Color vision is routinely screened during the regular examination to detect any gross color deficiencies. For occupations requiring an excellent “color sense” such as printer, art director, stage-scenery designer, cloth dyer, etc., or for the detection of an early stage of a disease, more extensive color tests are administered. One such test requires arranging a series of round, colored discs in the correct sequence of hues. The most sophisticated color test, the anomaloscope, used mostly in research, challenges the person to mix primary green and red light sources together to match a standard yellow light.

Electrodiagnostic Tests

Very sensitive instruments can detect and measure the electrical nerve impulses which are generated in the eye and travel through the optic nerve to the brain. Similar in operation to an electrocardiogram, an electroretinogram (ERG) can provide practical information about the functioning of the retina in patients with acquired or inherited retinal disorders.

The more comprehensive visual evoked response (VER) test will measure the electrical activity along the visual pathway all the way to the visual cortex of the brain. Electrodes are attached to specific spots on the head, but there is no discomfort. The VER makes it possible to differentiate the vision in each eye, assess the potential visual acuity, and detect amblyopia objectively. It can be extremely useful with young children or retarded adults whose subjective responses could be unreliable or difficult to obtain.

Ultrasonography, Echography

When the inside of the eye cannot be clearly viewed because of a hemorrhage, cloudy fluid or a cataract, ultrasonography is employed to “see” what’s inside. The technique generates sound waves and measures the returning echoes to harmlessly probe the eye and surrounding tissue for fractures, tumors, detachments, foreign bodies, etc. A very common use for ultrasonography is to measure the size and location of the eye’s structures prior to cataract surgery to calculate the needed power of the lens to be implanted.

Fluorescein Angiography

This is an invasive test to assess the blood circulation in the retina and choroid at the back of the eye, or to verify the presence of a tumor. Fluorescein, a dye which glows in ultraviolet light, is injected into a vein and quickly circulates into the retinal vessels. Photographs taken every few seconds through a cobalt blue filter can pinpoint leaking, obstructed and/or new blood vessels. Because of a small but serious health-risk factor from the injected fluorescein, this procedure is used if the information cannot be gained in any other manner.

Gonioscopy

A gonioscope is essentially a contact lens fitted with tiny mirrors to view the angle opening between the cornea and iris inside the eye. The information gained can differentiate between open or closed angle glaucoma; inspect for tumors and lesions; recognize injury induced tears; evaluate effectiveness of laser treatments.

Interferometry

When a dense cataract is present, it is very important to estimate what degree of vision will be available after the cataract is removed. Since the view and inspection of the back of the eye is blocked by the cataract, the doctor may be unaware that retinal disease may also be present. If there is, removing the cataract will leave the person disappointed in the scantiness of sight improvement.

The interferometer focuses an intense, coherent source of regular or laser light into the eye to establish an approximate idea of the reclaimable vision. The instrument is also practical for predicting the eventual sight attainable after treatment for amblyopia.

Glare Tester

Cataracts or other opacities in the eye will often cause increased sensitivity to glare because they scatter the incoming light. If the glare source is bright enough it will functionally reduce your sight. For instance, a person may see 20/30 in normal illumination, but barely see 20/200 in very bright light.

A glare testing instrument can document the levels of glare which creates a disability, and can help determine if tints applied to the glasses can be beneficial in minimizing the effects. Another use for the instrument is to measure the time it takes to recover sight after the retina is dazzled with very bright light. This mimics entering a darkened area after exposure to sunlight, or being “blinded” by oncoming headlights in night driving. While the glare-recovery time normally increases with age, very slow recovery can also be caused by disease or vitamin deficiency.

Radiology, CT-Scan, MRI

Suspected fractures of any of the bones making up the eye socket will require X-ray pictures to identify the breaks. For complicated fractures with muscle entrapment, to localize foreign bodies, and investigate for suspected tumors, Computed Tomography (CT-SCAN) makes diagnosis easier. Magnetic Resonance Imaging (MRI) is more useful to differentiate between diseases of soft tissues, though it should not be employed when a metallic foreign body is present.

Cell Counts

The inner layer of the cornea, the endothelium, plays a crucial role in maintaining the transparency and health of the cornea. Unlike the surface epithelial layer, the endothelium doesn’t grow new cells to replace damaged ones. The remaining cells enlarge to fill in the spaces. (Long term contact lens wear seems to be implicated with changes in the cell shapes.)

Before cataract removal or corneal surgery, an instrument is often used to estimate the number and determine the condition of the cells. Since many are lost during surgery, the information helps assess the risk and success of the surgical procedure.

Pachometry

There are instances when it is important to know the thickness of the cornea and the depth of the anterior chamber of the eye. The pachometer, an instrument attached onto the biomicroscope (slit lamp) will accomplish this. A very useful application is to measure corneal swelling or thickening after contact lenses are worn for an extended time.

