臨床醫學英語(第一, 二, 三講)

Clinical Medicine English

Lesson One docDisease: Its Symptoms and Treatments

2002-08-01


Diseases and treatments can be categorized in several ways: by their cause, by the system of the body affected, by severity, by the usual form of treatment, by the likelihood of recurrence, or by the expected outcome. A physician studies patient's medical history, symptoms, current physical condition, and medical test results in order to make a diagnosis and answer these kinds of questions: Is the condition serious (major) or minor? Is the patient suffering from a chronic problem or an acute attack? If there is a tumor, is it benign or malignant (cancerous)? Is it localized or widespread? If the patient has a runny nose and a postnasal drip, are these conditions caused by an infection or an allergy? If there is an infection, what type of germ is it caused by? Is the disease communicative (contagious) or non-contagious? Is this a physical or a mental illness, or both? What is the treatment of choice? What is the course of the illness likely to be? Is the patient's illness curable or incurable? Is it fatal? Is the patient terminally ill? Tentative diagnoses sometimes begin with patients, who notice abnormal changes in their bodies. These changes are called symptoms. Two obvious and disturbing symptoms which usually lead patients to consult a physician promptly are severe bleeding (hemorrhaging) and pain. A pain that is bearable but persistent is often labeled an ache by patients. The most common are the headache and the stomach ache. A pain in the stomach may indicate simple indigestion or a more serious ailment such as an ulcer or dysentery. A headache may be associated with colds, the flu, sinus infections, and head injures.

There are many other common symptoms of ill health. Fever is one. Normal body temperature is 98.6°Fahrenheit or 37°Celsius. A temperature higher than normal may indicate that the body is fighting an infection. Another common symptom is coughing. A cough may be dry, or it may produce a lot of phlegm (thick mucus) or sputum (a substance containing a variety of material expelled from the respiratory tract). Coughs are associated with ailments of the nose, throat, chest, and lungs. Fainting, dizziness, and persistent fatigue are other symptoms that something is wrong. One possible cause is a low red blood cell count, a condition known as anemia, which
itself may be a symptom of a serious illness. The symptoms of nausea and vomiting are associated with stomach and intestinal disorders such as the flu (influenza), food poisoning, or dysentery, but they can also result from inner-ear disorders that affect the balance mechanism. Sweating, itching, and rashes are symptoms of problems such as allergies, insect bites, or skin irritations.

Sometimes a patient's various symptoms fit together and form what is called a syndrome, a group of symptoms that collectively indicate the presence of a particular disease or condition. An example of this is Reye's syndrome, an acute, very serious childhood illness that in its first stage is characterized by abdominal pain, vomiting, severe weakness, and liver dysfunction. In order to treat an illness successfully and prevent a recurrence, a physician usually needs to identify not only the condition but also its cause. The first step is to ascertain whether the illness is infectious or noninfectious. An infectious disease is caused by microorganisms (minute living bodies that are invisible to the naked eye). These tiny organisms (bacteria, viruses, fungi, protozoa, or worms) are also called pathogens or, more commonly, germs. Infectious diseases are often (but not always) communicable (contagious), which means that an infected person can pass the disease to another through direct or indirect contact. Diseases not caused by pathogens are classified as noninfectious. In this category are chronic degenerative diseases characterized by the breakdown of tissues and /or organs (often the result of aging), congenital defects (those existing from birth), hormonal disorders, environmental and occupational diseases, immunological diseases, and mental illness. One cause of illness that doctors dislike even thinking about is the iatrogenic disorder (an abnormal condition caused by the physician's treatment). Finally, there are disease conditions labeled idiopathic C which means without any recognizable causes.

Whether a person exposed to pathogens becomes ill or not depends upon the body's ability to resist microorganisms. This ability is termed immunity and may be natural or acquired. Natural immunity is provided by such bodily defense mechanisms as (1) the skin, tears, and the mucous membranes that line the mouth, nose, and bronchial tubes; (2) harmless bacteria in the body which interfere with the growth of harmful germs; (3) stomach juices that are highly acidic and also contain disease-fighting chemicals; and (4) specialized white blood cells that live in the tissues, fluids, and blood.

