Health Society of South Africa

THE RETINA BOOK

The Retina: A Vulnerable Tissue

If you have been diagnosed as having a retinal problem, you're not alone. The retina - which is about 1 millimeter thick and has the consistency of wet tissue paper - is the delicate inner lining of the eye that is subject to a number of sight-threatening problems which affect millions of people. In order to understand better how retinal problems can affect your sight, let's first take a look at how vision occurs.

The Path of Vision
Light reflected from external objects enters the pupil.
The lens focuses the light ...
Through the transparent, gel-like vitreous ...
And onto the retina. Through a complex chain of chemical reactions, the retina - which is composed of a number of layers - changes light into electrical impulses.
The electrical impulses, or messages, travel along nerve fibres that collect at the optic disc - the beginning of the optic nerve.
The optic nerve then carries these messages to the brain. When the messages are received by the brain, vision occurs.

If any part of the delicate retina is damaged, it's very likely that some degree of vision will be lost.

The Retinal Map

If the cup-shaped retina is viewed from the front and flattened out, it provides a map showing the areas that are responsible for different types of vision.

Macula (central vision)
Peripheral retina (side vision)
Optic disc, where nerves exit to the brain and where blood vessels enter and exit.

Vision Controlled by the Macula
Light-sensing cells called cones are responsible for central vision. Cones are most common in the macula at the centre, and are hardly found at all at the edge of the retina. A diseased macula causes difficulty in reading and in seeing distant objects, such as street signs. Colour vision is also the product of cones.

Vision Controlled by the Peripheral Retina
Side vision - or the ability to see to the side as you focus straight ahead - is the responsibility of another type of light-sensing cell called rods. Rods are more numerous in the peripheral retina. If this outer region is damaged, it's difficult to move around without bumping into things or to fix your gaze on a moving object. Night vision is also the product of rods.

Common Retinal Problems
The retina is subject to a number of problems that can result in some type of visual impairment, depending on the area of the retina that's affected. This booklet discusses three common problems: macular degeneration, retinal detachment and diabetic retinopathy. Each problem affects vision differently and each is treated in a different way.

Note: Any of these retinal problems can be severe enough to cause legal blindness, and retinal detachment and diabetic retinophthy can even lead to total blindness if not brought under control. Legal blindness is a condition of low vision that, unlike total blindness, may be compensated to varying degrees by using vision aids.
Fortunately, far more can be done today than even a few years ago to treat most retinal problems and to help preserve vision. This information was prepared to help you understand your retinal problem and what can be done to treat it.

Diagnosing Retinal Problems

After taking your medical history and giving you a visual acuity test, your doctor can use any of a number of tests to gather information about your retinal problem. In several of these tests, your doctor can look into your eye to view the retina directly.

Indirect Ophthalmoscopy
Your doctor will use an ophthalmoscope attached to a head-band, while holding a magnifying lens, to get an overall view of your retina. By pressing a thimble-like probe around the edge of your eye (a technique called scleral depression), your doctor can check the outermost peripheral retina for tears, detachments or other abnormalities.

Direct Ophthalmoscopy
Using a hand-held ophthalmoscope as you are seated, your doctor can check the central retina, including the macula, for signs of degeneration or vascular disease.

For both kinds of ophthalmoscopy, your doctor will first dilate your pupils with drops. A bright light is used in both tests which may feel warm and may cause some discomfort.

Slit Lamp
A slit lamp is a microscope that illuminates and magnifies the structures inside your eye. When used along with a hand-held magnifying contact lens, it enables your doctor to examine small area of the retina in great detail. Your eyes will be dilated beforehand, and a topical anaesthetic will be applied so that the contact lens can rest on your eye.

Fluorescein Angiography&nbsp;
To get a better view of the retina's blood vessels, your doctor may need to give you an intravenous injection of a dye called fluorescein, which takes only a few seconds to reach the eye. In a darkened room, photographs will then be taken with a special camera focused on the retina.

Ultrasound
This test uses sound waves far above the range of hearing to explore the structures within the eye. Echoes from the sound waves are reflected back from the retina and are converted into an image that is recorded.

