Intraocular lens glistenings.

Glistenings are fluid-filled microvacuoles that form within an intraocular lens (IOL) optic when the IOL is in an aqueous environment. The phenomenon of glistenings has been reported most commonly in hydrophobic acrylic IOLs. However, this phenomenon has also been described in silicone and hydrophilic acrylic IOLs, as well as in other materials such as poly(methyl methacrylate). The incidence of glistenings varies widely and has been reported from approximately 11% to 100% in several series. The topic of glistenings was thoroughly discussed in a review/ update article by Werner. Multiple studies have evaluated the possible mechanism of glistening formation within IOLs. The most commonly described theory proposed for the formation of glistenings is that polymers absorb water when immersed in an aqueous environment over an extended period of time and that if the water vapor detaches from its surrounding matter and gathers into a voidwithin the polymer network of the IOL, a visible water drop forms. As the light is reflected and scattered at water–polymer interfaces, a sparkling or glistening-like appearance of these fluid-filled vacuoles is noted because the refractive index of water is different from that of the polymer. A more recent theory has been proposed; ie, that glistenings are the result of relatively slow-moving hydrophilic impurities within the IOL material that segregate out of the matrix material into polymer voids, giving rise to osmotic pressure differences between the cavity and the external medium in which the IOL is immersed. Influx of water into these cavities deforms the surrounding polymer until it causes permanent deformation and the cavities grow. Factors that have been consistently associated with glistening formations are changes in temperature, IOL manufacturing and packaging techniques, as well as an association with breakdown of the blood–aqueous barrier. The most significant factor in the formation of glistenings is the time following cataract surgery, as glistening formation as well as the intensity of glistenings has been significantly associated with a longer follow-up time. In this issue, Colin et al. (pages 1140–1146) present results of a study analyzing the incidence of glisteningswith the latest generation of a hydrophobic acrylic posterior IOL that has a yellow tint. This retrospective study evaluated 111 eyes of 74 patients who had cataract surgery with implantation of a monofocal hydrophobic acrylic posterior chamber IOLwith an aspheric