Photocoagulation therapy is a method of treating detachments (tears) of the retina (the layer of light-sensitive cells at the back of the eye) with an argon laser. The high-intensity beam of light from the laser is converted into heat, which forces protein molecules in the affected tissue to condense and seal the tear.
The purpose of photocoagulation therapy is to reattach a torn or detached portion of the retina and/or prevent further growth of abnormal blood vessels in the retina that can cause a detachment.
The incidence of RD in the United States is about 0.3%, or one in 15,000 people.
The most common risk factors associated with RD are extreme nearsightedness (5% risk); cataract removal without lens implantation (2%); and cataract removal with loss of the vitreous body during surgery (10%). It is estimated that 15% of people with RD in one eye will eventually develop it in the other eye.
Males account for 60% and females for 40% of patients with RD below the age of 45. Above age 45, there is no significant gender difference.
With regard to racial or ethnic background, the incidence of RD is higher among Jews in the United States than in the general population; the incidence of RD among African Americans is lower than average.
Structure of the human eye
To fully understand how photocoagulation therapy works, it is helpful to have a basic picture of the structure of the human eye. The retina is the innermost tunica, or covering, of the posterior part of the eyeball. It is made of several layers of cells, one of which contains the rod and cone cells that are sensitive to light. Behind the retina are the other two tunicae of the eye, the choroid and the sclera. The sclera is a tough white layer of tissue that covers the exterior of the eyeball. At the front of the eye, the sclera is continuous with a transparent area of tissue known as the cornea.
At the back of the eye, the retina is continuous with the optic nerve. The macula, which is a yellowish oval-shaped area that is the central point of vision, lies in the center of the retina. In front of the retina is the vitreous body, which is also known as the vitreous humor, or simply the vitreous. The vitreous body is a clear gel that consists primarily of water and collagen fibers.
Types of retinal detachment (RD)
RHEGMATOGENOUS. A rhegmatogenous RD is the most common of the three types of retinal detachment. The word rhegmatogenous comes from a Greek word that means "tear." A rhegmatogenous RD typically occurs in older people. As the vitreous body in the center of the eyeball ages, it shrinks and pulls away from the retina. This separation is called a posterior vitreous detachment (PVD). A PVD is not the same thing as a retinal detachment, although it may slightly increase the risk of an RD. In places where the retina is still attached to the vitreous body, a small hole or tear can develop. Over time, fluid can seep into the area around the hole or tear and thus enlarge the area of detached tissue.
TRACTION. Traction RDs are most often found in adults with diabetic retinopathy or infants with retinopathy of prematurity (ROP). Diabetic retinopathy is a disorder that develops when the patient's diabetes affects the small blood vessels in the eye. Although diabetic retinopathy is more severe in patients with type 1 diabetes (insulin-dependent), it can also occur in patients with type 2. Retinal detachment is most likely to occur in a subtype of the disorder known as proliferative diabetic retinopathy. The term proliferative refers to the abnormal growth of new blood vessels along the surface of the vitreous body. These new blood vessels can bleed into the vitreous body and form scar tissue that pulls on the retina. Eventually, the scar tissue can exert enough pulling force to cause a retinal detachment.
In ROP, a traction RD can develop because premature birth interrupts the normal development of the blood vessels in the baby's eyes. After the baby is born, some of these blood vessels grow along the retina, bleed into the vitreous body, and form scar tissue similar to that found in diabetic retinopathy. Retinal detachment in ROP can be treated with photocoagulation.
EXUDATIVE. Exudative RDs occur when tissue fluid builds up in the space between the retina and the choroid underneath it. If enough fluid leaks into this space, it can push the retina away from the choroid and cause it to detach. Exudative RDs are associated with certain inflammatory disorders of the eye; tumors, including melanoma (cancer) of the choroid; and a congenital disorder known as Coats' disease, which affects the growth of the blood vessels in the retina.
Risk factors for retinal detachment
Retinal detachment is associated with a number of different factors and conditions, including:
- extreme nearsightedness
- genetic factors (retinal detachment tends to run in families)
- premature birth (the risk of ROP is highest in premature infants weighing less than 2.2 lb [1 kg] at birth)
- type 1 or type 2 diabetes
- cataract surgery
- sickle cell disease
- Coats' disease
- Eales' disease
- Marfan's syndrome
- breast cancer or melanoma
- history of previous retinal detachment
- age (Retinal detachment is most common in people between the ages of 40 and 70.)
- traumatic injury to the eye
- laser in situ keratomileusis surgery ( LASIK , a procedure done to correct vision without the need for glasses or contact lenses)
Photocoagulation therapy for retinal detachment is usually performed with an argon laser. A laser is a device that produces high-intensity, narrowly focused monochromatic light by exciting atoms and causing them to give off their energy in phases. The word laser comes from "light amplification by stimulated emission of radiation." An argon laser uses ionized argon to generate its light, which is in the blue-green portion of the visible light spectrum.