Other Tests
Your doctor may check your colour vision and your eyes' ability to adapt to changes in light. Electrical monitoring tests may be done, such as electroretinography and electro-oculography. Visual field testing of your central or side vision may also be performed.

Although most retinal problems do not require immediate treatment, your doctor may recommend that treatment (often performed with a laser) be done within the next few days.

Facts About Laser Treatment

Retinal problems can often be brought under control with laser treatment. In order to understand how a laser works, imagine sunlight that is focused by a magnifying glass to burn a hole in paper. Similarly, a laser is a highly concentrated beam of light that creates a tiny spot of light that creates a tiny spot of heat. When this light strikes the retina, the heat it creates works to repair the damaged area by a process called photocoagulation.

How the Laser Works
1. The laser is a low-energy, highly concentrated light that is beamed through a special lens into your eye.
2. The light passes freely through the transparent structures of the eye and continues on through the transparent layers of the retina.
3. The light is stopped by the pigment layer of the retina, where it is converted into heat. The heat coagulates, or congeals, the retinal layers.

What the laser can do:
Repair weak areas in the pigment layer
Seal breaks in the transparent layer
Destroy abnormal blood vessels

What Happens During Laser Treatment
Laser treatment can be performed in your doctor's office or in the outpatient department of a hospital. First, you'll be given drops to dilate your pupils, followed by a topical anaesthetic, and possibly a local anaesthetic injected behind the eye as well. Then you'll be seated in front of a laser machine in a dimly lit room, and a contact lens will be placed on your eye. If a local anaesthetic is not used, you may be asked to fix your gaze in several directions to expose different areas of the retina to the laser. If a local anaesthetic is administered, you will not be asked to move your eye. Instead, a special contact lens that contains mirrors will be used to direct the laser beam. During the treatment, you may see flashes of bright green or red light that may cause sensations of warmth, and which can be a bit uncomfortable.

Afterwards
After treatment, you'll need to have someone take you home where you should rest for the remainder of the day. Because your dilated eyes may take several hours to return to normal, you may need a pair of dark glasses. Your eye may ache slightly for the rest of the day, and you may have some irritation from the contact lens. An aspirin-substitute (acetaminophen) can provide relief. If you've had a local anaesthetic, your eye may be covered with a patch, which you can remove yourself after several hours. Your vision may be slightly blurred for the next few days.

Follow-up care
Your doctor will probably want to see you in about a week to check for complications. After that, you will have periodic follow-up examinations. It may be a month or more before the results of your treatment will be apparent.

Note
Laser treatment is generally intended to preserve your existing vision by halting the progress of your retinal problem. Do not expect it to restore lost vision or to improve your existing vision, unless your doctor tells you specifically that it will achieve these results.

Macular Degeneration

Macular degeneration affects the macula, the area of the retina that is responsible for central vision and colour perception. This condition tends to become worse with time and can best be described as a process of "wear and tear." As the tissues break down, fluid may collect under the retina, causing the layers of the retina to separate.

The Course of Macular Degeneration
The normal macula. Fluids nourish the pigment layer of the retina - the pigment layer separates the transparent layer of the retina from the fluids - the transparent layer contains light-sensing cones and rods.

The degenerating macula. Cells in the pigment layer no longer fit tightly together, allowing fluid to seep underneath the transparent layer - the layers may become detached, disarranging cones and rods and distorting vision - in later stages, the cones and rods themselves may degenerate and die, causing blind spots.

How Vision is Affected.
Although macular degeneration usually affects both eyes, it may first occur in one eye only. Unfortunately, when this happens you may be unaware of changes in your vision because your "good" eye compensates for the weak one.
Generally, macular degeneration does not lead to total blindness - usually only central and colour vision are affected. Because the peripheral retina remains healthy, peripheral (side) vision is retained along with your ability to see in the dark. Most affected is your ability to see fine detail, to read and to see well enough in the distance to drive.