Acquired immunity is developed by exposure to germs and their products and depends on specific antibodies produced by sensitized plasma cells. Introducing germs into the body artificially in a controlled manner stimulates the body to produce the antibodies that will prevent the growth of the same antigen in the future. Vaccines are used to produce an acquired immunity. A person is vaccinated with a living but weakened germ, a killed germ, or a toxic poison from the germ. Because this acquired immunity often does not last a lifetime, it may be necessary to immunize people periodically with booster shots of the vaccine.

Whether a person's illness is infectious or noninfectious, there is always the hope that the doctor and the pharmacist will have a 「magic potion」 which, once swallowed, will make all signs and symptoms of disease disappear forever, substances prescribed or recommended to treat illness are called drugs or medicine. In past centuries, people often found effective drugs through a process of trial and error. Today, medical personnel have a clear idea of how and why a particular drug works and what its side effects and contraindications are. The Physician's Desk Reference lists and describes various drugs on the market in the United States and shows illustrations of them. About 2,000 different drugs are currently available for the treatment of illness, and new ones are continually being developed.

Many drugs are available by prescription only. These drugs are potent and may be dangerous if taken in an overdoes. Some are addictive; therefore, their use must be strictly controlled. A patient can buy these medicines only if a doctor writes a prescription (or order) for a pharmacist to fill. Antibiotic drugs are often called 「miracle drugs」 because of their ability to bring rapid improvement and quick cures of some serious infections. Penicillin, a well-known antibiotic, is generally effective against a variety of bacterial infections. Made from fungi, penicillin inhibits the growth of disease―producing microorganisms. The mycin drugs, such as streptomycin, often work where penicillin fails or when a patient is allergic to penicillin. Narcotic drugs such as codeine and morphine can also be obtained only with a prescription. They are addictive and thus can be sued only in restricted dosages. Originally derived from opium and now mostly synthetic, they are excellent painkillers, but in excessive amounts they can cause coma or death.

Other familiar drugs include digitalis (which helps strengthen the failing heart), anticoagulants (which prevent blood clots), and diuretics (which help remove excess fluid from the body). Insulin is used in the treatment of diabetes.

Although there is no drug to cure the upper respiratory viral infection called the common cold, many drugs help to relieve the symptoms. Aspirin is an effective painkiller and anti-inflammatory drug, but it is contraindicated for colds or flu because it has been suspected of being a contributory cause of Reye's syndrome. To relieve the aches that accompany a cold or the flu, physicians generally prescribe acetaminophen (commonly known by the brand name Tylenol), especially for children. A decongestant may decrease nasal stuffiness and relieve a runny nose. Gargling with salt water or sucking on lozenges or hard candy can soothe a sore throat.

Many other over-counter medications are used (and often overused) by the general public, including laxatives (to relieve constipation), tranquilizers, sedatives, sleeping pills, and pep ills (stimulants). Over-the Ccounter (nonprescription) drugs enable people to handle minor medical problems without spending money or time consulting a doctor. However, many people waste money on drugs that do not help their specific condition or that may even do more harm than good.

Of course, medication is just one of many ways to treat illness. Among the other tools which physicians use are surgery, radiation therapy, chemotherapy, special equipment prescribed for patient use, and non-musical recommendations for a change in a patient's life (following special diets, increasing or altering habits of exercise, moving to a different climate, decreasing workload and stress, and so on).

As medical science becomes more and more sophisticated, people live longer and develop more chronic and debilitating conditions that require medical treatment. In highly industrialized societies, pollution has created an increase in allergic and other conditions that require medical care. The challenge of modern medicine is to meet the changing medical needs of rapidly changing societies in which people have very high (sometimes unreasonably high) expectations of their doctors' curative powers. People want to live long lives and to fell as good at 80 as they felt at 20. doctors are not magicians, but research continues with the hope that someday, whatever people's ages, they will never fell "over the hill".


