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. Keratoconus can cause substantial distortion of vision, with multiple images, streaking and sensitivity to light all often reported by the patient. Keratoconus is the most common dystrophy of the cornea, affecting around one person in a thousand, and it seems to occur in populations throughout the world, although some ethnic groups experience a greater prevalence than others. It is typically diagnosed in the patient's adolescent years and attains its most severe state in the twenties and thirties. Image File history File links Download high resolution version (527x800, 234 KB) Courtesy of Indiana University School of Medicine, Department of Ophthalmology File history Legend: (cur) = this is the current file, (del) = delete this old version, (rev) = revert to this old version. ... 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 International Statistical Classification of Diseases and Related Health Problems 10th Revision (ICD-10) is a coding of diseases and signs, symptoms, abnormal findings, complaints, social circumstances and external causes of injury or diseases, as classified by the World Health Organization (WHO). ... // 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. ... The Mendelian Inheritance in Man project is a database that catalogues all the known diseases with a genetic component, and - when possible - links them to the relevant genes in the human genome. ... The Disease Bold textDatabase is a free website that provides information about the relationships between medical conditions, symptoms, and medications. ... MedlinePlus (medlineplus. ... eMedicine is an online clinical medical knowledge base that was founded in 1996. ... An abscess on the skin, showing the redness and swelling characteristic of inflammation. ... For other uses, see Eye (disambiguation). ... 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. ... This article is about the geometric object, for other uses see Cone. ... In mathematics, the concept of a curve tries to capture the intuitive idea of a geometrical one-dimensional and continuous object. ... This does not cite any references or sources. ... Photophobia (also light sensitivity) or fear of light, is a symptom of excessive sensitivity to light and the aversion to sunlight or well-lit places. ... Dystrophy is any condition of abnormal development, usually due to malnutrition, especially denoting the degeneration of muscles (muscular dystrophy). ... “Adolescent” redirects here. ...

Keratoconus is a little-understood disease with an uncertain cause, and its progression following diagnosis is unpredictable. If afflicting both eyes, the deterioration in vision can affect the patient's ability to drive a car or read normal print. In most cases, corrective lenses are effective enough to allow the patient to continue to drive legally and likewise function normally. Further progression of the disease may require surgery including transplantation of the cornea. Despite its uncertainties, keratoconus can be successfully managed with a variety of clinical and surgical techniques, and often with little or no impairment to the patient's quality of life. In general, a diagnosis (plural diagnoses) has two distinct dictionary definitions. ... A bifocal corrective eyeglasses lens A corrective lens is a lens worn on or before the eye, used to treat myopia, hyperopia, astigmatism, and presbyopia. ... “Surgeon” redirects here. ...

History

Practical observations on conical cornea, Nottingham's ground-breaking text on keratoconus, 1854

In a 1748 doctoral dissertation, the German oculist Burchard Mauchart provided an early description of a case of keratoconus,^[1] which he called staphyloma diaphanum. However, it was not until 1854 that British physician John Nottingham clearly described keratoconus and distinguished it from other ectasias of the cornea.^[1] Nottingham reported the cases of "conical cornea" that had come to his attention, and described several classic features of the disease, including polyopia, weakness of the cornea, and difficulty matching corrective lenses to the patient's vision.^[2] In 1859 British surgeon William Bowman used an ophthalmoscope (recently invented by Hermann von Helmholtz) to diagnose keratoconus, and described how to angle the instrument's mirror so as to best see the conical shape of the cornea.^[3] Bowman also attempted to restore the vision by pulling on the iris with a fine hook inserted through the cornea and stretching the pupil into a vertical slit, like that of a cat. He reported that he had had a measure of success with the technique, restoring vision to an 18-year old woman who had previously been unable to count fingers at a distance of 8 inches (20 cm). By 1869, when the pioneering Swiss ophthalmologist Johann Horner wrote a thesis entitled On the treatment of keratoconus,^[4] the disorder had acquired its current name. The treatment at that time, endorsed by the leading German ophthalmologist Albrecht von Gräfe, was an attempt to physically reshape the cornea by chemical cauterization with a silver nitrate solution and application of a miosis-causing agent with a pressure dressing.^[1] In 1888 the treatment of keratoconus became one of the first practical applications of the then newly-invented contact lens, when the French physician Eugène Kalt manufactured a glass scleral shell which improved vision by compressing the cornea into a more regular shape.^[5] Since the start of the twentieth century, research on keratoconus has both improved understanding of the disease and greatly expanded the range of treatment options. Image File history File links Download high resolution version (604x807, 44 KB) Summary Frontpiece of John Nottinghams 1854 Practical Observations on Conical Cornea, now more commonly known as keratoconus. ... Image File history File links Download high resolution version (604x807, 44 KB) Summary Frontpiece of John Nottinghams 1854 Practical Observations on Conical Cornea, now more commonly known as keratoconus. ... This article is about the branch of medicine. ... Burchard David Mauchart (1696-1751) was professor of anatomy and surgery at the University of Tübingen, Germany, and a pioneer in the field of ophthalmology. ... An aneurysm (or aneurism) (from Gr. ... Diplopia, commonly known as double vision, is the perception of two images from a single object. ... Sir William Bowman Sir William Bowman (July 20, 1816 - March 29, 1892) was a British surgeon and anatomist. ... The ophthalmoscope, invented by Hermann von Helmholtz, is an instrument used to examine the eye. ... Hermann Ludwig Ferdinand von Helmholtz (August 31, 1821 – September 8, 1894) was a German physician and physicist. ... In anatomy, the iris (plural irises or irides) is the most visible part of the eye of vertebrates, including humans. ... The human eye The pupil is the central transparent area (showing as black). ... Johann Friedrich Horner (born 27 March 1831, died 20 December 1886) was an ophthalmologist based at the University of Zurich, Switzerland. ... Albrecht von Gräfe (May 22, 1828 - July 20, 1870), German oculist, son of Karl Ferdinand von Gräfe, was born at Berlin. ... R-phrases , S-phrases , , , , Flash point non-flammable Supplementary data page Structure and properties n, εr, etc. ... Miosis should not be confused with meiosis, the cellular division process involved in sexual reproduction. ... A pair of contact lenses, positioned with the concave side facing upward. ... Eugène Kalt (1861-1941) was a French ophthalmologist who developed the first known application of a contact lens for the correction of keratoconus. ...

