In order to see sharply and clearly, light must pass into the eye through a crystal-clear lens. A loss of transparency, or clouding, of the normally clear lens is what is referred to as a cataract.
A cataract usually develops slowly and causes no pain. It may take ten years to develop in one eye, but only a year to develop in the other eye. There are various types of cataracts, which can form at any age, including newborns.
In the early stages, most cataracts are thought to be a normal part of aging and not a disease at all. During the aging process, chemical changes in the body occur, including in the lens, rendering it less transparent. At first, cloudiness may affect only a small part of the lens, and the person may be unaware of any vision loss. Over time, however, as the cataract grows larger, it clouds more of the lens. When significantly less light reaches the retina, the vision becomes impaired to where no shapes or movements are seen, only light and dark.
History
The origin of the word “cataract” is somewhat obscure. The Greeks and Romans thought cataracts were evil liquids that flowed into the eye. A papyrus dating to 1500 BCE, describes what was probably a cataract under the phrase “the mounting of water in the eye”. The Greeks used the words hypochysis and hypochyma, meaning “water underneath”.
The Romans used the Latin term suffusis to describe a cataract as a suffusion, or overspreading. During the Middle Ages, the Arabs translated the term for cataract into an Arabic word meaning “black water”. Later, that Arabic word was translated back into Latin as the word cataracta – a waterfall – which eventually became the English “cataract.”
Although cataracts were recognized more than 3,000 years ago, it took centuries for doctors and scientists to begin to understand its nature and causes. Such scholars as Leonardo da Vinci (1452-1519) and Andreas Vesalius (1514-1564) staunchly maintained that a cataract was an evil humor or phlegm that covered or clouded the front of the lens, rather than a disease of the lens itself. The true nature of the cataract was first published by Warner Rolfink (1599-1673), an anatomy professor in Jena, Germany. Rolfink learned of the French surgeon François Quarre, who believed that a cataract was merely a clouded lens. By dissecting the eyes of executed criminals (of which there were many, it seems), Rolfink confirmed his theory.
How Cataracts Form
To understand how cataracts form, we must start at the beginning by learning about the lens of the human eye. The lens is a transparent organ about the size of a pea that sits just behind the iris, the coloured part of the eye. There are three parts to the lens: capsule, nucleus, and cortex. The capsule is the thin membrane that completely surrounds the lens. During younger years, the center of the lens (the nucleus), is soft, almost like custard. By the fifties and sixties, the nucleus has become sclerotic, or hard. The rest of the lens, the cortex, is made up of long, arching fibers, running from top to bottom. As aging progresses, the older fibers are pushed to the center of the lens and compacted, while the newer, looser fibers are closer to the outside.
The function of the lens is to refract, or bend, light rays to focus them to a clear image on the back of the eye. The lens, being somewhat elastic, will change shape in order to focus light rays properly. It will automatically become fatter for close objects and thinner for distant ones. Starting as early as age twenty, the lens slowly begins to lose its elasticity, until around the age of forty, it cannot change shape enough to bring close objects into focus and corrective lenses are then necessary. If even a very small part of the lens becomes cloudy enough to block rays of light – whether it is the central nucleus, the outer cortex, or the thin surrounding capsule – that part becomes known as an opacity. If enough opacities form in the lens to affect vision, or if a general loss of transparency occurs, the end result is a cataract, or a cataractous lens. The underlying theme that runs through all the symptoms of a cataract is that the eyesight becomes worse.
Causes for cataract formation are many and stem from several sources. As mentioned before, aging is the major cause. Prolonged exposure to ultraviolet light is another contributor. Damage to the lens by oxidation, the same process that causes iron to rust, is also a factor. Various systemic diseases also contribute to eye problems, including cataracts. Heredity poses another threat. Other factors include fetal development, nutritional deficiencies, and certain professions. People with the genetic disease, galactosemia, in which the sugar galactose cannot be properly metabolized and builds up in the body, are particularly prone to cataract formation.
