Retinal Tears and Detachments
The retina is a thin sheet of light-sensitive nerve tissue lining the inside of the eye. It is the tissue that turns light into electrical signals which are sent to the brain. It can be compared to the film in a camera. In order to function properly, it must be attached to the retinal pigmented epithelium (RPE), a layer of supportive cells under the retina. The vascular layer beneath the retina is the choroid, which is contiguous with the ciliary body and iris.
The vitreous is a jelly-like material that fills most of the space inside the eye. It is 99% water, and the gel comes from a protein called collagen. As we age, the vitreous fibers condense, "liquefy" and may pull forward or "collapse." When this happens, the vitreous separates from the retina. This can result in the eye seeing flashes and floaters. Vitreous liquefaction and separation are more likely to occur, and occur at an earlier age, in patients who are nearsighted, diabetic, and in patients with previous cataract surgery. This can also occur after injuries or eye inflammation.
In the majority of patients, the vitreous gel separates completely and without problems. In some patients, however, the vitreous is more adherent, and the separation can cause a tear in the retina. These tears are often small and located in the peripheral retina, an area which is not typically used for vision. Therefore, decreased vision from a tear alone is highly unusual, and often the only symptoms produced by a retinal tear are flashes and/or floaters. It does not cause pain or redness of the eye. This is why anyone with flashes or the sudden onset of new floaters should be examined. Most, but not all, retinal tears should be treated. Typically, symptomatic retinal tears are treated while asymptomatic round holes can be safely observed. Patients at especially high risk for a detachment (nearsighted, history of detachment in the other eye) are often treated prophylactically. Treatment for a retinal tear is aimed at creating an adhesion between the retina and underlying choroid and RPE. This can be done in two ways depending on the size and location of the tear(s).
- Laser - if the tear is posterior enough and there is no intervening vitreous hemorrhage, laser can be used to "spot weld" the retina to the underlying choroid and RPE. Enough burns to create 3-4 rows of laser spots around the tear(s) are made. Topical anesthetic drops are applied and a contact lens is used to focus the laser on the retina. Activity is limited for at least 1 week until the laser scars become strong enough to be considered "permanent."
- Cryotherapy - if the tear is anterior or if there is intervening vitreous hemorrhage that prevents the entire tear from being visualized, the tear is frozen using a cryoprobe. Topical anesthetic is given first, followed by subconjunctival injection of lidocaine (a local anesthetic). Under visualization with an indirect ophthalmoscope, liquid nitrogen is used to freeze around the tear from the outside of the globe. The eye is generally patched for a couple of hours. Activity is limited for up to 2 weeks because the cryotherapy scars take slightly longer to become "permanent."
A retinal detachment is a separation of the retina from the back wall of the eye, and is estimated to occur in about 1 in 10,000 people per year. When there is a tear in the retina, liquid from the vitreous cavity may pass through the tear, and separate the retina from the RPE. Normal eye movement causes additional fluid currents within the eye which generally causes the detachment to become larger. Once separated from the supporting RPE cells, detached areas of the retina progressively lose vision.
|This patient has a retinal detachment which extends from about the 1:00 to 7:00 position when looking at the eye. It is characterized by edematous (swollen) retinal tissue which has a whitish, corrugated appearance.|
Most people notice floaters and flashes before the retina detaches, which usually indicates a retinal tear. As the detachment occurs, a gradually enlarging dark area may be seen. Some people have compared this to a curtain coming down, or a shade being drawn in front of the eye. The dark area may begin in any part of the field of vision, but typically starts in the peripheral visual field. If the dark area reaches the center of the field of vision, the eye will not be able to see fine detail. It is possible for the retinal detachment to involve the entire retina.
The typical time frame to repair a retinal detachment primarily depends on whether or not the central retina (macula) is detached or not. If it is not detached (and central vision is good), generally repair is performed within 24-48 hours. If the macula is detached (and central vision is poor), repair is generally scheduled within the next 7-10 days. Other factors that influence timing of repair include the patient's general medical health, the timing of the patient's last food/drink intake, the need for preoperative clearance, the need to stop blood thinning medications (coumadin), and the location of the detachment. Timing may also depend on anesthesiologist or operating room availability as well.
Limited Retinal Detachments
A few small peripheral retinal detachments may not require surgical intervention. Often, laser is used to create a barricade behind the detachment to help prevent the detachment from extending. Because this does not attempt to fix the detachment, there is always a risk of it requiring further treatment.
Surgery for Retinal Detachments
Most retinal detachments require surgery to reposition the separated retina against the back wall of the eye. There are several methods in use today. The type of surgery used depends on the type and extent of detachment, and the preference of the patient and retina surgeon.
