In our last blog we have discussed the structure of the eye. However just to refresh our memory, an eye works like a camera. The light coming from an object is focused by the cornea and the lens, which act as focusing mechanisms, onto the film of the eye, known as the retina. The space between the back of the lens and the retina is filled with a jelly-like substance known as vitreous.
The vitreous is attached to the retina throughout in young age group. However, as a person grows old the vitreous starts becoming liquefied and separates from the retina. This process is known as posterior vitreous detachment (PVD). It happens in middle age people and is usually a harmless natural process. Most of the patients feel the presence of black spots, floaters, suddenly appearing in front of the eye and some patients may also feel lightning flashes inside the eye. Over a period of 1 to 2 months the flashes and the floaters reduce in frequency and severity.
However in certain patients, the vitreous is densely attached to the retina at certain points. When posterior vitreous detachment takes place, at these points of dense adhesions retina gets torn. These pairs are known as horseshoe tears (HST) or retinal holes depending on their appearance. In some individuals, there are areas of pre-existing weakness in the peripheral part of the retina known as lattice degeneration. The retina gets torn easily at the sites of lattice degeneration.
Through these holes the liquefied vitreous goes behind the retina. The retina gets separated from the choroid in these patients. This is known as retinal detachment. Since the retina cannot function normally, the vision of the eye starts deteriorating. In early stages the patient may feel like a curtain falling in front of their eyes. Certain patients may feel a sudden increase in the number of floaters or an increase in the intensity of flashes of light. The vision significantly reduces when macula gets detached.
METHODS FOR TREATMENT:
1. Retinal laser
In this treatment modality very intense light is used to strengthen the retina around the area of tear or lattice degeneration. If a horseshoe tear or retinal hole is detected before retinal detachment develops or in early stages of retinal detachment, retina laser can be used to avoid the development or progression of retinal detachment, so that it does not threaten Central vision. Chances of progression of retinal detachment are much less after retinal laser though it may still happen in a few patients as it takes about 10 to 14 days for the effect of laser is fully achieved. A retinal laser can also be done prophylactically in patients with extensive lattice degeneration especially if the patient has developed retinal detachment in other eye or has a strong family history of retinal detachment.
2. Pneumatic retinopexy
In this procedure, a small bubble of gas known as C3F8 or SF6 is injected in the vitreous cavity. This pushes the detached retina back in its place. To keep the retina in its place cryopexy is done. This procedure is useful in very few patients who have a retinal detachment of the superior quadrant and have one or two retinal tears very close to each other.
3. Scleral buckle
In this procedure a small piece of silicone rubber is the suture to the sclera over the area where the retinal tear is present and the fluid present under the retina is removed externally. This pushes the sclera and retina towards each other. To keep the retina in its place external cryopexy is done before suturing the silicone rubber. Usually post-operatively there is significant redness of the eye and pricking sensation for a period of 1 to 2 months following scleral buckle this procedure is generally done in younger age group patients. It may also be performed along with vitrectomy surgery.
In this procedure tiny incisions are made in the sclera, around the cornea about 3.5 mm behind the limbus. Very thin pencil-like instruments are inserted in the vitreous cavity. The vitreous which is causing traction on the retina is completely removed and retina is pushed back in its place with air. To retain the retina in its place retinal laser is done intraoperatively. Till the effect of laser comes, the vitreous cavity is filled with medical-grade silicone oil or C3F8 / SF6 gas. If silicone oil is used it needs to be removed after 2 to 4 months which requires another surgery. If gas is used it gets absorbed over a period of 1 to 2 months. But till the time gas gets absorbed vision is very low. Whether to use gas or silicone oil depends on the surgeon’s choice in a particular case. As mentioned before vitrectomy may have to be combined with a scleral buckling procedure. The patient is usually advised to maintain a face-down / prone position for three weeks after the surgery. This has to be maintained for 12 to 14 hours per day.
The purpose of retinal detachment surgery is to reattach the retina in its original place. The vision that the patient gets after surgery depends on the strength of the vision cells in the retina. Vision may not be as clear as one gets after cataract surgery or that present in other normal eyes. However if the surgery is delayed the chances of retina settling in place permanently get reduced and vision recovery is also very poor. Hence the surgery has to be performed on an emergency or priority basis depending on the case scenario in a particular case.
In certain cases even after the surgery the retina gets contracted and detaches from its place again. In such cases repeat surgery may be necessary.
The results of retinal detachment surgery are very gratifying with improvements in surgical techniques and instrumentation in today’s era. However the retinal detachment must be diagnosed and operated upon at the earliest to save the eye and to save the vision.