Ophthalmodynamometer

An instrument designed specifically to measure the systolic and diastolic blood pressure of arterioretinal vessels. It will often detect increasing intracranial pressure before other symptoms appear. (This instrument is giving way to more sophisticated methods.)

A field of vision testing instrument. The patient fixates a central target with one eye and responds to flashing and/or moving spots of light. An internal computer will analyze and provide a printed copy of the field of view.

If you lose either the central vision or the peripheral vision, you can be considered legally blind. You would suppose that having nice, clear central sight would be adequate, but it just isn’t by itself. Why not? Roll two sheets of paper into small tubes, hold them up against your eyes and look through them. You can definitely watch TV and reading can be mastered, but try walking around in unfamiliar surroundings or descending a flight of stairs. Driving an automobile with any degree of safety would be impossible. Conversely, if your central sight is lost, you can walk around, but you would not be able to read or easily recognize people’s faces.

There are many diseases which can decimate either the central or peripheral vision. Glaucoma is the classical example of one that gradually shrinks the peripheral vision until, in the final stage, only the narrow central sight remains.

Rather than the entire peripheral view being lost, it’s more likely that a section or portion is missing. Usually, you won’t even be aware of it because the blank area is filled in by the sight of the other eye. However, if the loss is to the outside or downward, and cannot be filled in, you may find yourself bumping into objects. These sector field losses can be caused by aneurisms, hemorrhages, tumors, etc.

The testing is generally done with computerized instruments which flash tiny spots of light against a blank background. The location, size and density of the missing area is plotted and recorded for analysis.

Amsler Grid

As the name implies, a grid of fine lines is used to detect subtle changes and distortions in the perceived view. While staring, with one eye at a time, at the central fixation dot, some portion of the lines may be seen to be missing or not perfectly straight. Retinal swelling, hemorrhages and certain diseases are the cause. Often, a patient will be given an Amsler grid to keep at home to monitor changes.

Contrast Sensitivity

The ability to see an object in dim light or to detect an object against a background of almost similar shading, depends on a person’s sensitivity to discern small differences in contrast.

The visual system has several subsystems (channels) each best tuned in to a particular level of contrast. The normal visual acuity test (20/40, 20/20, etc.) uses high contrast letters and is relatively insensitive for revealing any problems with the lower contrast channels. It’s of interest because, after all, most of our general seeing is not concerned with reading black letters on a white background at 20 feet.

There are normal variations among individuals, but aging, eye diseases, diseases affecting the visual system, amblyopia and the use of certain medications can have negative consequences.

Your contrast sensitivity can be screened with a test that takes only a few minutes. The test is also useful in predicting improvement with a prescription change or a tinted lens, and it can alert the doctor to avoid a change or tint which could worsen the problem.

Extensive Color Testing

Color vision is routinely screened during the regular examination to detect any gross color deficiencies. For occupations requiring an excellent “color sense” such as printer, art director, stage-scenery designer, cloth dyer, etc., or for the detection of an early stage of a disease, more extensive color tests are administered. One such test requires arranging a series of round, colored discs in the correct sequence of hues. The most sophisticated color test, the anomaloscope, used mostly in research, challenges the person to mix primary green and red light sources together to match a standard yellow light.

Electrodiagnostic Tests

Very sensitive instruments can detect and measure the electrical nerve impulses which are generated in the eye and travel through the optic nerve to the brain. Similar in operation to an electrocardiogram, an electroretinogram (ERG) can provide practical information about the functioning of the retina in patients with acquired or inherited retinal disorders.

The more comprehensive visual evoked response (VER) test will measure the electrical activity along the visual pathway all the way to the visual cortex of the brain. Electrodes are attached to specific spots on the head, but there is no discomfort. The VER makes it possible to differentiate the vision in each eye, assess the potential visual acuity, and detect amblyopia objectively. It can be extremely useful with young children or retarded adults whose subjective responses could be unreliable or difficult to obtain.

Health of the eye

Complications affecting the health of the eye are extremely rare, but are possible. During the early healing phase, the eye is susceptible to infection. You will be asked to follow certain instructions, including using antibiotic eyedrops. Carefully following these instructions will decrease the infection rate to far below 1 percent. Even if an infection does occur, use of antibiotic eyedrops should control the infection.

Steroid eyedrops are very important after excimer laser treatment, because they are used to control the healing response. However, if used improperly for too long, these drops can damage the eye by causing cataracts or glaucoma. It is very important to go to all scheduled follow-up appointments, especially if you are still using steroid eyedrops.

Decrease in best Spectacle Corrected Vision

Best spectacle corrected vision is the best vision obtainable when wearing the optimal pair of glasses. It is a measure of the best vision possible with glasses. Of course, you probably will no longer use glasses or contact lenses for distance vision after the surgery, so you may not even be aware if your best possible vision is slightly different.

