Xerophthalmia
Encyclopedia
Xerophthalmia is a medical condition in which the eye
fails to produce tears
. It may be caused by a deficiency in vitamin A
and is sometimes used to describe that lack, although there may be other causes.
Xerophthalmia caused by a severe vitamin A deficiency is described by pathologic dryness of the conjunctiva
and cornea. The conjunctiva
becomes dry, thick and wrinkled. If untreated, it can lead to corneal ulceration and ultimately to blindness
as a result of corneal damage.
Xerophthalmia is a term that usually implies a destructive dryness of the conjunctival epithelium
due to dietary vitamin A deficiency — a rare condition in developed countries, but still causing much damage in developing countries. Other forms of dry eye are associated with aging, poor lid closure, scarring from previous injury, or autoimmune diseases such as rheumatoid arthritis
and Sjögren's syndrome
, and these can all cause chronic conjunctivitis
. Radioiodine therapy can also induce xerophthalmia, often transiently, although in some patients late onset or persistent xerophthalmia has been observed.
The damage to the cornea in vitamin A associated xerophthalmia is quite different from damage to the retina
at the back of the globe, a type of damage which can also be due to lack of vitamin A, but which is caused by lack of other forms of vitamin A which work in the visual system. Xerophthalmia from hypovitaminosis A is specifically due to lack of the hormone-like vitamin A metabolite retinoic acid
, since (along with certain growth-stunting effects) the condition can be reversed in vitamin A deficient rats by retinoic acid supplementation (however the retinal damage continues). Since retinoic acid cannot be reduced to retinal
or retinol
, these effects on the cornea must be specific to retinoic acid. This is in keeping with retinoic acid's known requirement for good health in epithelial cells, such as those in the cornea.
, which are clumps of keratin
debris that build up inside the conjunctiva and night blindness, which precedes corneal ulceration and total blindness.
Human eye
The human eye is an organ which reacts to light for several purposes. As a conscious sense organ, the eye allows vision. Rod and cone cells in the retina allow conscious light perception and vision including color differentiation and the perception of depth...
fails to produce tears
Tears
Tears are secretions that clean and lubricate the eyes. Lacrimation or lachrymation is the production or shedding of tears....
. It may be caused by a deficiency in vitamin A
Vitamin A
Vitamin A is a vitamin that is needed by the retina of the eye in the form of a specific metabolite, the light-absorbing molecule retinal, that is necessary for both low-light and color vision...
and is sometimes used to describe that lack, although there may be other causes.
Xerophthalmia caused by a severe vitamin A deficiency is described by pathologic dryness of the conjunctiva
Xerosis
Xerosis cutis is the medical term for dry skin.It can have many different causes, including general dehydration, atopic dermatitis, Vitamin A deficiency, and maybe diabetes. Treatment is primarily symptomatic. "Xero", meaning dry or dehydrated, "osis" usually referring to a medical disease or...
and cornea. The conjunctiva
Conjunctiva
The conjunctiva covers the sclera and lines the inside of the eyelids. It is composed of rare stratified columnar epithelium.-Function:...
becomes dry, thick and wrinkled. If untreated, it can lead to corneal ulceration and ultimately to blindness
Blindness
Blindness is the condition of lacking visual perception due to physiological or neurological factors.Various scales have been developed to describe the extent of vision loss and define blindness...
as a result of corneal damage.
Xerophthalmia is a term that usually implies a destructive dryness of the conjunctival epithelium
Epithelium
Epithelium is one of the four basic types of animal tissue, along with connective tissue, muscle tissue and nervous tissue. Epithelial tissues line the cavities and surfaces of structures throughout the body, and also form many glands. Functions of epithelial cells include secretion, selective...
due to dietary vitamin A deficiency — a rare condition in developed countries, but still causing much damage in developing countries. Other forms of dry eye are associated with aging, poor lid closure, scarring from previous injury, or autoimmune diseases such as rheumatoid arthritis
Rheumatoid arthritis
Rheumatoid arthritis is a chronic, systemic inflammatory disorder that may affect many tissues and organs, but principally attacks synovial joints. The process produces an inflammatory response of the synovium secondary to hyperplasia of synovial cells, excess synovial fluid, and the development...
and Sjögren's syndrome
Sjögren's syndrome
Sjögren's syndrome , also known as "Mikulicz disease" and "Sicca syndrome", is a systemic autoimmune disease in which immune cells attack and destroy the exocrine glands that produce tears and saliva....
, and these can all cause chronic conjunctivitis
Conjunctivitis
Conjunctivitis refers to inflammation of the conjunctiva...
. Radioiodine therapy can also induce xerophthalmia, often transiently, although in some patients late onset or persistent xerophthalmia has been observed.