Oxidation is a normal part of metabolism occurring throughout the body and has been linked to many disorders, including cancer and heart disease as well as cataract formation. Oxidation releases chemicals called free radicals that, in the heart, turn cholesterol rancid and clog the arteries. In the eye, the sources of oxidation include UV radiation (ultraviolet light), x-rays, and even cosmic radiation.
Over the years, the constant bathing of the lens in light causes the delicate protein arrangement in the lens to become damaged. Transparency, an all-important property of the lens, suffers and vision becomes blurred. UV light is not only damaging to the skin, but also to the eyes. Astronauts are showing signs of cataracts after being exposed to cosmic radiation.
As the earth’s ozone layer continues to deplete, a startling number of new cases of cataracts will emerge in addition to all the cancers and weakened immunities in general. The good news is, if oxidation is the cause of many cataracts, blocking this oxidation is sure to be a good preventative measure. Antioxidant supplements appear to be the help that is needed in the prevention or, at the very least, the slowing down of their formation.
Studies have shown that about 15% of patients suffering from cataracts will also have diabetes. The longer the duration of the disease, especially in females, the more likely the chance of developing a cataract. Juvenile diabetic patients tend to have wider fluctuations in blood sugar than those with adult-onset diabetes. It is this wide variation that is thought to cause the swelling of the lens of the eye, the loss of transparency, and the resulting cataract.
Before the discovery of insulin, it was not uncommon for a juvenile diabetic to develop a sudden, blinding cloudiness of the lens, called a sugar cataract, brought on by an out-of-control blood sugar level. In the 1980s, researchers finally established the validity of this association and found that, indeed, too much sugar in the blood does cause cataracts!
Three sugars, in particular, have been studied. Two were found to have a direct effect on human cataract formation – glucose (table sugar) and galactose (found in milk and dairy products). These sugars, known as aldose sugars, dissolve into the lens of the diabetic and then converts into substances that cause the lens to swell rapidly and, with the aqueous fluid surrounding it, acts like a dry sponge suddenly immersed in water. This bloating of the lens with fluid upsets the delicate balance that keeps it clear, resulting in a dense cataract.
The offender appears to be a seemingly innocent-appearing enzyme (aldose reductase) which is triggered by high levels of sugar in the eye. This enzyme converts the aldose sugars which can significantly increase the risk of cataract formation. Several pharmaceutical companies are trying to develop a blocker for this enzyme. Cataract and laser surgery have proven helpful in maintaining vision for the diabetic, but nothing beats good control of the disease at the onset.
The stimulus for the work on glucose, diabetes, and sugar cataracts actually came from a study of infants with galactosemia, a rare disease that affects about one in 18,000 newborns. Galactosemia results in severe malnutrition for the baby, no matter how much milk it drinks. The reason is an enzyme that is lacking which allows the baby to digest galactose, the principal sugar in milk. Without this enzyme, the baby cannot obtain proper nourishment and will die within a month or two.
One of the effects of undigested galactose in the newborn is that it is converted by the enzyme, aldose reductase, to a substance that accumulates in the lens of the eye in very high amounts, causing severe cataracts. These dense, white cataracts are the first sign of this otherwise fatal disease; and the treatment is simple – take the baby off all milk products and substitute soy milk, which lacks the milk sugar galactose. If recognized before four weeks of age, the prognosis is excellent.
The cataracts will disappear and the baby’s health will return to normal. Although galactosemia is an extreme example of the disorder, larger populations of young children and adults display a milder form of the disorder, called milk intolerance, which is a partial loss of the same enzyme. Although there is no official scientific link with this and senile cataracts, there certainly is evidence for it in juvenile cataracts.
A congenital cataract is usually discovered by the parent who notices a white pupil in the baby’s eye instead of the normally black one. There are many causes, but the common denominator is something interferes with the normal development of the lens in the fetus. Medications taken by the mother during pregnancy can adversely affect the developing eye, especially cortisone-type drugs and certain tranquilizers.
Preterm babies are more likely to have cataracts than full-term babies. German measles or rubella infection, especially in the last part of the first trimester, can seriously affect the developing eye, causing congenital cataracts in the majority of cases. Congenital cataracts represent not only a technical challenge (surgery), but also a rehabilitative one.
