NationMaster - Encyclopedia: Astigmatism (eye)

Astigmatism is an affliction of the eye, where vision is blurred by an irregularly shaped cornea. The cornea, instead of being shaped like a sphere, is more oval-like and reduces the cornea's ability to focus light. Astigmatism is a refractive error of the eye in which there is a difference in degree of refraction in different meridians. So, rather than the surface topology of the eye being spherical, it has two curves, one steeper than the other, in a similar way to the shape of an oval. The condition is typically characterized by an aspherical, non-figure of revolution cornea in which the corneal profile slope and refractive power in one meridian is greater than that of the perpendicular axis. Astigmatism causes difficulties in seeing fine detail, and can often be corrected by prosthetic lenses with a cylindrical lens (i.e. a lens that has different radii of curvature in different planes), contact lenses, or refractive surgery. The International Statistical Classification of Diseases and Related Health Problems (most commonly known by the abbreviation ICD) provides codes to classify diseases and a wide variety of signs, symptoms, abnormal findings, complaints, social circumstances and external causes of injury or disease. ... The following codes are used with International Statistical Classification of Diseases and Related Health Problems. ... // H00-H59 - Diseases of the eye and adnexa (H00-H06) Disorders of eyelid, lacrimal system and orbit (H00) Hordeolum and chalazion (H000) Hordeolum and other deep inflammation of eyelid (H001) Chalazion (H01) Other inflammation of eyelid (H010) Blepharitis (H011) Noninfectious dermatoses of eyelid (H02) Other disorders of eyelid (H020) Entropion... The International Statistical Classification of Diseases and Related Health Problems (most commonly known by the abbreviation ICD) provides codes to classify diseases and a wide variety of signs, symptoms, abnormal findings, complaints, social circumstances and external causes of injury or disease. ... The following is a list of codes for International Statistical Classification of Diseases and Related Health Problems. ... Refraction error, also known as refractive error, is an error in the focusing of light by the eye and a frequent reason for reduced visual acuity. ... A human eye. ... The straw seems to be broken, due to refraction of light as it emerges into the air. ... A MÃ¶bius strip, an object with only one surface and one edge; such shapes are an object of study in topology. ... For other uses, see sphere (disambiguation). ... In geometry, an oval or ovoid (from Latin ovum, egg) is any curve resembling an egg or an ellipse. ... The cornea is the transparent front part of the eye that covers the iris, pupil, and anterior chamber, providing most of an eyes optical power [1]. Together with the lens, the cornea refracts light and, as a result, helps the eye to focus. ... Look up Slope in Wiktionary, the free dictionary. ... A right circular cylinder An elliptic cylinder In mathematics, a cylinder is a quadric surface, with the following equation in Cartesian coordinates: This equation is for an elliptic cylinder, a generalization of the ordinary, circular cylinder (a = b). ... A lens. ... A pair of contact lenses when not inserted in the eye. ... Refractive eye surgery is any eye surgery used to improve the refractive state of the eye and decrease dependency on glasses or contact lenses. ...

Astigmatism occurs when either the cornea or the lens of the eye is not a figure of revolution or, in other words, is not perfectly smooth or round. As a result, the eye has different focal points in different planes. For example, the image may be clearly focused on the retina in the horizontal (sagittal) plane, but not in front of the retina in the vertical (tangential) plane. Light from a single point of a distant object and light from a single point of a near object being brought to a focus by changing the curvature of the lens. ... Human eye cross-sectional view. ...

In some cases vertical lines (e.g., walls) may appear to the patient to be leaning over like the tower of Pisa. This article or section does not adequately cite its references or sources. ...

Types of astigmatism

Image File history File links I created this image myself. ... Image File history File links I created this image myself. ...

Based on asymmetry of structure

Based on Axis of the Principal Meridians

Based on focus of the principal meridians

Prevalence

According to an American study published in Archives of Ophthalmology, nearly 3 in 10 children between the ages of 5 and 17 have astigmatism [1]. A recent Brazilian study found that 34% of the students in one city were astigmatic [2]. Regarding the prevalence in adults, a recent study in Bangladesh found that nearly 1 in 3 (32.4%) of those over the age of 30 had astigmatism[3].

