17 June 2010

Re: Glistenings in IOL materials

Dr. George Beiko asked me to review and comment on his 29 March 2010 letter to you regarding the “glistenings” that develop in one manufacturer’s injected-molded, yellow-tinted intraocular lenses (IOLs). Glistenings are fluid-filled microvacuoles that cause undesirable light scattering in patients’ eyes. I’m familiar with this subject from the perspective of a clinician/educator (as a professor of ophthalmology for the past 25 years) as well as a physicist (as a researcher in physiological optics for over 40 years).

I fully agree with Dr. Beiko’s analysis, but there is additional information that you may find useful.

As you know, modern cataract surgery replaces aging, cloudy, yellowed crystalline lenses with transparent IOLs made of acrylic or silicone materials. Patients benefit in two ways. First, there is a large reduction in light scattering (“straylight”) in patients’ eyes that pre-operatively made lighter objects appear darker and darker objects appear lighter. Decreasing straylight increases patients’ sensitivity to contrast, improving their quality of life by making it easier for them to drive, recognize faces and do other important things in modern society. Second, eliminating crystalline lens yellowing permits more blue light to reach the retina, improving patients’ (1) health by increasing their circadian photoreception (provided by blue-light sensitive ganglion photoreceptors in the retina) and (2) vision in dim environments (provided by blue-light sensitive rod photoreceptors in the retina).

Most patients are pleased with their visual improvement after successful cataract surgery, regardless of the type of implanted IOL. Glistenings are not present immediately after surgery. As Dr. Beiko stated in his letter, however, they increase with time in prominence and density. As they develop, light scattering increases. It’s difficult for patients to articulate the visual problems that glistenings cause. They also have no way to effectively quantify subtle visual losses as glistenings progress. Common clinical tests such as visual acuity are insensitive to straylight from glistenings because they only measure abnormalities involving light deviations over very small angles (less than roughly 0.1 degrees) whereas straylight from glistenings produces large angle light deflections (1 to 90 degrees). But absence of evidence is not evidence of absence when measurements are made with ineffective methodologies to document the effects of plainly visible IOL material defects. A similar situation is light scattering from obviously dirty spectacles: visual quality can be degraded appreciably without significantly affecting visual acuity.

Patients and physicians assume their IOLs will stay transparent. Most of them do, but some injection-molded IOLs do not, as Dr. Beiko documented. The development and progression of glistenings in injection-molded IOLs is the fault of the manufacturing process, not the patient or surgeon. Most ophthalmologists would be outraged if glistenings developed in their camera lenses, so it’s surprising that glistenings are often ignored in their patients’ implanted IOLs. Many cataract surgeons refuse to use IOLs that develop glistenings. They can do so because they have the freedom to choose amongst the many alternative IOLs that are in their patients’ best interest.

Yellow-tinted IOLs were designed to simulate an aging crystalline lens in the hope of reducing the risk of age-related macular degeneration (AMD), but (1) IOL chromophores cannot prevent AMD because cataract surgery does not cause it and (2) yellow-tinted IOLs provide far less retinal photoprotection than senescent crystalline lenses that don’t prevent AMD. Glistenings unintentionally complete the undesirable simulation of crystalline lens senescence by causing an age-related loss of IOL transparency.

IOL materials that develop glistenings are still around because (1) standard visual tests are insensitive to IOL material flaws that are seen easily in slitlamp examination and (2) there aren’t enough conscientious doctors around like Dr. Beiko who is willing to take the time to confront a huge corporation in the relentless pursuit of his patients’ best vision and health. There are many IOL manufacturers. Glistenings are a problem with IOL optic material from only one of them. By the time you need cataract surgery, that material will probably have been superseded by one that stays transparent. People who need cataract surgery can’t wait. Dr. Beiko is trying to protect them. I hope you can help him.

Sincerely yours,

Martin A. Mainster, Ph.D., M.D., FRCOphth.
Luther and Ardis Fry Professor Emeritus of Ophthalmology
University of Kansas School of Medicine