In a laser photocoagulation treatment, the patient is asked to sit in front of the instrument. After applying anesthetic eye drops, the ophthalmologist places a contact lens on the patient's eye and focuses the laser beam through it. He or she operates the laser by foot. The patient may see a brief burst of blue-green light. When the laser beam reaches the retina at the back of the eye, its light is absorbed by the pigment in the cells and converted to heat, which seals the edge of the retinal detachment against the underlying choroid. The procedure is short, taking about 10–30 minutes.
The diagnosis of retinal detachment requires direct examination of the eye as well as taking the patient's medical history. The diagnosis may be made in some cases by an optometrist, who is a health professional qualified to examine the eye for diseases and disorders as well as taking measurements for corrective lenses. If the symptoms of RD appear suddenly, however, the patient is more likely to be diagnosed by an ophthalmologist, who is a physician specializing in treating disorders of the eye.
PATIENT HISTORY. Retinal detachment is not usually painful, and the patient's eye will look normal from the outside. In almost all cases, a patient with RD consults a doctor because he or she is having one or more of the following visual disturbances:
- blurring of vision that is not helped by blinking the eye
- a gray or black curtain or shade coming across the field of vision from one direction
- floaters, which appear as moving black spots in front of the eye (The sudden appearance of a large group, or "shower," of floaters is a serious symptom of RD.)
- flashes of light
- objects appearing wavy or distorted in shape
- blind spot in the visual field
The visual symptoms of retinal detachment may develop either gradually or suddenly. In a very small number of cases, a sudden retinal detachment may cause complete loss of vision in the affected eye.
Patients who have gone to a primary care physician or emergency room for these visual symptoms are referred to an ophthalmologist. Many ophthalmologists will give patients a piece of paper with a circle on it and ask them to draw what they are seeing on the circle in the area corresponding to the part of their visual field that is affected. In some cases, the location of the spots, light flashes, or shadows that a patient sees is a clue to the part of the retina that is detached.
The ophthalmologist will take a patient history, asking about a family history of eye disorders; previous diseases or disorders of the eye; other diseases or disorders that the patient may have, particularly diabetes or sickle cell disease; and a history of head trauma, direct blows to the eye, or surgical removal of a foreign body from the eye. If the patient suffered a head or eye injury within the past six months, the ophthalmologist will ask whether the visual disturbances started at the time of the injury or several months later.
EYE EXAMINATION. After taking the history, the ophthalmologist will examine the eye itself. This examination has several parts, including:
- A test of visual clarity or sharpness. This test is the same one used by an optometrist when fitting a patient for glasses or contact lenses.
- An external check for bleeding or any other signs of trauma to the eye.
- A test that measures the response of the pupil of the eye to changes in light intensity. One sign of RD is a difference in the pupillary reaction between the affected eye and the normal one. The pupil will not contract as far as it normally does when the doctor shines a light into the affected eye.
- A test that measures the amount of fluid pressure inside each eyeball. In RD, the affected eye typically has a lower pressure measurement than the other eye.
- Examination of the eye with a slit lamp, which is an instrument with a high-intensity light source that can be focused as a thin sliver of light. The examiner uses the slit lamp together with a binocular ophthalmoscope (an instrument that looks like a microscope with two eyepieces) in order to check first the front and then the back of the eye for any abnormalities. To check the front part, the doctor will touch the side of the eye with a strip of paper containing an orange dye. The dye stains the film of tear fluid on the outer surface of the eye, making it easier to see the structures in the front of the eye. Patients with RD usually have normal results for this part of the slit-lamp examination. In the second part, the doctor puts some drops in the patient's eye to make the pupil dilate. This procedure allows him or her to see the structures in the back of the eye. If the patient has RD, the doctor may see the retina lifted upward or forward, possibly moving back and forth. The retina will have a grayish color with darker blood vessels visible. It may have a pitted surface resembling an orange peel, and there may also be a line visible at the edge of the detachment.
LABORATORY AND IMAGING STUDIES. Today, there are no laboratory tests for retinal detachment. Ultrasound, however, can be used to diagnose retinal detachment if the doctor cannot see the retina with a slit lamp because of cataracts or blood seeping into the vitreous body. If the RD is exudative, ultrasound can be used to detect a tumor or hemorrhage underneath the retina.
Treatment of RD follows as soon as possible after the diagnosis; however, an immediate procedure is not usually necessary since the time frame for treatment of a detached retina is several hours rather than only a few minutes.
If the patient has suffered a traumatic injury to the eye, the eye may be covered with a protective shield prior to treatment.