For the majority of people, a mild decrease in best corrected vision is usually not noticed. A moderate loss of best corrected visual acuity would be noticed by every patient and might make it hard to work in occupations that require fine vision. Severe loss of best corrected visual acuity is exceedingly rare and in fact has not occurred in any of the FDA sponsored tests.

Some professionals, such as commercial airplane pilots, care very much about their best corrected vision. These pilots must have best corrected vision of 20/20 in both eyes to maintain their licenses, so they should carefully consider the small risk of less than 20/20 best corrected vision.

In one large FDA study, 6 percent of PRK patients experienced some decrease in best spectacle corrected vision during the first six months. This decreased to 1 percent by the end of the first year. Importantly, every patient in this study achieved 20/20 best spectacle corrected vision one year after surgery (b).

Either an irregularity or excessive haziness in the corneal surface could cause a decrease in best corrected vision. A common unevenness is known as a “central island,” which is a slightly raised area near the center of the cornea. “Central islands” usually resolve as the healing progresses. Some haziness almost always occurs in PRK as the ‘cornea heals, but it is usually minor and does not affect vision. A small number of people will form excessive haze, which will cause a decrease in the best corrected vision. In one large study, 1 percent of PRK patients had clinically important haze during the first six months after treatment, but only 0.2 percent of patients had clinically important haze two years after treatment (b). Haze is even less of a problem in LASIK patients. When haze does occur, additional steroid drops are given.

In LASIK, unevenness of the flap, or in the tissue beneath the flap, could result in some decrease in best corrected vision. Small irregularities smooth out during the initial three months after the procedure, resulting in a gradual but noticeable improvement in vision. In rare cases, the doctor may choose to lift and reposition the flap, or to apply more laser treatment under the flap.

With age the capsule becomes thicker and less permeable, and the general metabolic activity of the lens, which even in youth is of a low order, slows down still further. Eventually degenerative changes, which have a variety of causes, start within the lens and inevitably provoke a loss of transparency — a cataract.

The earliest stage of a cataract is the accumulation of fluid between the lens fibres. Although at this point there may be no true loss of transparency, as the process continues the protein of the lens fibres coagulates, a development which in time leads to complete opacification. It is rather as though the lens had changed from white of egg into a hard-boiled egg.

These changes, which are a normal part of the ageing process in the lens, may also be initiated by a very wide variety of factors, such as injury, certain drugs, infections, and metabolic disturbances elsewhere in the body. Cataract may be present at birth (congenital) or may be acquired later in life.

Congenital Cataract

As previously stated the lens starts to develop at about the sixth week of embryonic life. If at that time the mother has an attack of rubella (German measles) there is a very significant risk that the lens development will be abnormal and that the baby will be born with a congenital cataract. Furthermore, there is a strong possibility that other organs which are developing at much the same time will also be affected — for instance, the inner ear, the heart, and the brain. It may be that these defects are incompatible with life, in which case a miscarriage will occur. However, if the baby is born alive, cataract may be present and may indeed become denser as time passes. Sadly, removal of these cataracts often does not benefit sight, as the retina also may have been affected by the virus.

By no means all congenital cataracts are the result of rubella. All sorts of noxious stimuli during pregnancy, such as injuries or infections, may result in an opacification of part of the lens. If the stimulus is of short duration, then clear lens fibres may be laid down outside the opaque ones, leading to a laminated appearance. These cataracts are called zonular cataracts as only one zone of the lens is involved.

Some congenital cataracts run in families, such as the Coppock cataract named after an Oxfordshire family: 288 descendants of John Coppock, who was born in 1774, were affected over the next seven generations.

Acquired Cataract

Ageing

Most people acquire a cataract by the simple process of getting older. Such cataracts are of two main types, nuclear and cortical. In the nuclear variety the central part of the lens becomes harder and optically denser, and takes on a yellow-brown colour. These cataracts develop very slowly and are usually associated with increasingly short sight, so that reading vision is affected much less than distance vision.

Cortical cataract, on the other hand, affects the outer layers of the lens, and opacities develop which may affect both near and distant vision. Again, progression may be very slow, but if the opacities are mainly in the back part of the lens, even a small cataract may cause reading difficulty, as it is in this region that rays of light entering the eye are being focused more closely.

Diabetes

Cataract is some 10 times more common in people with diabetes mellitus than in the population as a whole. These cataracts may be just the same as those caused by the ageing process, but they appear earlier in life and tend to progress more rapidly. A second type — the true diabetic cataract — occurs in much younger patients. It appears suddenly, usually in juvenile-onset insulin-dependent diabetics. The first variety is common, the latter rare.

Other less common metabolic conditions may also be associated with cataract formation.

Cataract associated with other eye diseases Long-standing intraocular inflammation, retinal detachment, and severe glaucoma may be complicated by cataract, but often the severity of the associated condition will have effectively destroyed the sight and the cataract plays little part in the problem.

