Sclerocornea | |
---|---|
This condition can be inherited in an autosomal dominant manner | |
Specialty | Ophthalmology |
Sclerocornea is an extremely rare congenital anomaly of the eye, it is considered a form of congenital corneal opacity (CCO) with no clear gender bias, in which the cornea blends with sclera, having no clear-cut boundary. [1] The extent of the resulting opacity varies from peripheral to total (sclerocornea totalis). While the exact historical origins of its documentation are unclear, studies on sclerocornea has long been recognized in ophthalmology as a rare but significant anomaly going as far back as the 1960's. [2] The severe form is thought to be inherited in an autosomal recessive manner, but there may be another, milder form that is expressed in a dominant fashion. In some cases the patients also have abnormalities beyond the eye (systemic), such as limb deformities and craniofacial and genitourinary defects.
According to one tissue analysis performed after corneal transplantation, the sulfation pattern of keratan sulfate proteoglycans in the affected area is typical for corneal rather than scleral tissue. [3]
Sclerocornea may be concurrent with cornea plana.
Sclerocornea causes parts or all of the cornea to become cloudy. This cloudiness can be partial or complete. The more of the cornea that is affected, the worse a persons vision will be. The main area affected is the cornea, but the issue can also spread to nearby parts of the eye, like the limbus and front eye structure, such as the iris . Since Sclerocornea is present from birth and does not develop later in life there are no short-term symptoms or signs. The condition usually affects both eyes and it does not worsen overtime, the symptoms and severity are present from birth and generally remain stable. [1]
As a result and depending on the variety, the patient may have poor vision from birth and in some cases problems with eye movement, such as nystagmus or strabismus . Over time, people may develop severe farsightedness, glaucoma, and other eye issues. [4]
The exact cause of Sclerocornea is not fully understood, but it is believed to involve genetics and developmental factors during fetus development. Sclerocornea can be inherited genetically, as autosomal dominant or recessive trait, with the latter form often being more severe. [1] There are findings suggesting that a genetic locus at chromosome 22q11.2 plays a crucial role in the formation and development of the eye during the early stages of embryonic growth. [5] This gene in some cases are associated with the genetic disorders like Digeorge syndrome, PHACES syndrome, Dandy-walker malformation, and Hurler syndrome making genetic counseling important.
The condition is thought to occur because the neural crest cells dont move or develop correctly between the 7th and 10th week of pregnancy. These cells are important for forming many parts of the eye structures, and abnormalities in their formation can lead to issues. [1]
Recent research has highlighted the role of mutation/deletion in the RAD21 gene. A 2019 study suggest that beyond its known role in cell division and chromosome organization, RAD21 may also contribute to the development of peripheral sclerocornea. [6]
The main problem affected in sclerocornea occurs in the cornea, which doesn’t develop correctly and starts to look more like the white part of the eye (the sclera). The condition is thought to occur because certain cells, called neural crest cells, don’t move or develop as they should during the 7th and 10th weeks of gestation. When these cells do not migrate correctly, the cornea does not develop into a clear structure. Instead, it becomes opaque and the boundary of the cornea is found to be poorly defined. [7]
Under a microscope, the cornea’s layers, known as stromal lamellae, are disorganized, have extra blood vessels, and the cornea’s structure is different from the usual structure of cornea's. Even though the cornea becomes more like the sclera, it still has some unique markers that show it retains some of its original characteristics. [1]
Scientists don’t fully understand how all the changes happen, but they think it could be due to problems with certain genes such as 22q11.2. There are also studies coming out stating that a mutation or deletions in the gene RAD21 might be causing the bad development of neural crest cells. [8]
Diagnosis typically involves a pediatric ophthalmologist after a basic outpatient examination and might require a geneticist for counseling if an inherited form is suspected. A slit-lamp examination is used to evaluate the cornea. Imaging techniques, such as anterior segment optical coherence tomography (ASOCT), can help assess the depth of the opacity and the structure of the anterior segment of the eye. Other evaluations include under anesthesia to get measurement of corneal thickness with ultrasound pachymetry. [9] [10]
Misdiagnosis can happen due to overlapping features with other congenital corneal opacities. Diagnostic delays may happen if systemic associations are not immediately recognized. [11]