Diagnosis
Your doctor can check the macula for signs of damage using direct ophthalmoscopy. In addition, you may be given some special tests. Using the grid test, in which you look at a grid of intersecting lines similar to graph paper, your doctor can determine from "blind spots" or distortion whether you central vision has begun to be affected. With the color vision test, damage to the cones of the macula may be revealed when you try to pick out symbols or letters camouflaged in coloured patterns. Fluorescein angiography may be done to check the blood vessels of the macula and guide possible treatment.

Treatment
There is no cure for macular degeneration, but early laser treatment may possibly help to slow the progress of the disease. the laser can sometimes work to repair weak areas of the macula by destroying worn-out tissue and allowing new tissue to grow. It may also destroy abnormal blood vessels, preventing bleeding and severe scarring. If you have macular degeneration, your doctor may have you do the grid test at home everyday. You should call your doctor immediately if you see a change in the grid.

Low Vision Aids
If laser treatment is not appropriate for you or if it does not completely stop the process, you may be able to compensate for much of your visual loss by using low vision aids. Your doctor can direct you to the nearest low vision clinic where you can explore a variety of special devices designed for people with partial loss of vision.
There are other steps you can take to make life easier. Your public library may have large print books and agencies for the blind can lend you recordings of books. Magnifying TV screens are available, though expensive. The telephone company can even install a special dial free of charge.

Note: Macular degeneration is most common in older adults. If you are over 50, have your eyes checked regularly. Reporting symptoms early allows the disease to be diagnosed and possibly treated before it progresses too far.

Retinal Breaks and Detachment

Because the retina is such a delicate structure, it's vulnerable to breaks that can often ultimately cause the retinal layers to become detached from each other. Some people are predisposed by heredity to have retinal breaks. Early detection and treatment of breaks and detachment can help to prevent blindness or severe damage to vision.

Retinal Breaks
How Retinal Breaks Develop
As part of the ageing process, the vitreous gel can shrink and pull away from the retina. Although the vitreous is only loosely attached to the retina, as it pulls away, a break may occur at a weak spot in the retina. Degeneration of retinal tissue over time can also cause breaks to develop. Breaks usually occur in the peripheral retina, where there is little effect on vision. They can lead to retinal detachment which does cause severe loss of vision.

How Vision is Affected
Retinal breaks may occur gradually and do not always cause symptoms. The warning signs, sudden flashes of light, floaters and smoke or cobwebs, only infrequently indicate retinal degeneration, breaks or detachment. Even if these symptoms disappear in a few days, it's important for you to have your eyes checked by your doctor.

Diagnosis
Your doctor will use indirect ophthalmoscopy with scleral depression and a slit lamp to locate any breaks. If the breaks are insignificant and do not require treatment, your doctor will probably want to see you periodically to follow their progress. It will be extremely important for you to monitor your own vision, and to report any unusual symptoms - such as a change in the pattern of floaters - to your doctor at once.

Treatment for Retinal Breaks
If your doctor feels that treatment would be beneficial, there are two methods that can be used to repair retinal breaks.

Cryotherapy (cold treatment)
Cryotherapy may be performed in your doctor's office or in the outpatient department of a hospital. After you are given a local or topical anaesthetic, a freezing probe is applied to the surface of your eye over the point of the break. The extreme cold penetrates to the retina and freezes only the area around the break. As the frozen area heals, scar tissue forms and attaches the retinal layers together at the edges of the break. After the anaesthetic wears off, you may have some discomfort for a day or so. This procedure is most useful for breaks around the outer edge of the retina.

Laser treatment
The laser creates a tiny burn at the point of the break, and "welds" the separated layers of the retina back together.

After treatment
If discomfort persists after laser treatment or cryotherapy, your doctor may prescribe a mild pain medication - although an aspirin-substitute (acetaminophen) is usually adequate. You will probably be cautioned to avoid vigorous physical activities, especially contact sports. Don't strain or lift heavy objects.

Note: Even after treatment, new breaks can occur. Any recurring symptoms must be reported to your doctor at once. Remember, the sooner breaks are detected and treated, the greater the chances that a detachment can be prevented. If a detachment does occur, however, there are surgical procedures that can often work to reattach the retina and help restore your vision.