Cataract and drugs

The most important drugs in common use that may cause cataract are the corticosteroids. These drugs are of great value in the treatment of asthma and some inflammatory conditions. When steroids are given systemically (by mouth or injection) and over an extended period they may cause cataract. Used as drops or ointment they may lead to a rise in pressure in the eye (glaucoma). People on steroids should not be deterred from using such drugs because of these possibilities. The drugs will be regularly and routinely monitored, as will the condition for which steroids have been prescribed. If cataract does develop, it can always be treated.

Injury

If the capsule of the lens is damaged, either by a penetrating injury or by a foreign body within the eye, cataract rapidly develops. A severe injury may also result in a lens opacity even without rupture of the capsule, but such an opacity is often not progressive. Some foreign bodies in the eye, especially if they are made of copper, brass, or iron, give rise to cataract even if the capsule did not at first suffer damage.

Cataract caused by injury may require urgent treatment at a very early stage.

Cataract as an industrial disease

Occupational cataract is seldom seen nowadays, as it is usual to take appropriate steps to avoid it, but in the past some workers were very much at risk because of the nature of their occupation. For instance, cataract was common among the chain makers of Worcester in the nineteenth century, and even today may be found among glassblowers and steelworkers who have not worn appropriate goggles to protect themselves against the heat and the damaging infra-red light from molten material. Those working with ionising radiation (x-rays, etc.) were also at risk before the dangers of such radiation were recognised.

Acquired lens opacities are usually progressive, although their advance may be extremely slow. On the other hand, congenital opacities other than rubella cataracts tend to be stable and generally do not lead to significant loss of sight. This is thought to be due to the fact that the influence which started the opacity was effective only for a period and did not permanently impair the normal lens metabolism.

All the symptoms of cataract are visual, the usual complaint being of a general mistiness of sight, more particularly for distance vision, as reading is often unaffected in the earlier stages. One eye is frequently worse than its fellow, but sooner or later both eyes alter. At this stage dazzle may be a cause of great distress. In normal lighting conditions vision may not be seriously disturbed, but in bright sunlight it becomes obscured by dazzle in the same way that a dirty windscreen becomes almost opaque in the headlights of oncoming cars. In this situation patients may be greatly helped by wearing a brimmed hat or tennis shade. Tinted glasses are of limited assistance because it is the direction of the light as much as its brilliance that causes the trouble.

These difficulties result from the early separation of the lens fibres by fluid, a disruption that may lead to other unexpected symptoms as well — for instance, double vision. Whereas double vision generally results from some muscle imbalance between the two eyes, double vision in one eye only, which is much less common, is usually due to a disturbance in the clear media of the eye. The fibre separation may also have a prismatic effect, breaking up the incoming light into its constituent spectral colours. A patient looking at a street light may therefore notice coloured rings or haloes around it. It is most important that this symptom is distinguished from the very much more serious haloes which are seen by patients suffering from acute glaucoma. In that case the haloes are accompanied by blurring, aching discomfort, or, indeed, severe pain, and their appearance tends to be episodic. On the other hand, the haloes in cataract are present at all times and are not associated with any discomfort. Pain is never a symptom of cataract.

Some patients notice a disturbance in their colour vision. As the cataract develops, blues become subdued and reds enhanced. It is interesting to notice the change in the style of certain painters as their cataracts develop. Turner and Rembrandt are two who are often cited as examples. Their paintings show much more red and orange in later life as their cataracts developed and absorbed more blue and green light, allowing only oranges and reds to reach the retina.

As the cataract becomes more dense, the central (nuclear) part of the lens becomes harder and the effective power of the lens becomes greater. As a result the eye becomes relatively short-sighted. Near vision may paradoxically become clearer than before. When people are suddenly able to do without their reading glasses they should be wary of the implications.

Eventually, when the cataract has become really dense, the proteins within it have become coagulated. Useful vision is seriously affected, but it is never lost altogether. Even the densest cataract will allow some light to reach the retina.

The First Examination

When a patient is first suspected of having cataract he will be examined in the eye clinic to decide the exact cause of visual failure, whether any other eye disease is present and the degree to which the cataract has advanced. A number of tests are carried out to assess the level of visual function, after which the eye itself is examined for any anatomical or physiological abnormality. Both distance and near vision are investigated.

