Keratoconus ( KC ) is an eye disorder that causes progressive corneal depletion. It can produce blurred vision, double vision, nearsightedness, astigmatism, and light sensitivity. Usually both eyes are affected. In more severe cases, scar tissue or circles may be seen inside the cornea.
While the cause is unknown, it is believed to be due to a combination of genetic, environmental, and hormonal factors. About seven percent of those affected have a family history of the condition. Proposed environmental factors include eye rubbing and allergies. The underlying mechanism involves changing the cornea to a cone shape. Diagnosis is done by examination with a slit lamp.
Initially the condition can usually be corrected with glasses or soft contact lenses. Because disease worsens special contact lenses may be necessary. In most people, the disease is stable after a few years without severe vision problems. In a small amount of scar tissue on the cornea occurs and corneal transplantation is necessary.
Keratoconus affects about 1 in 2000 people. This happens most often in children of late age to early adulthood. While it occurs in all populations it may be more frequent in certain ethnic groups such as Asian descent. This word comes from the Greek kÃÆ' Â © ras which means cornea and Latin c? Nus which means cone.
Video Keratoconus
Signs and symptoms
People with early keratoconus usually see slight blurred vision and come to their doctor looking for corrective lenses for reading or driving. In the early stages, the symptoms of keratoconus may not be different from other eye bias defects. As the disease progresses, vision deteriorates, sometimes quickly. Visual acuity becomes impaired at all distances, and night vision is often poor. Some individuals have eyesight on one eye that is clearly worse than the other. The disease is often bilateral, though asymmetric. Some develop photophobia (sensitivity to bright light), eye strain from squinting for reading, or itching in the eyes, but usually there is little or no pain sensation. This may cause a luminous object to appear as a cylindrical pipe with the same intensity at all points.
The classic symptom of keratoconus is the perception of some "ghost" shadows, known as polarized polyopia. This effect is most evident with high-contrast planes, such as the point of light on a dark background. Instead of seeing only one point, a person with keratoconus sees many images from that point, spreading in a chaotic pattern. This pattern usually does not change from day to day, but over time, it often takes on a new form. People also usually see streaking and igniting distortion around the light source. Some even see moving images relative to each other with their heart rate. The dominant eye optical aberration in keratoconus is coma. The visual distortion experienced by the person comes from two sources, one of which is the irregular corneal surface deformation, and the other is scarring that occurs at its open tops. These factors act to form areas of the cornea that map images to different locations of the retina. The effect may worsen under low-light conditions, because the dark-adapted pupils dilate to expose more irregular corneal surfaces.
Maps Keratoconus
Genetics
Six genes have been found related to the condition. These genes include BANP-ZNF469, COL4A4, FOXO1, FNDC3B, IMMP2L and RXRA-COL5A1. Others may also exist.
Pathophysiology
Despite much research, the cause of keratoconus remains unclear. Some sources suggest that keratoconus may arise from a number of different factors: genetic, environmental or cellular, which can form a trigger for disease. After initiation, the disease usually progresses with progressive dissolution of the Bowman lining, which lies between the corneal epithelium and the stroma. When both are in contact, the cell and structural changes in the cornea affect its integrity and lead to prominent characteristics and scarring of the disorder. In each individual corneal keratoconic, degenerative depletion areas coexist with areas undergoing wound healing can be found. Scar tissue appears to be an aspect of corneal degradation; However, recent, large multicenter studies showing abrasion by contact lenses may increase the likelihood of these findings by a factor above two.
Numerous studies have shown keratoconic corneas to show signs of increased activity by proteases, an enzyme class that destroys multiple collagen crosslinks in the stroma, with decreased expression of protease inhibitors simultaneously. Other studies have shown that reduced activity by the enzyme dehydrogenase aldehyde may be responsible for the accumulation of free radicals and oxidizing species in the cornea. Whatever the pathogenetic process, the damage caused by activity within the cornea may result in a decrease in its thickness and biomechanical strength. At the ultrastructural level weakening of the corneal tissue is associated with disorders of regular arrangement of collagen layer and collagen fibril orientation. While keratoconus is considered a non-inflammatory disorder, one study showed the use of rigid contact lenses by people causing the overexpression of proinflammatory cytokines, such as IL-6, TNF-alpha, ICAM-1, and VCAM-1 in tear fluid.