Features

Symptoms

A simulation of the multiple images seen by a person with keratoconus.
"... a candle, when looked at, appears like a number of lights, confusedly running into one another" — Nottingham^[2]

People with early keratoconus typically notice a minor blurring of their vision and come to their clinician seeking corrective lenses for reading or driving.^[6][7] At early stages, the symptoms of keratoconus may be no different from those of any other refractive defect of the eye. As the disease progresses, vision deteriorates, sometimes rapidly. Visual acuity becomes impaired at all distances, and night vision is often quite poor. Some individuals have vision in one eye that is markedly worse than that in the other eye. Some develop photophobia (sensitivity to bright light), eye strain from squinting in order to read, or itching in the eye.^[6] There is however normally little or no sensation of pain. Image File history File links Kc_simulation. ... Image File history File links Kc_simulation. ... Diplopia, commonly known as double vision, is the perception of two images from a single object. ... The term symptom (from the Greek meaning chance, mishap or casualty, itself derived from συμπιπτω meaning to fall upon or to happen to) has two similar meanings in the context of physical and mental health: Strictly, a symptom is a sensation or change in health function experienced by a patient. ... 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. ... Traditional Snellen chart used for visual acuity testing. ... Night-vision is seeing in the dark. ... Photophobia (also light sensitivity) or fear of light, is a symptom of excessive sensitivity to light and the aversion to sunlight or well-lit places. ... Asthenopia is an ophthalmological condition that manifests itself through nonspecific symptoms such as fatigue, red eyes, eye strain, pain in or around the eyes, blurred vision, headache and occasional double vision. ... An itch (Latin: pruritus) is an uncomfortable sensation felt on an area of skin that causes a person or animal to desire to scratch that area. ... “Hurting” redirects here. ...

The classic symptom of keratoconus is the perception of multiple 'ghost' images, known as monocular polyopia. This effect is most clearly seen with a high contrast field, such as a point of light on a dark background. Instead of seeing just one point, a person with keratoconus sees many images of the point, spread out in a chaotic pattern. This pattern does not typically change from day to day, but over time it often takes on new forms. Patients also commonly notice streaking and flaring distortion around light sources. Some even notice the images moving relative to one another in time with their heart beat. Diplopia, colloquially known as double vision, is the perception of two images from a single object. ... Left side of the image has low contrast, the right has higher contrast. ... Photograph of NASA lunar lander containing lens flare. ...

Signs and diagnosis

Prior to any physical examination, the diagnosis of keratoconus frequently begins with an ophthalmologist's or optometrist's assessment of the patient's medical history, particularly the chief complaint and other visual symptoms, the presence of any history of ocular disease or injury which might affect vision, and the presence of any family history of ocular disease. An eye chart, such as a standard Snellen chart of progressively smaller letters, is then used to determine the patient's visual acuity. The eye examination may proceed to measurement of the localised curvature of the cornea with a manual keratometer,^[8] with detection of irregular astigmatism suggesting a possibility of keratoconus. Severe cases can exceed the instrument's measuring ability.^[7] A further indication can be provided by retinoscopy, in which a light beam is focused on the patient's retina and the reflection, or reflex, observed as the examiner tilts the light source back and forth. Keratoconus is amongst the ophthalmic conditions that exhibit a scissor reflex action of two bands moving toward and away from each other like the blades of a pair of scissors.^[9][7] In medicine, the physical examination or clinical examination is the process by which the physician investigates the body of a patient for signs of disease. ... In general, a diagnosis (plural diagnoses) has two distinct dictionary definitions. ... 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. ... The medical history of a patient (sometimes called anamnesis [1][2] ) is information gained by a physician by asking specific questions, either of the patient or of other people who know the person and can give suitable information (in this case, it is sometimes called heteroanamnesis). ... The chief complaint (CC) is a concise statement describing the symptom, problem, condition, diagnosis, physician recommended return, or other factor that is the reason for a medical encounter[1]. See also Medical history Category: ... Traditional Snellen chart. ... Traditional Snellen chart. ... An optotype is a standardized symbol for testing vision. ... Traditional Snellen chart used for visual acuity testing. ... Traditional Snellen chart used for visual acuity testing. ... A keratometer, also known as a ophthalmometer, is a diagnostic instrument for measuring the curvature of the anterior surface of the cornea, particularly for assessing the extent and axis of astigmatism. ... Astigmatism is an affliction of the eye, where vision is blurred by an irregularly shaped cornea. ... Retinoscopy is a technique to obtain an objective measurement of the refractive condition of a patients eye. ... Human eye cross-sectional view. ... Different types of scissors - sewing, kitchen, paper Scissors are a tool used for cutting thin material which requires little force. ...