Notes:

1. Normal body temperature is 98.6 Fahrenheit or 37 Celsius

Fahrenheit 華氏溫度的
Celsius (or Centigrade) 攝氏溫度的
  華氏溫度換算成攝氏溫度  減去32再乘以5/9
  攝氏溫度換算成華氏溫度  乘以9/5再加32

2. over the hill 在衰退中

Supplementary Reading

Blood Facts

The average adult has about five to six quarts of blood, flowing through some 60 000 miles of blood vessels. The blood makes a complete journey round the body about once a minute, carrying nutrients and oxygen to all the cells and collecting waste products from them, circulating hormones, and distributing antibodies to fight infection.

Every second of every day, you manufacture 10 million new red blood cells. Add to this stream a large dose of white blood cells, millions of platelets and an assortment of nutrients and it might seem that your veins contained merely a useless soup of organic odds and ends. How does the boy coordinate these components into the finely blended mixture we call bloods?

Close to half your blood is made of red cells, white cells and platelets, all of which incubate in the bones. Each of these life sustaining agents begins as a stem cell, a sort of hematological embryo that idles in the marrow until ordered to develop into one of the three discrete blood cell types.

Red cells ferry oxygen throughout the body. Alerted by a chemical alarm from the kidneys, which continuously monitor the blood for dropping oxygen levels, a hormone called erythropoietin directs the marrow to build a fresh supply of red cells.

White blood cells protect the body from disease and infection by ingesting or ousting microscopic intruders. They are found in a number of forms and produced in a number of ways. For example, a hormone called granulopoietin signals the marrow to produce white cells of the disease-fighting variety; foreign substances called antigens trigger the manufacture of others that specialize in battling infection. As a precaution, the marrow houses a standby force of fully developed white cells. So vigilant is this reserve platoon that it may interpret even routine exercise as a sign of potential bodily injury and flood the system to tend to illusory wounds.

For legitimate emergencies, the body also keeps on hand a supply of platelets, disk-shaped bodies whose job is to facilitate clotting. Platelets mature from stem cells whenever the body nourishes them with the hormone thrombopoietin. Only a bit of the hormone is manufactured at a time, which prevents platelet production from running amuck. When the thrombopoietin is totally consumed, the platelet population stops growing.

Red cells, white cells and platelets are transported in the body by plasma, a thin liquid that makes up the other half of the blood. Though complex, plasma is only 10 percent organic substances. The remainder is water, a component that must always be present in precise concentrations. Should the blood become either too diluted or too viscous, the kidneys retain or excrete surplus water until the proper balance is reached.

A single blood cell will travel through its plasma medium for as much as 120 days until it is ultimately washed ashore in the spleen, the junkyard of the circulatory system. Although trillions of cells meet this fate daily, all are replaced as effortlessly as they are discarded. In fact, the cellular contents of the blood are entirely destroyed and renewed 300 times over the course of an 80 year life span. But despite such upheaval, the river of life flows on.

The average person can lose a pint of blood without danger, and that is why this is the amount usually chosen for blood donating. However, the loss of blood from a wound should always be taken seriously. At a blood donating center, a pint of blood is given under carefully controlled conditions. In the case of accidental bleeding, not only would it be hard to judge the amount of blood being lost, but there is the added risk of infection from germs that may enter a wound. It has been shown that the body can lose of two pints of blood will often cause shock.

In this age of biotic medicine, scientists have been making steady progress in their quest for an artificial substitute for human blood. Drawing upon the work of American scientists over the last decade, medical researchers at the Green Cross Corp. of Japan, are refining a milky-white liquid called Fluosol-DA could be a life-saving breakthrough for patients who receive blood transfusions and now must depend upon donated, natural blood supplies. For one thing, artificial blood does not need to match the particular blood type of the recipient; it is universally acceptable. Perhaps more important, it is free of the risks of communicable diseases such as hepatitis or AIDS (acquired immune deficiency syndrome). And unlike natural blood, Fluosol-DA can be carried easily in ambulances.

Scientists have also developed a second generation of this blood substitute that solves the problem of blood storage. Donated blood has a shelf life of only a few weeks. Even the original Fluosol-DA, which lasts significantly longer, needs to be stored in a frozen state. But the new blood substitute can be stored for long periods at room temperature without deteriorating. The new artificial blood has been under development for about two years, and so far it promises to last that long. But its actual room-temperature shelf life may turn out to be even longer as research continues. Green Cross is planning to manufacture the original Fluosol-DA about a year from now. it is currently undergoing tests by the Food and Drug Administration in the  United States and government approval is also being sought in Japan. The newer version may be ready for clinical use in four or five years.

