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Corneal dystrophies were commonly subdivided depending on its specific location within the cornea into "anterior", "stromal", or "posterior" according to the layer of the cornea affected by the dystrophy.
In 2015 the ICD3 classification was published. and has classified disease into four groups as follows:
Epithelial and subepithelial dystrophies
- Epithelial basement membrane dystrophy
- Epithelial recurrent erosion dystrophies (EREDs)—Franceschetti corneal dystrophy, Dystrophia Smolandiensis, and Dystrophia Helsinglandica
- Subepithelial mucinous corneal dystrophy
- Meesmann corneal dystrophy
- Lisch epithelial corneal dystrophy
- Gelatinous drop-like corneal dystrophy
Bowman Layer dystrophies
- Reis–Bücklers corneal dystrophy
- Thiel–Behnke corneal dystrophy
- Stromal dystrophies-
- TGFB1 corneal dystrophies
- Lattice corneal dystrophy, type 1 variants (III, IIIA, I/IIIA, IV) of lattice corneal dystrophy
- Granular corneal dystrophy, type 1
- Granular corneal dystrophy, type 2
Stromal dystrophies
- Macular corneal dystrophy
- Schnyder crystalline corneal dystrophy
- Congenital stromal corneal dystrophy
- Fleck corneal dystrophy
- Posterior amorphous corneal dystrophy
- Central cloudy dystrophy of François
- Pre-Descemet corneal dystrophy
Endothelial dystrophies
- Fuchs' dystrophy
- Posterior polymorphous corneal dystrophy
- Congenital hereditary endothelial dystrophy
- X-linked endothelial corneal dystrophy
The following (now historic) classification was by Klintworth:
Superficial dystrophies:
- Epithelial basement membrane dystrophy
- Meesmann juvenile epithelial corneal dystrophy
- Gelatinous drop-like corneal dystrophy
- Lisch epithelial corneal dystrophy
- Subepithelial mucinous corneal dystrophy
- Reis-Bucklers corneal dystrophy
- Thiel–Behnke dystrophy
Stromal dystrophies:
- Lattice corneal dystrophy
- Granular corneal dystrophy
- Macular corneal dystrophy
- Schnyder crystalline corneal dystrophy
- Congenital stromal corneal dystrophy
- Fleck corneal dystrophy
Posterior dystrophies:
- Fuchs' dystrophy
- Posterior polymorphous corneal dystrophy
- Congenital hereditary endothelial dystrophy
Main differential diagnosis include various causes of monoclonal gammopathy, lecithin-cholesterol-acyltransferase deficiency, Fabry disease, cystinosis, tyrosine transaminase deficiency, systemic lysosomal storage diseases, and several skin diseases (X-linked ichthyosis, keratosis follicularis spinolosa decalvans).
Historically, an accumulation of small gray variable shaped punctate opacities of variable shape in the central deep corneal stroma immediately anterior to Descemet membrane were designated deep filiform dystrophy and cornea farinata because of their resemblance to commas, circles, lines, threads (filiform), flour (farina) or dots. These abnormalities are now known to accompany X-linked ichthyosis, steroid sulfatase deficiency, caused by steroid sulfatase gene mutations and are currently usually not included under the rubric of the corneal dystrophies.
In the past, the designation vortex corneal dystrophy (corneal verticillata) was applied to a corneal disorder characterized by the presence of innumerable tiny brown spots arranged in curved whirlpool-like lines in the superficial cornea. An autosomal dominant mode of transmission was initially suspected, but later it was realized that these individuals were affected hemizygous males and asymptomatic female carriers of an X-linked systemic metabolic disease caused by a deficiency of α-galactosidase, known as Fabry disease.
To clarify whether Thiel–Behnke corneal dystrophy is a separate entity from Reis-Bucklers corneal dystrophy, Kuchle et al. (1995) examined 28 corneal specimens with a clinically suspected diagnosis of corneal dystrophy of the Bowman layer by light and electron microscopy and reviewed the literature and concluded that 2 distinct autosomal dominant corneal dystrophy of Bowman layer (CBD) exist and proposed the designation CDB type I (geographic or 'true' Reis-Bucklers dystrophy) and CDB type II (honeycomb-shaped or Thiel–Behnke dystrophy). Visual loss is significantly greater in CDB I, and recurrences after corneal transplantation seem to be earlier and more extensive in CDB I.