If keratoconus is suspected, the ophthalmologist or optometrist will search for other characteristic findings of the disease by means of slit lamp examination of the cornea.^[10] An advanced case is usually readily apparent to the examiner, and can provide for an unambiguous diagnosis prior to more specialised testing. Under close examination, a ring of yellow-brown to olive-green pigmentation known as a Fleischer ring can be observed in around half of keratoconic eyes.^[11] The Fleischer ring, caused by deposition of the iron oxide hemosiderin within the corneal epithelium, is subtle and may not be readily detectable in all cases, but becomes more evident when viewed under a cobalt blue filter.^[7] Similarly, around 50% of subjects exhibit Vogt's striae, fine stress lines within the cornea caused by stretching and thinning.^[11] The striae temporarily disappear while slight pressure is applied to the eyeball.^[7] A highly pronounced cone can create a V-shaped indentation in the lower eyelid when the patient's gaze is directed downwards, known as Munson's sign.^[6] Other clinical signs of keratoconus will normally have presented themselves long before Munson's sign becomes apparent,^[12] and so this finding, though a classic sign of the disease, tends not to be of primary diagnostic importance. 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. ... The slit-lamp examination looks at structures that are at the front of the eye (the anterior segment): The eyelid, the sclera (white outer structure of the eye), conjunctiva (membranes lining the eyelid and sclera surface), iris (colored part of the eye), natural crystalline lens, and the cornea (thin transparent... Fleischer rings are pigmented rings in the peripheral cornea, resulting from iron deposition in basal epithelial cells,. They are usually yellowish to dark-brown, and may be complete or broken. ... Hemosiderin Image of a kidney viewed under a microscope. ... Cobalt Blue is a DC Comics supervillain and an enemy to the Flash. ... A thin, narrow groove or channel, or a thin line or band especially if several of them are parallel or close together. ... An eyelid is a thin fold of skin and muscle that covers and protects an eye. ... In medicine, a sign is a feature of disease as detected by the doctor during physical examination of a patient. ...

Corneal topogram of a keratoconic eye

A handheld keratoscope, sometimes known as Placido's disk, can provide a simple non-invasive visualization of the surface of the cornea by projecting a series of concentric rings of light onto the cornea. A more definitive diagnosis can be obtained using corneal topography, in which an automated instrument projects the illuminated pattern onto the cornea and determines its topology from analysis of the digital image. The topographical map indicates any distortions or scarring in the cornea, with keratoconus revealed by a characteristic steepening of curvature which is usually below the centreline of the eye.^[1] The technique can record a snapshot of the degree and extent of the deformation as a benchmark for assessing its rate of progression. It is of particular value in detecting the disorder in its early stages when other signs have not yet presented.^[13] Image File history File links Corneal_topography_right_ax. ... Image File history File links Corneal_topography_right_ax. ... A keratoscope, sometimes known as Placidos disk, is an ophthalmic instrument for assessing the shape of the anterior surface of the cornea. ... The term non-invasive in medicine has two meanings: A medical procedure which does not penetrate or break the skin or a body cavity, i. ... A corneal topogram. ...

Once keratoconus has been diagnosed, its degree may be classified by several metrics:^[14]

• The steepness of greatest curvature from mild (< 45 D), advanced (up to 52 D) or severe (> 52 D);
• The morphology of the cone: nipple (small: 5 mm and near-central), oval (larger, below-center and often sagging), or globus (more than 75% of cornea affected);
• The corneal thickness from mild (> 506 μm) to advanced (< 446 μm).

Increasing use of corneal topography has led to a decline in use of these terms.^[14] A dioptre, or diopter, is a non-SI unit of measurement of the optical power of a lens or curved mirror, which is equal to the reciprocal of the focal length measured in metres (i. ... A dioptre, or diopter, is a non-SI unit of measurement of the optical power of a lens or curved mirror, which is equal to the reciprocal of the focal length measured in metres (i. ... A dioptre, or diopter, is a non-SI unit of measurement of the optical power of a lens or curved mirror, which is equal to the reciprocal of the focal length measured in metres (i. ...

Epidemiology

The National Eye Institute reports that keratoconus is the most common corneal dystrophy in the United States, affecting approximately 1 in 2,000 Americans,^[15][16] but some reports place the figure as high as 1 in 500.^[17] The inconsistency may be due to variations in diagnostic criteria,^[7] with some cases of severe astigmatism interpreted as those of keratoconus, and vice versa.^[12] A long-term study found a mean incidence rate of 2.0 new cases per 100,000 population per year.^[16] It is suggested that males and females, and all ethnicities appear equally susceptible, though some recent studies have cast doubt upon this,^[18] suggesting a higher prevalence amongst females; the literature however varying as to its extent. Also, a study carried out in the UK^[19] suggests that people of an Asian heritage are 4.4 times as likely to suffer from keratoconus as Caucasians, and are also more likely to be affected with the condition earlier. The National Eye Institute (NEI) is one of the US National Institutes of Health that was established in 1968. ... This article needs to be cleaned up to conform to a higher standard of quality. ...

Keratoconus is normally bilateral^[16] (affecting both eyes) although the distortion is usually asymmetric and is rarely completely identical in both corneas.^[7] Unilateral cases tend to be uncommon, and may in fact be very rare if a very mild condition in the better eye is simply below the limit of clinical detection.^[12] It is common for keratoconus to be diagnosed first in one eye and not until later in the other. As the condition then progresses in both eyes, the vision in the earlier-diagnosed eye will often persist to be poorer than that in its fellow.

