Physical and chemical factors underlying glistening formation in hydrophobic acrylic intraocular lens materials

Abstract

Purpose : Glistenings are opacifications that cause light scattering within intraocular lenses (IOLs). In hydrophobic IOLs, glistenings are likely microvacuoles filled with aqueous humor. Improved manufacturing practices and polymerization processes have reduced glistening formation in IOLs. This study evaluated the underlying factors leading to glistening formation in hydrophobic acrylic IOLs.

Methods : Five hydrophobic acrylic IOL material samples were manufactured by varying the IOL production process. Glistening density was rated on a 5-point scale (level 1, lowest; level 5, highest; NIDEK Co., Ltd.). Factors that were changed during the IOL production process included, the concentration of the cross–linking agent, solvent, and drying conditions. To promote glistening formation, each sample was immersed in water at 60°C for 2 h, then left in situ at room temperature for 24 h. The material microstructure was examined by atomic force microscopy. Specific surface area was determined with a steam adsorption method. The composition of each sample was determined by Raman spectrophotometry. Internal cracking and differences in sample composition were examined by computed tomography (CT).

Results : Glistenings were observed as particles of 30–50 μm diameter and 3–5 μm in height when the samples were wet, but not dry. Glistenings developed in regions rich in hydrophilic functional groups. The level-5 materials adsorbed more water than the level-1 materials. CT did not reveal any internal cracks or differences in material composition in regions with glistenings formation compared to regions without glistenings. Fewer glistenings formed in highly cross-linked samples. Residual solvent that remained in the sample resulted in a high-density of glistenings, however, these glistenings were not observed after drying at 60°C for over 24 h.

Conclusions : The outcomes of this study suggest that material and manufacturing process affect glistening formation in IOLs. Glistening formation was increased in areas rich in hydrophilic functional groups and in materials with a high specific surface area or a low density of cross-links. Glistenings can be reduced by fully drying the IOL materials and avoiding direct contact between solvents and the IOL materials.

This is an abstract that was submitted for the 2018 ARVO Annual Meeting, held in Honolulu, Hawaii, April 29 - May 3, 2018.