Congenital stromal corneal dystrophy (CSCD), also called Witschel dystrophy, is an extremely rare, autosomal dominant form of corneal dystrophy. Only 4 families have been reported to have the disease by 2009. The main features of the disease are numerous opaque flaky or feathery areas of clouding in the stroma that multiply with age and eventually preclude visibility of the endothelium. Strabismus or primary open angle glaucoma was noted in some of the patients. Thickness of the cornea stays the same, Descemet's membrane and endothelium are relatively unaffected, but the fibrills of collagen that constitute stromal lamellae are reduced in diameter and lamellae themselves are packed significantly more tightly.
In the recessive form corneal clouding is observed at birth or within the neonatal period, nystagmus is often present, but no photophobia or epiphora is seen. In the autosomal dominant type corneal opacification is usually seen in the first or second year of life and progresses slowly, and nystagmus is infrequently seen.
Thiel–Behnke dystrophy, or Corneal dystrophy of Bowman layer, type II, is a rare form of corneal dystrophy affecting the layer that supports corneal epithelium.
The dystrophy was first described in 1967 and initially suspected to denote the same entity as the earlier-described Reis-Bucklers dystrophy, but following a study in 1995 by Kuchle et al. the two look-alike dystrophies were deemed separate disorders.
Congenital hereditary corneal dystrophy (CHED) is a form of corneal dystrophy which presents at birth.
Granular corneal dystrophy is diagnosed during an eye examination by an ophthalmologist or optometrist. The lesions consist of central, fine, whitish granular lesions in the cornea. Visual acuity is slightly reduced.
Granular corneal dystrophy is a slowly progressive corneal dystrophy that most often begins in early childhood.
Granular corneal dystrophy has two types:
- Granular corneal dystrophy type I , also corneal dystrophy Groenouw type I, is a rare form of human corneal dystrophy. It was first described by German ophthalmologist Arthur Groenouw in 1890.
- Granular corneal dystrophy type II, also called Avellino corneal dystrophy or combined granular-lattice corneal dystrophy is also a rare form of corneal dystrophy. The disorder was first described by Folberg et al. in 1988. The name Avellino corneal dystrophy comes from the first four patients in the original study each tracing their family origin to the Italian province of Avellino.
Oguchi disease present with nonprogressive night blindness since young childhood or birth with normal day vision, but they frequently claim improvement of light sensitivities when they remain for some time in a darkened environment.
On examination patients have normal visual fields but the fundos have a diffuse or patchy, silver-gray or golden-yellow metallic sheen and the retinal vessels stand out in relief against the background.
A prolonged dark adaptation of three hours or more, leads to disappearance of this unusual discoloration and the appearance of a normal reddish appearance. This is known as the Mizuo-Nakamura phenomena and is thought to be caused by the overstimulation of rod cells.
Other conditions with similar appearing fundi include
- Cone dystrophy
- X-linked retinitis pigmentosa
- Juvenile macular dystrophy
These conditions do not show the Mizuo-Nakamura phenomenon.
FED may be discovered as an incidental finding at a routine visit to an optometrist. or by an ophthalmologist during assessment for cataract surgery. As a result of irregularities on the inner surface of the cornea, affected individuals may simply notice a reduction in the quality of vision or glare or haloes particularly when driving at night. Individuals with symptomatic Fuchs' dystrophy typically awaken with blurred vision which improves during the day. This occurs because the cornea is normally more swollen in the morning due to nocturnal fluid retention in the absence of normal evaporation due to the lids being closed. During waking hours this fluid evaporates once the eyes are open. As the disease worsens vision remains blurred despite evaporation due to endothelial pump failure and fluid retention. As Fuchs' dystrophy typically occurs in older individuals there may also be cataract of the lens, which also reduces vision.
