By
Jonathan Yoken, MD
Photodynamic
Laser Treatment (PDT) and Visudyne™
Lasers have been used to treat the "wet" form of macular
degeneration for more than two decades. Traditionally, a highly
focused beam of laser light is aimed at the source of the leakage,
which photocoagulates or seals the leaking vessels. While this
is effective, any retina in contact with the leak is also destroyed.
While further loss of vision can be arrested, a permanent gray
spot of varying size may block a portion of field of vision.
The macula
serves the center of our visual field, and is used for reading
and detail work. If a leak is present beneath the macula, it creates
a difficult choice: do we allow the leak to grow and potentially
destroy a large area of the central vision, or do we seal the
leak with laser and accept that a portion of the detail vision
will be lost?
Fortunately,
a new laser technique has evolved which can seal leaks at the
center of the macula without damaging the central vision. Photodynamic
laser treatment (PDT) involves administering an IV medication
before the laser treatment is done, which super-sensitizes the
leaking vessels to the laser beam. This allows the use of a very
low energy laser, sometimes referred to a "cold" laser,
which seals the leak but leaves the overlying retinal cells intact.
The FDA recently
approved the first photodynamic IV drug, Visudyne. This treatment
appears to be very safe. There is one very important restriction:
following the treatment, the patient cannot be exposed to bright
sunlight for 3 days. After this interval, the patient can return
to normal activity.
It is important
to understand that photodynamic laser with Visudyne does not help
everyone with macular degeneration. Only patients with active
leakage under the retina-the "wet" form-are candidates
for this treatment. The leaks must be very active and well defined
(also known as "classic" leaks) and cannot exceed a
certain size. In general, leaks that have been present for a long
time generally do not benefit from PDT.
PDT with Visudyne
most often helps to stabilize vision or slow the progression of
vision loss. Only a portion of patients will show any improvement
in vision. There is a strong possibility that the leaks may reopen,
in which case more that one course of PDT laser treatment may
be needed. In fact, most patients require on average three treatments
spaced out over a period of one year.
Despite these
limitations, PDT is an exciting new approach that offers hope
in the battle against visual loss in macular degeneration. Research
continues in further refinements of this technique, and other
photodynamic IV medications are currently under study.