A recent Polish study revealed that "with-the-rule astigmatism" may lead to the onset of myopia[4]. Normal vision. ...

A number of studies have found that the prevalence of astigmatism increases with age[5].

Diagnosis

Symptoms

Although mild astigmatism may be asymptomatic, higher amounts of astigmatism may cause symptoms such as blurry vision, squinting, asthenopia, fatigue, or headaches.^[1]^[2]^[3] Asthenopia is an ophthalmological condition that manifests itself through unspecific symptoms such as fatigue, eye strain, pain in or around the eyes, blurred vision, headache and occasional double vision. ...

Signs and tests

There are a number of tests used by ophthalmologists and optometrists during eye examinations to determine the presence of astigmatism and to quantify the amount and axis of the astigmatism.^[4] A Snellen chart or other eye chart may initially reveal reduced visual acuity. A keratometer may be used to measure the curvature of the steepest and flattest meridians in the cornea's front surface.^[5] A corneal topographer may also be used to obtain a more accurate representation of the cornea's shape.^[6] An autorefractor or retinoscopy may provide an objective estimate of the eye's refractive error and the use of Jackson cross cylinders in a phoropter may be used to subjectively refine those measurements[6] [7] [8]. An alternative technique with the phoropter requires the use of a "clock dial" or "sunburst" chart to determine the astigmatic axis and power.^[7]^[8] Ophthalmology is the branch of medicine which deals with the diseases of the eye and their treatment. ... Optometrists are primary care practitioners for vision and ocular health concerns. ... Traditional Snellen chart used for visual acuity testing. ... Traditional Snellen chart. ... Traditional Snellen chart. ... Traditional Snellen chart used for visual acuity testing. ... A keratometer, also known as a ophthalmometer, is a surgical device for measuring the curvature of the anterior surface of the cornea, particularly for assessing the extent and axis of astigmatism. ... An automated refractor, or autorefractor, is a computer-controlled machine used during an eye examination to provide an objective measurement of a persons refractive error and prescription for glasses or contact lenses. ... Retinoscopy is a technique to obtain an objective measurement of the refractive condition of a patients eye. ... A refractor in use The name and shape of the PHOROPTORÂ® is a registered trademark of Reichert, Inc. ...

Treatment

Astigmatism may be corrected with eyeglasses, contact lenses, or refractive surgery. Various considerations involving ocular health, refractive status, and lifestyle frequently determine whether one option may be better than another. In those with keratoconus, rigid gas permeable contact lenses often enable patients to achieve better visual acuities than eyeglasses. If the astigmatism is caused by a problem such as deformation of the eyeball due to a Chalazion, treating the underlying cause will resolve the astigmatism. Keratoconus (from Greek: kerato- horn, cornea; and konos cone), is a degenerative non-inflammatory disorder of the eye in which structural changes within the cornea cause it to thin and change to a more conical shape than its normal gradual curve. ... Traditional Snellen chart used for visual acuity testing. ... A chalazion, also known as a Meibomian gland lipogranuloma, is a cyst in the eyelid that is caused by inflammation of the meibomian gland, usually on the upper eyelid. ...

References

See also

Related conditions

Hyperopia, also known as hypermetropia or colloquially as farsightedness or longsightedness, is a defect of vision caused by an imperfection in the eye (often when the eyeball is too short or when the lens cannot become round enough), causing inability to focus on near objects, and in extreme cases causing... Keratoconus (from Greek: kerato- horn, cornea; and konos cone), is a degenerative non-inflammatory disorder of the eye in which structural changes within the cornea cause it to thin and change to a more conical shape than its normal gradual curve. ... Normal vision. ... Presbyopia is the eyes diminished power of accommodation that occurs with aging. ...

Other

An eyeglass prescription is a written order by an ophthalmologist or an optometrist to an optician for eyeglasses. ... Refractive eye surgery is any eye surgery used to improve the refractive state of the eye and decrease dependency on glasses or contact lenses. ... A lens. ... This does not adequately cite its references or sources. ... An optician is an individual who makes and adjusts optical aids. ... Optometry (Greek: optos meaning seen or visible and metria meaning measurement) is the health care profession concerned with examination, diagnosis, and treatment of the eyes and related structures and with determination and correction of vision problems using lenses and other optical aids [1]. An optical refractor (also called a phoropter...