Distance vision

This is measured by the Snellen chart (the optician’s chart with letters diminishing in size) (Figs. 3/1a and 3/lb). The size of the letters on the chart is defined according to a geometrical principle. In former times astronomers found that for the human eye to be able to see as distinct from each other two binary (second-order) stars they had to be separated by 1 minute (the 60th part of 1 degree) of arc. This became accepted as the normal resolving power (the ability to distinguish very small objects) of the eye, and the Snellen visual acuity chart is constructed on this assumption. Each letter on the chart is of such a size that its every detail subtends an angle of 1 minute and the whole letter an angle of 5 minutes at defined distances. The usual charts range from a letter subtending 5 minutes of arc at 60 metres down to 6 or even 5 metres. The patient reads the smallest letters that he can see at a distance of 6 metres and this is then recorded as a fraction, the numerator (the first figure or figure above the line) being the test distance (i.e. 6 metres) and the denominator being the distance at which the letter, correctly read, subtends an angle of 5 minutes. Thus, if only the top letter is read, vision is said to be 6/60. Such a letter would be correctly seen by a normal subject 60 metres away. Normal vision, then, is recorded as 6/6 (in America this becomes 20/20 because feet rather than metres are used).

Near vision

Close vision is usually measured with reading types. These consist of a number of passages which have been printed using different sizes of Times Roman types. Type is measured by points, a point being 1/72 of an inch. Normal close vision is about N (for near) 5 — that is, 5- point type or letters 5/72 of an inch high can be read with ease with the appropriate reading glasses.

When examining you an ophthalmologist will test eye-pressure through the simple expedient of placing his fingers on your closed eyelids. The experienced physician will know immediately whether the pressure is unusually high, but even so he is unlikely to be able to distinguish, using this technique, between more than four grades: namely soft, normal, suspicious and high. Accurate measurement requires instruments. Such instruments have to touch the cornea, which is therefore suitably anaesthetized beforehand, using a special kind of drop. Several types of local anaesthetic drop exist, e.g. amethocaine, pentocaine and xylocaine. One instrument blows a puff of air on to the cornea and then measures the degree of corneal flattening that results. This does not require a local anaesthetic. Other kinds of test attempt to induce the pressure of the eye to rise (e.g. by using a dark room, making the patient read something, or infusing drops that make the eyes dilate). The purpose is to measure the pressure under conditions that may occur regularly in your life. For example, the dark room may help simulate what happens to your eyes while you are asleep, while the use of drops enables the doctor to examine the angle of the eye, to see whether it is unusually occluded by the iris. Such tests may be termed challenge tests. But of equal importance are tests that establish whether the optic nerve is healthy. These consist in looking at the disc, or head, of the optic nerve with instruments that magnify the retina. The sensitivity of the retina can also be assessed by various light-threshold tests, especially using colours. You look into a black box as the practitioner operates a filter that allows only tiny pinpricks of progressively less faint light to flash up before you. This plots any defect in your whole field of vision. It is usually necessary to conduct two or three different investigations. The results of these are then analysed together and, with knowledge of your general health and your family background, a diagnosis can be made. In some instances, where the eye-pressure fluctuates significantly during the course of a day, it is necessary to repeat the tests several times at different intervals before a realistic evaluation can be made.

Thus the diagnosis of chronic simple glaucoma, at least in its early stages, is not easy. It is an insidious affliction in more ways than one. There is, however, another kind of glaucoma, called acute congestive glaucoma, which is much more readily identified. Its onset is marked by a sudden, severe pain, redness in the eye and high cloudation of the cornea. In addition, the pupil may become dilated, and the eye-pressure is likely to be abnormally high. Unless you are treated almost immediately you will rapidly become generally ill, because of the persistence of the pain. You will develop severe stomach cramps, may vomit, and perhaps even collapse. Immediate treatment of such cases is essential, and if you do not respond to intensive outpatient care you may require admission to hospital for surgery.

This type of acute glaucoma can be preceded by sub-acute attacks, which you may pass off as some kind of normal eyestrain and therefore not bring it to the attention of a doctor. Before the acute attack commences, the visual fields and eye- pressure may have been perfectly normal; hut unless the suddenly exaggerated pressure can be swiftly controlled a substantial and permanent loss of vision is likely to occur.

There are many different reasons why eye-pressure may suddenly increase. Inflammation inside the eye can cause the angle between cornea and iris to become closed. The same is true of internal tumours and post-operational infections. Even cataract, where it causes the inner crystal lens to swell, can lead to a relatively sudden increase in eye-pressure.

Treatment for Glaucoma

Treatment depends upon the type of glaucoma experienced by the patient. Diagnosis is therefore all-important, and there are some ophthalmologists who have specialized in this one area because of its public health importance.

Chronic simple glaucoma is best treated conservatively with drugs (eye-drops). Only if these fail is surgery used. On the other hand, a lifetime’s dependence on a drug is not desirable, and therefore some surgeons operate early. If the operation is successful no further medication will be required. Thus the management of glaucoma varies from practitioner to practitioner. Where surgery is not or has not become essential, the age of the patient may well be a consideration. If the patient is very old it seems wiser, on several grounds, to continue with a medical treatment.

