TREATMENT OF RETINOPATHY OF
PREMATURITY
Fortunately, in
most patients with retinopathy of prematurity, the abnormal retinal
vessels disappear or regress spontaneously. If the vessels continue to
proliferate and place the eye at risk of retinal detachment and visual
loss, treatment of the retinopathy is indicated. Most treatment for ROP
is done with laser photocoagulation, but other treatment modalities are
sometimes used, depending upon the stage of the disease.
CRYOTHERAPY
Several reports have described a beneficial
effect of a freezing technique called cryotherapy in the treatment of
ROP. Cryotherapy involves placing a very cold probe on the outside wall
of the eye (the sclera) and freezing until an ice ball forms on the
retinal surface. Multiple applications of cryotherapy are done in order
to treat the entire avascular area anterior to the neovascular ridge.
Treatment of the ridge itself is avoided, since the ridge tends to bleed
and cause vitreous hemorrhage if frozen.
CRYOTHERAPY
FOR
ROP
This drawing shows cryotherapy applications to
the anterior avascular retina, with nearly confluent spots. The
mechanism of action of cryotherapy is not completely understood. The
neovascular ridge may be the result of vasogenic growth factors produced
by the poorly oxygenated anterior retina. If this is true, the
cryotherapy probably works by destroying parts of the retina (thereby
reducing the demand for oxygen) and/or by thinning the tissue under the
retina (allowing more oxygen to diffuse into the area).
A large multicenter randomized trial of cryotherapy (the CRYO-ROP study)
was undertaken in 1985, supported by the National Eye Institute. The International
Classification of ROP was used to evaluate patients (premature
infants weighing 1250 grams or less at birth) enrolled in the study.
Infants in the study were treated with cryotherapy if they developed
"threshold" ROP - stage 3 ROP in zones 1 or 2 involving at
least 5 clock hours with plus disease. Infants with bilateral disease
had one eye treated and the other left untreated. Enrollment in the
study was stopped earlier than expected because the preliminary results
showed such a strong effect of cryotherapy in preventing severe vision
loss. Cryotherapy was found to reduce the risk of retinal detachment or
retinal fold involving the macula (the two main causes of decreased
vision in ROP) from 43% in the untreated eyes to 21% in the treated
eyes. Cryotherapy quickly became the standard of care for infants with
threshold ROP.
Cryotherapy does have potential complications. The procedure is often
performed under general anesthesia because of the pain involved, and
general anesthesia can be risky for premature infants. Performing
cryotherapy without anesthesia, however, is probably even more stressful
and dangerous for the infant. There may be slowing of the heart rate (bradycardia)
and breathing (apnea), and cardiorespiratory arrest may occur in as many
as 5% of cases. The procedure is painful, and narcotics are usually
needed afterwards, which can decrease the respiratory drive and make it
difficult to get the infant off mechanical ventilation. There is
significant swelling of the eyelids and conjunctiva which may persist
for a week or longer, making re-examination of the eyes difficult.
Unintentional treatment of the neovascular ridge may result in vitreous
hemorrhage which may take weeks to clear.
LASER PHOTOCOAGULATION
Argon laser photocoagulation has been used for
many years for the treatment of retinal vascular diseases such as
diabetic retinopathy in adults. Xenon arc photocoagulation in infants
with ROP was reported as early as 1970, before the use of cryopexy, but
the difficulty in treating the far periphery of the retina made this
technique much less useful than cryopexy. With the advent of indirect
laser delivery systems in the late 1980's, laser treatment of ROP became
a practical alternative.
Laser treatment for ROP is similar to cryotherapy in that the avascular
retina anterior to the neovascular shunt is treated, and the mechanism
of action is probably the same. The laser spot size is significantly
smaller than a spot of cryotherapy, so more spots are needed, usually
600-1000 spots of laser as compared to 30-50 spots of cryotherapy. Since
laser is a direct treatment of the retina and its underlying tissue
instead of the entire thickness of the eye wall, there is less
inflammation and presumably less damage to other ocular structures.