Preparation for photocoagulation therapy consists of eye drops that dilate the pupil of the eye and numb the eye itself. The laser treatment is painless, although some patients require additional anesthetic for sensitivity to the laser light.
Patients who have had photocoagulation therapy for retinal detachment are asked to have a friend or family member drive them home. The reason for this precaution is that the eye medication used to dilate the pupil of the patient's eye before the procedure takes several hours to wear off. During this period, the eye is unusually sensitive to light. The patient can go to work the next day with no restrictions on activity.
The most common risks of laser photocoagulation therapy are mild discomfort at the beginning of the procedure and the possibility that a second laser treatment will be needed to reattach the retina securely.
Over 90% of retinal detachments can be repaired with prompt treatment, although sometimes a second procedure is needed. About 40% of patients treated for retinal detachment will have good vision within six months of surgery. The results are less favorable if the retina has been detached for a long time or if there is a large growth of fibrous tissue that has caused a traction detachment. These patients, however, will still have some degree of reading or traveling vision after the retina has been reattached. In a very small minority of patients, the surgeon cannot reattach the retina because of extensive growths of fibrous scar tissue on it.
Morbidity and mortality rates
The mortality rate for laser photocoagulation treatment of retinal detachment is extremely low; morbidity depends to a large extent on the cause of the RD. A study done in 2001 reported that laser therapy for rhegmatogenous RDs is as effective as pneumatic retinopexy or scleral buckling , but has the advantage of fewer complications after the procedure. In the treatment of ROP, laser photocoagulation has been found to be more effective than cryopexy in reducing the infant's risk of nearsightedness in later life.
Alternatives to laser photocoagulation as a treatment for RD depend on the location and size of the retinal detachment. Photocoagulation treatment works best on small tears in the retina. One alternative for the treatment of small areas of detachment is cryopexy, which is performed as an outpatient procedure under local anesthesia. In cryopexy, the ophthalmologist uses nitrous oxide to freeze the tissue underneath the retinal tear. This procedure leads to the formation of scar tissue that seals the edges of the tear in place.
Pneumatic retinopexy is a procedure that can be used if the RD is located in the upper part of the eye. After numbing the patient's eye with a local anesthetic, the ophthalmologist injects a small bubble of gas into the vitreous body. The gas bubble rises and presses the torn part of the retina back against the underlying choroid. The bubble is slowly absorbed over the next two weeks. The ophthalmologist then uses either photocoagulation or cryopexy to complete the reattachment of the retina.
If the RD is large, the doctor may decide to perform a scleral buckle treatment or a vitrectomy. These procedures are more invasive than laser photocoagulation or cryopexy; however, they are still usually done as outpatient procedures. In a scleral buckle procedure, the doctor attaches a tiny silicon band to the sclera. The buckle, which remains in the eye permanently, puts pressure on the retina to hold it in place.
In a vitrectomy, the ophthalmologist removes the vitreous body and replaces it with air or a saline solution that puts pressure on the retina to hold it in place. Vitrectomies are usually performed if there is a very large tear in the retina; if the macula is involved; or if blood that has leaked into the vitreous body is interfering with diagnosis or treatment.
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"Retinopathy of Prematurity." Section 19, Chapter 260 in The Merck Manual of Diagnosis and Therapy, edited by Mark H. Beers, and Robert Berkow. Whitehouse Station, NJ: Merck Research Laboratories, 1999.
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American Academy of Ophthalmology. P. O. Box 7424, San Francisco, CA 94120-7424. (415) 561-8500. http://www.aao.org .
American Optometric Association. 243 North Lindbergh Blvd., St. Louis, MO 63141. (314) 991-4100. http://www.aoanet.org .
Canadian Ophthalmological Society (COS). 610-1525 Carling Avenue, Ottawa ON K1Z 8R9 Canada. http://www.eyesite.ca .
Diabetic Retinopathy Foundation. 350 North LaSalle, Suite 800, Chicago, IL 60610. http://www.retinopathy.org .
Wills Eye Hospital. 840 Walnut Street, Philadelphia, PA 19107. (215) 928-3000. http://www.willseye.org .
Rebecca Frey, PhD
WHO PERFORMS THE PROCEDURE AND WHERE IS IT PERFORMED?
Laser treatment of retinal detachment is performed by an ophthalmologist, who has specialized in the medical and surgical treatment of eye disorders. Ophthalmology is one of 24 specialties recognized by the American Board of Medical Specialties.
Photocoagulation therapy for retinal detachment is done as an outpatient procedure, either in the ophthalmologist's office or in an ambulatory surgery center.
QUESTIONS TO ASK THE DOCTOR
- What are my chances of having normal vision after the laser therapy?
- What is the likelihood of my needing another laser treatment?
- Am I likely to develop retinal detachment in my other eye?
- How often should I schedule preventive eye examinations from now on?