Prognosis

Patients with keratoconus typically present initially with mild astigmatism, commonly at the onset of puberty, and are diagnosed as having the disease by the late teenage years or early 20s. In rare cases keratoconus can occur in children or not present until later adulthood.^[7] A diagnosis of the disease at an early age may indicate a greater risk of severity in later life.^[1][20] Patients' vision will seem to fluctuate over a period of months, driving them to change lens prescriptions frequently but as the condition worsens, contact lenses become required in the majority of cases. The course of the disorder can be quite variable, with some patients remaining stable for years or indefinitely, while others progress rapidly or experience occasional exacerbations over a long and otherwise steady course. Most commonly, keratoconus progresses for a period of ten to twenty years^[12] before the course of the disease generally ceases. Astigmatism is an affliction of the eye, where vision is blurred by an irregularly shaped cornea. ... Puberty refers to the process of physical changes by which a childs body becomes an adult body capable of reproduction. ... A pair of contact lenses, positioned with the concave side facing upward. ...

Corneal hydrops

In advanced cases, bulging of the cornea can result in a localized rupture of Descemet's membrane, an inner layer of the cornea. Aqueous humor from the eye's anterior chamber seeps into the cornea before Descemet's membrane reseals. The patient experiences pain and a sudden severe clouding of vision, with the cornea taking on a translucent milky-white appearance known as a corneal hydrops.^[21] Although disconcerting to the patient, the effect is normally temporary and after a period of six to eight weeks the cornea usually returns to its former transparency. The recovery can be aided non-surgically by bandaging with an osmotic saline solution. Although a hydrops usually causes increased scarring of the cornea, occasionally it will benefit a patient by creating a flatter cone, aiding the fitting of contact lenses.^[21] Very occasionally, in extreme cases, the cornea thins to the point that a partial rupture occurs, resulting in a small, bead-like swelling on the cornea that has been filled with fluid. When this occurs, a corneal transplant can become urgently necessary to avoid complete rupture and resulting loss of the eye.^[21] Image File history File links Corneal-hydrops. ... Image File history File links Corneal-hydrops. ... Descemets membrane is the basement membrane that lies between the corneal proper substance, also called stroma, and the endothelial layer of the cornea. ... The aqueous humour is the clear, watery fluid that fills the complex space in the front of the eye which is bounded at the front by the cornea and at the rear by the front surface or face of the vitreous humour. ... The anterior chamber if the fluid-filled space inside the eye between the iris and the corneas innermost surface, the endothelium . ... Osmosis is the net movement of water across a partially permeable membrane from a region of high solvent potential to an area of low solvent potential, up a solute concentration gradient. ... In medicine, saline is a solution of sodium chloride (a substance also commonly known as table salt) in sterile water, used frequently for intravenous infusion, rinsing contact lenses, and nasal irrigation (or the yogic practice called jala neti). ... Cornea Transplant A cornea transplant, also known as a corneal graft or penetrating keratoplasty, is a surgical procedure where a damaged or diseased cornea is replaced by a donor. ...

Pathophysiology and cause

Despite considerable research, the etiology of keratoconus remains somewhat of a mystery.^[1] A number of sources suggest that keratoconus likely arises from a number of different factors: genetic, environmental or cellular, any of which may form the trigger for the onset of the disease.^[22][23] Once initiated, the disease normally develops by progressive dissolution of Bowman's layer,^[7] the membrane lying between the corneal epithelium and stroma. As the two come into contact, cellular and structural changes in the cornea adversely affect its integrity and lead to the bulging and scarring that are characteristic of the disorder. Within any individual keratoconic cornea, there may be found regions of degenerative thinning coexisting with regions undergoing wound healing. This article is about the medical term. ... The Bowmans membrane, or Bowmans layer, is a smooth layer in the eye. ... This article is about the epithelium as it relates to animal anatomy. ... The substantia propria (or stroma of cornea) is fibrous, tough, unyielding, and perfectly transparent. ...

The visual distortion experienced by the patient comes from two sources, one being the irregular deformation of the surface of the cornea; the other being scarring that occurs on its exposed highpoints. These factors act to form regions on the cornea that map an image to different locations on the retina and give rise to the symptom of monocular polyopia. The effect can worsen in low light conditions as the dark-adapted pupil dilates to expose more of the irregular surface of the cornea. Scarring appears to be an aspect of the corneal degradation; however, a recent, large, multi-center study suggests that abrasion by contact lenses may increase the likelihood of this finding by a factor of over two.^[24] Human eye cross-sectional view. ... Diplopia, colloquially known as double vision, is the perception of two images from a single object. ... The human eye The pupil is the central transparent area (showing as black). ...

A number of studies have indicated that keratoconic corneas show signs of increased activity by proteases,^[22] a class of enzymes that break some of the collagen cross-linkages in the stroma, with a simultaneous reduced expression of protease inhibitors.^[25] Other studies have suggested that reduced activity by the enzyme aldehyde dehydrogenase may be responsible for a build-up of free radicals and oxidising species in the cornea.^[26] It seems likely that, whatever the pathogenetical process, the damage caused by activity within the cornea results in a reduction in its thickness and biomechanical strength. Proteases (proteinases, peptidases, or proteolytic enzymes) are enzymes that break peptide bonds between amino acids of proteins. ... Ribbon diagram of the enzyme TIM, surrounded by the space-filling model of the protein. ... Tropocollagen triple helix. ... Gene expression, or simply expression, is the process by which the inheritable information which comprises a gene, such as the DNA sequence, is made manifest as a physical and biologically functional gene product, such as protein or RNA. Several steps in the gene expression process may be modulated, including the... HIV protease in a complex with the protease inhibitor ritonavir. ... Aldehyde Dehydrogenase Aldehyde dehydrogenases are a group of enzymes that catalyse the oxidation (dehydrogenation) of aldehydes. ... In chemistry free radicals are uncharged atomic or molecular species with unpaired electrons or an otherwise open shell configuration. ... Pathogenesis is the mechanism by which a certain etiological factor causes disease (pathos = disease, genesis = development). ...

