The retina is essentially a thin sheet of light-sensitive nerve tissue that lines the back wall of the eye, much like wallpaper lines a wall of a room. If the retina tears, fluid can seep behind the retina through the opening caused by the tear. The gradual accumulation of fluid results in further separation of the retina from the eye wall, much like wallpaper peeling off of a house wall. This is termed a retinal detachment. Contrary to popular belief, retinal detachments don't only occur in boxers and those who have experienced trauma; in fact, most retinal detachments occur through no fault of the patient.
Retinal detachment can affect any age group, male or female. Across the population, they occur in approximately 1 out of every 7000 people. There is a higher incidence with increasing nearsightedness; these eyes are longer and the retina tends to be stretched and thinned with a higher tendency to tear. Individuals with a condition called lattice degeneration are about 10 times as likely to develop a retinal detachment. Lattice degeneration is a condition in which the peripheral retina is thinned and has abnormal adhesion of the vitreous gel this predisposes the retina to tearing. Certain inflammatory conditions and infections are associated with a higher incidence of retinal detachment. Retinal detachments are particularly common with certain viral infections of the retina. Trauma is a definite cause in a certain percentage of retinal detachments. In certain cases, no definite cause can be identified.
Clinical Appearance & Symptoms
The key retinal defect in the above type of retinal detachment is a retinal tear. The thin retinal tissue is prone to tear when it is pulled upon by vitreous gel, the substance that fills the vitreous cavity. As we age, this gel normally liquefies and separates from the retina in a process called vitreous detachment. As the gel separates, two symptoms are often experienced. First, collagen particles suspended in the vitreous cavity can produce a sensation of floaters; patients often describe "cobwebs" or "bugs" in their vision. Second, any pulling on the retina stimulates the light sensors in this nerve tissue; this often results in flashes that are described as white lightning streaks.
When the vitreous gel pulls on the retina, the most common result is a gradual release of the gel and resolution of symptoms. The flashes often disappear completely, while floaters tend to linger. In some cases, the traction of the gel on the retina occurs near a blood vessel; this can result in sheering of the blood vessels and bleeding into the vitreous cavity. The patient experiences a different type of floaters caused by blood cells floating in the liquefied vitreous gel; sometimes this is severe enough to cause temporary blindness.
Finally, as a precursor to retinal detachment, vitreous traction on the retina can result in tearing of the retinal tissue. Floaters can be caused by pigment cells released from the space under the retina. At the first signs of floaters or flashes, individuals are advised to consult with their retinal specialist immediately. It is hoped that the tear(s) can be identified and sealed before fluid (liquefied gel) starts to seep under the retina and cause retinal detachment.
Left alone, fluid will generally continue to accumulate under the retina and peel the retina off of the eye wall (Figure 3-6). At the early stages, patients often notice a shadow in their peripheral (side) vision. As time progresses, the shadow gets closer and closer to the central vision. Eventually, the center of vision (the macula) usually will detach if left untreated. It is very important to try to repair a retinal detachment before the central vision is involved, as macular involvement often results in permanent visual loss or symptoms. Once the macula detaches, it is still important to reattach it to attempt to restore as much vision as possible.
The reason that retinal detachment is so critical is that it is a potentially blinding disease. The retina depends on two blood supplies to function properly and allow one to see. The first blood supply is within the retina. The second is on the back wall of the eye. When a retina detaches, it is separated from this second blood supply and the retinal nerve tissue is starved of oxygen and nutrition. The longer the retina is detached, the more nerve cells ultimately die. After a retinal detachment is repaired and the blood supply is restored, cells often recover; however, cells that have died cannot be replaced and this is what is responsible for potential permanent visual loss.
When a retinal detachment is suspected, your retinal specialist will perform a detailed examination of the retina. The purpose is to identify the extent of the retinal detachment, find any retinal tear(s), and plan surgical repair. He or she will also be looking for any complicating conditions such as lattice degeneration. The examination process almost always involves pressing gently on the surface of the eye while looking in with a lens, a technique called scleral depression. This allows for a complete and accurate evaluation of the entire retina.
Treatment of retinal detachment (regardless of technique) depends upon three factors: finding the retinal tear(s), sealing the retinal tear(s), and supporting the retinal tear(s).
A surgical approach will be formulated based on many variables including: number and location of tears, size of retinal detachment, degree of nearsightedness, presence of lattice degeneration, presence of vitreous hemorrhage, presence of a natural lens or cataract surgery, and age/health of the patient, among others.
