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Glistenings
Glistenings are fluid-filled microvacuoles, or tiny bubbles of liquid, that form in an intraocular lens implant. To appreciate the importance of glistenings to your vision after cataract surgery, it is first necessary to understand a few facts about normal vision, cataracts, cataract surgery, and intraocular lens implants.
Normal vision
Figure 1 is a diagram of the eye. The clear part at the front of the eye is called the cornea. The coloured part of the eye (which gives us our eye colour) is called the iris. Muscle fibres in the iris control the size of the pupil, the black area in the centre of the iris. The pupil controls the amount of light entering the eye. Behind the pupil is the clear natural lens, which focuses light on the retina at the back of the eye.
Figure 1. Diagram of normal eye shown in cross section
How do we see?
Normally, light enters the eye through the clear cornea and passes through the pupil. The lens of the eye, which lies behind the pupil, works much like the lens of a camera, to focus light onto the retina at the back of the eye. The ability of the lens to change the focus of the eye allows us to see both up close and far away. The cells of the retina transmit signals through the optic nerve to the posterior part of the brain, which interprets what we see. So, the ability to see requires a clear cornea, clear lens, healthy retina, healthy optic nerve and undamaged brain
Cataracts
Cataracts develop within the lens.
The lens is made up of water and protein molecules. In the normal lens, these molecules have a specific arrangement that ensures that the lens stays clear. All the light that enters the lens passes through it and travels to the retina. The top picture of Figure 2 shows a normal lens.
Figure 2. Normal lens at top and lens with cataract at bottom
As we age, however, the proteins of the lens start to clump together and cloud the lens. This clouded area is called a cataract. Over time, as a cataract grows larger, it clouds more of the lens and affects vision more and more. Cataracts tend to become a problem for many people during their 60s or 70s. At the bottom of Figure 2 is a lens with a cataract in the middle.
How does a cataract affect vision?
Very small cataracts have little effect on vision, but as a cataract increases in size you may notice some blurring, or fuzziness, of your vision. You may also have a problem with glare, especially when driving at night. A problem mostly with night vision, glare from oncoming headlights may make it difficult to see objects or people in front of you. Glare can also be a problem during the day if you are looking toward the sun or a bright light. These vision problems occur because the lens is no longer clear and is unable to focus light on the retina properly. Instead, the cataract scatters light passing through the lens, causing blurring and glare (Figure 3). Other effects of cataracts on vision are poor night vision, fading of colours, and double vision.
Figure 3. Light is focused on the retina by a normal lens but scattered by a lens with cataracts, causing blurred vision and glare.
Cataract surgery
Cataract surgery is a short procedure that removes the cloudy lens in your eye and replaces it with a clear artificial lens, called an intraocular lens implant. The procedure itself is usually performed on an outpatient basis under local anesthesia in the hospital or outpatient surgery centre. Medication to help
you relax and special numbing eye drops ensure that the procedure is as comfortable as possible for you.
How is cataract surgery performed?
The surgeon makes a tiny incision about one-tenth of an inch in length at the side of the eye and opens the capsule, or envelope, in which your lens sits. An ultrasound probe is then inserted to break apart the cataract and remove the lens. Once the lens has been removed, an intraocular lens is inserted into the lens capsule and positioned properly in the eye. The tiny incision in the eye does not usually require sutures—it is designed to be self-sealing. After the procedure is completed, the surgeon places a protective shield over the eye. Then, after a brief stay in the recovery room, you are able to go home and resume most of your normal activities.
When will I be able to see after cataract surgery?
Vision may be blurred after surgery, depending on the amount of swelling or inflammation. Some people can see well right away, but most people have better vision within the first week after the procedure. Complete healing usually takes two months, although the vision is usually stable by four to six weeks after surgery.
Intraocular lenses
Many types of intraocular lens implants are available. These include monofocal lenses (which focus light either for distance or for near), multifocal and accommodating lenses (which are designed to provide a larger range of vision, from distance to intermediate to near), and toric lenses (which correct for astigmatism). After discussing the options with you, your surgeon will choose the most appropriate lens that meets your needs.
Are all intraocular lenses the same?
Intraocular lenses differ. They may be made of different materials. They may be manufactured using different processes. Once inserted into the eye, however, all intraocular lenses help replace the function of the normal lens and help people see better after cataract surgery.
How long do intraocular lenses last?
Intraocular lenses are very durable and should last for your entire life. These same lenses are used in eye surgery for children, where we expect them to last for their entire lifespan.
Will my vision remain improved after cataract surgery?
In most cases, vision remains improved after cataract surgery. Two problems that may affect vision can, however, develop after cataract surgery.
The first problem is posterior capsular opacification, which results from clouding of the lens capsule, the envelope in which the lens implant was placed. This condition can cause symptoms similar to those of a cataract. Posterior capsular opacification becomes more common many years after cataract surgery. This problem is also more common in younger patients. A simple laser treatment (laser capsulotomy) can restore clear vision.