External links

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Pathology of the eye (primarily H00-H59)

eyelid, lacrimal system and orbit: Stye - Chalazion - Blepharitis - Entropion - Ectropion - Lagophthalmos - Blepharochalasis - Ptosis - Xanthelasma Pathology (from Greek pathos, feeling, pain, suffering; and logos, study of; see also -ology) is the study of the processes underlying disease and other forms of illness, harmful abnormality, or dysfunction. ... A human eye. ... A stye (also spelled sty) or hordeolum is an infection of the sebaceous glands at the base of the eyelashes. ... A chalazion, also known as a Meibomian gland lipogranuloma, is a cyst in the eyelid that is caused by inflammation of the meibomian gland, usually on the upper eyelid. ... Blepharitis is inflammation of the eyelids. ... Entropion is a medical condition in which the eyelids fold inward. ... Ectropion is a condition of loose eyelids. ... Lagophthalmos describes difficulty in complete closure of the eyelid over the eyeball. ... Blepharochalasis is an inflammation of the eyelid that is characterized by exacerbations and remissions of eyelid edema, which results in a stretching and subsequent atrophy of the eyelid tissue. ... In ophthalmology, ptosis is an abnormally low position (drooping) of the upper eyelid. ... Xanthelasma (or xanthelasma palpebrarum) are sharply demarcated yellowish collections of cholesterol underneath the skin, usually around the eyes. ...

conjunctiva: Conjunctivitis - Pterygium - Subconjunctival hemorrhage A pterygium, meaning wing, is a benign growth of the conjunctiva. ... A subconjunctival hemorrhage is a common and relatively minor post-LASIK complication. ...

sclera, cornea, iris and ciliary body: Scleritis - Keratitis - Corneal ulcer - Snow blindness - Thygeson's superficial punctate keratopathy - Fuchs' dystrophy - Keratoconus - Keratoconjunctivitis sicca - Iritis - Uveitis Scleritis is a serious inflammatory disease that affects the white outer coating of the eye, known as the sclera. ... A corneal ulcer is an inflammatory condition of the cornea involving loss of its outer layer. ... Snowblind redirects here. ... Thygesons superficial punctate keratopathy (TSPK) is a disease of the eyes. ... Fuchs dystrophy is a slowly progressing corneal disease that usually affects both eyes and is slightly more common in women than in men. ... Keratoconus (from Greek: kerato- horn, cornea; and konos cone), is a degenerative non-inflammatory disorder of the eye in which structural changes within the cornea cause it to thin and change to a more conical shape than its normal gradual curve. ... Keratoconjunctivitis sicca (KCS), also called keratitis sicca,[1] sicca syndrome,[1] xerophthalmia,[1] dry eye syndrome (DES),[1] or simply dry eyes,[1] is an eye disease caused by decreased tear production or increased tear film evaporation commonly found in humans and some animals[2]. Keratoconjunctivitis sicca is Latin and... Iritis is a form of anterior uveitis and refers to the inflammation of the iris of the eye. ... Uveitis specifically refers to inflammation of the middle layer of the eye, termed the uvea but in common usage may refer to any inflammatory process involving the interior of the eye. ...

lens: Cataract Human eye cross-sectional view, showing position of human lens. ...

choroid and retina: Retinal detachment - Retinoschisis - Hypertensive retinopathy - Diabetic retinopathy - Retinopathy - Retinopathy of prematurity - Macular degeneration - Retinitis pigmentosa - Macular edema Retinal detachment is a disorder of the eye in which the retina peels away from its underlying layer of support tissue. ... Retinoschisis is an uncommon eye disease characterized by the abnormal splitting of the retinas sensory layers, usually in the outer plexiform layer, with resulting loss of visual function [1]. The retina, which consists of multiple layers of interconnected nerve and pigment cells, separates into separate layers resulting in a... Hypertension, or high blood pressure that does not respond to treatment, has several ocular manifestations. ... Diabetic retinopathy is retinopathy (damage to the retina) caused by complications of diabetes mellitus, which could eventually lead to blindness. ... Retinopathy is a general term that refers to some form of non-inflammatory damage to the retina of the eye. ... Retinopathy of prematurity (ROP), previously known as retrolental fibroplasia (RLF), is a disease of the eye that affects prematurely born babies. ... Listen to this article Â· (info) Â· play in browser This audio file was created from an article revision dated 2005-07-19, and may not reflect subsequent edits to the article. ... Normal vision. ... Macular edema occurs when fluid and protein deposits collect on or under the macula, causing it to thicken and swell. ...