臨床醫學英語第二講 Apical Cyst

2002-08-01


The apical cyst is a significant lesion. Among the periapical disorders only the acute apical periodontitis and the chronic apical periodontitis occur more frequently. Most agree that the apical cyst is a true cyst, i.e., a pathologic cavity which is lined with epithelium and often fluid-filled. The term apical cyst is substituted (again for mnemonic reasons) in place of the time-honored 「radicular cyst.」 The prefix 「apical」 directs attention to the location of the cyst and also suggests the etiology as endodontic in nature. The adjective 「radicular」, while it implies root, also signifies that the cyst may be at any location along the root. Thus a 「lateral cyst」 and the 「apical cyst」 are both 「radicular cysts」.

The presence of epithelium within apical inflamma tory lesions has been repeatedly confirmed. This epithelium, with few exceptions, is derived from the epithelia rests of Malassez. The apical cyst develops within such
apical lesions and from this epithelium. Actually a lined cystic can develop at the site of either the chronic or the suppurative form of periodontitis. The latter metamorphosis (suppurative periodontitis to apical cyst) is, of course, less often seen.

Why and how does the cystic cavity form? The consensus views inflammation as the primary stimulus. Excited by inflammation, the epithelial cells in the apical area proliferate widely. The reticular pattern of their growth at this stage is quite dramatic. Mitosis occurs in the basal layer of cells along the periphery of the epithelial cords and clusters. More and more layers of squamous cells are produced. Eventually, the central cells of this epithelial mass die, because they have become too far removed from the connective tissue which is their source of nourishment. The common death of central epithelial cells leads to necrosis; necrosis to liquefaction, liquefaction to the apical cyst a fluidfilled cavity within epithelium. There remains unanswered. Of course, an important question. Why do only some lesions of chronic apical periodontitis become apical cysts when epithelium and inflammation are present in all?

Growth of the apical cyst is a slow process. At the outset the cyst can be likened to an epithelial parasite within the apical 「granuloma.」 Once established, the apical cyst will occasion ally press on its own into new
territory far beyond the 「granuloma,」 into the cavity of the maxillary sinus, for example. In such an instance the original connective tissue lesion and additional alveolar bone give way before the cyst. Most apical cists remain small. Many, in fact, stay within the limits of the inflammatory lesion which preceded them. For others, the process of local expansion continues, but at an extremely slow rate.

How does the minute cyst become a larger one? A continued apical inflammation, the unending mitosis of epithelial cells of the cyst wall, the unending mitosis of epithelial cells of the cyst wall, the necrosis and liquefaction of cells, epithelial and other, which are desquamated into the cyst cavity, the resultant increase in cyst content, and finally, the resorption of bone in response to pressure from this growing volume of cyst fluid-all
contribute to the expansion.

Apical cysts have in common epithelium, a central lumen lined by the epithelial sheet, a fluid or semi-fluid substance within the lumen, and an outer capsule of connective tissue. When the cyst is young, its epithelium is continuous with the network of epithelium which has already ramified at the apex of the tooth. Later the accessory fingers and cords seem to 「retract」, leaving a consolidated cyst wall. Round cells often permeate both the epithelium and the immediate connective tissue. They also enter the cyst fluid in quantity. Should inflammation dominate, the epithelial lining may be thinned or interrupted.

A curious fluid tills the cavity of the cyst. Its slippery yet crystalline feel, and the often amber tint, render this fluid unique. Erythrocytes are rarely found when the fluid is aspirated from a cyst in situ. Free-floating epithelial cells and leukocytes, however, are often detected. Cholesterol is sometimes abundant and always unmistakable when encountered. The connective tissue wall of the cyst is usually composed of an inner and an outer layer. The inner zone, made up of inflammatory connective tissue, underlies the epithelium in all its ramifications. The outer peripheral layer is the true 「capsule」 of the cyst. Collagenous fibers here are often densely arranged. Their connections with the alveolar bone are comparatively loose, however. For this reason, it is often possible to enucleate an apical cyst intact. Occasionally, tooth and cyst are removed as one.

