Tears and Detachments
Retinal detachment affects approximately 1 in 10,000 people each year. If left untreated, most retinal detachments will lead to loss of vision. An understanding of some of the normal anatomy of the eye may be useful in understanding how retinal tears and detachment occur and the symptoms which they may cause.
The retina is a thin tissue that lines much of the inside of the eye. The center portion of the retina is called the macula. The macula is responsible for fine central vision and for color vision. The more peripheral parts of the retina provide peripheral vision. The vitreous is a jelly like substance, which fills the center of the eye. The vitreous is normally clear and as such will normally not affect vision. The vitreous is attached to the retina in many areas.
In some regards, the way in which the eye works may be compared to a camera. In a camera, light is focused by the lens onto a film, where an image is formed. In the eye, the cornea (a clear structure forming part of the front wall of the eye) and the lens focus light onto the retina where an image is formed. The retina then converts this image into neural signals, which are transmitted to the brain.
Floaters, flashing lights and posterior vitreous detachment:
When we are young, the vitreous is normally a clear structure which does not affect our vision. As we age, however, changes may occur within the vitreous. Some parts of the vitreous may become more liquefied; other parts of the vitreous may condense and start to shrink. As the vitreous shrinks it may pull away from its attachments to the back part of the eye. This separation of the vitreous from its attachments to the back part of the eye is called a posterior vitreous detachment. Posterior vitreous detachments occur as a normal aging event but may be more common or occur earlier in people who are nearsighted (myopic), have undergone cataract surgery or who have had eye trauma or inflammation.
As a result of these changes within the vitreous, small clumps or strands may develop in the vitreous. As light passes through the vitreous, these small clumps or strands may cast shadows on the retina. We see these shadows as floaters. Although the floaters appear to us to be outside of the eye, they are actually within the eye. The floaters can have many different shapes. While most often they appear as dots or lines, sometimes they can also appear like circles, clouds, cobwebs or even like a spider or a fly. Most of the time, these objects will appear to move. Floaters can also be caused by bleeding or inflammation in the eye.
The vitreous pulling away from the retina can also cause the sensation of seeing flashing lights. These sometimes appear like “lightening streaks” in the eye. The sensation of flashing lights is not, however always a sign of the vitreous pulling on the retina. Other conditions such as a migraine can also cause the sensation of seeing flashing lights.
At times, a posterior vitreous detachment may occur without associated symptoms. While most posterior vitreous detachments do not lead to more serious problems, sometimes a retinal tear or detachment may arise as a result of a posterior vitreous detachment. Because of the risk of there being an associated retinal tear or detachment, anyone having the new onset of floating spots or flashing lights should undergo a careful retinal evaluation.
Retinal tear and detachment:
As the vitreous pulls away from the retina during a posterior vitreous detachment, the retina may at times tear. Retinal detachment occurs if fluid from within the vitreous passes through the tear and collects under the retina, causing the retina the separate from the underlying tissue (retinal pigment epithelium). The retinal tear may be associated with the symptoms of a posterior vitreous detachment (flashing lights and floaters). However as most retinal tears occur in the more peripheral parts of the retina, a retinal tear will usually not cause loss of vision unless there is progression to retinal detachment. The detached retina is not capable of normal sight and as the retinal detachment enlarges and approaches the central part of the retina there will be an enlarging area of vision loss. This is sometimes described as a shadow or veil covering the vision. Sometimes retinal tears occur without associated floaters or flashing lights. In these cases, the first symptoms to occur may be the loss of vision due to retinal detachment.
Not all retinal tears will lead to retinal detachment. At times, a retinal hole or tear may be found during a routine eye exam without there having been any associated symptoms. In this situation, the risk of progression to retinal detachment may be low and treatment of the retinal tear in this situation may not always be needed. However, retinal tears associated with symptoms suggesting that there has been a recent posterior vitreous detachment are usually felt to be of high risk of progression to retinal detachment and should, under most circumstances be treated in order to minimize the risk of progression to retinal detachment. Retinal tears, if detected early, can usually be treated in such a way as to avoid retinal detachment.
Treatment of Retinal Tears:
Retinal tears can be treated using either laser photocoagulation or cryotherapy. Laser photocoagulation is a procedure where a special light is directed to the retina and used to create burns in the retina surrounding the retinal tear. Cyrotherapy is a procedure where a freeing probe is placed on the surface of the eye and used to create a freeze extending to the retina surrounding the retinal tear. Whether laser photocoagulation or cryotherapy is used, as the eye heals a scar will form sealing the retinal tear and in most cases preventing a retinal detachment from occurring. Both laser photocoagulation and cryotherapy are usually performed in the doctor’s office. Treatment of retinal tears is usually successful in preventing retinal detachment. Unfortunately, occasionally even after treatment of a retinal tear, retinal detachment may still occur. Therefore, if any new symptoms arise following treatment of a retinal tear, the retina should be re-examined and even in the absence of new symptoms, continued follow-up after treatment of a retinal tear is needed.