Most drugs used in the care of glaucoma have specific effects, but these cannot always be easily analysed, and sometimes there are side-effects. One of the least expensive and best behaved drugs is Pilocarpine. This can be used as often as four or five times a day, and even in the night. It works by constricting the pupil and thus opening the angle between cornea and iris. Possibly it has other beneficial effects upon the drainage of fluids from the eye, but these are only partly understood. Timoptol (timolol), on the other hand, is a drug that operates by suppressing fluid formation. Possibly it blocks the automatic nerve supply to the blood vessels in the ciliary region. However, if it is used with patients who are either asthmatic or who have constrictive vascular heart disease, there can be some serious complications. As with all potent drugs, one has to accept that side-effects are inevitable. Unfortunately these may not always be apparent from laboratory and animal experiments, and even well-tested drugs are sometimes used by humans for several months or years before their defects become measurable.

Pilocarpine and Timoptol, which are available in various concentrations, are the two most commonly used drugs in the treatment of glaucoma. But, apart from drugs (of which there are several), laser rays have also been used more recently to open up the angle of the eye, and/or make tiny holes in the iris to enable the fluid to move freely from the middle to the front of the eye without blocking the angle. The use of laser outpatient treatment has attracted a great deal of publicity, but while it certainly has its adherents inside the profession, the long-term effects are still being studied. Conventional surgery can also do this, as well as create new filtering channels so that high eye- pressure will rapidly stabilize to normal. In general, however, the treatment of glaucoma is as problematic as is its diagnosis, and requires- highly qualified and experienced practitioners to obtain the best results.

But what causes these changes? What causes glaucoma? Is it genetic? Is the decay built into our genes or is it due to outside factors? Can glaucoma be brought on by the wrong diet, by drugs, or by other environmental factors? Perhaps the answer lies, once more, in a combination of both genes and environment. Some people may be genetically programmed to be vulnerable to certain sorts of environment. This at least would explain why some diets seem to have an adverse effect on some individuals and not on others. Certainly some types of glaucoma recur in the same family (though of course members of one family will tend to react the same way to an environmental etiology).

Equipment has been designed to measure accurately the pressure in the eye and to test the field of vision. There are also tests to measure the flow of aqueous fluid from the eye when stress is put upon the eye-pressure system. But even if an early diagnosis is made, treatment is not necessarily effective, and the final outcome can be almost complete loss of the fields of vision except at the centre of sight. Affected individuals can still see clearly in the distance, and can read clearly, but they are unable to move about with any confidence, because they cannot see anything that is not directly in front of them. They have lost their peripheral vision, and in acute cases they may even have difficulty in following a line of print. Such a condition is called `tunnel vision‘, and is accounted a form of blindness, a fact little _understood or appreciated by the general public.

The onset of this kind of glaucoma is very slow and many patients do not know that they are affected. Sometimes the first noticeable indication is a loss of colour hue discrimination. It occurs most frequently in post-industrial ‘civilized’ communities, but this may simply be because in such communities the average life-span is longer, or because, in technological societies, people are more likely to damage their eyes by too much close-work. Even so, senile or elderly glaucoma has a relatively low incidence. About two per cent of the population over fifty will have eye-pressure above the normal, but only in perhaps 0.2 per cent (one in every five hundred) of the age group will specific treatment be sought or required.

Because it tends mostly to affect people over fifty there are possible connections with senile peripheral blood vessel degeneration, which affects other sensitive tissues in the body. There are, however, other causes and types of the glaucomous condition, of raised intra-ocular pressure. Some of these are too rare to be worth describing here, but others are not.

Infantile glaucoma occurs when the baby is born with an abnormal outflow of fluid from the eye. This often means that the angle of the eye has developed without adequate outflow channels. At birth the tissues of the eye are soft, and as the eye-pressure increases the eye becomes bigger. This can be a painful condition, and the baby may be distressed and unhappy. The cornea of the infant suffering glaucoma appears especially large and is sometimes cloudy. The eyes, also unnaturally big, will look red. There will be quiet periods, without pain, but diagnosis is essential. The condition can be treated either with drugs (eye-drops) or with surgery, opening up new channels for drainage of the fluid from the eye. If treatment is not provided, however, the eye may become very severely affected, and treatment at a later stage will be pointless.

There is also a condition of juvenile glaucoma, equally rare, but, like the infantile form, capable of leading to a loss of vision. It is generally considered a late development of the infantile condition.

Some doctors consider minor forms of glaucoma to be present in children who subsequently become myopic. Early high eye- fluid pressure, in this view, causes the eye to elongate and thus cause short-sightedness. Increased pressure owing to excessive close-work is often cited as the classic explanation of myopia, but in fact this has never been substantiated clinically.

The aqueous humour is formed from the ciliary processes behind the iris and flows over the front surface of the crystalline lens, through the pupil and into the front chamber of the eye. Normally it cannot get into the cornea, since this ‘front window’ of the eye has to be kept transparent. Indeed, the cornea is normally busy keeping itself free of all excess water. If, however, the pressure in the eye does become excessively high, then the aqueous humour will get into the cornea and cause it to swell and become water-logged. To prevent this happening there is a natural drainage system that acts as a regulatory device on the eye’s pressure.