A genetic predisposition to keratoconus has been observed, with disease affecting certain families, and events reporting a concordance on identical twins. The frequency of occurrence in close family members is not clearly defined, although it is known to be much higher than the general population, and studies have obtained estimates ranging from 6% and 19%. Two studies involving isolated, largely homogeneous, controversial communities have mapped the location of putative genes to chromosomes 16q and 20q. Most genetic studies approve autosomal dominant inheritance models. The rare autosomal dominant form of severe keratoconus with anterior polar cataracts is caused by mutations in the area of ​​the mir-184 seed, a highly expressed microRNA on the corneal and anterior lenses. Keratoconus is diagnosed more often in people with Down syndrome, although the reasons for this relationship have not been determined.
Keratoconus has been linked to atopic diseases, which include asthma, allergies, and eczema, and not infrequently some or all of these diseases attack one person. Keratoconus is also associated with Alport syndrome, Down syndrome and Marfan syndrome. Numerous studies show a strong eye rubbing contributes to the development of keratoconus, and people should be discouraged from exercise. Keratoconus differs from ectasia caused by LASIK eye surgery. Post-LASIK Ectasia has been linked to the removal of excessive eye-stromal eye tissue during surgery.
Diagnosis
Prior to the physical examination, keratoconus diagnosis often begins with the assessment of an ophthalmologist or an ophthalmologist on a person's medical history, especially a major complaint and other visual symptoms, a history of eye disease or injury that may affect vision, and a family history of eye disease. The eye chart, like the standard Snellen graph of smaller letters, is then used to determine the visual acuity of a person. Eye examination may proceed to a localized corneal curvature measurement with a manual keratometer, with irregular astigmatism detection indicating the possibility of keratoconus. Severe cases may exceed the ability to measure instruments. Further indications may be given by retinoscopy, where the rays are focused on a person's retina and reflections, or reflexes, are observed as the examiner tilts the light source back and forth. Keratoconus is among the eye conditions that exhibit the movement of the scissor reflex from two bands moving in the direction and away from each other like a scissor blade.
If keratoconus is suspected, the ophthalmologist or ophthalmologist will look for findings of other disease characteristics by examining the slit lamp on the cornea. Advanced cases are usually readily apparent to testers, and can provide an unambiguous diagnosis before more specialized testing. Under close examination, the yellow-brown to olive-green pigment ring known as the Fleischer ring can be observed in about half of the keratoconic eye. The Fleischer Ring, caused by the deposition of hemosiderin iron oxide in the corneal epithelium, is smooth and may not be easily detectable in all cases, but becomes more pronounced when viewed under a cobalt blue filter. Similarly, about 50% of subjects showed Vogt stria, good stress lines within the cornea caused by stretching and thinning. Striae temporarily disappears while a slight pressure is applied to the eyeball. A very prominent cone can create a V-shaped curve in the lower eyelid when the view of a person is directed downwards, known as the Munson sign. Other clinical signs of keratoconus usually appear naturally well before Munson's sign becomes clear, and these findings, despite the classic signs of the disease, are less likely to be of major diagnostic importance.
A handheld keratoscope, sometimes known as "Placido's disk", can provide simple non-invasive visualization of the corneal surface by projecting a series of concentric circles of light into the cornea. A more definitive diagnosis can be obtained by using a corneal topography, where the instrument automatically projects the illuminated pattern onto the cornea and determines its topography from digital image analysis. Topographic maps indicate distortion or scarring in the cornea, with keratoconus expressed by steep curvature characteristics that are usually below the midline of the eye. This technique can record a snapshot of the extent and extent of deformation as a benchmark to assess its rate of development. This is of particular value in detecting interference at an early stage when other signs have not been presented.
