exist: primary and secondary calcification. In the present study, the quantity of calcium phosphate was evaluated in both groups, and the impact on optical impairment was examined by assessing straylight and light loss.

Light transmission and straylight were quantified in 10 cases of primary calcification and 8 cases of secondary calcification in explanted hydrophilic intraocular lenses of the same lens model for each group. The light loss induced by calcification was evaluated at a wavelength of 546 nm for the central 3 mm aperture using a power meter (PM100D, Thorlabs Inc., Newton, USA) and an optical bench setup (Optispheric IOL Pro 2 optical bench, Trioptics GmbH, Wedel, GER). Straylight was measured employing a straylight meter (C-quant, Oculus Optikgeräte GmbH, Wetzlar, GER). The quantity of calcium phosphate was determined through thermogravimetry and inductively coupled plasma optical emission spectrometry (ICP-OES).

Primary calcification resulted in higher calcium phosphate amounts within the lens polymer than secondary calcification. Correspondingly, higher straylight values (M = 289,27 deg²/sr, SD = 162,24) and lower light transmission (M = 9,47 µW, SD = 1,51) were found in primary calcification than in secondary calcification (M = 88,88 deg²/sr, SD = 50,63 and M = 10,50 µW, SD = 1,72, respectively). Light transmission was reduced to 69,51 % and 77,84 % of a control lens in primary and secondary calcification. In both groups, strong and significant (p < 0,05) negative correlations of light transmission and straylight were found (r = -0,71 vs. r = -0,93).

ICP-OES was demonstrated as a feasible method for quantifying calcium phosphates in calcification. Optical impairment in intraocular lens calcification appears to be significantly influenced by the density of the calcium phosphate crystals in the lens polymer. In our study, both types of calcification exhibited a high potential for inducing glare phenomena, with the primary type resulting in more severe symptoms than the secondary one.