Researchers are finding that Fuchs' is a genetically heterogeneous disease, and many different genes and loci have been associated as contributing to a small percentage of overall Fuchs' cases. Certain genetic lesions have been correlated with more severe disease and earlier onset. Therefore, some individuals may experience symptoms of the disease at a much earlier age, while others may not experience symptoms until late in life.
X-linked endothelial corneal dystrophy (XECD) is a rare form of corneal dystrophy described first in 2006, based on a 4-generation family of 60 members with 9 affected males and 35 trait carriers, which led to mapping the XECD locus to Xq25. It manifests as severe corneal opacification or clouding, sometimes congenital, in the form of a ground glass, milky corneal tissue, and moon crater-like changes of corneal endothelium. Trait carriers manifest only endothelial alterations resembling moon craters.
As of December 2014, the molecular basis for this disease remained unknown, although 181 genes were known to be within the XECD locus, of which 68 were known to be protein-coding.
Fuchs' dystrophy, also referred to as Fuchs' corneal endothelial dystrophy (FCED) and Fuchs' endothelial dystrophy (FED), is a slowly progressing corneal dystrophy that usually affects both eyes and is slightly more common in women than in men. Although early signs of Fuchs' dystrophy are sometimes seen in people in their 30s and 40s, the disease rarely affects vision until people reach their 50s and 60s.
The condition was first described by Austrian ophthalmologist Ernst Fuchs (1851–1930), after whom it is named. In 1910, Fuchs first reported 13 cases of central corneal clouding, loss of corneal sensation and the formation of epithelial bullae, or blisters, which he labeled 'dystrophia epithelialis corneae'. It was characterized by late onset, slow progression, decreased visual acuity in the morning, lack of inflammation, diffuse corneal opacity, intense centrally, and roughened epithelium with vesicle-like features.
A shift to the understanding of FCED as primarily a disease of the corneal endothelium resulted after a number of observations in the 1920s. Crystal-like features of the endothelium were noted by Kraupa in 1920, who suggested that the epithelial changes were dependent on the endothelium. Using a slit lamp, Vogt described the excrescences associated with FCD as drop-like in appearance in 1921. In 1924, Graves then provided an extremely detailed explanation of the endothelial elevations visible with slit-lamp biomicroscopy. A patient with unilateral epithelial dystrophy and bilateral endothelial changes was described by the Friedenwalds in 1925; subsequent involvement of the second eye led them to emphasize that endothelial changes preceded epithelial changes. As only a subset of patients with endothelial changes proceeded to epithelial involvement, Graves stated on 19 October 1925 to the New York Academy of Medicine that "Fuchs' epithelial dystrophy may be a very late sequel to severer cases of the deeper affection".
Treatment options include contact lenses and intrastromal corneal ring segments for correcting refractive errors caused by irregular corneal surface, corneal collagen cross-linking to strengthen a weak and ectatic cornea, or corneal transplant for advanced cases.
The presentation of Ullrich congenital muscular dystrophy in an affected individual is as follows:
- Muscle weakness
- Difficulty walking
- Contractures (neck)
- Joint looseness
There is another retinal disease in Briards known as hereditary retinal dysplasia. These dogs are night blind from birth, and day vision varies. Puppies affected often have nystagmus. It is also known as lipid retinopathy.
Progressive vision loss in any dog in the absence of canine glaucoma or cataracts can be an indication of PRA. It usually starts with decreased vision at night, or nyctalopia. Other symptoms include dilated pupils and decreased pupillary light reflex. Fundoscopy to examine the retina will show shrinking of the blood vessels, decreased pigmentation of the nontapetal fundus, increased reflection from the tapetum due to thinning of the retina, and later in the disease a darkened, atrophied optic disc. Secondary cataract formation in the posterior portion of the lens can occur late in the disease. In these cases diagnosis of PRA may require electroretinography (ERG). For many breeds there are specific genetic tests of blood or buccal mucosa for PRA.