A genetic predisposition to keratoconus has been observed,^[27] with the disease running in certain families,^[28] and incidences reported of concordance in identical twins.^[10] The frequency of occurrence in close family members is not clearly defined, though it is known to be considerably higher than that in the general population,^[1] and studies have obtained estimates ranging between 6% and 19%.^[29] A responsible gene has not been identified: two studies involving isolated, largely homogenetic communities have contrarily mapped putative gene locations to chromosomes 16q and 20q.^[29] However, most genetic studies agree on an autosomal dominant model of inheritance.^[6] Keratoconus is also diagnosed more often in people with Down syndrome, though the reasons for this link have not yet been determined.^[30] Keratoconus has been associated with atopic diseases, which include asthma, allergies, and eczema, and it is not uncommon for several or all of these diseases to affect one person. A number of studies suggest that vigorous eye rubbing may contribute to the progression of keratoconus, and that patients should be discouraged from the practice.^{[31][32][33][34][35]} Concordance as used in genetics means the presence of the same trait in both members of a pair of twins, or in sets of individuals. ... For other uses, see Gene (disambiguation). ... Figure 1: A representation of a condensed eukaryotic chromosome, as seen during cell division. ... An autosome is a non-sex chromosome. ... In genetics, the term dominant gene refers to the allele that causes a phenotype that is seen in a heterozygous genotype. ... In medicine, the atopic syndrome is the clustering of eczema, allergic conjunctivitis, allergic rhinitis and asthma in certain individuals. ... This article needs cleanup. ... For the beetle, see Exema. ...

Treatment

Contact lenses

Main article: Contact lens

In early stages of keratoconus, spectacles can suffice to correct for the mild astigmatism. As the condition progresses, spectacles may no longer provide the patient with a satisfactory degree of visual acuity, and most clinical practitioners will move to managing the condition with contact lenses. A pair of contact lenses, positioned with the concave side facing upward. ... A pair of modern glasses Glasses, also called eyeglasses or spectacles are frames, bearing lenses worn in front of the eyes normally for vision correction, eye protection, or for protection from UV rays. ...

Rigid gas permeable lens for keratoconus

In keratoconic patients, contact lenses improve vision by means of tear fluid filling the gap between the irregular corneal surface and the smooth regular inner surface of the lens, thereby creating the effect of a smoother cornea. Many specialized types of contact lenses have been developed for keratoconus, and affected people may seek out both doctors specialized in conditions of the cornea, and contact-lens fitters who have experience managing patients with keratoconus. The irregular cone presents a challenge^[22] and the fitter will endeavour to produce a lens with the optimal contact, stability and steepness. Some trial-and-error fitting may prove necessary.^[12] Image File history File links KC-lens. ... Image File history File links KC-lens. ... The tear system. ...

Traditionally, contact lenses for keratoconus have been the 'hard' or rigid gas-permeable variety, although manufacturers have also produced specialized 'soft' or hydrophilic lenses. A soft lens has a tendency to conform to the conical shape of the cornea, thus diminishing its effect. To counter this, hybrid lenses have been developed which are hard in the centre and encompassed by a soft skirt. Soft or hybrid lenses do not however prove effective for every patient.^[36] The adjective hydrophilic describes something that likes water (from Greek hydros = water; philos = friend). ...

Some patients also find good vision correction and comfort with a "piggyback" lens combination, in which gas permeable rigid lenses are worn over soft lenses, both providing a degree of vision correction.^[37] One form of piggyback lens makes use of a soft lens with a countersunk central area to accept the rigid lens. Fitting a piggyback lens combination requires experience on the part of the lens fitter, and tolerance on the part of the keratoconic patient.

Scleral lenses are sometimes prescribed for cases of advanced or very irregular keratoconus; these lenses cover a greater proportion of the surface of the eye and hence can offer improved stability.^[38] The larger size of the lenses may make them unappealing or uncomfortable to some, however their easier handling can find favour with patients with reduced dexterity, such as the elderly. A scleral lens is a large type of contact lens that rests on the sclera and creates a tear-filled vault over the cornea. ...

Surgical options

Corneal transplant

Main article: Cornea transplant

Corneal transplant for keratoconus, approximately 1 week after surgery. Multiple light reflections indicate folds in the cornea which later resolved.

Between 10% and 25% of cases of keratoconus^[23][39][40] will progress to a point where vision correction is no longer possible, thinning of the cornea becomes excessive, or scarring as a result of contact lens wear causes problems of its own, and a corneal transplantation or penetrating keratoplasty becomes required. Keratoconus is the most common grounds for conducting a penetrating keratoplasty, generally accounting for around a quarter of such procedures.^[41] The corneal transplant surgeon trephines a lenticule of corneal tissue and then grafts the donor cornea to the existing eye tissue, usually using a combination of running and individual sutures. The cornea does not have a direct blood supply, and so donor tissue is not required to be blood type matched. Eye banks check the donor corneas for any disease or cellular irregularities. Cornea Transplant A cornea transplant, also known as a corneal graft or penetrating keratoplasty, is a surgical procedure where a damaged or diseased cornea is replaced by a donor. ... Image File history File links No higher resolution available. ... Image File history File links No higher resolution available. ... A trephine () is a surgical instrument. ... In medicine, grafting is a surgical procedure to transplant tissue without a blood supply. ... Organ donationcan only be peformed by untrained workers who do not have a drivers license and are poor. ... It has been suggested that suture material be merged into this article or section. ... This article is about human blood types (or blood groups). ... Eye banks retrieve and store eyes for cornea transplants and research. ...

