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by
Lawrence A. Yannuzzi, MD
Manhattan
Eye, Ear & Throat Hospital
LuEsther
T. Mertz Retinal Research Center
New York, New York
(from
Volume 7, Issue 1, 1999)
Macular
degeneration in patients with pseudoxanthoma elasticum
(PXE), like the very common correlate seen in age-related
macular degeneration, comes in two forms. The first is a
so-called dry form of degeneration where there is loss of
cells or so-called atrophy of the tissue layers in the
macular region. Very little is known about the causative
factors for this development, but the same pathological
changes seen elsewhere in PXE patients are likely to be
playing a role. These include so-called elastin
degeneration and calcific deposition. In short, this means
that there is a defect in the elastic tissue behind the
macula and a mineralized or calcific change making the cells
very fragile and subject to cracks, which can be seen
clinically by the ophthalmologists. These have been termed
angioid streaks since they are curvilinear and resemble
blood vessels and their branching course.
The second mechanism for severe loss of vision is the
neovascularized type. This presentation is more devastating
because it takes a sudden or precipitous course compared to
the insidiously progressive loss of vision seen with the dry
form of degeneration. The primary event is the development
of an abnormal blood vessel that emerges from the
circulation behind the retina (choroidal neovascularization).
The advent of these vessels is poorly understood, but the
clinical manifestations are very similar to the advancing
course seen in age-related macular degeneration. The
vessels tend to leak water or plasma from the circulation
and eventually bleed, setting the occasion for scar
formation and destruction of the overlying retina. In this
newsletter I will make some suggestions regarding the dry
form of degeneration. In an upcoming newsletter, I will
discuss new approaches to the treatment of the
neovascularized form.
The loss of cells or atrophy has been linked to
photo-oxidative stress. This means a chronic light exposure
may have a damaging effect on the elastic tissue layers of
the macula, just the way it also affects skin. The only way
to accomplish coating the macula with a “skin block” effect
is by using sunglasses to filter out harmful light. The
principal offender of light damage is due to the intensity
as well as the duration and also to the specific
wavelength. That is, the blue portion of visible light is
known to be more phototoxic to the macula, and of course,
the most damaging effects are induced by ultraviolet light.
Some ultraviolet light is filtered out by the normal cornea
and the aging lens of the eye, particularly after age 35.
Protection of the macula with sunglasses, particularly
tinted with a color that blocks out blue light as well as
the ultraviolet light, is recommended in a bright
environment (at the beach, sailing skiing, or just on a
sunny day).
Another way to protect the macula from photo-oxidative
damage is by the use of supplemental vitamins, specifically
the so-called antioxidants. (Vitamins A, C, E, selenium,
zinc and glutathione are among this group). It is not
necessary to use any form of supplemental vitamin with a
fancy name linking it to the eye or macula. A simple
over-the-counter product at low cost is all that is
recommended. Some formulations have fancy names, but they
are essentially generic preparations with high prices.
Another way to reduce photo-oxidative damage to the macula
would be through the use of a diet that is heavy on the
green leafy side of the menu rather than the fat side of the
menu.
While sunglass filtration of light and supplemental
antioxidants are a very rational and attractive approach to
preservation of the macula, there is a lack of scientific
studies that prove the efficacy and safety of this
approach. A major study is currently under way through the
National Eye Institute on thousands of patients followed
over many years to establish the value of this form of
treatment.
One form of treatment that does not need any further
research is the issue of smoking. Patients with macular
degeneration, or any vascular disease, should not smoke or
even be in a secondary smoking environment. The oxygenation
of blood and poor vascular perfusion, or hypoxia, are known
causative factors for the proliferation of abnormal vessels
and also pose a risk for age-related macular degeneration.
In the future, there likely will be a better way to
repopulate cells lost from atrophy or program cell depth,
known as apoptosis. The culture of fetal cells (the harvest
for the transplantation of the cells under the macula) is
now technically possible; however, results have been poor
because of allergic reactions – or possibly rejection
phenomena – but above all, because of poor cellular
connections between tissue layers needed to establish
physiological connections fro the reception and transmission
of visual images.
One last point is the fragility of the eye in PXE. Because
of the degeneration that is evolving in the back of the
macula, the tissue layers are very fragile, even to minimal
degrees of trauma. Therefore, it is advisable for patients
with angioid streaks from PXE to wear protective lenses when
involved in any activity that may result in inadvertent
trauma. In particular, wearing proper protective lenses in
contact sports such as basketball and racket games is highly
recommended. Some of the worst hemorrhages in the macula
that I have seen over 30 years of caring for patients with
macular disease have been in patients with angioid streaks
and PXE following even moderate degrees of trauma. A
probable inherent clotting abnormality is likely to
accentuate small hemorrhages, resulting in larger ones.
In an upcoming issue, I will talk about the most devastating
of all mechanisms for loss of vision from macular
degeneration and PXE – neovascularized degeneration – and
some new treatments to manage these vessels and their
consequential scarring.
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