Retinal Detachment
For more than 20 000 people every year in the USA, retinal breaks do lead to detachment. Your chances of developing a detachment are greater if:

You are severely nearsighted
You have a family history of retinal detachment
You have had the lens of your eye removed during cataract surgery
You have suffered a severe blow to the eye or head

The Course of Retinal Detachment
The transparent layer of retina, which is subject to breaks, contains the light-sensing cones and rods. When a break occurs, fluid from the vitreous cavity seeps beneath the transparent layer, and separates it from the pigment layer. As the cones and rods are lifted away from the pigment layer, vision becomes darkened and distorted.

How Vision is Affected
Detachment may occur gradually or quite suddenly, but it is almost always accompanied by dramatic symptoms. If the macula (central retina) detaches, vision may be reduced to light perception or hand movements only.
As the retina detaches, "shadow" may appear, as though a dark curtain had been drawn across the field of vision. Total blurring can also result.

Diagnosis
Your doctor will use a slit lamp and indirect ophthalmoscopy with scleral depression to evaluate the extent of detachment and to locate retinal breaks.

Note: Even a minor detachment requires treatment to prevent total loss of vision. Contact your doctor immediately if you begin to have symptoms of detachment.

Treatment: Reattachment Surgery
Preparing for surgery
The day before surgery you will enter the hospital where a medical examination, routine laboratory tests, a chest x-ray and an electrocardiogram (EKG) will probably be done. Any health problem that might interfere with anaesthesia or surgery must be investigated before surgery can be performed.

What happens during surgery
After administering a local or general anaesthetic, your doctor will locate the breaks in the retina and freeze the area of the breaks using cryotherapy. To help the detached transparent layer of the retina settle back down onto the pigment layer, your doctor may drain the fluid from between the layers. Then a silicone band will be partly or entirely wrapped around your eye to indent it slightly inward. This pushes the pigment layer into contact with the detached retina. Scar tissue then forms in the frozen area, which reattaches the layers. The band is held in place by nylon sutures, and though it will remain permanently in your eye, it probably won't be seen or felt.

Recovering from surgery
Your hospital stay will usually last only a few days, and you'll probably be up and around long before you go home. Your eye may be patched for about a week after surgery. Medication in the form of eye drops will probably be prescribed. Your doctor will arrange for you to have periodic follow-up examinations until your eye has completely healed.

What to expect from surgery
In fewer than 1 out of 6 surgeries is a second operation necessary to reattach the retina successfully. How well surgery can restore your vision, though, depends largely on whether the central portion of the retina has become detached. If only the peripheral retina is detached, your chance of regaining your normal vision is well over 50 percent. In any case, surgery that succeeds in reattaching the retina will either restore some vision or will at least prevent further visual loss. If retinal detachment is not operated on, progressive visual loss will occur, probably resulting in blindness.

Diabetic Retinopathy

Among people who have had diabetes for more than 10 years, almost half develop a complication called diabetic retinopathy. This condition causes abnormalities in the tiny blood vessels that nourish the retina, and usually affects both eyes at the same time. Severe visual loss - including total blindness - can result if treatment is not begun early.

Background Diabetic Retinopathy

The course of background diabetic retinopathy
During this early stage of diabetic retinopathy, the blood vessels in the central retina leak a clear fluid called serum which causes tissue swelling within the macula. This condition, know as macular oedema, results in a blurring of central vision. The serum is reabsorbed by the blood vessels, and the blurring generally lasts only a few days at a time. If the leakage occurs faster than the serum can be reabsorbed, though, the blurring is ongoing. Particles of fat and protein from the serum, called exudates, are reabsorbed more slowly. The retinal blood vessels can also bleed into the retina, but vision is not usually affected because the haemorrhages are very small and do not occur within the central macula.

How vision is affected
If the serum accumulates in the central macula, vision will be blurred. If the central macula is not affected, there may be no symptoms at all. There is no pain, and there are no outward symptoms such as bloodshot eyes, irritation or discharge.