The acute recovery period can take four to six weeks and full post-operative vision stabilization often takes a year or more but most transplants are very stable in the long term.^[40] The National Keratoconus Foundation reports that penetrating keratoplasty has the most successful outcome of all transplant procedures, and when performed for keratoconus in an otherwise healthy eye, its success rate can be 95% or greater.^[23] The sutures used usually dissolve over a period of three to five years but individual sutures can be removed during the healing process if they are causing irritation to the patient.

In the USA, corneal transplants (also known as corneal grafts) for keratoconus are usually performed under sedation as outpatient surgery. In other countries, such as Australia and the UK, the operation is commonly performed with the patient undergoing a general anaesthetic. All cases a require careful follow-up with an eye surgeon (ophthalmologist) for a number of years. Frequently, vision is greatly improved after the surgery, but even if the actual visual acuity does not improve, because the cornea is a more normal shape after the healing is completed, patients can more easily be fitted with corrective lenses. Complications of corneal transplants are mostly related to vascularization of the corneal tissue and rejection of the donor cornea. Vision loss is very rare, though difficult-to-correct vision is possible. When rejection is severe, repeat transplants are often attempted, and are frequently successful.^[42] Keratoconus will not normally reoccur in the transplanted cornea; incidences of this have been observed, but are usually attributed to incomplete excision of the original cornea or inadequate screening of the donor tissue.^[43] The long-term outlook for corneal transplants performed for keratoconus is usually favorable once the initial healing period is completed and a few years have elapsed without problems. A hospital today is an institution for professional health care provided in part by physicians and nurses. ... Transplant rejection occurs when the immune system of the recipient of a transplant attacks the transplanted organ or tissue. ... Visual loss results in the absence of vision where it existed before, which can happen either acutely (i. ...

DALK transplants

One way of reducing the risk of rejection is to use a newer technique called a Deep Anterior Lamellar Keratoplasty, referred to as DALK. In a DALK graft, only the outermost epithelium and the main bulk of the cornea, the stroma, are replaced; the patient's rearmost endothelium layer is retained, giving some additional structural integrity to the post-graft cornea.^[44] Because a graft rejection usually begins in the endothelium, the chance of a rejection episode is greatly reduced. Furthermore, it is possible to transplant tissue from a donor which has been freeze-dried. The freeze-drying process ensures that this tissue is dead, so there is no chance of a rejection.^[44] Corneal endothelium is the inner most layer of the cornea, the corneal endothelium is actually a monolayer of squamate epithelial cells lining the anterior chamber of the eye. ... Freeze drying (also known as Lyophilization) is a dehydration process typically used to preserve a perishable material, or to make the material more convenient for transport. ...

Some surgeons prefer to remove the donor epithelium, others leave the donor's cells in place. Removing it can cause a slight improvement in overall vision, but a corresponding increase in visual recovery time.

Epikeratophakia

Rarely, a non-penetrating keratoplasty known as an epikeratophakia (or epikeratoplasty) may be performed in cases of keratoconus. The corneal epithelium is removed and a lenticule of donor cornea grafted on top of it.^[22] The procedure requires a greater level of skill on the part of the surgeon, and is less frequently performed than a penetrating keratoplasty as the outcome is generally less favorable. It may however be seen as an option in a number of cases, particularly for young patients.^[45]

Corneal ring segment inserts

Main article: Intrastromal corneal ring segments

A pair of Intacs inserts.

A recent surgical alternative to corneal transplant is the insertion of intrastromal corneal ring segments. A small incision is made in the periphery of the cornea and two thin arcs of polymethyl methacrylate are slid between the layers of the stroma on either side of the pupil before the incision is closed.^[46] The segments push out against the curvature of the cornea, flattening the peak of the cone and returning it to a more natural shape. The procedure, carried out on an outpatient basis under local anaesthesia, offers the benefit of being reversible and even potentially exchangeable as it involves no removal of eye tissue.^[46] A pair of Intacs® inserts. ... Image File history File links Intacsonfinger2. ... Image File history File links Intacsonfinger2. ... Structure of methyl methacrylate, the monomer that makes up PMMA Polymethyl methacrylate (PMMA) or poly(methyl 2-methylpropenoate) is the synthetic polymer of methyl methacrylate. ... The human eye The pupil is the central transparent area (showing as black). ... Local anesthesia is any technique to render part of the body insensitive to pain without affecting consciousness. ...

The two principal types of intrastromal rings available are known by the trade names of Intacs and Ferrara rings. Intacs are flatter and less centrally placed than the prismatic Ferrara rings. Intacs were first approved by the Food and Drug Administration (FDA) in the United States in 1999 for myopia; this was extended to the treatment of keratoconus in July 2004.^[47] Ferrara rings await FDA approval for keratoconus. A development on the concept involves the injection of a transparent synthetic gel into a channel bored through the stroma. As the gel polymerises, it stiffens and takes on similar properties to the pre-formed rings.^[48] hi “FDA” redirects here. ... Normal vision. ...

Clinical studies on the effectiveness of intrastromal rings on keratoconus are in their early stages, and results have so far been generally encouraging,^[49][50] though they have yet to enter into wide acceptance with the refractive surgery community. In common with penetrating keratoplasty, the requirement for some vision correction in the form of spectacles or hydrophilic contact lenses may remain subsequent to the operation. Potential complications of intrastromal rings include accidental penetration through to the anterior chamber when forming the channel, post-operative infection of the cornea, and migration or extrusion of the segments.^[50] The rings offer a good chance of vision improvement even in otherwise hard to manage eyes, but results are not guaranteed and in a few cases may worsen. An infection is the detrimental colonization of a host organism by a foreign species. ...