Stages
Once keratoconus has been diagnosed, its degree can be classified by several metrics:
- The greatest curvature of 'light' (& lt; 45D), 'sophisticated' (up to 52D) or 'heavy' (& gt; 52D);
- Conical morphology: 'nipple' (small: 5 mm and near-central), 'oval' (larger, below middle and often sag), or 'globus' (more than 75% of corneas affected);
- Thickness of cornea from light (& gt; 506? m) to advanced (& lt; 446? m).
Increased use of corneal topography has led to a decrease in the use of these terms.
Treatment
Lens
In the early stages keratoconus, glasses or soft contact lenses are sufficient to correct mild astigmatism. As the condition progresses, this may no longer provide people with a satisfactory level of visual acuity, and most practitioners will move to manage conditions with rigid contact lenses, known as rigid, gas-permeable (RGP) lenses. The RGP lens provides a good level of visual correction, but does not restrain conditions.
In people with keratoconus, rigid contact lenses improve vision through tear fluid that fills the gap between the irregular surface of the cornea and the smooth interior surface of the lens, creating a finer corneal effect. Many special types of contact lenses have been developed for keratoconus, and the affected person may seek both special doctors under corneal conditions, and contact lens drivers who have experience managing people with keratoconus. Irregular cones present challenges and builders will try to produce lenses with optimal contact, stability, and steepness. Some trial-and-error fits may be required.
Hybrid lens
Traditionally, contact lenses for keratoconus have become 'hard' or RGP varieties, although manufacturers have also produced special 'soft' or hydrophilic lenses and, most recently, silicone hydrogel lenses. The soft lens has a tendency to adapt to the corneal corneal shape, thus reducing its effect. To counter this, hybrid lenses have been developed that are hard in the middle and covered by soft skirts. However, the soft or previous generation hybrid lens does not prove to be effective for everyone. Early generation lenses have been discontinued. The fourth generation of hybrid lens technology has improved, giving more people a choice that combines the comfort of soft lenses with the visual acuity of RGP lenses.
sclera lens
Scleral lenses are sometimes prescribed for advanced keratoconus cases or very irregular; this lens covers a larger proportion of the surface of the eye and therefore can offer increased stability. Easier handling can find benefits with people with reduced agility, like parents.
Pitching
Some people find good vision correction and comfort with a combination of "piggyback" lenses, in which RGP lenses are worn over soft lenses, both providing a level of vision correction. One form of piggyback lens utilizes a soft lens with a countersunk center area to receive rigid lenses. Fitted piggyback lens combinations require experience in the fitter parts of the lens, and tolerance of the part of the person with keratoconus.
Surgery
Corneal transplant
Between 11% and 27% of cases of keratoconus will continue to the point where vision correction is no longer possible, corneal thinning becomes excessive, or scarring due to contact lens wear causes its own problems, and corneal transplantation or penetrating keratoplasty becomes necessary. Keratoconus is the most common reason for performing translucent keratoplasty, generally accounting for about a quarter of the procedure. Corneal transplant surgeons damage the lenticule of the corneal tissue and then transplant the donor cornea into the existing eye tissue, usually using a combination of walking and individual seams. The cornea has no direct blood supply, so donor tissue is not needed to be matched with blood type. The eye bank checks the donor cornea for diseases or cellular aberrations.
The acute recovery period may take four to six weeks, and postoperative vision stabilization often takes a year or more, but most transplants are very stable over the long term. The Keratoconus National Foundation reports that keratoplasty penetration has the most successful outcome of all transplant procedures, and when performed for keratoconus in healthy eyes, the success rate can be 95% or greater. Used sutures usually dissolve over a period of three to five years, but individual stitches can be removed during the healing process if they cause irritation to the person.
