Colour vision deficiency Health Dictionary

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Colour Vision Deficiency: From 1 Different Sources

Any abnormality in colour vision that causes difficulty distinguishing between certain colours. Total absence of colour vision (monochromatism) is rare. The most common types of colour vision deficiency are reduced discrimination of red and green. Most cases of red and green colour vision deficiency are caused by defects in the light-sensitive cells in the retina. These defects are usually inherited, although occasionally defects are caused by retinal or optic nerve diseases or injury. The inherited defects tend to be sex-linked (see genetic disorders), which means that the majority of sufferers are male. A person with a severe green deficiency has difficulty distinguishing oranges, greens, browns, and pale reds. In severe red deficiency, all reds appear dull. A much rarer deficiency in which blue cannot be distinguished may be inherited or may be due to degeneration of the retina or optic nerve.

Health Source: BMA Medical Dictionary
Author: The British Medical Association

Colour Blindness

See VISION – Defective colour vision.... colour blindness

Double Vision

See SQUINT.... double vision

Vision

Broadly speaking, vision is the ability to see.

Pathway of light from the eye to the brain Light enters the EYE by passing through the transparent cornea, then through the aqueous humour ?lling the anterior chamber. It then passes through the pupil, through the lens and the vitreous to reach the retina. In the retina, the rod and cone photoreceptors detect light and relay messages in the form of electrochemical impulses through the various layers of the retina to the nerve ?bres. The nerve ?bres carry messages via the optic nerve, optic chiasma, optic tract, lateral geniculate body and ?nally the optic radiations to the visual cortex.

Here in the visual cortex these messages are interpreted. It is therefore the visual cortex of the BRAIN that ‘sees’.

Visual acuity Two points will not be seen as two unless they are separated by a minimum distance. This distance is such that the objects are so far apart that the lines joining them to the eye enclose between them (subtend) an angle of at least one minute of a degree. This amount of separation allows the images of the two points to fall on two separate cones (if the light from two points falls on one cone, the two points would be seen as a single point). There are many tests of visual acuity. One of the more common is the Snellen test type. This is made up of many letters of di?erent size. By conventions the chart is placed 6 metres away from the patient. Someone able to see the lowest line at this distance has a visual acuity of 6/4. If they are only able to see the top letter they have 6/60 vision. ‘Normal’ vision is 6/6.

Colour vision ‘White light’ is made up of component colours. These can be separated by a prism, thereby producing a spectrum. The three cardinal colours are red, green, and blue; all other colours can be produced by a varying mixture of these three. Colour vision is a complex subject. The trichromat theory of colour vision suggests that there are three types of cones, each type sensitive to one of the cardinal colours. Colour perception is based on di?erential stimulation of these cone types. The opponent colour theory suggests that each cone type can generate signals of the opposite kind. Output from some cones can collaborate with the output from others or can inhibit the action of other cones. Colour perception results from these various complex interactions.

Defective colour vision may be hereditary or acquired, and can occur in the presence of normal visual acuity. HEREDITARY DEFECTIVE COLOUR VISION is more common in men (7 per cent of males) than women (0·5 per cent of females). Men are affected, but women convey the abnormal gene (see GENES) to their children. It occurs because one or more of the photopigments of the retina are abnormal, or the cones are damaged. Red-green colour defect is the most common. ACQUIRED DEFECTIVE COLOUR VISION is the result of disease of the cones or their connections in the retina, optic nerve or brain – for example, macular disease, optic neuritis. Col-our vision can be impaired but not lost as a result of corneal opaci?cation or cataract formation (see under EYE, DISORDERS OF).

TESTS OF COLOUR VISION These use specially designed numbers made of coloured dots surrounded by dots of confusing colour (e.g. plates).... vision

Vision Tests

Most vision tests examine a person’s sharpness of VISION (visual acuity) and often of the ?eld of vision (see VISION, FIELD OF). Refraction tests assess whether a person has an error that can be corrected with glasses such as ASTIGMATISM, HYPERMETROPIA or MYOPIA. Visual acuity is tested using a Snellen chart when the patient tries to read letters of di?ering standard sizes from 6 metres away. The optician will prescribe lenses to correct any defects detected by vision tests.... vision tests

Vision, Disorders Of

The list of disorders resulting in poor or dim vision is huge. Disturbance of vision can result from an uncorrected refractive error, disease or injury of the cornea, iris, lens, vitreous, retina, choroid or sclera of the EYE. It may also result from disease or injury to the structures comprising the visual pathway from the retina to the occipital cortex (see VISION – Pathway of light from the eye to the brain) and from lesions of the structures around the eye – for example, swollen lids, drooping eyelids. (See EYE, DISORDERS OF.)... vision, disorders of

Blurred Vision

Refer: ALCOHOLISM, CATARACT, CONJUNCTIVITIS, DIABETES, ECLAMPSIA, GLAUCOMA, IRITIS, MIGRAINE, MULTIPLE SCLEROSIS, RETINITIS, SHOCK. ... blurred vision

Alpha-antitrypsin Deficiency

A rare genetic disorder in which a person is missing the enzyme alpha1-antitrypsin, which protects the body from damage by other enzymes.