Treatment of Retinal Detachment:
Some retinal detachments, if diagnosed when the detachment is small, may be treatable with only laser photocoagulation or cryotherapy. More often, however, if retinal detachment occurs, more extensive surgery is usually needed. The surgical procedures, which are frequently used for repair of retinal detachment, include pneumatic retinopexy, scleral buckle and vitrectomy.
When pneumatic retinopexy is used for repair of a retinal detachment, a gas bubble is injected into the vitreous cavity. The patient is then positioned in such a way so that the gas bubble pushes against the retinal tear and temporarily seals the tear, which has caused the retinal detachment. With the retinal tear covered by the gas bubble, the fluid that has accumulated under the retina will usually be reabsorbed by the eye within one or two days. As the gas bubble will also be reabsorbed by the body, it is necessary to also create a more permanent seal surrounding the retinal tear. To create this permanent seal, pneumatic retinopexy is done in conjunction with either retinal cryopexy or laser photocoagulation. Sometimes the retinal cryopexy will be done prior to the injection of the gas bubble. On other occasions, however, the cryopexy or laser photocoagulation will be done on a subsequent day, after there has been clearing of the subretinal fluid. Depending on which gas is used, the bubble takes between two and six weeks to be cleared from the eye. Pneumatic retinopexy can usually be performed in the doctor’s office. While pneumatic retinopexy is a good option for the repair of many retinal detachments, not all retinal detachments are suitable for this type of repair.
Scleral buckling surgery is another good option for repair of many retinal detachments. In scleral buckling surgery a buckling element, usually a piece of silicone, is sutured to the sclera (the outer wall of the eye) in such a way as to indent the wall of the eye. This indentation reduces the traction that is created by the vitreous pulling on the retinal tear, thereby allowing the tear to close. Cryotherapy is usually used in this procedure as well, to create a permanent seal surrounding the retinal tear. The fluid which has collected under the retina is either surgically removed or is allowed to spontaneously reabsorb. Sometimes a gas bubble will also be injected into the vitreous cavity as part of this procedure. Scleral buckling surgery is performed in an operating room. It is frequently done under local anesthesia and the patient will usually return home the same day as the surgery.
Sometimes, particularly in more complicated retinal detachments; it may be preferable or necessary to remove the vitreous in order to reattach the retina. This procedure is called a vitrectomy (also called pars plana vitrectomy). Vitrectomy may be used in combination with the other techniques already described. During vitrectomy surgery, small incisions are made through the sclera, which allow microsurgical instruments to be introduced into the vitreous. The vitreous, along with any scar tissue, which may also be present, is removed. In this way the traction on the retina is eliminated. The fluid that has collected under the retina is surgically removed. The vitreous cavity is then usually filled with a gas bubble. Sometimes in more complicated retinal detachments the vitreous cavity may instead be filled with silicone oil. The retina tear is surrounded with laser photocoagulation. A scleral buckle may be placed in conjunction with vitrectomy. Vitrectomy surgery is performed in an operating room. The patient will usually return home the same day as the surgery.
The choice of which of these procedures is most appropriate for the repair of a retinal detachment is dependent on many factors. These include the location of the responsible retinal tears and the presence or absence of scar tissue on the retina (proliferative vitreoretinopathy). The decision of which method of retinal detachment surgery is best can only be made after a careful evaluation. Fortunately, with these techniques, it is possible to successfully repair most retinal detachments. While most retinal detachments are successfully repaired with a single operation, in some cases more than one operation may be needed.
The amount of vision recovered after successful retinal detachment surgery is variable. The most important factors influencing the postoperative vision are whether the macula is detached prior to surgery and the duration the detachment has been present. If retinal detachment surgery can be done before the detachment has extended to the macula (the center portion of the retina which is responsible for central vision) the likelihood of maintaining good central vision is excellent. In many cases, however, a retinal detachment may not be detected until after the central vision is affected. If the macula is detached prior to the surgical repair, there is usually some permanent vision loss even after successful retinal detachment surgery. While it is common to obtain some improvement in vision shortly after surgery, the final best vision may at times take 6 months, a year, or even longer to obtain.