ocular muscles, binocular movement, accommodation and refraction: Strabismus - Ophthalmoparesis - Progressive external ophthalmoplegia - Esotropia - Exotropia - Refractive error - Hyperopia - Myopia - Astigmatism - Anisometropia - Presbyopia For the protein Strabismus, see Strabismus (protein) Strabismus, also known as heterotropia, squint, crossed eye, cockeyed, wandering eye,weak eye or wall eyed, is a condition in which the eyes are not properly aligned with each other. ... Ophthalmoparesis is a physical finding in certain neurologic illnesses. ... Progressive external ophthalmoplegia is a disorder of the mitochondria. ... Person exhibiting esotropia of the right eye Esotropia is a form of strabismus where one or both of the eyes turn inward. ... Exotropia is a form of strabismus where the eyes are deviated outward. ... Refraction error, also known as refractive error, is an error in the focusing of light by the eye and a frequent reason for reduced visual acuity. ... Hyperopia, also known as hypermetropia or colloquially as farsightedness or longsightedness, is a defect of vision caused by an imperfection in the eye (often when the eyeball is too short or when the lens cannot become round enough), causing inability to focus on near objects, and in extreme cases causing... Normal vision. ... Anisometropia is a condition in which the lenses of the two eyes have different focal lengths; that is, are in different states of myopia (nearsightedness) and hyperopia (farsightedness). ... Presbyopia is the eyes diminished power of accommodation that occurs with aging. ...

Visual disturbances and blindness: Amblyopia - Leber's congenital amaurosis - Scotoma - Color blindness - Achromatopsia - Nyctalopia - Blindness Amblyopia, or lazy eye, is a disorder of the eye. ... Lebers congenital amaurosis is a rare inherited eye disease that appears at birth or in the first few months of life, typically characterized by nystagmus, sluggish or no pupillary responses, and severe vision loss or blindness. ... The word scotoma is derived from the Greek word for darkness. ... Color blindness in humans is the inability to perceive differences between some or all colors that other people can distinguish. ... Achromatopsia is the inability to see color. ... Nyctalopia (Greek for night blindness) is a condition making it difficult or impossible to see in the dark. ... Blindness is the condition of lacking visual perception due to physiological or psychological factors. ...

Commonly associated infectious diseases: Trachoma Onchocerciasis Binomial name Onchocerca volvulus Bickel 1982 Onchocerciasis (pronounced ) or river blindness is the worlds second leading infectious cause of blindness. ...

Other: Glaucoma - Floater - Leber's hereditary optic neuropathy - Red eye - Argyll Robertson pupil - Keratomycosis - Xerophthalmia - Aniridia For other uses, see Floater (disambiguation). ... Leberâ€™s hereditary optic neuropathy (LHON) or Leber optic atrophy is a mitochondrially inherited (mother to all offspring) form of acute or subacute loss of central vision that may lead to degeneration of retinal ganglion cells (RGCs) and their axons; this affects predominantly young adult males. ... Many primary care physicians often deal with patients with red eyes In medicine, red eye is a non-specific term to describe an eye that appears red due to illness, injury, or some other condition. ... In medical terminology, Argyll Robertson pupils are small, irregular pupils that accommodate but do not react normally to light. ... A fungal keratitis is an inflammation of the eyes cornea (called keratitis) that results from infection by a fungal organism. ... Xerophthalmia (Greek for dry eyes) is a medical condition in which the eye doesnt produce tears. ... Aniridia is a rare congenital condition characterized by the underdevelopment of the eyes iris. ...

Contents

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