The disease mainly affects tissues in the lungs, resulting in emphysema, and the liver, causing cirrhosis.

The effects of alpha1-antitrypsin deficiency may not become apparent until after the age of 30.

There is no cure, but symptoms can be relieved by drug treatment.

In severe cases, a liver transplant may be a possibility.... alpha-antitrypsin deficiency

Tunnel Vision

Loss of the peripheral visual field to the extent that only objects straight ahead can be seen clearly. Tunnel vision is most commonly caused by chronic glaucoma. Retinitis pigmentosa is another possible cause.... tunnel vision

Acquired Immune Deficiency Syndrome (aids)

A severe manifestation of infection with the Human immunodeficiency virus (HIV).... acquired immune deficiency syndrome (aids)

Deficiency Disease

Any disease resulting from the absence from the diet of any substance essential to good health: for example, one of the vitamins.... deficiency disease

Glucose-6-phosphate-dehydrogenase (g6pd) Deficiency

A deficiency in the enzyme G6PD resulting in a haemolytic anaemia. This haemoglobinopathy contraindicates the use of the 4-aminoquinolines such as primaquine for the radical treatment of benign tertian and ovale tertian malaria.... glucose-6-phosphate-dehydrogenase (g6pd) deficiency

Iron-deficiency Anaemia

See anaemia, iron-deficiency.... iron-deficiency anaemia

Lactase Deficiency

A condition in which there is an absence of lactase, an enzyme that breaks down lactose (milk sugar), in the cells of the small intestine.

Lactase deficiency results in a reduced ability to digest lactose, also known as lactose intolerance.

The condition may be permanent, or may occur temporarily after gastroenteritis, particularly in young children.

Symptoms include abdominal cramps, bloating, flatulence, and diarrhoea, all of which are caused by the laxative effect of the undigested sugar in the intestines.

Treatment is with a lactose-free diet.... lactase deficiency

Vision, Field Of

When the eye looks at a speci?c point or object, that point is seen clearly. Other objects within a large area away from this ?xation point can also be seen, but less clearly. The area that can be seen around the ?xation point, without moving the eye, is known as the ?eld of vision. The extent of the ?eld is limited inwards by the nose, above by the brow and below by the cheek. The visual ?eld thus has its greatest extent outwards from the side of the head. The ?eld of vision of each eye overlaps to a large extent so that objects in the centre and towards the inner part of each ?eld are viewed by both eyes together. Because the eyes are set slightly apart, each eye sees objects in this overlapping part of the ?eld slightly di?erently. It is because of this slight di?erence that objects can be perceived as three-dimensional.

Defects in the visual ?eld (scotomas) can be produced by a variety of disorders. Certain of these produce speci?c ?eld defects. For example, GLAUCOMA, some types of brain damage and some TOXINS can produce speci?c defects in the visual ?eld. This type of ?eld defect may be very useful in diagnosing a particular disorder. The blind spot is that part of the visual ?eld corresponding to the optic disc. There are no rods nor cones on the optic disc and therefore no light perception from this area. The blind spot can be found temporal (i.e. on the outer side) of the ?xation point. (See also EYE.)... vision, field of

Anaemia: Iron Deficiency

An estimated 15 per cent of the female population suffers from this form of anaemia. A deficiency of nutritional iron is responsible for oxygen starvation of the blood due to insufficient haemoglobin. Number of red cells is reduced.

Aetiology: heavy menstrual loss, feeble constitution from hereditary weakness, poor diet, hidden or known blood loss from gastric ulcer, pregnancy, bleeding piles or insufficient food minerals: iron, copper, calcium, etc, chronic liver or kidney disease, worms, anorexia nervosa, rheumatoid arthritis, tuberculosis. Symptoms. Tiredness, dizziness, breathlessness, palpitations, pale face and mucous membranes. White of eyes may be blue. Enlarged flabby tongue often bears impression of teeth marks. Hair lifeless, fingernails brittle and ridged. There may be angina, tinnitus and general reduced efficiency.

Treatment. The object is to achieve absorption of iron to raise normal haemoglobin levels and increase red cells. Echinacea has a reputation for regeneration of red cells. Herbs used with success: Echinacea, Gentian, Motherwort, Mugwort, Barberry, Hops, Nettles, Saw Palmetto, Chaparral, Red Clover, Dandelion.