In order for the baby to regain useful vision, the eye must start to see immediately after surgery. This is accomplished through the use of thick cataract glasses, a contact lens, or in some cases, an intraocular lens implant, as those used in adults. If good vision is not restored early after cataract surgery, the eye will become “lazy” and vision will be poor despite a successful operation.
Traumatic cataracts are more common in children. This type develops from an injury to the eye, like an object penetrating the eye and touching the delicate clear lens, or one that jars the lens enough to damage it. “Fourth of July” parades and firecrackers are the biggest contributors. More injuries are sustained on this particular day alone when a child runs waving a flag, falls, and the stick jabs into the eye. Similar injuries can happen at any time, including at school with a pencil, scissors, or any object in their hands.
The lack of certain nutrients is another major contributor to the formation of cataracts. Vitamins, particularly those of A and B2, protein, and mineral deficiencies are common denominators either alone, or in combination, in those with cataracts. Although the role of nutrition in cataract formation in the United States is said to be “unclear,” it is quite convincing in third world and underdeveloped countries. More specifically, life-threatening diarrhea and dehydration have been directly implicated in the formation of cataracts.
In India alone, almost two million new cases of blindness each year are attributed to severe diarrhea. Low levels of calcium can also lead to cataracts. The cause is not from a lack of the mineral in the diet as much as an improper function of the parathyroid glands. These four tiny glands in the neck regulate the level of calcium in the blood; and their malfunction will cause a low level in the blood regardless of how much calcium is consumed.
Cigarette smoke is another contributor, which is compounded not only by the smoke, but the nutrient loss that comes from this addiction. Overall good dietary habits cannot be overstressed when it comes to preventing so many diseases and disorders, and the formation of cataracts is no exception.
Other causes of cataracts are more rare and often bizarre. A hypermature cataract is extremely rare but needs to be removed quickly. In addition, cataracts are more prone to form within some professions, especially glass blowers, apparently from constant exposure to intense heat, and electrical workers who can develop cataracts from electric shocks. Patients undergoing electroconvulsive shock treatments are more susceptible to cataracts as well.
Such eye diseases as iritis (inflammation of the iris) can lead to cataracts. These formations are referred to as secondary cataracts. Cataracts are also fairly common in those taking continuous doses of cortisone for prolonged periods of time as a treatment for such disorders as arthritis, asthma, gastrointestinal problems, and autoimmune-type diseases as lupus.
Prednisone and other cortisone preparations cause a specific type of opacification on the back part of the lens just under the capsule. These cataract formations are called posterior subcapsular cataract (PSC) and indicative of prolonged cortisone use.
Risk factors for developing cataracts include aging, race, and gender (cataracts are more common in women than men and in blacks more than in whites), diabetes, a family history, previous eye injury, inflammation, or surgery, prolonged corticosteroid use, excessive consumption of alcohol, excessive exposure to sunlight, exposure to high levels of radiation (as from cancer therapy, and smoking).
There are ways to prevent cataracts, although they cannot be avoided altogether. Regular eye exams are the key to early detection. Do not smoke, as this produces free radicals. Eat plenty of fresh fruits and vegetables. Limit alcohol. Protect the eyes from the damaging ultraviolet rays of the sun. And last, but certainly not least, follow the treatment plan for other medical problems – as diabetes – where risks to the eyes significantly increases the likelihood of developing cataracts.
Symptoms of a cataract
- Not seeing clearly. This is the first complaint and the most common. It may come so gradually and subtly that both the patient and doctor hardly notice. Others wait until vision is decidedly altered before seeking help. Cataracts typically do not cause any change in the appearance of the eye or in the production of tears. Pain, redness, itching, irritation, aching in the eye or a discharge from the eye may be signs of other eye disorders. A cataract is not dangerous to the physical health of the eye unless it becomes completely white, a condition known as a hypermature cataract. This can cause inflammation, pain, and headache.
