The retina is the tissue paper thin membrane in the back of the eye that acts like the film' in a camera. The retina collects information from the images projected upon it and sends it along the optic nerve to the brain, where it is interpreted and experienced as sight.
Retinal Disorders—Diabetic retinopathy
The long-term damage to capillaries in the eye manifests itself especially in the retina, resulting in diabetic retinopathy. Macular swelling (macular edema) can results as damaged capillary walls becoming abnormally permeable. Alternatively, the growth of new blood vessels (proliferative diabetic retinopathy) can result from the complete clogging of large beds of capillaries. These problems develop separately and sometimes together.
Diabetic macular edema
Patches of capillaries damaged by high blood sugar may leak serum, including fat and protein, into the adjacent retinal tissue. This tissue swelling causes the retina in that area to malfunction. If the affected area involves the center of the retina, gradually developing blurry vision results. Surgery to reduce mascular swelling is done using the laser, sometime over the course of several months.
Proliferative diabetic retinopathy
Laser treatment for proliferative diabetic retinopathy is more involved than for macular edema. Ultimately somewhere between 700 and 2000 burn spots are made in the peripheral retina. This substantial cauterization destroys much of the starving retinal tissue. Dead retinal tissue no longer asks for new blood vessels to grow, resulting in cessation of growth and often shrinkage of the new blood vessels observed. Because this does not happen instantaneously, it is possible to perform a laser treatment and have further vitreous hemorrhage occur after the treatment.
Although this is inconvenient, the natural history of vitreous hemorrhage is to gradually clear. Unfortunately, such clearance can take several months. If laser treatment has been placed before the hemorrhage, the new blood vessels that caused it are likely to be withering rather than growing. Therefore, the ultimate visual outcome is expected to be substantially better in those eyes with prior treatment.
Proliferative diabetic retinopathy laser treatment (called panretinal photocoagulation) is usually done with placement of a local anesthetic. Bupivacaine, lidocaine, or a combination of the two is injected into the tissue near the eye. With this the eye goes either partially or completely "to sleep," so that the treatment can be performed entirely painlessly. The anesthetic sometimes produces temporary double vision, which is best relieved by patching one eye for a number of hours.
When the eye wakes up, there is sometimes a headache or brow ache which usually is relieved quite well with acetominophen, or in the unusually severe case with ice held over the closed eye. Head elevation and avoidance of heavy lifting and strenuous exercise can also be helpful during the early period following the treatment. The eye may be quite light sensitive. Sunglasses help.
Vision is often quite blurry for a few days and moderately blurry for as long as a few months. Initially, there are many shimmering specks in the peripheral part of the vision corresponding to the areas of laser treatment. This gradually fades over a period of months.
Retinal Disorders—Macular Degeneration
When the light sensing cells (cones) in the macula (the most central portion of the retina) gradually stop working and eventually die, it is called macular degeneration.
In the case of "wet" macular degeneration, it is sometimes possible to treat the problem in its early stages with laser surgery. The highly focused beam of light seals the leaking blood vessels that damage the macula. This procedure can slow the rate of vision loss, but cannot halt macular degeneration. Laser surgery also leaves a small, permanently dark "blind spot" at the point of each laser contact. Overall, the procedure can preserve more sight than it damages.
Retinal Disorders—Retinal Detachment
Retinal detachments are, in principle, fixed by finding all of the tears and adequately closing them. It is both that simple and that complex.
There are two commonly used initial methods for repairing a detached retina. One, pneumatic retinopexy, is known as the "bubble procedure." The other, scleral buckling, is known simply as the "buckle." Both procedures almost always are done on an outpatient basis, under local anesthetic.
The "bubble" and the "buckle" both involve irritating the tissue around each of the retinal tears. This is typically done by looking into the eye using the indirect ophthalmoscope while pushing gently on the outside of the eye using a freezing (cryopexy) probe. The tip of the probe becomes very cold, 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, once the retina is brought back into contact with the tissue underneath it. This scar forms over the next two weeks or so. Both the bubble and buckle are the same up to this point. After this, they differ.
The bubble procedure
In the bubble procedure, an injection of an expanding gas is made into the back of the eye. The patient is then asked to position themselves over the next 7-10 days in such a manner that the bubble, rising in the fluid in the back of the eye, plugs the tear(s). This reestablishes the suction, the fluid underneath the retina reabsorbs, and the retina reattaches. After that, the bubble is used like a splint.
When the eye wakes up, the bubble is seen as a shimmering surface which is distinguishable from the retinal detachment by the fact that it is always seen as being on the floor no matter which way the head is moved. The bubble is reabsorbed by the blood stream and expelled through the lungs as a natural process over the next 7-10 days.
Advantages and disadvantages
The bubble procedure produces only minimal discomfort and vision that will return tends to return quickly over a matter of days or weeks.
It has two disadvantages. Physical inability to maintain the position is one disadvantages to doing this procedure. Secondly, the procedure works only 7 or 8 out of 10 times. This does not mean that the other 2 or 3 out of 10 eyes go blind. It usually means that these eyes will later need scleral buckling, the other, more extensive procedure. Usually, the need for scleral buckling is obvious within the first few days.
The scleral buckle
The buckle begins, like the bubble, with anesthetic and freezing treatment. The tissues around the eye are then opened so that access can be gained to the side of the eyeball. A piece of silicone rubber is then sewn in such a way that when the sutures are tightened, the silicone indents the eye wall, making a hill on the inside of the eye for the tear to rest upon. Often, some of the fluid under the retina is drained out of the eye. The drainage and the indentation from the buckle usually close the breaks.
Advantages and disadvantages
This procedure works 9 or 9.5 times out of 10 as a first procedure. The major advantage is that the "buckle" typically does not require any special positioning. Furthermore, this procedure can be used to repair retinal detachments to which the bubble procedure cannot be usefully applied.
The disadvantage is it typically hurts considerably more, at least for the following day or two, than the bubble procedure. Vision that will return does so more slowly, typically over weeks or months, rather than days or weeks.
Once the retina is successfully reattached, the process of visual improvement begins. In the case where the center of the retina has not detached, the visual results are usually quite good. When the center of the retina has been detached, the visual results are less impressive, only rarely as good as the vision prior to the detachment, but sometimes close to it.
As stated above, the most common problem with each of these procedures is the possibility that the retina may not be attached in one operation. A subsequent attempt at repair can be entertained using a combination of these procedures or other available techniques.
About 7 in 100 eyes develop some generalized scarring referred to as PVR (proliferative vitreoretinopathy) which shortens the retina, makes it less elastic, and sometimes holds the breaks open despite efforts to close them. Usually, some combination of techniques can be used to repair retinas that develop this problem, but sometimes, even with the best efforts, PVR results in blindness.
Other risks include infection, perforation of the eye with the anesthetic needle, bleeding, double vision, glaucoma, and acceleration of cataract formation. All of these complications are quite uncommon.