Bitter herbs stimulate absorption of vital nutrients from the stomach, toning liver and pancreas, increasing the appetite; usually given half hour before meals. See: BITTERS.

Gentian. 1 teaspoon fine-cut chips to 2 cups cold water steeped 8 hours (overnight). Dose: Half-1 cup thrice daily before meals.

Tea. Formula. Combine: Agrimony 1; Barberry bark 1; Nettles 2; White Poplar bark half. Place 1oz (30g) in 1 pint (500ml) cold water and bring to boil. Simmer 10 minutes. Drink cold: Half-1 cup thrice daily, before meals.

Powders. Formula. Echinacea 2; Gentian 1; Kelp 1; pinch Red Pepper. Dose: 500mg (two 00 capsules or one-third teaspoon) thrice daily, before meals.

Liquid extracts. Formula: Echinacea 1; Queen’s Delight 1; Ginseng 1; Ginger quarter. Dose: 30-60 drops in water, thrice daily, before meals.

Infusion Gentian Co Conc BP (1949). Dose: 30-60 drops.

Diet. Dandelion coffee, as desired. Molasses. Desiccated liver.

Floradix. A pre-digested iron preparation. Readily assimilable by the body. Compounded by Dr Otto Greither (Salus Haus). Iron is fed onto yeast which breaks down the metal and absorbs its cells. Other tonic ingredients include extracts of nettles, carrots, spinach, fennel, Vitamin C plus supplements;

Angelica root, Mallow, Horsetail, Yarrow, Juniper and Rosehips. Not chemically preserved.

Avoid chocolate, egg yolk, tea, coffee, wheat bran.

Supplements. Daily. Vitamin C (1g morning and evening). Vitamin B12, Folic acid 400mcg. Vitamin C is the most potent enhancer of iron absorption. Multivitamin containing iron.

Note: Iron absorption is decreased by antacids, tetracyclines, phosphates, phytates (phytic acid from excessive intake of wholewheat bread), and excessive calcium supplements. Lack of stomach hydrochloric acid impairs iron absorption, especially in the elderly. ... anaemia: iron deficiency

Bile Secretion Deficiency

Bile is a greenish-yellow alkaline substance secreted by the liver which emulsifies fat and prevents putrefaction in the intestines. An aid to pancreatic juices.

Alternatives. To stimulate flow, Boldo, Horsetail, Dandelion, Blue Flag root, Milk Thistle, Bogbean, Burdock. Teas, capsules, tablets, Liquid extracts, or Tinctures.

A. Vogel recommends: Barberry, Centuary, St John’s Wort, Sarsaparilla.

Combination tea. Equal parts: Peppermint leaves, Milk Thistle, Dandelion root. 1 teaspoon to each cup boiling water; infuse 15 minutes, 1 cup thrice daily for limited period (1 month).

Bile in the urine. (Bilviria)

Arthur Barker: Liquid Extract Black root 1oz (30ml). Liquid Extract Cornsilk 1oz (30ml). Essential Peppermint 30 drops (2ml). Water to 8oz (240ml). 2 teaspoons in water 3 times daily before meals.

Diet. Dandelion coffee. Artichokes.

See: CHOLAGOGUES. CHOLERETICS. ... bile secretion deficiency

Acquired Immune Deficiency Syndrome

see AIDS.... acquired immune deficiency syndrome

Ada Deficiency

see adenosine deaminase deficiency.... ada deficiency

Adenosine Deaminase Deficiency

(ADA deficiency) a genetic disorder affecting about one baby in 25,000 and characterized by a defect in adenosine deaminase (ADA), an enzyme that is involved in purine metabolism. Deficiency of this enzyme results in selective damage to the antibody-producing lymphocytes; this in turn leads to a condition known as *severe combined immune deficiency (SCID), in which the affected baby has no resistance to infection and must be entirely isolated from birth. Such children have only about a 50% chance of surviving for six months. See also gene therapy.... adenosine deaminase deficiency

Anaemia, Iron-deficiency

The most common form of anaemia caused by a deficiency of iron, an essential constituent of haemoglobin. The main cause of iron-deficiency anaemia is iron loss due to heavy or persistent bleeding; the most common cause in women of childbearing age is menstruation. Other causes include blood loss from the digestive tract due to disorders such as erosive gastritis, peptic ulcer, stomach cancer, inflammatory bowel disease, haemorrhoids, and bowel tumours (see colon, cancer of). Prolonged use of aspirin and other nonsteroidal anti-inflammatory drugs (NSAIDs) can cause gastrointestinal bleeding. In some countries, hookworm infestation of the digestive tract is an important cause of anaemia. Rarely, bleeding may also occur as a result of disorders of the urinary tract (such as kidney tumours or bladder tumours).

