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by Lorraine Lica, Ph. D.
Age related macular degeneration (ARMD) is the major cause of irreversible visual impairment in people over 60.
A significant fraction of
people with ARMD suffer further deterioration of their visual acuity because of cataracts. In fact, in one Icelandic study, all of the people over the age of 83 with macular
degeneration also had cataracts (1). These people have had to decide whether to proceed with cataract surgery in the face of uncertain information about the ultimate result.
Accordingly, a recent report from Dr. Ayala Pollack and colleagues (2) about the effects of cataract surgery on the progression of pre-existing macular degeneration has important
consequences for an increasing number of people. Although hints of a negative effect of cataract surgery have been put forward previously (e.g. 3, 4), Drs. Pollack, Marcovich,
Bukelman, and Oliver used a new approach with a clever experimental control.
They studied 47 subjects (whose ages ranged from 67 to 94 years) who all had similar early-stage
age-related maculopathy, with no leakage from neovascularization, no other retinal disorders, no myopia, and no previous laser treatment for retinal problems. The severity of the
macular degeneration was similar in both eyes of each subject.
The authors incorporated an internal control into their experiment by looking at people who had cataract surgery
(with implantation of intraocular lenses containing UV protection) performed on one eye only. This way the eyes not subjected to surgery served as controls. For each eye subjected to
cataract surgery, there was a corresponding eye (termed the fellow eye ) that wasn't subjected to the surgery but was maintained in nearly the same environment as the surgical eye;
variables such as diet, medication, and exposure to light would be the same for each pair of eyes.
The subjects were monitored for a year using the customary means of
monitoring macular degeneration -- fluorescein angiography and fundus examination. Thirty-eight (80.9%) patients had no change in the macula of their surgical eye. Nine surgical eyes
(19.1%) progressed to wet ARMD, but only two fellow eyes that were not subjected to cataract surgery (4.3%) progressed to wet ARMD. (In other studies, the yearly incidence of new
lesions of wet ARMD in the general population over 65 is 6.4%, so Dr. Pollack and colleagues consider this 4.3% progression rate in the fellow eyes to be comparable to what would have
happened if no surgery had been performed.)
There is a nearly 4.5 fold difference in the progression to wet ARMD in surgical eyes over the fellow eyes. We can see that this
result implicates cataract surgery as an important risk factor in the exacerbation of macular degeneration.
Macular degeneration patients contemplating cataract surgery will
also want to note the severity of the loss of vision in the post-surgery eyes; all of the nine eyes that progressed to the wet form had a final visual acuity of 20/200 or worse. These
eyes were all 20/80 or better before surgery.
The authors of this report say they do not yet understand the relationship between the surgical procedure and the increase in the
risk for progression to wet ARMD nor why some people's eyes progress and others do not. Nevertheless, this report serves to alert patients about real risks of cataract surgery and
also paves the way for research to determine how to manage the parameters relevant to successful cataract surgery for the millions of people whose sight is or will be affected by both
macular degeneration and cataracts.
Glossary
experimental control: the part of an experiment that provides a standard of comparison. The control subjects and
experimental subjects are treated exactly the same except for the one variable being tested.
fellow eye: in this study, the eye in an individual's pair of eyes that is not
subjected to cataract surgery.
fluorescein angiography: a procedure where fluorescein, a fluorescent dye, is injected into a patient's arm, and then the retina and macula are
photographed. The dye helps visualize any new blood vessels or abnormality that might be present.
fundus examination or funduscopy: visual examination of the retina with an
ophthalmoscope.
neovascularization: the accumulation of new blood vessels derived from a layer of connective tissue adjacent to the retina (i.e., the choroid). The neovascular
form of ARMD is also called the "wet" form or "exudative" form of ARMD and is responsible for approximately 90% of the severe visual loss (20/200 or worse) due to
ARMD.
Further Reading
Background
For information on cataracts and cataract surgery, check the American Ophthalmology Association Website on Cataracts.
For More Details
1. Jonasson, F. and Thordarson, K . 1987. Prevalence of ocular disease and blindness in a rural area in the eastern region of Iceland during 1980 through 1984.
Acta Ophthalmol. Suppl. 182: 40-43.
2. Pollack, A., Marcovich, A., Bukelman, A., and Oliver, M. 1996. Age-related macular degeneration after extracapsular cataract extraction
with intraocular lens implantation. Ophthalmology 103: 1546-1554.
3. Stolba, U., Binder, S., and Velikay, M. 1989. L'extraction du cristallin avec implantation influence-t-elle
l'evolution de la degenerescence maculaire liee a l'age? J. Fr. Ophthalmol. 12: 897-901.
4. van der Schaft, T.L., Mooy, C.M., de Bruji, W.C., Mulder, P.G.H., Pameyer, J.H., and
de Jong, P.T.V.M. 1994. Increased prevalence of disciform macular degeneration after cataract extraction with implantation of an intraocular lens. British J. Ophthalmol. 78:441-445.
Posted May 22, 1997 |
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