In the United States, corneal transplantation (also known as corneal graft) for keratoconus is usually performed under sedation as an outpatient operation. In other countries, such as Australia and the UK, these operations are generally performed with people undergoing general anesthesia. All cases require careful follow-up with an ophthalmologist (ophthalmologist or optometrist) for several years. Often, vision is greatly improved after surgery, but even if the actual visual acuity does not improve, because the cornea is a more normal form after healing is completed, people can be more easily mounted with corrective lenses. Complications of corneal transplantation are mostly associated with corneal tissue vascularization and donor corneal rejection. Loss of vision is very rare, although a difficult vision to correct is possible. When rejection is severe, repeated transplants are often attempted, and often succeed. Keratoconus usually will not recur in the transplanted cornea; this incident has been observed, but is usually associated with an incomplete excision of the original cornea or inadequate screening of the donor tissue. The long-term view for corneal transplantation performed for keratoconus is usually advantageous after the initial healing period is over and several years have passed without any problems.
One way to reduce the risk of rejection is to use a technique called deep anterior keratoplasty (DALK). In DALK graft, only the outermost epithelium and most of the cornea, stroma, are replaced; the rearmost endothelium layer and the remaining Descemet membrane, providing some additional structural integrity for the postgraft cornea. Furthermore, it is possible to transplant the freeze-dried donor network. The frozen drying process ensures the tissue is dead, so there is no possibility of rejection. Research from two trials in Iran provides low to moderate evidence that graft rejection is more likely to occur in penetrating keratoplasty than in DALK, although the possibility of graft failure is similar to both procedures.
Epikeratophakia
Rarely, nonpenetrating keratoplasty known as epikeratophakia (or epikeratoplasty) can be performed in cases of keratoconus. The corneal epithelium is removed and the donor corneal lentisule is grafted on it. This procedure requires a greater skill level in the surgeon's part, and is less common than translucent keratoplasty, as the result is generally less favorable. However, this can be seen as an option in a number of cases, especially for young people.
Corneal ring implants
The possible surgical alternative for corneal transplantation is the insertion of intrastromal corneal ring segments. Small incisions are made at the periphery of the cornea and two thin arc of polymethyl methacrylate slip between layers of stroma on both sides of the pupil before the incision is sealed. The segment pushes out against the curvature of the cornea, flattening the top of the cone and returning it to a more natural form. This procedure offers the benefits of being reversible and potentially even redeemable because there is no removal of eye tissue.
Radial keratotomy
Radial keratotomy is a refractive surgery procedure in which the surgeon makes an oral-like incision pattern into the cornea to modify its shape. This early surgical choice for myopia has been replaced by LASIK and other similar procedures. LASIK is completely contraindicated in keratoconus and other corneal depletion conditions because removal of corneal stromal tissue will further damage the already thin and weak cornea. For the same reason, radial keratotomy is also generally not used for people with keratoconus.
Prognosis
Patients with keratoconus usually present initially with mild astigmatism and myopia, generally at the onset of puberty, and are diagnosed by teenagers or early 20s. This disease can, however, be present or develop at any age; in rare cases, keratoconus may be present in children or not until adulthood. Diagnosis of disease at an early age may indicate a greater risk of severity later in life. The vision of the patient will appear to fluctuate for several months, prompting them to frequently alter the prescription of the lens, but as the condition worsens, contact lenses are required in most cases. Traveling disorders can vary greatly, with some patients remaining stable for years or indefinitely, while others develop rapidly or experience occasional exacerbations for long periods of time and are stable. Most often, keratoconus lasts for a period of 10 to 20 years before the course of the disease generally stops in the third and fourth decades of life.
Corneal Hydrops
In advanced cases, a corneal bulge may cause local rupture of the Descemet membrane, the inner lining of the cornea. The aqueous humor of the anterior chamber of the eye seeps into the cornea before the resection of the Descemet membrane. The patient experiences severe and severe pain and vision, with the cornea taking a milky white translucent appearance known as corneal hydrops.
Although it confuses the patient, the effect is usually temporary and after a period of six to eight weeks, the cornea usually returns to its original transparency. Recovery may be assisted non-surgically by dressing with an osmotic salt solution. Although hydrops usually cause increased scarring of the cornea, it will sometimes benefit the patient by creating a flat cone, assisting the installation of contact lenses. Corneal transplantation is usually not indicated during corneal hydrops.