Iron deficiency may also be caused or worsened by lack of iron in, or its poor absorption from, the diet.

The symptoms are those of the underlying cause, along with a sore mouth or tongue, and those common to all forms of anaemia, such as fatigue and breathlessness. The diagnosis is made from blood tests and tests to look for an underlying cause. Treatment is given for the cause, along with a course of iron tablets or, very rarely, injections.... anaemia, iron-deficiency

Colour Vision

The ability to see different parts of the colour spectrum. Light perceived by the human eye consists of electromagnetic radiation (energy waves) with a spectrum of different wavelengths

between about 400 and 700 nanometres. Different wavelengths produce sensations of violet, indigo, blue, green, yellow, orange, and red when they fall on the retina and stimulate nerve signals, which are processed in the brain.

As light falls on the retina, it strikes light-sensitive cells called rods and cones. The rods can detect all visible light, but only the cones can distinguish colour. There are 3 types of cones: red-sensitive, blue-sensitive, and green-sensitive. Each responds more strongly to a particular part of the light spectrum. Because the cones are most concentrated in a central area of the retina called the fovea, colour vision is most accurate for objects viewed directly and is poor at the edges of vision. When light hits a cone, it causes the cone to emit an electrical signal, which passes to the brain via the optic nerve. Colour perception requires a minimum level of light, below which everything is seen as shades of grey. (See also colour vision deficiency; eye; perception; vision.)... colour vision

Vision, Loss Of

Inability to see. This may develop slowly or suddenly and may be temporary or permanent, depending on the cause. Vision loss may affect 1 or both eyes. It can cause complete blindness or may affect only peripheral, or only central, vision.

Progressive loss of visual clarity is common with advancing age and may be due to a number of disorders (see vision, disorders of).

Sudden loss of vision may be caused by disorders such as hyphaema, severe uveitis, vitreous haemorrhage, or retinal haemorrhage.

Optic neuritis can reduce vision in 1 eye.

Damage to the nerve connections between the eyes and brain, or to the visual area of the brain, can cause loss of peripheral vision and may be a result of embolism, ischaemia, tumour, inflammation, or injury.... vision, loss of

Binocular Vision

the ability to focus both eyes on an object at the same time, so that a person sees one image of the object he is looking at. It is not inborn, but acquired during the first few months of life. Binocular vision enables judgment of distance and perception of depth. See also stereoscopic vision.... binocular vision

Colour Flow Ultrasound Imaging

see Doppler ultrasound.... colour flow ultrasound imaging

Deficiency

n. (in genetics) see deletion.... deficiency

Deficiency Disease

any disease caused by the lack of an essential nutrient in the diet. Such nutrients include *vitamins, minerals, *essential amino acids, and *essential fatty acids.... deficiency disease

Field Of Vision

see visual field.... field of vision

Harlequin Colour Change

an unusual phenomenon in newborn babies characterized by transient red colour changes to half of the body, well demarcated at the midline. It is seen usually 2–5 days after birth and can last from 30 seconds to 20 minutes before fading away. It may recur when the infant is placed on his or her side as the intensity of the erythema appears to be gravity-dependent.... harlequin colour change

Severe Combined Immune Deficiency

(SCID) a rare disorder that usually manifests itself within the first three months of life by severe bacterial, fungal, and viral infection and *failure to thrive. It is due to reduced numbers of T and B *lymphocytes – white blood cells necessary for fighting infection. Some cases are caused by *adenosine deaminase deficiency. The only treatment currently available is a bone-marrow transplant, but *gene therapy offers hope for the future.... severe combined immune deficiency

Stereoscopic Vision

(stereopsis) perception of the shape, depth, and distance of an object as a result of having *binocular vision. The brain receives two distinct images from the eyes, which it interprets as a single three-dimensional image.... stereoscopic vision

Glucose-6-phosphate Dehydrogenase Deficiency

a hereditary disorder – an X-linked condition (see sex-linked) – in which the absence of the enzyme glucose-6-phosphate dehydrogenase (G6PD), which functions in carbohydrate metabolism, results in the breakdown of the red blood cells (*haemolysis), usually after exposure to *oxidants, such as drugs, or infections. The breakdown causes acute attacks that are characterized by pallor, loin pain, and rigors. There are several varieties of G6PD deficiency, which is most common in people of African, Middle Eastern, and Mediterranean descent. Treatment involves identifying and avoiding agents that trigger the haemolysis and treating acute attacks symptomatically. See also favism.... glucose-6-phosphate dehydrogenase deficiency

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