The outermost perimeter, of course, is the alveolar bone. Always responsive, the bone tells its own story of growth or status quo in the life of the cyst. evidences of new peripheral bone are often seen. These may reflect a narrowing of the width of the connective tissue zone as the inflammatory process diminishes. The majority of jaw sections available to us show trabeculae of compact bone on the margins of the apical cysts. In fact, the bone which forms the cystic enclosure and the bone of the alveolar tooth socket (alveolar bone proper) present a similar appearance.

The apical cyst shares many of the clinical and roentgenographic features of chronic apical periodontitis. This is to be expected. After all, the cyst arises as a rule within an existing apical 「granuloma」 and often remains a minor feature of that inflammatory tissue mass. Both grow slowly. Both are asymptomatic. Seldom does either expand to a size greater than that of a large pea. On a roentgenographic basis alone, distinction between the two is usually impossible.

The roentgenogram can reveal neither the epithelial lining nor the fluid content of a cyst. The observation of a fine radiopaque line on the circumference of the area cannot be considered diagnostic. Several studies have made clear that this 「condensation」 of peripheral bone is not limited to the apical cyst, but occurs in the case of chronic apical periodontitis as well. It is interesting to note that both 「granuloma」 and cyst may be invisible in the roentgenogram. Should either lesion grow entirely within cancellous bone, the intact outer cortical plate of the alveolar process can impart a normal image despite the presence o the lesion inside.

Direct observation of apical lesions at the time of surgery reveals much to the dentist. But many a small cyst, we may be sure, passes unnoticed during the clinical inspection. Only serial microscopic sections, carefully studied, will reveal the epitheliumline cavity of the early cyst.

Notes

1. There remains unanswered, of course, an important question.本句是倒裝句，句末的an important question 是主語，用there或here引導的句子常用倒裝語序。
2. once established是帶有連詞的分詞短語，作狀語。此類結構也可看作是省略了構成某成分的從句。
3. Should inflammation dominate = If inflammation should dominate. 帶有動詞were, had, should的條件狀語從句，有時不用if 來引導，而用上述的倒裝語序來表示。
4. in situ 在原位，在原地。

[Supplementary Reading]

Structure of the Tooth


The greater part of the tooth consists of dentine. The root dentine is covered by a thin layer of cementum and the dentine of the crown is covered by enamel. Internally, the dentine contains the dental pulp in the pulp chamber. The root of the tooth occupies a socket in the alveolar bone to which it is attached by the connective tissue fibres of the periodontal membrane.

1. The pulp: The pulp consists of loose connective tissue and carries the blood, lymphatic and nerve supply to the tooth. Where it meets the dentine, the surface of the pulp is covered by a layer of odontoblasts. These are columnar cells with oval nuclei, and each cell has a process that lies within a corresponding tubule in the dentine. Immediately internal to the odontoblast layer there is a narrow cell-free zone.

2. Dentine: Physically and chemically dentine is very similar to bone, consisting of 30 per cent organic material and water, and 70 per cent inorganic material. As in bone, the organic fraction consists of collagen fibrils embedded in a mucopolysaccharide cementing substance, and the inorganic fraction consists mainly of calcium phosphates in the form of apatite crystals. Unlike bone, however, dentine contains no cell bodies but only cell processes, those of the odontoblasts, in the dentinal tubule. The dentinal tubules are 2 to 3 in diameter and each runs through the whole thickness of the dentine from the cell body of the odontoblast to the outer surface of the dentine. There are cross-communications between the tubules, containing anastomosing branches of the odontoblast processes. Calcification of the outer surface of the dentine. There are cross-communications between the tubules, containing anastomosing branches of the odontoblast processes. Calcification of the dentine occurs in spherical or globular masses or calcification is incomplete the separate globules can be seen, with the uncalcified or hypocalcified ground substance in between them. Such areas are referred to as interglobular dentine.

3. Enamel: Mature enamel can be studied only in ground sections unless special methods are employed, since it is completely removed by routine histological decalcification. The inorganic material is an apatite and small organic fraction is mainly of keratinous nature. Enamel consists of rods or prisms in an interprismatic substance that is slightly less mineralized than the rods themselves. Each rod runs from the enamel-dentine junction through the whole thickness of the enamel to its surface, following a slightly wavy course. The rods have a 「fish-scale」 appearance in cross-section, with an average diameter of 4u.