Diagnosis
Your doctor will use both direct and indirect ophthalmoscopy and a slit lamp with a contact lens to spot abnormal vessels. Fluorescein angiography can best assess just how far the condition has progressed.

Early treatment
Once there is evidence that diabetic retinopathy has developed, your doctor may advise laser treatment. The laser will be used to seal the abnormal blood vessels that have leaked serum into the retina.
Even if laser treatment is not able to halt the progress of the disease entirely, it may be of value in reducing the amount of further visual loss by delaying the onset of proliferative diabetic retinopathy.

Note: If you have diabetes, you should see your doctor for a complete eye examination once a year to detect any evidence of diabetic retinopathy early. If your vision has begun to be affected, more frequent visits - as often as every 3 to 4 months - will be necessary to monitor the disease properly.

Proliferative Diabetic Retinopathy

The longer you've had diabetes, the greater your chance of developing proliferative diabetic retinopathy. In this advanced stage - which affects almost 1 in 10 diabetics - new abnormal blood vessels spread ("proliferate") over the inner surface of the retina, and may even grow out into the vitreous.

These vessels frequently bleed into the vitreous, blocking light from reaching the retina, and causing vision to become cloudy. Connective tissue grows along with these vessels, causing additional distortion of vision. This tissue can shrink with time, pulling the retina toward the vitreous and off its underlying structures. This is known as a traction retinal detachment.

How vision is affected
Even a little bleeding into the vitreous can cause vision to become cloudy. Usually though, small amounts of blood are reabsorbed within a few days, and the cloudiness passes. But if the bleeding persists, your vision may remain clouded for months and you may see a red hue.
Distortion and blurring caused by connective tissue in the vitreous will be apparent if the central retina is being pulled. These symptoms may not be noticed at all if the peripheral retina is affected.

Diagnosis
Direct and indirect ophthalmoscopy, a slit lamp with contact lens and fluorescein angiography can usually tell your doctor what areas of the retina are in need of treatment. If the vitreous is clouded with blood, ultrasound can be used to check for detachment of the retina.

Treatment
Fortunately, more than half of all cases of proliferative diabetic retinopathy can be stabilised by the use of a laser technique called pan-retinal photocoagulation. In this procedure, the entire peripheral retina is given a "scatter treatment" with the laser. A certain amount of healthy retinal tissue is destroyed, but the further growth of new blood vessels is usually curtailed. This technique may also cause many existing abnormal vessels to regress. Although this treatment causes some loss of peripheral (side) vision and night vision, it frequently works to preserve central and colour vision, which are far more important.

Because such a large area of retina is being treated, your doctor may want to spread the treatment over two or three half-hour sessions, each a week or so apart. One eye is treated at a time, and the effects will not be apparent for many weeks or even months.

Laser treatment of the macula may also be necessary, just as with background diabetic retinopathy.
Because there may be a need for laser treatment after pan-retinal photocoagulation, you will need check-ups as often as your doctor recommends.

Vitrectomy
If proliferative diabetic retinopathy has already caused extensive damage to the eyes, the surgical removal of the vitreous - called a vitrectomy - may be necessary to preserve the ability to see gross forms. Vitrectomy removes longstanding blood from the inner eye and cuts away scar tissue, which relaxes any pulling on the retina. Vitrectomy is only performed when diabetes has severely affected vision.

If you are a candidate for vitrectomy, your doctor will provide you with more detailed information on the benefits and risks of this procedure.

Remember, if you're diabetic, be sure to have an eye examination at least once a year - and more often if your doctor recommends it. Because treatment for diabetic retinopathy can only work to maintain your vision at it's current level, it's absolutely essential to have the disease diagnosed and treated as early as possible.

For millions of people, retinal disease presents a very real threat to their eyesight. Fortunately, with the recent advances in diagnostic techniques and treatment, much more can be done today than ever before to help preserve vision. This information deals with three common retinal problems - macular degeneration, retinal detachment and diabetic retinopathy. It will help you understand your eye problem, but it is not a substitute for professional medical advice and treatment.