Pneumatic retinopexy is the newest method for retinal detachment repair. However, it is most suitable for a few types of detachment. Generally this works best in patients without previous cataract surgery, with retinal tears within two clock hours of each other, and with tear locations in the upper half of the retina. Generally, there also should not be any areas of retinal pathology in the lower retina. With modifications of this technique, patients who don't meet these criteria can also be successfully treated.
In this procedure, the causative tear or tears are identified and treated, typically with cryotherapy. A gas bubble is then injected directly into the eye. The patient positions their head so that the gas bubble pushes against the area of the retinal tear(s) for approximately 1-2 weeks. Additional laser may be used to treat the peripheral (attached) retina during the procedure, or later as the gas bubble absorbs and more of the retina reattaches. The success rate is approximately 60%, but the procedure can be done in the office with local anesthetic. If the procedure does not reattach the retina, additional surgical methods can be used with excellent success rates and no adverse effects on visual outcome.
Scleral buckling was the first type of operation for a detached retina. In this procedure, the causative retinal tear or tears are located and treated with cryotherapy. A flexible piece of silicone rubber is then permanently sewn to the sclera (white of the eye) to support the area of tears and detachment. This indents or "buckles" the eye helping prevent fluid from passing through the tear. Fluid may be drained from under the detached retina by creating an external incision in the sclera and choroid. Additionally, a small gas bubble may be injected to help keep the retina attached to the buckle while the cryotherapy scars form.
Vitrectomy is another surgical method to treat some types of retinal detachment. It can be used alone or in combination with a scleral buckle in detachments with unusual or difficult features, such as very large tears, scar tissue on the retina, excessive blood in the vitreous, or detachments that failed by other methods. First, as much of the vitreous gel as possible is removed from the eye. Second, the fluid that has accumulated under the retina is removed to flatten the retina. Third, laser is applied to the peripheral retina and around all tears to help secure the retina in place. Fourth, a long acting gas bubble or silicone oil bubble is placed into the eye to hold the retina in place while the laser and/or cryotherapy scars heal.
A nonexpansile concentration of a long-acting gas (SF6 or C3F8) is used. For most patients, strict postoperative positioning is recommended for 7-14 days. A patient will position their head so that the bubble pushes against the retinal tear(s) while the laser and/or cryotherapy scars form.
Travel by air or to high altitudes is prohibited while the gas bubble is present, as it would expand in the lower atmospheric pressure and severely increase the intraocular pressure. In addition, dental work or general anesthetic with nitrous oxide (laughing gas) is contraindicated because it diffuses into the gas bubble also causing it to expand. Vision is very blurry while the gas bubble is present. Depending on the type, the bubble may remain in the eye for about 2 weeks (SF6) to 2 months (C3F8).
If it is impossible for the patient to maintain positioning, or if the detachment is very complex, a clear silicone oil can be used instead of gas. Face down positioning is overnight, and the patient can be in any position other than flat on his/her back while the silicone oil is present. However, this approach necessitates an additional surgical procedure for oil removal approximately 3 months later. Because of the different refractive properties of silicone oil, vision is also very blurry while the oil is present.
With current methods, at least 80-90% of patients can be successfully treated with a single procedure. A total of 90-95% of patients can be repaired with additional procedures. Because some cellular degeneration can occur within hours after a detachment, many people do not get back perfect vision. If the macula (the central, most sensitive part of the retina) was not affected by the detachment, about 2 out of 3 eyes will get back reading vision. If this area was affected, only about 1 out of 3 eyes will get back reading vision. Younger patients (60 or less) with a macula-off retinal detachment have a better average postoperative visual acuity (20/50) than those 61 and older (20/80), probably due to a generally more healthy retina. It is impossible to predict visual recovery other than to say that it only possible if the retina is reattached. However, this must be compared to the minimal, if any, chance of visual improvement without repair of the retinal detachment.
Anywhere from 5-10% of patients will develop abnormal scar tissue on the retina which will cause the retina to detach after initially successful surgery. This is called proliferative vitreoretinopathy (PVR) and represents a major challenge to retinal surgeons. It is felt to be an abnormal, excessive healing response whereby cells typically under the retina, such as those of the RPE, gain access to the vitreous cavity of the eye through retinal tear(s). Additional cells may be released by the cryotherapy and/or laser required to treat these tears. They proliferate and form membranes which contract and exert tension on the retina. This traction opens previously treated tears and causes new tears to be formed as well. Unfortunately this is a poor prognostic sign. Vitrectomy and scleral buckle methods are used to try to maximize success rates in these cases. However, in a way analogous to picking a scab, the membranes have a tendency to grow back when removed surgically.