4. Cementum: Cementum is a modified type of bone that covers the dentine of the tooth root in a thin layer. Two varieties of cementum occur normally, acellular and celluar. Acellular or primary cementum, the type first formed, covers the root from the enamel-cementum junction to close to the apex. As the name implies, this thin layer of cementum is homogeneous and contains no cells. Cellular or secondary cementum covers the apical portion of the root. Lacunae containing the cementocytes are present, in a similar manner to the lacunae for osteocyte in bone. The cementocytes are very similar morphologically to osteocytes, though they are usually somewhat larger. The processes of the cementocytes do not radiate in all directions like those of osteocytes, but tend to be directed away from the dentine towards the periodontal membrane. Well-marked incremental lines running parallel with the root surface are seen in the cementum and it is quite normal to find successive increments of both acellular cementum occurring in any order or distribution. Cementum is continuously deposited throughtout life. The principal function of cementum is to give attachment to fibres of the periodontal membrane.

5. Periodontal membrane: The connective tissue fibres, generally termed the periodontal membrane, constitute a suspensory ligament that attaches the tooth to bony alveolus. Fibres are attached to the cementum, and for the most part rum in bundles to the alveolar bone. Those from the cementum nearest to the crown, however, run across the alveolar crest to the cementum of the adjacent tooth, and some also rum into the gingival.

Good on you, mate! but I reckon it might be too long for some of our forumites here.

Thanks. Next time if I see the doctor, I will describe my feelings and symptom more exactly. Thanks, Adelyn. I am looking forward  to more coming.

臨床醫學英語第三講Examination of the Eye

2002-08-01

The exposed position of the eye lends itself readily to external inspection. The biomicroscope allows of a detailed examination under 15 to 30 magnifications of the conjunctiva, cornea, anterior chamber, iris, lens, vitreous, and portions of the retina. Gonioscopy provides a direct view of the filtration angle and the base of the iris while improved methods of indirect ophthalmoscopy bring into view the entire retina out to the oraserrata and beyond. Thus there is little of the eye that does not lend itself to observation. Perimetry and campimetry provide an indirect means of integrity of evaluating the integrity of the visual pathway from the eyeball to the occipital cortex.

Examination of the eye is richly rewarding to the diligent observer. No other organ in the body mirrors evidence of so many variegated remote diseases, intracranial and systemic. Complete evaluation of the eyes includes a survey of 50 per cent of the cranial nerve in whole or in part, and ophthalmoscopy affords the only opportunity for direct visualization of blood vessels. Visual acuity should always be estimated, preferable with the Snellen chart. When vision is less than 20/200, the distance at which fingers can be counted is measured. If fingers cannot be counted, the ability of the patient to recognize the direction of hand movement is determined. Below this level vision is recorded as light projection when a light is on or off. This degree of impairment of vision is a short step from total blindness.

In examining the fundus, the characteristic of the optic disc to be noted are the color, cupping and outline. The normal disc exhibits a pinkish color with a pale central depressed area, the physiologic cupping. The remainder of the fundus generally appears bright orange-red in color with the retinal vessels coursing over it from the disc. Variations from the normal are noted such as pallor of the disc or blurring of the margins with distention of the veins or increased cupping of the margins with distention of the veins or increased cupping of the disc extending to its margins. In the retina, hemorrhages, white spots of exudates, pigmentary disturbances or other variations from the normal are noted.

Opacities of the cornea, lens, or vitreous are seen as light to dark grayish or black spots against the background of the orange-red fundus reflex, and the location of an opacity, whether in the cornea or lens, is determined by parallax. With the patient』s eye held steady and maintaining the beam of light through the pupil the examiner moves the ophthalmoscope up and down or sideways. If the opacity appears to move in the opposite direction, it is in the cornea. No motion of the opacity places it in the anterior layers of the lens while apparent movement in the same direction locates it in the middle or posterior layers of the lens. The distinctive feature of vitreous opacities is their actual movement on motion of the eye. Thus, I the patient moves hi eye up and down and then holds is steady, opacities in the vitreous will be seen to swirl about, since they are present in a semifluid medium, whereas opacities in the cornea or lens are fixed and occupy the same position in the papillary reflex as before the eye moved. An estimate of intraoclar pressure can be obtained by palpation of the globe through the lids. The tonometer provides a simple and more reliable pressure of the intraocular pressure.

