Retinal Detachment

The eye functions like a living camera.  The front part of the eye, consisting of the cornea (the clear cover of the eye) the lens and the iris (the coloured portion of the eye), acts to focus light on the back of the eye, much like the lens and aperture system of a camera focuses light on a piece of film.  The retina, similar to the film, is a thin layer of tissue that lies against the back surface of the eye wall.  The image obtained by the retina is transmitted via the optic nerve to the brain.

Unlike a camera, the image obtained by the retina is not of uniform clarity or sharpness.  Only the central portion of the retina, the macula (a very small area only about the size of a 5 cent piece) is sensitive enough to provide high quality vision for tasks such as reading or driving.  The remainder of the retina, the peripheral retina, is for side vision.  The retina outside of the macula, which makes up more than 95% of the retina, is not capable of the fine detailed vision.

The vitreous is the clear gel that fills the central cavity of the eye.  The vitreous may liquefy with age and eventually separates from the retina. This is called a vitreous detachment . Separation of the vitreous is often accompanied by seeing floaters.  These appear as dots, spots or curly lines that appear suspended in front of you and move with your eye.

Flashes of light are also a common symptom of a vitreous detachment.  These are due to pulling on the retina as the vitreous separates.  If a retinal blood vessel is broken from the pulling, a vitreous haemorrhage can occur.  The patient may see a small amount of blood as a shower of spots.  Larger haemorrhages can cause large dark blobs in the visual field or an overall decrease in vision.  If the retina is weak in a certain area, a retinal tear can occur as the vitreous separates and pulls away from the retina.
Picture
 

Retinal detachment usually occurs as a consequence of the vitreous separating from the retina. Retinal detachment occurs when liquid vitreous passes through the break and goes under the retina.  The retina will then start to detach from the underlying tissue.  As most breaks occur in the far peripheral retina, detachment will first cause loss of a portion of the side vision.  This can be seen as a dark shadow involving the peripheral vision.  As the detachment extends towards the macula, the shadow will also enlarge.  Central vision will be lost if the macula detaches.  Without surgical repair, most detachments will eventually involve the entire retina and all vision will be lost.

When the retina detaches, it separates from the eye wall and is removed from some of its blood supply and source of nutrition.  The retina will degenerate and lose its ability to function if it remains detached.  Central vision will be permanently lost if the macula remains detached
Picture
Prevention of Retinal Detachment 

If a retinal break is discovered before a detachment occurs, it can be treated to prevent retinal detachment.  Usually laser is used to create a series of welds surrounding the break to seal the retina to the underlying tissue.  This prevents fluid from passing through the break and detaching the retina.  Rarely, the laser cannot be used and a retinal cryoprobe is used to treat the break.  The cryoprobe creates a freezing reaction to produce welds around the break. 

Once a detachment occurs, it is almost always too late to use the laser or cryoprobe.  This is why it is so important to be examined promptly if you have symptoms of a PVD (flashes, floaters, shower of spots).  Treatment of retinal breaks with the laser or cryoprobe is usually very successful and retinal detachment can be avoided.  Unfortunately, retinal tears will lead almost immediately to detachment or there may not be any symptoms of a PVD or retinal tear.  For these and other reasons, many people will have a retinal detachment when first examined.

Treatment of Retinal Detachment 

Over 70% of retinal detachments can be repaired with a single procedure.  Currently, these are 3 different surgical approaches to repairing a detachment, scleral buckle procedure, vitrectomy and pneumatic retinopexy.

 

1.  Scleral Buckle

This surgical procedure has been in use for many years.  The procedure involves treating all retinal breaks with laser or the cryoprobe and supporting them with a scleral buckle.  The buckle is a piece of solid silicone, the type and shape of the buckle is chosen to suit the location and number of retinal breaks.  The buckle is sewn onto the outer wall of the eyeball (sclera) to create an indentation inside the eye.  The buckle is positioned so that it indents and closes the retinal break.  Once the break is closed, the fluid under the retina (subretinal fluid) will usually spontaneously resolve over 1-2 days.  Sometimes the subretinal fluid is drained from the eye at the time of surgery.  Post-operatively one can resume most activities within several days.
Picture
2.  Vitrectomy

Small incisions are made into the wall of the eye to allow the introduction of instruments into the vitreous cavity (the middle of the eyeball).  The vitreous is removed using a vitreous cutter.  Then a variety of instruments (scissors, forceps, pics, lasers etc) and techniques (excision of tractional bands, gas or silicone oil fill etc) are used to reattach the retina.  It is sometimes important to maintain a specific head position for a few days after surgery to keep the retina attached while it adheres to the underlying tissue layer
.
Picture
3.  Pneumatic Retinopexy

This is a good way to repair a straightforward retinal detachment, especially if there is a single break located in the upper portion of the retina.  A gas bubble is injected into the middle part of the eye (vitreous cavity).  It is then critical to position the head so that the gas bubble covers the retinal break and the subretinal fluid will disappear within 1-2 days.  The retinal break is either treated with cryopexy before the bubble is injected or with laser after the subretinal fluid has disappeared.  The main advantage of this approach is that it avoids some of the complications of scleral buckling and vitrectomy surgery.  The main disadvantages are the requirement for precise head positioning for up to 7 days following the procedure and a slightly lower initial success rate as compared to a scleral buckle or vitrectomy.  If the retina is not reattached by a pneumatic retinopexy procedure, a scleral buckle or vitrectomy can be done.


Picture
Sometimes, a scleral buckle is combined with a vitrectomy. 

If the retina does not reattach after surgery, or detaches again after initial success, it is usually due to the development of either a new retinal tear or scar tissue on the surface of the retina. It is then usually necessary to do a vitrectomy.  If a vitrectomy was done initially, it is often necessary to go back and do another vitrectomy. 

As you can see, there is no set way to repair a detachment and procedures can be used in different combinations and sequences depending on the specific situation.

Results 

The visual result depends mainly on the state of the retina before surgery.  If the macula has not detached, good central vision will usually be retained following successful repair.  However, if the macula is detached and central vision is impaired by the detachment, there may be permanent loss of central vision even if the retina is successfully repaired.  The longer the macula is detached, the more likely there will be loss of vision due to irreversible damage.  In general, if the centre of the macula is detached for more than 4-5 days, there will be significant loss of central vision following surgery.