Cryosurgery, or cryotherapy, is a technique that destroys abnormal tissue by freezing the cells. Cryotherapy can be used in the treatment of cataracts.
The procedure is used to treat cataracts. A cataract is a form of clouding that develops in the lens of the eye. The crystalline lens consists mainly of protein matter and water. Normally, the protein is packed so as to allow light to pass through the lens. A cataract forms when protein molecules start aggregating and clump together, eventually clouding the lens and blocking light. If left untreated, cataracts may eventually cause blindness. Cryotherapy is performed to remove the clouding protein matter from the lens.
In the United States, approximately 50% of people between the ages 65 and 74, and 70% of those over age 75 have a cataract, with women affected more often than men. African Americans experience impaired vision from both cataracts and glaucoma at twice the rate of Caucasian Americans, primarily due to lack of treatment.
Cryotherapy involves the application of a very cold probe to the outside of the eye, which, because of the thin nature of the eye wall (sclera), transmits the freezing temperature to the retina. The intense cold stimulation to the retina can seal abnormal leaky retinal blood vessels. This technique is indicated for the treatment of cataracts that obscure the passage of light into the eye, thus limiting the effectiveness of techniques such as laser therapy.
Cryotherapy uses a cryogenic substance, such as liquid nitrogen, to freeze the cataract. At a temperature of -320°F (-196°C), liquid nitrogen is the coldest cryogenic substance available. The ophthalmologist uses a device to direct a small spray of liquid nitrogen directly onto the cataract. Freezing may last from five to 20 seconds, depending on the size of the cataract. A second freeze-thaw cycle may be required. Sometimes, the ophthalmologist will insert a small needle connected to a thermometer to make certain the cataract is cooled to a low enough temperature to guarantee destruction. In another option, liquid nitrogen or another cryogen is circulated through a probe to cool it to low temperatures. The probe is then brought into direct contact with the cataract to freeze it. The freeze time can take two to three times longer than with the spray technique.
In order to see the back of the eye properly, the examining ophthalmologist uses two powerful microscopes, the slit lamp and ophthalmoscope. Eye drops are also often used to make the pupil bigger, so that the back of the eye can be seen more clearly. The effect of these drops wears off after a few hours. Once a cataract has been diagnosed to the point that it is interfering with daily activities and normal lifestyle, an appointment is made to treat the cataract.
For cryotherapy, the patient may be asked to skip breakfast, depending on the time of surgery. Upon arrival for cryotherapy, he or she is given eye drops, and perhaps medications to help relax. A local or topical anesthetic is used to make the procedure painless. The patient may see light and movement, but will not be able to see the cryotherapy when it is performed. The skin around the eye is thoroughly cleansed, and sterile coverings are placed around the patient's head.
After cryotherapy, a patch is placed over the operated eye and the patient is asked to rest for a while. The attending physician checks to see if there are any problems, such as bleeding. Most people who have cataract cryotherapy go home the same day. They need to make arrangements for a ride since they can not drive. After the procedure, the doctor schedules exams to check the progress of the vision. Eyedrops or pills may be given to help healing and to control pressure inside the eye. The patient is also asked to wear an eye shield or eyeglasses to help protect the eye, and he or she is told to avoid rubbing or pressing the eye, and to not lift heavy objects because bending increases pressure in the eye. Walking, climbing stairs, and light household chores can be performed.
Narcotic analgesia may be required after the procedure to relieve pain. Cryotherapy also causes significant swelling of the eye and eyelid, which makes postoperative assessment difficult. Problems after cryotherapy are rare, but can occur and may include infection, bleeding, inflammation (pain, redness, swelling), loss of vision, or light flashes. With careful medical attention, these problems usually can be treated successfully.
Surgical treatment for cataracts usually results in excellent vision. However, if other problems are present besides the cataract, as for example degeneration of the retina or optic nerve, results will not be as favorable.
The alternative treatment for cataracts is surgical cataract removal, which is one of the most common surgical procedures performed in the United States. Approximately 90% of patients who undergo this surgery experience improved vision. Two procedures are commonly used to surgically remove a cataract: phacoemulsification and extracapsular surgery. There are no medications, dietary supplements, exercises, or optical devices that have been shown to prevent or cure cataracts.
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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.
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
American Academy of Ophthalmology. Cataract Brochure 051084. 2002.
American Academy of Ophthalmology. Cataract Surgery, Better than Ever. August 14, 2001 [cited April 2003]. http://www.aao.org/aao/news/release/081401.cfm .
Monique Laberge, Ph.D.
Cryotherapy can be done in the treating physician's office. The physician is usually an ophthalmologist, specialized in the treatment of cataracts. 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 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, surgical, and refractive training and experience in eye care.