The visual fields can be roughly estimated by confrontation but the perimeter and tangent screen yields more accurate information.

The color of the macular area and presence o a foveal reflex are noted. The retina is examined for scars, detachments, tumor, or pigmentary disturbances.


Cataract

By definition a cataract is an opacity in the lens. For practical purposes, however, the term is best applied to those opacities of the lens that impair sight.

1. Classification and etiology: Cataracts are classified according to the age of the individual, etiology, and the morphologic characteristics of the opacity.

The mechanism of the development of cataract is unknown. Heredity is an important factor in many instances of congenital cataract, and injury to the lens precedes development of traumatic cataract. Many forms of radiant
energy such as infrared rays, X-rays, or radium emanation are known to cause cataract. However, little is known concerning the etiology in the large and important class of senile cataracts.

(a) Congenital cataracts: These vary in size, shape, location, and density. They occur in one eye or both and are usually non-progressive.

(b) Traumatic cataract: This occurs as a result of injury. Starting as a localized opacity the cataract progresses to complete opacification of the lens, a mature cataract.

(c) Complicated cataract: This occurs as a result of various intraocular diseases such as uveitis, retinitis pigmentosa, or high myopia.

(d) Senile cataract: This occurs in older age groups in eyes that are otherwise quite healthy. The majority of individuals beyond the age of 60 develop lenticular opacities of various types involving the periphery of the lens, and a relatively small number of these individuals develop senile cataracts. Senile cataracts can generally be classified as cortical or nuclear depending on whether the opacification begins in the cortex or in the nucleus of the lens. The two types may develop together in the same lens.

(e) Miscellaneous cataracts: Cataracts also occur as a result of toxic effects of chemicals, from ionizing radiation, in metabolic disorders such as diabetes mellitus and parathyroid tetany, and with neurologic disease such as myotonic dystrophy.

2. Symptoms and signs: The principal symptom of developing cataract is failing vision. In the course of the development of the nuclear sclerotic type of senile cataract halos of ranbow colors around lights are frequently
observed.

Stages of cataract development are classified as incipient, immature, mature, and hypermature, according to the degree and extent of opacification. Within certain limits visual acuity can be correlated with the stage of cataract development, and it is frequently important to be able to state whether a given cataract is sufficient to account for the degree of visual impairment in an eye. In the hypermature stage the cataract may swell and cause glaucoma, or toxic liquefied cortex may seep through the capsule causing iritis.

Visual impairment is slight ot moderate in the incipient stage, moderate to marked in the immature stage, and marked in the mature and hypermature stage where vision is reduced to light projection. This is the ability to state from what direction a light is coming when a small pocket flashlight is held in various places before the eye. Failure to project the light accurately suggests a lesion posterior to the cataract.

3. Diagnosis: The diagnosis of cataract is made by ophthalmoscopic examination, observing the opacities as spots against the background of the fundus reflex. Their location in the lens is determined by parallax and lack of motion except as the eye moves. As the cataract increases fundus details are obscured and gradually lost to view in a dull reddish reflex which passes through stages of dark red to gray to black when the cataract is in a mature stage. In the late stages the cataract is readily visible with a flashlight as a grayish white or white papillary reflex.


Notes:

1. lend itself to 有助於，適宜於。例如：The rural environment lends itself to the restoration of her health. 農村環境有助於她恢復健康。
2. from which a light is coming 光線從那兒來。關係代詞which代替direction，引出定語從句，在從句中作介詞from的賓語。
3. when a light is on or off 什麼時候開燈或關燈。When為連詞，引出賓語從句。
4. swirl about 打漩；about在此用作副詞，作「輪轉」講。
5. whether 是否，連詞，在此引出賓語從句，作depending on 的賓語。
6. and gradually lost to view 逐漸看不見了，gradually前面省略了助動詞are.