Early studies on intrastromal corneal rings involved use of two segments to cause global flattening of the cornea.^[51] A later study reported that better results could be obtained for those cones located more to the periphery of the cornea by using a single Intacs segment. This leads to preferential flattening of the cone below, but also to steepening the over-flat upper part of the cornea.^[52]

Radial keratotomy

Main article: Radial keratotomy

Radial keratotomy is a refractive surgery procedure where the surgeon makes a spoke-like pattern of incisions into the cornea to modify its shape. This early surgical option for myopia has been largely superseded by LASIK and other similar procedures. LASIK itself is absolutely contraindicated in keratoconus and other corneal thinning conditions as removal of corneal stromal tissue will further damage an already thin and weak cornea.^[53] Radial keratotomy (RK) is a refractive surgical procedure to correct myopia. ... Refractive eye surgery is any eye surgery used to improve the refractive state of the eye and decrease dependency on glasses or contact lenses. ... Normal vision. ... LASIK is the acronym for Laser-Assisted in Situ Keratomileusis, a type of refractive laser eye surgery performed by ophthalmologists for correcting myopia, hyperopia, and astigmatism. ...

For similar reasons, radial keratotomy has also generally not been used for keratoconic patients.^[54][55] However, an Italian clinic has reported some success with a modified asymmetric radial keratotomy procedure,^[56] in which the incisions are confined to one sector of the eye. The corneal thickness is first measured using a pachymeter, then the surgeon makes cuts to a depth of 70–80% of the measured thickness. The patient may initially experience photophobia and fluctuation of vision, in common with other forms of refractive surgery.^[56] A pachymeter is a medical device used to measure the thickness of the eyes cornea. ... Photophobia (also light sensitivity) or fear of light, is a symptom of excessive sensitivity to light and the aversion to sunlight or well-lit places. ...

Asymmetric Radial Keratotomy

The A.R.K. consists in performing micro-incisions always respecting the optical zone as widely as possible performed (from 4 to 5.5 millimeters). The incisions are in acentripetal manner. We must: 1) designate the optical zone;

2) delimitate the degrees (30° à 270°) of treatment following the T.M.S. map;

3) calculate the number and the depth of incisions on the basis of the pachymetry. Decisions regarding the surgical program change according to the different cases, while the surgeon's experience in the field of refractive surgery plays afundamental part.

While performing the incisions, according to our statistic, unwanted micro-perforations can rarely happen and they don't normally need any treatment (rare case of suturing with 10-11 0 nylon suture). These microperforations were accidental and due to the excessive irregularity of the the cornea's thickness, particularly in those cases where keratoconus was in amore advanced phase (III).

The microperforations had no statistically significant effect on the final result.

The normal rule is to incise no more than 80% of the sickness.

Corneal Collagen Crosslinking with Riboflavin (C3-R)

A innovative treatment which has shown early success is Corneal Collagen Crosslinking with Riboflavin (C3-R), which involves a one-time application of riboflavin eye drops to the eye.^[25][57] The riboflavin, when activated by approximately 30 minutes illumination with UV-A light, augments the collagen cross-links within the stroma and so recovers some of the cornea's mechanical strength. C3-R, developed at the Technische Universität Dresden, has been shown to slow or arrest the progression of keratoconus, and in some cases even reverse it, particularly when applied in combination with intracorneal ring segments. A recent study showed that when C3-R was combined with Intacs, twice as much improvement occurred compared to Intacs alone.^[58] Riboflavin (E101), also known as vitamin B2, is an easily absorbed micronutrient with a key role in maintaining health in animals. ... Note: Ultraviolet is also the name of a 1998 UK television miniseries about vampires. ... With 34,993 students (2006), Dresden University of Technology (DUT; German:Technische Universität Dresden, TU Dresden or simply TUD) is the largest institute of higher education in the city of Dresden, the largest university in Saxony and one of the 10 largest universities in Germany. ...

Clinical trials are continuing, and while relatively few procedures have been performed, the technique is showing promise in treating early cases of the disease.^[59] Corrective lenses may still be required after the treatment but it is hoped that it could limit further deterioration in the patient's vision and reduce the case for keratoplasty. In health care, including medicine, a clinical trial (synonyms: clinical studies, research protocols, medical research) is a process in which a medicine or other medical treatment is tested for its safety and effectiveness, often in comparison to existing treatments. ...

Related disorders

Several other non-inflammatory eye disorders, generally rarer than keratoconus, also cause thinning of the cornea:^[12]

Keratoglobus

Keratoglobus is a very rare condition that causes corneal thinning primarily at the margins, resulting in a spherical, slightly enlarged eye. It may be genetically related to keratoconus.^[22]

Pellucid marginal degeneration

Pellucid marginal degeneration causes thinning of a narrow (1–2 mm) band of the cornea, usually along the inferior corneal margin. It causes irregular astigmatism that can often be corrected by spectacles. Differential diagnosis may be made by slit-lamp examination.^[10]

Posterior keratoconus

Keratoconus and posterior keratoconus are distinct disorders, despite their similar names. Posterior keratoconus is a rare abnormality, usually congenital, which causes a non-progressive thinning of the inner surface of the cornea, while the curvature of the anterior surface remains normal. Normally only a single eye is affected.^[22]

Keratoglobus (from Greek: kerato- horn, cornea; and globus round), is a degenerative non-inflammatory disorder of the eye in which structural changes within the cornea cause it to become extremely thin and change to a more globular shape than its normal gradual curve. ...