Absent a genetic test, animals of breeds susceptible to PRA can be cleared of the disease only by the passage of time—that is, by living past the age at which PRA symptoms are typically apparent in their breed. Breeds in which the PRA gene is recessive may still be carriers of the gene and pass it on to their offspring, however, even if they lack symptoms, and it is also possible for onset of the disease to be later than expected, making this an imperfect test at best.
Hair growth on the head is noticeably less full than normal, and the hairs are very weak; the rest of the body shows normal hair.
The macular degeneration comes on slowly with deterioration of central vision, leading to a loss of reading ability. Those affected may otherwise develop in a completely healthy manner; life expectancy is normal.
The most common symptoms of cone dystrophy are vision loss (age of onset ranging from the late teens to the sixties), sensitivity to bright lights, and poor color vision. Therefore, patients see better at dusk. Visual acuity usually deteriorates gradually, but it can deteriorate rapidly to 20/200; later, in more severe cases, it drops to "counting fingers" vision. Color vision testing using color test plates (HRR series) reveals many errors on both red-green and blue-yellow plates.
Corneal ectatic disorders or corneal ectasia are a group of uncommon, noninflammatory, eye disorders characterised by bilateral thinning of the central, paracentral, or peripheral cornea.
- Keratoconus, a progressive, noninflammatory, bilateral, asymmetric disease, characterized by paraxial stromal thinning and weakening that leads to corneal surface distortion.
- Keratoglobus, a rare noninflammatory corneal thinning disorder, characterised by generalised thinning and globular protrusion of the cornea.
- Pellucid marginal degeneration, a bilateral, noninflammatory disorder, characterized by a peripheral band of thinning of the inferior cornea.
- Posterior keratoconus, a rare condition, usually congenital, which causes a nonprogressive thinning of the inner surface of the cornea, while the curvature of the anterior surface remains normal. Usually only a single eye is affected.
- Post-LASIK ectasia, a complication of LASIK eye surgery.
- Terrien's marginal degeneration, a painless, noninflammatory, unilateral or asymmetrically bilateral, slowly progressive thinning of the peripheral corneal stroma.
Most infants with CMD will display some progressive muscle weakness or muscle wasting (atrophy), although there can be different degrees and symptoms of severeness of progression. The weakness is indicated as "hypotonia", or lack of muscle tone, which can make an infant seem unstable.
Children may be slow with their motor skills; such as rolling over, sitting up or walking, or may not even reach these milestones of life. Some of the more rarer forms of CMD can result in significant learning disabilities.
A cone dystrophy is an inherited ocular disorder characterized by the loss of cone cells, the photoreceptors responsible for both central and color vision.
Presentation of symptoms and signs varies considerably by form (DM1/DM2), severity and even unusual DM2 phenotypes. DM1 symptoms for DM2 include problems with executive function (e.g., organization, concentration, word-finding) and hypersomnia. Conduction abnormalities are more common in DM1 than DM2, but all people are advised to have an annual ECG. Both types are also associated with insulin resistance. Myotonic dystrophy may have a cortical cataract with a blue dot appearance, or a posterior subcapsular cataract.
DM2 is generally milder than DM1, with generally fewer DM2 people requiring assistive devices than DM1 people. In addition, the severe congenital form that affects babies in DM1 has not been found in DM2 and the early onset of symptoms is rarely noted to appear in younger people in the medical literature.
Symptoms may appear at any time from infancy to adulthood. DM causes general weakness, usually beginning in the muscles of the hands, feet, neck, or face. It slowly progresses to involve other muscle groups, including the heart. DM affects a wide variety of other organ systems as well.
The age of onset is in a child's infancy. Bilateral corneal opacification started in the second year of life and led to severe visual impairment. However, cornea surgery and replacement resulted in better vision.
Symptoms include a combination of spinocerebellar degeneration and corneal dystrophy. Mental retardation and slowly progressive cerebellar abnormalities were also diagnosed in patients. Other symptoms include corneal edema, thickening of Descemet membrane, and degenerative pannus. Abnormalities were found in muscle and sural nerves.