The damage to the cornea in vitamin A associated xerophthalmia is quite different from damage to the retina
Retina
The vertebrate retina is a light-sensitive tissue lining the inner surface of the eye. The optics of the eye create an image of the visual world on the retina, which serves much the same function as the film in a camera. Light striking the retina initiates a cascade of chemical and electrical...
at the back of the globe, a type of damage which can also be due to lack of vitamin A, but which is caused by lack of other forms of vitamin A which work in the visual system. Xerophthalmia from hypovitaminosis A is specifically due to lack of the hormone-like vitamin A metabolite retinoic acid
Retinoic acid
Retinoic acid is a metabolite of vitamin A that mediates the functions of vitamin A required for growth and development. Retinoic acid is required in chordate animals which includes all higher animals from fishes to humans...
, since (along with certain growth-stunting effects) the condition can be reversed in vitamin A deficient rats by retinoic acid supplementation (however the retinal damage continues). Since retinoic acid cannot be reduced to retinal
Retinal
Retinal, also called retinaldehyde or vitamin A aldehyde, is one of the many forms of vitamin A . Retinal is a polyene chromophore, and bound to proteins called opsins, is the chemical basis of animal vision...
or retinol
Retinol
Retinol is one of the animal forms of vitamin A. It is a diterpenoid and an alcohol. It is convertible to other forms of vitamin A, and the retinyl ester derivative of the alcohol serves as the storage form of the vitamin in animals....
, these effects on the cornea must be specific to retinoic acid. This is in keeping with retinoic acid's known requirement for good health in epithelial cells, such as those in the cornea.
Epidemiology and mechanical etiology
Xerophthalmia usually affects children under nine years old and "accounts for 20,000-100,000 new cases of childhood blindness each year in the developing countries." The disease is largely found in developing countries like many of those in Africa and Southern Asia. The condition is not congenital and develops over the course of a few months as the lacrimal glands fail to produce tears. Other conditions involved in the progression already stated include the appearance of Bitot's spotsBitot's spots
Bitot's spots are the buildup of keratin debris located superficially in the conjunctiva, which are oval, triangular or irregular in shape. These spots are a sign of vitamin A deficiency and are associated with conjunctival xerosis...
, which are clumps of keratin
Keratin
Keratin refers to a family of fibrous structural proteins. Keratin is the key of structural material making up the outer layer of human skin. It is also the key structural component of hair and nails...
debris that build up inside the conjunctiva and night blindness, which precedes corneal ulceration and total blindness.
Treatment
Treatment can occur in two ways: treating symptoms and treating the deficiency. Treatment of symptoms usually includes use of artificial tears in the form of eye drops, increasing the humidity of the environment with humidifiers, and wearing wrap around glasses when outdoors. Treatment of the deficiency can be accomplished with a Vitamin A or multivitamin supplement or by eating foods rich in Vitamin A. Treatment with supplements and/or diet can be successful until the disease progresses as far as corneal ulceration, at which point only an extreme surgery can offer a chance of returning sight.Prophylaxis
Prophylaxis consists of periodic administration of Vitamin A supplements. WHO recommended schedule, which is universally recommended is as follows :- Infants 6-12 months old and any older children weighing less than 8 kg - 100,000 IU orally every 3-6 months
- Children over 1 year and under 6 years of age - 200,000 IU orally every 6 months
- Infants less than 6 months old, who are not being breastfed - 50,000 IU orally should be given before they attain the age of 6 months
See also
- KeratoconjunctivitisKeratoconjunctivitisKeratoconjunctivitis is inflammation of the cornea and conjunctiva.When only the cornea is inflamed, it is called keratitis; when only the conjunctiva is inflamed, it is called conjunctivitis....
- Keratoconjunctivitis siccaKeratoconjunctivitis siccaKeratoconjunctivitis sicca , also called keratitis sicca, xerophthalmia or dry eye syndrome is an eye disease caused by eye dryness, which, in turn, is caused by either decreased tear production or increased tear film evaporation. It is found in humans and some animals...
- KeratomalaciaKeratomalaciaKeratomalacia is an eye disorder that leads to a dry cornea. One of its major causes is Vitamin A deficiency. When xerophthalmia persists for a long time, it results in keratomalacia. There is degradation of corneal epithelium which may also get vascularised. Later corneal opacities develop...
, also caused by vitamin A deficiency.
Further reading
- Medicine.Net. "Definition of Xerophthalmia." 26 May 2003. http://www.medterms.com/script/main/art.asp?articlekey=6040.
- Jellife DB. "Xerophthalmia: A World-wide Drive for Prevention." Journal of Tropical Pediatrics 1980; 26: ii-iii. 4 November 2009. http://tropej.oxfordjournals.org/cgi/pdf_extract/26/4/131.