Epidemiology
The National Eye Institute reports keratoconus is the most common corneal dystrophy in the United States, affecting about one in 2,000 Americans, but some reports place numbers as high as one in 500. Inconsistency may be due to variations in diagnostic criteria, with some cases of severe astigmatism defined as keratoconus , and otherwise . A long-term study found an average incidence rate of 2.0 new cases per 100,000 population per year. Some studies indicate a higher prevalence among women, or that people from South Asian ethnicity are 4.4 times more likely to suffer from keratoconus as Caucasian, and are also more likely to be affected by previous conditions.
Keratoconus is usually bilateral (affects both eyes) although distortion is usually asymmetrical and rarely altogether in both corneas. Unilateral cases tend to be uncommon, and may actually be very rare if very mild conditions in the eyes are better just below the limits of clinical detection. It is common for keratoconus to be first diagnosed on one eye and not until later on the other. When this condition develops in both eyes, vision in the previously diagnosed eye will often remain worse than the other eye.
History
The German biochemist Burchard Mauchart gave an early description in a 1748 doctoral dissertation on the case of keratoconus, which he called staphyloma diaphanum. However, it was not until 1854 that the English physician John Nottingham (1801-1856) clearly described keratoconus and distinguished it from other ectasias of the cornea. Nottingham reports the case of "corneal cones" of concern, and describes some of the classic features of the disease, including polyopia, corneal weakness, and difficulty adjusting corrective lenses with patient vision. In 1859, British surgeon William Bowman used an ophthalmoscope (recently discovered by Hermann von Helmholtz) to diagnose keratoconus, and described how to tilt the instrument's mirror so as to see the most conical shape of the cornea. Bowman also attempts to restore vision by pulling the iris with a fine hook inserted through the cornea and stretching the pupil into the vertical gap, as in the cat. He reported that he had a measure of success with the technique, restoring his eyesight to an 18-year-old woman who previously could not count fingers at a distance of 8 inches (20 cm).
In 1869, when Swiss physician pioneer Johann Horner wrote a thesis entitled In the treatment of keratoconus , the disorder has earned his current name. The treatment at the time, supported by the renowned German eye physician Albrecht von Graefe, was an attempt to physically reshape the cornea by chemical cauterization with a silver nitrate solution and the application of miosis-causing agents with pressure dressings. In 1888, keratoconus treatment became one of the first practical applications of newly discovered contact lenses, when French physician EugÃÆ'¨ne Kalt made scleral shell glass that enhanced vision by compressing the cornea into a more regular shape. Since the beginning of the 20th century, research on keratoconus has increased understanding of the disease and expanded the range of treatment options. The first successful corneal transplant to treat keratoconus was done in 1936 by Ramon Castroviejo.
Society and culture
Cost
According to findings from the Collaborative Longitudinal Evaluation of Keratoconus (CLEK), people who have keratoconus can be expected to pay more than $ 25,000 during their post-diagnosis period, with a standard deviation of $ 19,396. There is limited evidence on cross-linking costs of the cornea, a cost-effectiveness study estimating total treatment costs for one person as Ã, £ 928 ($ 1,392 US) in the UK National Health Service, but this may be as high as $ 2,500 per eye in other countries. The 2013 cost-benefit analysis by the Lewin Group for the Eye Bank Association of America estimates the average cost of $ 16,500 for each corneal transplant.
Related interruptions
Some other corneal ectatic abnormalities also cause corneal thinning:
- Keratoglobus is a very rare condition that causes thinning of the cornea especially at the edges, resulting in a rounded and slightly enlarged eye. May be genetically related to keratoconus.
- Sharp marginal degradation causes narrow corneal thinning (1-2 mm), usually along the margins of the inferior cornea. This leads to irregular astigmatism which, in the early stages of the disease can be corrected with glasses. The differential diagnosis can be done by slit-lamp examination.
- Posterior keratoconus, a distinct disorder with a similar name, is a rare, usually congenital, abnormality that causes thinning of the surface of the cornea, while the anterior curvature remains normal. Usually only one eye is affected.
- Post-LASIK ectasia is a complication of LASIK eye surgery.
References
External links
- Keratoconus in Curlie (based on DMOZ)
Source of the article : Wikipedia
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