There is much less pain and swelling with laser than with cryotherapy,
making re-examination easier and reducing the need for narcotics and
post-surgical mechanical ventilation. Also, since there is less pain,
lower doses of anesthetics with shorter durations of action can be used.
A small but well-designed randomized study by McNamara et al
(Ophthalmology 98:576-580, May 1991) showed that regression following
treatment occurred in 15 of 16 eyes randomized to laser and 9 of 12 eyes
randomized to cryotherapy. The difference between these groups is not
statistically significant, but the study shows that laser is at least as
effective as cryotherapy in reducing the risk of severe vision loss from
ROP. My personal experience has also been encouraging, with marked
improvement in success rates when I switched from cryotherapy to laser.
Most ophthalmologists treating ROP are now using laser, despite the lack
of a large randomized clinical trial.
SCLERAL BUCKLE
If laser or cryotherapy are unsuccessful in
preventing progression to stage 4 or 5 ROP, some surgical treatments are
available. If there is a shallow retinal detachment due to traction from
fibrovascular scar tissue, a procedure called scleral buckling may be of
benefit. Scleral buckling involves placing a silicone band around the
equator of the eye and tightening it to produce a slight indentation on
the inside of the eye. This band relieves the traction of the vitreous
gel pulling on the fibrous scar tissue and the retina, and allows the
retina to flatten back down onto the wall of the eye. Infants who have
had scleral buckling may maintain good vision in the eye, particularly
if the macula did not detach, as in stage 4A. The encircling band
usually needs to be removed some months or years later, since the eye
will continue to grow, producing gradually increasing compression of the
globe and induced nearsightedness.
VITRECTOMY
In cases of stage 5 ROP, with complete retinal
detachment due to scar tissue on the retina, scleral buckling is not
sufficient to relieve the traction. For these infants, a vitrectomy may
be considered. Vitrectomy involves making several small incisions into
the eye, and using a suction/cutter device to chop up and remove the
vitreous gel. The vitreous is replaced with a saline solution to keep
the eye formed, and the eye is able to maintain its shape and pressure
indefinitely without the vitreous gel. After the vitreous has been
removed, the scar tissue on the retina can be peeled or cut away,
allowing the retina to relax and lay back down against the eye wall. It
may take some weeks for the retina to become re-attached after the
surgery, and if holes or tears in the retina occur during the procedure,
the retina usually will not re-attach. The lens of the eye often has to
be removed to allow complete dissection of the scar tissue, but some
newer techniques are being tried that can preserve the lens.
The success rate for vitrectomy surgery for ROP is somewhat limited. The
published anatomic success rate, which means getting the retina
reattached to the wall of the eye, ranges from 25% to 50% of patients
undergoing surgery. The functional success rate, which means the ability
to see well, is significantly lower. Of eyes that have
"successful" vitrectomy surgery (anatomic success), only about
1/4 are able to see well enough to reach out and grab an object or
recognize patterns.
The disappointing visual results of surgery
underscore the need for careful screening and timely laser treatment for
patients at risk for visual loss. Traditionally, laser or cryotherapy
has been considered when the ROP reaches threshold (stage 3 in at least
5 clock hours with plus disease). This level for intervention was chosen
because it was known that infants with this degree of ROP have a 50%
chance of severe visual loss without treatment. Over time, many
ophthalmologists have been leaning toward earlier intervention in hopes
of further decreasing the risks of the disease. At present, I consider
laser treatment for infants with severe stage 2 and plus disease,
particularly if dense vitreous strands or intravitreal scar tissue is
beginning to form. I also consider intervention in stage 3 ROP without
plus disease or stage 3 ROP in less than 5 clock hours. Although we do
not yet have good randomized studies to support this shift in treatment
parameters, the anecdotal evidence is convincing.
The Country Hills Eye Center Home Page
Dr. Scott C. Richards Main Page
For information regarding the
Country Hills Eye Center phyician
specializing in retinal and diabetic eye diseases
www.countryhillseyecenter.eyemd.org
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