- Double Vision. This may be caused by an eye-muscle problem or a cataract that is not uniformly dense or opaque. One part of the lens may have more opacities than another, causing rays of light to split into two or even three different parts. This is especially true of a small cataract in the nucleus. If this happens, it is easy to test by simply covering the good eye and seeing if the double vision disappears. If it does, the cataract is not causing double vision and most likely it is the eye muscles that are at fault, causing the eyes to be misaligned. Eye muscle problems in children usually mean nothing more than a muscle imbalance, but eye muscle trouble in adults often stems from neurologic problems. If double vision in the bad eye would persist with the good eye covered, then it may well be caused by a cataract. In either case, an ophthalmologist must be seen.
- Second Sight. This cataract symptom is a newly acquired ability to read without one’s glasses. Enthusiasm is understandable but may indicate a developing cataract. Second sight occurs when the part of the lens first affected by the cataract process, changes. If it started in the central nuclear area, the nucleus will become hard, causing the lens to become fatter and optically stronger so that light will be focused in front of the retina. This nearsightedness result may be the only clue to the beginning of a cataract and may not even be visible to the doctor. Nearsightedness from a developing cataract also explains the necessity for frequent changes of eyeglasses. As the cataract matures, glasses will no longer maintain sight and surgery will be necessary.
- Paradoxical Vision. Poor vision in bright light and improved vision in dim light may seem contradictory at first, but the answer depends on the type of cataract that is forming and which part of the lens is affected. When most of the clouding is centered on the back or posterior surface of the lens, the cataract will have its greatest impact when the pupil is small, which happens in bright light. The brighter the light, the smaller the pupil, the worse the vision. This type of cataract (posterior subcapsular cataract or PSC) is more common in patients with diabetes and in those on long-term cortisone treatments for severe arthritis or asthma. This blocking of the “bull’s eye” in the lens may be quite incapacitating to a patient with even a relatively small PSC cataract, since the level of vision may be markedly reduced on anything other than a cloudy day. Drops to keep the pupil dilated may improve vision temporarily until cataract surgery is performed. The problem may not even be readily apparent in the ophthalmologist’s office because most of the time the room is kept fairly dark when tests are made. Should such a cataract be detected, another test should be undertaken with the lights on. This will give a more realistic assessment of diminished eyesight.
- Changes in Color Vision. This is a subtle alteration in the quality of vision that may be overshadowed by more noticeable alterations in its clarity. As the cataract progresses, the nucleus becomes more and more yellow. This yellowing happens as the cataract absorbs wavelengths of first violet and then blue light, effectively reducing those colors and making the environment appear yellowish. The opposite effect often occurs immediately after cataract surgery when a flood of blue and violet light enters the eye making everything look bluish.
Types of Cataracts
- After-cataract is a secondary one or one where any membrane of the pupillary area forms after an extraction or absorption of the lens.
- Atopic cataract often occurs in those with long-standing atopic dermatitis and usually appears in the twenties or thirties.
- Brown or brunescent cataract is a senile cataract that appears as a brown opacity.
- Capsular cataract consists of an opacity of the capsule of the lens.
- Complicated cataract is a senile cataract or one that forms in the elderly.
- Cortical cataract is an opacity in the cortex of the lens. It begins as whitish, wedge-shaped streaks on the outer edge of the lens cortex. As it slowly progresses, the streaks extend to the center and interferes with light passing through the nucleus. Both distance and near vision can be significantly impaired. Focusing problems and distortions are common, and there may also be a problem with glare and loss of contrast. Diabetics often develop cortical cataracts, which are the only type associated with exposure to ultraviolet light.
- Hypermature cataract is one in which the entire lens capsule is wrinkled and the contents have become solid and shrunken, or soft and liquid.
- Immature or Incipient cataract is an incomplete cataract where the lens is only slightly opaque and the cortex is clear.
- Intumescent cataract is a mature, progressing cataract. The lens becomes swollen from the osmotic effect of degenerated lens protein. This may lead to secondary angle closure, or acute, glaucoma.
- Lenticular cataract is one where the opacity of the lens does not affect the capsule.
- Mature cataract produces swelling and opacity of the entire lens but are generally removed before it reaches this stage.
- Nuclear cataract is the most common type and the one most associated with aging. It occurs in the center of the lens. In its early stages, as the lens changes the way it focuses light, the person may become more nearsighted or experience temporary improvement in reading vision. Some people may actually stop needing their reading glasses. This so-called “second sight” disappears as the lens gradually turns yellow or greenish and begins to cloud vision. As the cataract progresses, the lens may even turn brown.