The second problem is glistenings, a term which refers to fluid-filled microvacuoles, or tiny bubbles of liquid, that form in an intraocular lens. Most types of intraocular lenses have a small number of glistenings a few years after they are inserted in the eye (Figure 4A). This small number of glistenings does not
cause vision problems. However, certain intraocular lenses, specifically Alcon AcrySof® and Hoya iSymm™ can develop a very large number of glistenings (Figure 4B), which can cause problems with night vision.
Figure 4.
A. Photo of intraocular lens with minimal number of glistenings.
B. Photo of intraocular lens with large number of glistenings
Growing evidence indicates that the most commonly implanted lens in the world, the Alcon AcrySof® intraocular lens, develops glistenings (Figure 5), which affect night vision. People who have an AcrySof® intraocular lens in one eye and a different lens in the other eye have glistenings only in the eye with the AcrySof® intraocular lens. Thus, glistenings are related to the AcrySof® intraocular lens and not to the person.
Figure 5. High number of glistenings in AcrySof® intraocular lens
What causes glistenings in the AcrySof® intraocular lens?
Glistenings are caused by the manufacturing process of this lens. The AcrySof® intraocular lens is molded in a process that allows gaps to form within the AcrySof® material. When the lens is inserted in the eye, the temperature of the lens changes from room temperature to body temperature, allowing water to collect in the gaps and form tiny fluid-filled bubbles, or glistenings.1
How common are glistenings with AcrySof® intraocular lenses?
Glistenings are present in most people who have AcrySof® intraocular lenses.2 It has been shown that after 2 or 3 years, 90% of AcrySof® lenses have developed glistenings.
How long do glistenings with AcrySof® intraocular lenses keep increasing?
A study assessed persons with AcrySof® lenses after more than 10 years of follow-up. The study found that the number of glistenings kept increasing with time—it did not slow down or stop.3 Therefore, the impact of glistenings in an AcrySof® lens on a person’s vision will continue increasing over the lifetime of the person.
What is the effect of a large number of glistenings on vision?
Studies have demonstrated that intraocular lenses can restore a person’s vision to that of a 20-year-old adult. Glistenings, however, scatter light and can result in vision comparable to that of a 70-year-old person with cataracts—that is vision affected by glare and poor contrast.4 The glare caused by glistenings is called disability glare.
An intraocular lens with a large number of glistenings causes disability glare at night and when looking towards the light in the daytime. Such an affected lens may also interfere with a person’s ability to drive safely at night. Figure 6 illustrates a simulation of the effect of glistenings on night vision. It is important to note that the sharpness of vision in the daytime is affected very little—the primary problem with glistenings is with night vision. Figure 7 shows examples of different lens implants with glistenings.
Figure 6. Simulation of effect of glistenings on night vision. The photos on the right simulate the effect of glistenings. Significant glare is seen in the photos on the right. Glare makes it difficult to see the pedestrian in the lower picture on the right.
What can be concluded about AcrySof® intraocular lenses?
A recent review of the Alcon AcrySof® intraocular lens by the US Department of Health and Human Services stated the following:5 “…this commenter stated that the glistenings associated with AcrySof® Natural lenses that develops over time causes disability glare rather than reduces it." (p. 1009) and "We conclude that the AcrySof® Natural IOLs [intraocular lenses] do not demonstrate substantial clinical benefit in comparison with currently available IOLs." (p. 1010)
The evidence indicates that glistenings in AcrySof® intraocular lenses have a negative effect on vision. The goal of cataract surgery is to remove cloudy lenses and replace them with clear lenses that improve vision. AcrySof® intraocular lenses, with a high frequency of glistenings, do not accomplish this aim. Use of these lenses should be reconsidered.
A B
CD
Figure 7. Examples of glistenings. A: Darkfield photograph of Hoya iSymm™ lens implant with glistenings. B: Darkfield photograph of Alcon AcrySof® lens implant with glistenings. C: Darkfield photograph of AMO Tecnis® lens implant with minimal glistenings. D: Darkfield photograph of B&L enVista™ lens implant with
minimal glistenings.
References
1. Miyata A, Yaguchi S. Equilibrium water content and glistenings in acrylic intraocular lenses. J Cataract Refract Surg. 2004;30(8):1768-72 .
2. Christiansen G, Durcan FJ, Olson RJ, Christiansen K. Glistenings in the AcrySof® intraocular lens: pilot study. J Cataract Refract Surg. 2001;27(5):728-33.
3. Behndig A, Monestam E. Quantification of glistenings in intraocular lenses using Scheimpflug photography. J Cat Refract Surg 2009;35:7-14.
4. Van der Mooren M, Coppens J, Bandhauer M, Van den Berg T. Light scatter characteristics of acrylic intraocular lenses. Presented at Association for Research in Vision and Ophthalmology, May 6 – 10; Fort Lauderdale, FL:2007.
5. Department of Health and Human Services, Centers for Medicare & Medicaid Services, 42 CFR Parts 410, 411, 412, 413, 416, 419, and 489 [CMS-1504-FC and CMS-1498-IFC2], RIN 0938-AP82 and RIN 0938-AP80. November 2010. Available at http://www.ofr.gov/OFRUpload/OFRData/2010-
27926_PI.pdf. Accessed December 17, 2013.