Retinal cryopexy, also called retinal cryotherapy, is a procedure that uses intense cold to induce a chorioretinal scar and to destroy retinal or choroidal tissue.
Purpose
The retina is the very thin membrane in the back of the eye that acts like the "film" in a camera. It is held against the inside back portion of the eye by pressure from fluid within the eye. In the front part of the eye, the retina is firmly attached at a ring just behind the lens called the pars plana. In the back part of the eye, the retina is continuous with the optic nerve. In between the pars plana and the optic nerve the retina has no fixed attachments. The retina collects information from the images projected on it from the eye lens and sends it along the optic nerve to the brain, where the information is interpreted and experienced as sight.
Several disorders can affect the retina and retinal cryopexy is used to treat the following conditions:
retinal breaks or detachments
retinal ischemia (retinal tissue that lacks oxygen)
neovascularization (proliferation of blood vessels in the retina)
Coats' disease (abnormal retinal blood vessels that cause loss of vision)
Disease and disorders affecting the retina cause the majority of the visual disability and blindness in the United States. Retinal detachment occurs in one in 10,000 Americans each year, with middle-aged and older individuals being at higher risk than the younger population. Coats' disease usually affects children, especially boys, in the first 10 years of life, but it can also affect young adults. The condition affects central vision, typically in only one eye. Severity can range from mild vision loss to total retinal detachment and blindness. No cause has yet been identified for Coats' disease. According to the National Cancer Institute, retinoblastoma accounts for approximately 11% of cancers developing in the first year of life, and for 3% of the cancers developing among children younger than 15 years. In the United States, approximately 300 children and adolecents below the age of 20 are diagnosed with retinoblastoma each year. The majority of cases occur among young children, with 63% of all retinoblastoma occurring before the age of two years.
Description
Usually, retinal cryopexy is administered under local anesthesia. The procedure involves placing a metal probe against the eye. When a foot pedal is depressed, the tip of the cryopexy probe becomes very cold as a result of the rapid expansion of very cold gases (usually nitrous oxide) within the probe tip. When the probe is placed on the eye the formation of water crystals followed by rapid thawing results in tissue destruction. This is followed by healing and scar tissue formation.
In the case of retinal detachment, treatment calls for irritating the tissue around each of the retinal tears. Cryopexy stimulates scar formation, sealing the edges of the tear. This is typically done by looking into the eye using the indirect ophthalmoscope while pushing gently on the outside of the eye using the cryopexy probe, producing a small area of freezing that involves the retina and the tissues immediately underneath it. Using multiple small freezes like this, each of the tears is surrounded. Irritated tissue forms a scar, which brings the retina back into contact with the tissue underneath it.
Diagnosis/Preparation
The earlier the retinal disorder diagnosis is confirmed, the greater the chance of successful outcome. Diagnosis is based on symptoms and a thorough examination of the retina. An ophthalmoscope is used to examine the retina. This is a small, hand-held instrument consisting of a battery-powered light and a series of lenses that is held up to the eye. The ophthalmologist is able to see the retina and check for abnormalities by shining the light into the eye and looking through the lens. Eye drops are placed in the eyes to dilate the pupils and help visualization. Afterwards, an indirect ophthalmoscope is used. This instrument is worn on the specialist's head, and a lens is held in front of the patient's eye. It allows a better view of the retina. Examination with a slit lamp microscope may also be done. This microscope enables the ophthalmologist to examine the different parts of the eye under magnification. After instilling drops to dilate the pupil, the slit lamp is used to detect retinal tears and detachment. A visual acuity test is also usually performed to assessvision loss. This test involves reading letters from a standard eye chart.
Additional diagnostic procedures are used in the case of Coats' disease and retinoblastoma. Ultrasonography helps in differentiating Coats' disease from retinoblastoma. CT scan may be used to characterize the intraocular features of Coats' disease. MRI is another very useful diagnostic tool used to distinguish retinoblastoma from Coats' disease.
Aftercare
After the procedure, patients are taken to a recovery room, and observed for 30–60 minutes. Tylenol or pain medication is usually given. Healing typically takes 10–14 days. Vision may be blurred briefly, and the operated eye is usually red and swollen for some time following cryopexy. Cold compresses applied to the eyelids relieve some of the discomfort. Most patients are able to walk the day after surgery and are discharged from the hospital within a week. After discharge, patients are advised to gently cleanse their eyelids every morning, and as necessary, using warm tap water and cotton balls or tissues. Day surgery patients are usually allowed to go home two hours after the surgery is complete.