- Presenile cataract is a subcapsular senile cataract that forms in a person under the age of forty.
- Secondary cataract is usually a posterior subcapsular cataract that forms as a result of disease, especially iridocyclitis, or from such degeneration as chronic glaucoma or retinal detachment. A secondary cataract may also happen as a result of surgery, particulary glaucoma filtering or retinal reattachment.
- Senile cataract is one that forms as a result of the aging process and one most commonly found in the elderly. The word senile comes from the Latin word for “old” and has nothing to do with mental faculties or behavior. Over 90% of the cataracts in the US are senile cataracts, but not all seniors develop them.
- Subcapsular cataract starts as a small opaque area just under the capsule shell, forming at the back of the lens, right in the path of light on its way to the retina. This type of cataract may occur in both eyes, but will tend to be more advanced in one eye than the other. A subcapsular cataract often interferes with reading vision, reducing vision in bright light, and causing glare or halos around lights at night. Diabetics are more prone to developing this type of cataract as well as those who are nearsighted, have taken corticosteroids, or had an eye injury or eye surgery.
Cataract Surgery
- Removing the cataract. The most common procedure to remove a cataract is called phacoemulsification, in which the surgeon removes the cataract while leaving most of the lens capsule in place. The capsule will help support the lens implant when it is inserted. An alternative procedure called extracapsular cataract extraction is similar to phacoemulsification but requires a larger incision.
- Phacoemulsification. During this procedure (phaco for short), the surgeon makes a small incision, about 1/8 inch or 3 mm, where the cornea meets the conjunctiva and inserts a needle-thin probe. The surgeon then uses the probe, which vibrates with ultasound waves, to break up or emulsify the cataract and suction out the fragments. The lens capsule is left in place to provide support for the lens implant.
- Extracapsular cataract extraction. If the cataract has advanced beyond the point where phacoemulsification can effectively break up the clouded lens, the surgeon may opt for this procedure which requires a larger incision, about 3/8 inch or 10 mm, where the cornea and conjunctiva meet. Through this opening, the surgeon opens the lens capsule, removes the nucleus in one piece, and vacuums out the softer lens cortex, leaving the shell in one piece.
- Implanting the lens. When the cataract has been removed, a clear artificial lems is implanted into the empty lens capsule to replace the original clouded lens. This implant, also known as an intraocular lens (IOL), is made of plastic, acrylic, or silicone. It requires no care and becomes a permanent part of the eye. Some IOLs are rigid plastic and implanted through an incision that requires several stitches (sutures) to close. However, many IOLs are flexible, allowing a smaller incision that requires no stitches. The surgeon can fold this type of lens and insert it into the empty capsule where the natural lens used to be. Once in place, the lens unfolds to about 1/4 inch or 6 mm. Whether or not glasses were worn before surgery, after surgery reading glasses will still likely be required.
- After surgery. With phacoemulsification and foldable lens implants, surgical incisions are very small, and no sutures are required. If all goes well, healing will be fast, and vision will start to improve within days. If the surgery required a larger incision and sutures, full healing may take about four weeks. It is normal to feel mild discomfort for a couple of days following surgery, but avoid rubbing or pressing on the eye. The eyelids should be cleaned with cotton balls to remove any crusted discharge. Sometimes, an eye patch or shield is worn for added protection and medications may be prescribed to prevent infection and control eye pressure. The doctor should be contacted immediately if any of the following signs develop: a rare, but serious, infection known as endophthalmitis; vision loss; pain that persists despite the use of over-the-counter pain medications; a significant increase in eye redness; light flashes or multiple spots (floaters) in front of the eye; nausea, vomiting, or excessive coughing. Complications are relatively rare and most can be treated successfully. These include inflammation, infection, bleeding, swelling, retinal detachment, and glaucoma. The risks are greater for people who have other eye diseases or serious medical problems. Occasionally, cataract surgery fails to improve vision because of such conditions as glaucoma or macular degeneration.
