In the context of AIDS, when one hears about eye damage the phrase "CMV-retinitis" often comes to mind. In that sight-threatening complication — caused by a virus called cytomegalovirus or CMV — the light-sensitive portion of the eye, known as the retina, is infected and becomes swollen. What some researchers are finding, however, is that people with HIV/AIDS (PHAs) who do not have any obvious inflammation of the retina are developing subtle visual defects, including:
These defects appear to be caused not by CMV but rather by HIV. Moreover, the usual means of assessing retinal damage — fundus photography — does not appear to be sensitive enough to detect this subtle damage.
Researchers at the University of California at San Diego have been using an instrument called the Heidelberg Retina Tomograph. This device uses a laser beam to produce detailed 3-dimensional images of the retina and optic nerve in PHAs. The researchers found that HIV positive people who did not have any obvious eye disease had significant damage to the retina and optic nerve. Details about why this occurred appear later in this report.
Researchers recruited three groups of subjects:
The researchers did not release infomation on CD4+ and CD8+ cell counts, viral load or the type of anti-HIV treatment, if any, subjects were taking. All subjects had 3D images of their eyes produced and analysed.
The researchers found that while subjects with CMV retinitis had the most damage to their retinas, HIV positive subjects without this complication also had significant damage to their retina and optic nerve (which carries pictures from the eye to the brain). This research team has previously found that the optic nerve of PHAs who don't have CMV-retinitis can shrink by as much as 50%.
The standard of care for investigating retinal damage in PHAs is for ophthalmologists to use an instrument called a funduscope. However, ophthalmologists would not have been able to detect the damage to the retina documented in this study by using this instrument. The researchers therefore stated that "proper evaluation of HIV-associated damage to the retinal nerve fibre layer may need to include nerve fibre layer photography or confocal imaging techniques."
The researchers aren't sure exactly how HIV damages the nerves in the eye. They suspect that proteins produced by HIV or HIV-infected cells are toxic to nerves in the eye and cause cells in the retina and optic nerve to commit suicide, a process called apoptosis. This process is similar to the way in which HIV can cause brain cells to die. Hopefully, future studies will examine the impact of therapies, such as HAART and antioxidants like vitamins C and E and zinc, on this subtle damage to vision.
REFERENCES
1. Plummer DJ, Bartsch D-U, Azen SP, et al. Retinal nerve fiber layer evaluation in human immunodeficiency virus-positive patients. American Journal of Ophthalmology 2001;131:216:222.
2. Smith DG, Guillemin GJ, Pemberton L, et al. Quinolinic acid is produced by macrophages stimulated by platelet activating factor, Nef and Tat. Journal of Neurovirology 2001;7(1):56-60.
3. Jiang ZG, Piggee C, Heyes MP, et al. Glutamate is a mediator of neurotoxicity in secretions of activated HIV-1-infected macrophages. Journal of Neuroimmunology 2001;117(1-2):97-107.
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Copyright © 2001 - TreatmentUpdate. Reproduced with permission. Reproduction of this article (other than one copy for personal reference) must be cleared through the Editor, The Canadian AIDS Treatment Information Exchange, 555 Richmond St. West, Suite 505, Box 1104, Toronto, ON, M5V 3B1 • Phone: 416-203-7122 • Toll Free: 1-800-263-1638 • Fax: 416-203-8284 http://www.catie.ca.
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