Risks
Risks involved in retinal cryopexy include infection, perforation of the eye with the anesthetic needle, bleeding, double vision, and glaucoma. All of these complications however, are quite uncommon.
Normal results
If treated early, the outcome of cryopexy for Coats' disease may be successful in preventing progression and in some cases can improve vision, but this is less effective if the retina has completely detached. For retinal reattachments, the retina can be repaired in about 90% of cases. Early treatment almost always improves the vision of most patients with retinal detachment. Some patients, however, require more than one cryopexy procedure to repair the damage.
Morbidity and mortality rates
Survival rates for children with retinoblastoma are favorable, with more than 93% alive five years after diagnosis. Males and females have similar five-year survival rates for the period 1976–1994, namely 93 and 94% respectively. African American children had slightly lower survival rates (86%) than Caucasian children (94%).
Alternatives
Several alternatives to retinal cryopexy are available, depending on the condition being treated. A few examples include:
Laser photocoagulation. This type of surgery induces a therapeutic effect by destroying outer retinal tissue, thus reducing the oxygen requirements of the retina, and increasing oxygen delivery to the remaining retina through alterations in oxygen diffusion from the choroid. It is used for repairing retinal tears.
Pneumatic retinopexy. This procedure is used to reattach retinas. After numbing the eye with a local anesthesia, the surgeon injects a small gas bubble into the inside of the eye. The bubble presses against the retina, flattening it against the back wall of the eye. Since the gas rises, this treatment is most effective for detachments located in the upper portion of the eye.
Scleral buckle. With this technique, a tiny sponge or silicone band is attached to the outside of the eye, pressing inward and holding the retina in position. After removing the vitreous gel from the eye (vitrectomy), the surgeon seals a few areas of the retina into position with laser or cryotherapy.
Chemotherapy. Another alternative for neuroblastoma. Chemotherapy uses drugs to kill cancer cells. The drugs are delivered through the bloodstream, and spread throughout the body to the cancer site.
Packer, A. J., ed. Manual of Retinal Surgery. Boston: Butterworth-Heinemann, 2001.
Schepens, C. L., M. E. Hartnett, and T. Hirose, eds. Schepens'sRetinal Detachment and Allied Diseases. Boston: Butterworth-Heinemann, 2000.
Wong, D. and A. H. Chignell. Management of Vitreo-RetinalDisease: A Surgical Approach. New York: Springer Verlag, 1999.
PERIODICALS
Anagnoste, S. R., I. U. Scott, T. G. Murray, D. Kramer, and S. Toledano. "Rhegmatogenous retinal detachment in retinoblastoma patients undergoing chemoreduction and cryotherapy." American Journal of Ophthalmology 129 (June 2000): 817–819.
Palner, E. A., et al. "Cryotherapy for Retinopathy of Prematurity Cooperative Group. Multicenter trial of cryotherapy for retinopathy of prematurity: ophthalmological outcomes at 10 years." Archives of Ophthalmology 119 (2001): 1110–1118.
Steel, D. H., J. West, and W. G. Campbell. "A randomized controlled study of the use of transscleral diode laser and cryotherapy in the management of rhegmatogenous retinal detachment." Retina 20 (2000): 346–357.
Veckeneer, M., K. Van Overdam, D. Bouwens, E. Feron, D. Mertens, et al. "Randomized clinical trial of cryotherapy versus laser photocoagulation for retinopexy in conventional retinal detachment surgery." American Journal of Ophthalmology 132 (September 2001): 343–347.
ORGANIZATIONS
American Academy of Ophthalmology. P.O. Box 7424, San Francisco, CA 94120-7424. (415) 561-8500. <http://www.aao.org/index.html>.
New England Ophthalmological Society (NEOS). P.O. Box 9165, Boston, MA 02114. (617) 227-6484. <http://www.neos-eyes.org/>.
WHO PERFORMS THE PROCEDURE AND WHERE IS IT PERFORMED?
Retinal cryopexy is performed in the treating physician's office or in a hospital setting depending on the condition motivating the surgery. The physician is usually an ophthalmologist, specialized in the treatment of retinal disorders. An ophthalmologist is a physician who specializes in the medical and surgical care of the eyes and visual system and in the prevention of eye disease and injury. He or she has completed four or more years of college premedical education, four or more years of medical school, one year of internship, and three or more years of specialized medical and surgical and refractive training and experience in eye care.