Between the outermost portion of the iris and the back of the cornea is a very small space generally referred to as the angle of the eye, i.e. the angle between iris and cornea. This angle runs right round the eye, rather like a washer, except that a cross- section would in fact be wedge-shaped. It cannot be seen just by looking at the eye, and special instruments are required if the ophthalmologist wishes to inspect it. The angle is so much in a corner that whichever position you look at it, it remains hidden. The instrument normally used for an angle- examination is like a very large contact lens and is called a gonioscope. Through a gonioscope we can see how the angle is covered with a very fine threadlike tissue which acts like a sieve. Aqueous fluid, once it has passed through this sieve, enters small channels that lead to a circular canal that runs around the back of the cornea just in front of the angle. From there it passes through further minute channels out of the eye, draining into the blood vessels on the front of the eye globe.

In addition, when pressures permit, the aqueous humour fluid may also pass backwards into the vitreous jelly, and thence into other small blood vessels (capillaries) at the back of the eye.

Thus we have a system of fluid formation and fluid drainage. If the pressure in the eye becomes too great, the cornea will become cloudy. This causes coloured haloes around lights, more especially red haloes. Such haloes are a very early symptom of glaucoma, and are noticed mostly by patients at night looking at street lights or other white electric light. (The effect is, however, considerably reduced when looking at sodium strip lights, which tend to give out a halo of their own, and so early diagnosis is less frequent than was once the case.) High pressure in the eye can also affect the nutrition of the optic nerve. The small capillaries at the back of the eye become shrivelled, so that when one examines the back of the affected eye through an ophthalmoscope, the head of the nerve appears pale, and the superficial tissue surrounding it on the retina has disappeared. The nerve head, thus atrophied, looks like the opening of a cup. The nerves from the retina may suffer stress and loss of nutrition, but small areas of the optic nerve surface become affected first. (Reverting to the analogy between the retina and a radar dish, the optic nerve surface in this dish is at a point towards the middle, but in fact off-centre. Since the eye cannot transmit light at this point it causes a small, normally unnoticed lacuna in the picture that the eye sends to the brain, known as the ‘blind spot‘. Our blind spots are so organized that the blind spot of one eye is cancelled out, or compensated, by the other eye, so that unless you close one eye and deliberately search for a ‘hole’ in the field of vision of the other eye you will not notice anything unusual. The way to detect your blind spot is by focusing on a small object in the middle distance and then, with one eye closed, gyrating the head until the object momentarily `disappears’.)

At the Oxford Ophthalmological Congress the eye surgeon Harold Ridley reported the results of eight operations that he had performed to insert a Perspex lens. He thus founded a completely new branch of ophthalmic surgery. Ridley had treated many ocular injuries suffered by members of the Royal Air Force during World War II. Aircraft windshields (made of Perspex) had shattered after explosions or the impact of bullets, and Perspex fragments had penetrated the eyes of plane crews. Ridley had noticed how inert Perspex was in the eye and how little inflammation it caused.

None the less, lens implantation was not immediately adopted by the world’s surgeons. Complications were common in the early days, mainly because of unsophisticated surgical equipment and imperfect lens design. Only a few surgeons, mostly in Holland, Italy, and Britain, retained their interest.

The first intraocular lens was an almost exact replica of the human model. The cataract was removed by the extra- capsular method and a small lenticulus (artificial lens), of the same size and power, was inserted into the space previously occupied by the cataract. The lenticulus was made from polymethylmethacrylate (Perspex), a material much heavier than the biological lens that it replaced. Positioned as it was in the very fragile capsule just in front of the vitreous face, its weight meant that it was ill-supported. There was a strong tendency for it to dislocate because it put too great a strain on the zonular fibres.

To overcome this problem a new generation of ‘anterior chamber’ implants was designed. These lenses are placed in the fore part of the eye, in front of the iris. They are supported by a number of legs which stand on the iris itself. Although the lens is thereby more stable, it may rub against the back of the cornea. This may happen during insertion, may be caused by the lens being not precisely the right size, or may be due to the iris itself having been pushed forward. In any event, the contact between lens and cornea causes loss of corneal cells, which in turn may lead to loss of transparency.

An alternative to this type of lens is the ‘iris-supported’ lens. In this case the lens may be positioned either in front of or behind the pupil. It is held in place by a number of loops which hook the lenticulus to the iris. Although this method reduces the likelihood of the lens rubbing on the cornea, it interferes with the normal functioning of the pupil.

Another solution is to implant a posterior chamber `capsular fixated’ lens. This type of lens is the one which most closely mimics a human lens. Resembling the original Ridley lens it is, however, equipped with flexible loops attached to the lens edge. Following an extra-capsular extraction, this new lens is inserted into the capsular bag. The loops are then allowed to expand in order to hold the lens firmly in place without either distorting the pupil or endangering the cornea. The lens is held rigidly in the correct position.