See also

• List of eye diseases and disorders
• Ophthalmology

This is a partial list of human eye diseases and disorders. ... This article is about the branch of medicine. ...

References

Year 2007 (MMVII) is the current year, a common year starting on Monday of the Gregorian calendar and the AD/CE era. ... is the 247th day of the year (248th in leap years) in the Gregorian calendar. ... Year 2007 (MMVII) is the current year, a common year starting on Monday of the Gregorian calendar and the AD/CE era. ... is the 251st day of the year (252nd in leap years) in the Gregorian calendar. ... Year 2006 (MMVI) was a common year starting on Sunday of the Gregorian calendar. ... March 26 is the 85th day of the year (86th in leap years) in the Gregorian calendar. ... A digital object identifier (or DOI) is a standard for persistently identifying a piece of intellectual property on a digital network and associating it with related data, the metadata, in a structured extensible way. ...

External links

Keratoconus associations:

• Keratoconus Australia
• National Keratoconus Foundation, USA
• Keratoconus Self Help and Support Group, UK
• KC Global The Global Keratoconus Foundation
• KC Freedom The Global Keratoconus Freedom Group
• Keratoconus International
• A site for parents and families

Web articles on keratoconus:

• C3-R - A New Treatment to Strengthen the Cornea for Keratoectasia and Keratoconus.
• C3-R Treatment for Keratoconus
• Helping the Keratoconus Patient Cope by Bezalel Schendowich
• Keratoconus Watch
• Asymmetric Radial Keratotomy for the Correction of Keratoconus
• Case Studies

Individuals' experiences with keratoconus:

• John Ackerman's transplant diary and keratoconus resources
• Actor Mandy Patinkin describes his corneal transplant

Other:

• What Causes Keratoconus and Treatments including C3-R and Intacs
• Angeles Vision Clinic: What is Keratoconus and what are the treatment options?
• Homepage of the Collaborative Longitudinal Evaluation of Keratoconus (CLEK) Study
• Intacs: manufacturer's site
• Rose K Lens: manufacturer's site
• KeraSoft™2: manufacturer's site
• Vision Simulations: see what people with keratoconus see
• Facts About the Cornea and Corneal Disease The National Eye Institute (NEI)

   

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. ... Astigmatism is an affliction of the eye, where vision is blurred by an irregularly shaped cornea. ... 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). ... Aniseikonia is an ophthalmological condition caused by unequal retinal image sizes. ... Presbyopia (Greek word presbyteros (πρεσβύτερος), meaning elder) is the eyes diminished ability to focus that occurs with aging. ... This article is about the visual condition. ... 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. ... ... Hemeralopia is the exact opposite of Nyctalopia (Night Blindness). ... Photophobia (also light sensitivity) or fear of light, is a symptom of excessive sensitivity to light and the aversion to sunlight or well-lit places. ... Scintillating scotoma is the most common visual aura preceding migraine and was first described by 19th century physician Hubert Airy (1838–1903). ... Diplopia, commonly known as double vision, is the perception of two images from a single object. ... The word scotoma is derived from the Greek word for darkness. ... An anopsia (or anopia) is a defect in the visual field. ... Paris as seen with full visual fields Binasal hemianopia is the medical description of a type of partial blindness that is associated with certain lesions of the eye, and of the central nervous system, such as congenital hydrocephalus. ... Paris as seen with full visual fields Paris as seen with bitemporal hemianopsia Bitemporal hemianopsia is the medical description of a type of partial blindness that is associated with lesions of the optic chiasm, the area where the optic nerves from the right and left eyes cross near the pituitary... Homonymous hemianopsia is a medical term for a type of partial blindness resulting in a loss of vision in the same visual field of both eyes. ... Quadrantanopia (or quadrant anopia, as two words) refers to an anopia affecting a quarter of the field of vision. ... 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 relatively low light. ... This article is about the visual condition. ... Low vision is alternatively a general term used to describe lowered visual acuity, and a specific legal term in Canada and the United States used to designate someone with vision of 20/70 or less in the better eye with correction. ... The human eye The pupil is the central transparent area (showing as black). ... Anisocoria is a condition characterized by an unequal size of the pupils. ... Argyll Robertson pupils (“AR pupils”) are bilateral small pupils that constrict when the patient focuses on a near object (they “accommodate” with near vision), but do not constrict when exposed to bright light (they do not “react” to light). ... The pupil dilates instead of constricting when the light moves from the good eye to the bad eye. ... Marcus Gunn Phenomenon (a. ... Adie syndrome, also Adies syndrome, is caused by damage to the postganglionic fibers of the parasympathetic innervation of the eye and characterized by a tonically dilated pupil. ... Infection is also the title of an episode of the television series Babylon 5; see Infection (Babylon 5). ... Binomial name Onchocerca volvulus Bickel 1982 Onchocerciasis (pronounced ) or river blindness is the worlds second leading infectious cause of blindness. ... Nystagmus is involuntary eye movement that can be part of the vestibulo-ocular reflex (VOR), with the eyes moving first in the direction of the lesioned side (slow phase) followed by a quick correction (fast phase) to the opposite side or away from the lesioned side. ... Miosis should not be confused with meiosis, the cellular division process involved in sexual reproduction. ... // Mydriasis is an excessive dilation of the pupil due to disease or drugs. ... For other uses, see Floater (disambiguation). ... Leber’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. ... 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. ...