There are basically 3 procedures that can be performed:
- Pneumatic Retinopexy
- Scleral Buckle
A pneumatic retinopexy is the simplest technique, and can be performed in the office. The retinal specialist localizes the retinal tear(s) as with any retinal detachment. The tear(s) are then often sealed with a freezing treatment, called cryotherapy. A small gas bubble is then injected into the vitreous cavity with a small needle through the white of the eye. The patient is asked to position such that this bubble floats against the retinal tears and allows the freezing treatment to seal as the fluid under the retina dissipates. Alternatively, a laser treatment can be applied to seal the tear(s) after the fluid has dissipated. The patient is positioned for several days to allow the retina to heal properly. The gas bubble disappears on its own, usually within 2 weeks.
This procedure is most successful in patients with one tear located in the top half of the retina. It is also more successful in those that have natural lenses, as opposed to those that have undergone cataract surgery. Positioning is critical in this surgical technique. Therefore, those who cannot position should be excluded; reasons include back problems, neck problems, advanced age, young children, and mental disorder. Properly selected cases can expect a single procedure success rate around 85%. The healing is very rapid with this technique.
A scleral buckle must be performed in the operating room. As above, it involves locating the retinal tear(s). The tears are then often frozen with cryotherapy to seal them. Alternatively, a laser can be used to "spot weld" the retina after it is reattached; this often involves draining the accumulated fluid from under the retina. A thin plastic material is then sewn to the wall of the eye to indent the eye in the area of the tear(s). Often, this material is wrapped around the eye like a belt to support the retina for 360 degrees. The extra support provided by this device results in improved outcomes, with single surgery success rates close to 90%.
In order to properly place a scleral buckle, significant manipulation of the surface tissues of the eye must be performed. The eye is often bruised, red, and swollen following surgery and it can take up to 6 weeks to heal completely. Fortunately, the scleral buckle can almost never be seen following surgery and the eye looks completely normal once it heals. The scleral buckle is generally left on the eye permanently. In certain cases, the buckle must be removed if there is associated infection or if it works its way through the surface tissues (a process called extrusion). Individuals undergoing scleral buckling may also experience increased nearsightedness following surgery, and there may be a discrepancy in the size of objects between the two eyes. In some cases, there may be a droop in the eyelid or lack of full movement of the eye caused by the scleral buckle. Bleeding is generally the worst complication of scleral buckling; fortunately, this is not common.
Vitrectomy surgery must be performed in the operating room (see treatments/Vitrectomy). It involves complete removal of the vitreous gel through tiny openings made in the eye wall. The fluid is then drained from under the retina, and the retinal tear or tears are treated with laser. The entire vitreous cavity is filled with a gas bubble to press on the tears and allow the laser to seal while the retina is healing. The gas bubble usually lasts between 1 and 8 weeks, depending on the gas used and its concentration. This is in contrast to pneumatic retinopexy (above) where a smaller gas bubble is injected due to the presence of vitreous gel within the eye that is not removed.
Vitrectomy surgery is highly successful, with single surgery success rates approaching 95%. It is particulary valuable in patients who have previously had cataract surgery. Rare complications include bleeding and infection. In patients who have not had cataract surgery, cataract progression is more rapid following vitrectomy surgery. Vitrectomy is often combined with scleral buckling (above) in certain patients in an attempt to improve success rates in particularly high risk cases.
The most common complication of retinal detachment surgery (regardless of technique) is redetachment of the retina. This generally occurs through two mechanisms. First, new tears in the retina can develop after surgery. Fluid can enter these new tears and start the retinal detachment process all over again. Further surgery is necessary in these cases.
Second, scar tissue can grow on the surface of the retina following repair of retinal detachment. This can be thought of as an aggressive healing response. Unfortunately, the scar tissue often pulls on the retina, opens up old or new tears, and results in redetachment. This type of retinal detachment is particularly complicated and requires advanced surgical techniques to attempt to repair; in addition, the visual results are sometimes disappointing. Surgery is generally approached using vitrectomy techniques to access the inside of the eye, particularly the retinal surface. Fine instruments are used to peel the scar tissue off of the retina, allowing it to lay flat against the wall of the eye. Often times, an oil bubble is injected into the eye to achieve long-term support (as opposed to a gas bubble that dissipates in 1 to 8 weeks, as described above). Once the retina is stabilized, a second surgery is required if the oil bubble is to be removed.
With modern techniques, over 98% of retinal detachments can be successfully reattached. Those with extensive scar tissue and/or those left untreated for an extended period of time tend to have the worst outcomes. Patients are strongly advised to see their eyecare professional at the first signs of flashes, floaters, or shadows in their vision. Early intervention can often times lead to better outcomes, although any retinal detachment can ultimately lead to blindness.