The image presented to the retina by any intraocular lens is almost the size of that in the normal eye. For this reason intraocular lenses are particularly appropriate for patients who retain good vision in one eye. It is most useful for those who have had one of their eyes damaged by injury — for instance, in a road-traffic accident. Indeed, this is sometimes the only acceptable method of optical correction.

Since implanted lenses mimic normal human lenses, it might seem proper to give every patient a plastic lens. However, the long-term effects of placing plastic in the eye are unknown. It is possible that the human body’s defence mechanism will attack the implanted lens, whose plastic will then deteriorate. Moreover, if the corneal cell loss (and consequent impairment of transparency) is extensive, sight will deteriorate. If there has been previous corneal damage from another eye disease (for example, glaucoma, or a long-term inflammatory condition), the danger of further cell loss is unacceptable.

Any degeneration at the back of the eye, which might lead to a detached retina in, for instance, very shortsighted people or diabetic patients who are at risk of developing retinal complications, is considered by many surgeons to contra-indicate an implant — particularly of the iris-supported type of lens. It is necessary to dilate the pupil widely in order to examine the back of the eye satisfactorily. If an intraocular lens is present, this procedure becomes difficult, and the lens itself may be dislodged during the inspection.

Despite these complications, there is undoubtedly an important place for the intraocular lens implant. The design and manufacture of the lenses are being continuously researched. Better lens materials have been developed. Ways of making the operation itself simpler and safer are being investigated. Methods of avoiding and treating subsequent problems are being explored. In the early 1970s the popularity of the operation increased rapidly. This was due largely to the introduction of the operating microscope, the development of finer surgical instruments and suture materials, and an increasing appreciation by ophthalmic physiologists of the eye’s response to the introduction of foreign materials. Today more implant operations are being undertaken, although the practice is by no means universal.

For patients who were short-sighted before a cataract operation, high-powered optical correction is rarely necessary, and therefore implants and contact lenses need not be considered. Reading spectacles will probably be required, however, as the removal of the crystalline lens considerably reduces the eyes’ powers of accommodation. In cases of severe short sight patients may well find that they can see in the distance in a way they have never been able to before.

As has been stated, spectacles can be prescribed after a cataract operation, but some patients like neither the type of magnified vision that spectacles give nor the resultant appearance. Provided, however, that they do not restrict the patient’s physical enjoyment of life, spectacles are the safest means of correction, though by no means the most optically efficient. For patients who have one good and one aphakic eye only an implant or a contact lens will result in good binocular vision.

Where complications exist prior to a cataract-removal operation some preliminary surgery may be necessary; and again further surgery may be required after the main operation. Thus the unfortunate patient may be submitted to a series of operations, both big and small. In most cases the preparatory operation is carried out to correct or prevent a complication. For example, if the retina is thought to be weak before cataract removal, a retinal sealing procedure may be carried out several weeks in advance. Some surgeons will prefer to treat the retina during the main operation, while others will wait until several weeks after. Much depends upon the nature of the retinal problem being treated, and upon the surgeon’s preferred techniques. In all cases, however, such treatment may be termed preventative. Again, if the patient is found to have glaucoma as well as a cataract, the surgeon may suggest glaucoma surgery before cataract removal, and allow several months to elapse between the two operations. Alternatively he may recommend medication for the glaucoma and design his cataract operation in such a way as to ensure continuing low pressure for the eye in question.

The modern cataract patient often claims that laser beams were used during cataract-removal surgery. In fact this is seldom the case. Some surgeons have used lasers to produce acceleration of the cataract, but this is always done a few weeks before the main surgery. After cataract-surgery persistent membranes in the pupil may also be obliterated by laser. Laser-treatment is chiefly used, however, to seal up holes in the retina, open spaces in the drainage areas of the anterior chamber angle and other specialized use, but it is not used during the routine removal of cataract. What the public is most likely to be referring to is phako-emulsification technique. This is when a probe disintegrates the cataract and permits a washout procedure of the remaining lens material.

In some instances a re-operation is required after cataract removal. These operations are usually for the purposes of breaking open any membranes that may form after extra-capsular procedures, or to remove soft lens matter (i.e. the peripheral part of the crystalline lens). Where complications such as retinal detachment or glaucoma occur, they are treated in the normal manner.

Retinal detachment does occur in at least two to three per cent of all cataract operations, and in severe myopia can be as high as one in three patients. Retinal detachment is by no means always preventable but, where visibility of the fundus permits, preliminary retinal treatment, either by cryotherapy or laser coagulation, can be given.

Therefore, while modern technology has generally reduced a problematic operation into a well-defined procedure of known hazards, there still remain areas of doubt and speculation which are best determined by the patient and surgeon consulting together.