Primary treatment for Sclerocornea is Penetrating keratoplasty (PK), it is only considered for severe cases although success rates are variable due to risks like graft rejection and glaucoma. In a study, of 8 patients with peters anomaly and 10 with sclerocornea, underwent penetrating keratoplasty when they were 5 years or younger. The graft survival was poor in patients with sclerocornea compared to those with peters anomaly. [12] Another study showed failure in 75% of the cases of PK (penetrating keratoplasty) in patients with sclerocornea. It is said that the presence of opacity or vascularization in the limbus and in the peripheral cornea and the diameter of the patients cornea were correlated with graft failure. [13]
Non surgical options include refractive correction, such as glasses or contacts if possible or optical iridotomy, this can be considered for milder cases. [1]
The prognosis depends on the extent of the condition. Visual outcomes depend on the timing and extend of intervention. [14] Treatment of sclerocornea has a high rate of failing however those that succeed with treatment are likely to have favorable outcomes. [15] The poor prognosis of corneal transplantation in sclerocornea is related to corneal vascularization, related to changes in the eye mostly glaucoma, and the need for related surgeries such as lensectomy, a surgical procedure that removes the eye's natural lens and replaces it with an implant and vitrectomy, among others. In patients with partial sclerocornea, optical correction, with glasses, should be performed early in order to avoid amblyopia due to high hyperopia. [16]
Sclerocornea is a rare disorder, with no clear gender bias. In one study, 14 patients were diagnosed with a congenital corneal opacity over a 40-year study period, yielding a birth prevalence of 1 in 5188 live births. The mean age at diagnosis was 7.5 months (range 0–48 months) and 9 (64.3%) were males. Out of the 14 patients diagnosed only 2 of them had sclerocornea. [17] This condition also often accompanies other congenital disorders such as peters anaomly, affecting its distribution and manifestation. [11]
Recent research has focused on the genetic causes of sclerocornea and improving treatment options. Studies have identified that mutations in specific genes play a role in different forms of the condition.
GJA8 Mutations: Researchers found that mutations in the GJA8 gene can cause a severe form of sclerocornea, where the entire cornea is affected. This highlights the importance of testing for GJA8 mutations in patients with severe anterior segment abnormalities. [18]
RAD21 Variant: Another study linked a RAD21 variant to peripheral sclerocornea, suggesting that this mutation alters chromosome structure and gene expression, contributing to the condition. [8]
One of the main challenges in sclerocornea research is the rarity of the disease, which makes large-scale studies difficult. However, ongoing collaborative efforts and case reports are helping to expand understanding, particularly in developing new treatment strategies and documenting unique cases [19]
Keratoconus (KC) is a disorder of the eye that results in progressive thinning of the cornea. This may result in blurry vision, double vision, nearsightedness, irregular astigmatism, and light sensitivity leading to poor quality-of-life. Usually both eyes are affected. In more severe cases a scarring or a circle may be seen within the cornea.
Eye surgery, also known as ophthalmic surgery or ocular surgery, is surgery performed on the eye or its adnexa. Eye surgery is part of ophthalmology and is performed by an ophthalmologist or eye surgeon. The eye is a fragile organ, and requires due care before, during, and after a surgical procedure to minimize or prevent further damage. An eye surgeon is responsible for selecting the appropriate surgical procedure for the patient, and for taking the necessary safety precautions. Mentions of eye surgery can be found in several ancient texts dating back as early as 1800 BC, with cataract treatment starting in the fifth century BC. It continues to be a widely practiced class of surgery, with various techniques having been developed for treating eye problems.
A red eye is an eye that appears red due to illness or injury. It is usually injection and prominence of the superficial blood vessels of the conjunctiva, which may be caused by disorders of these or adjacent structures. Conjunctivitis and subconjunctival hemorrhage are two of the less serious but more common causes.
Corneal transplantation, also known as corneal grafting, is a surgical procedure where a damaged or diseased cornea is replaced by donated corneal tissue. When the entire cornea is replaced it is known as penetrating keratoplasty and when only part of the cornea is replaced it is known as lamellar keratoplasty. Keratoplasty simply means surgery to the cornea. The graft is taken from a recently deceased individual with no known diseases or other factors that may affect the chance of survival of the donated tissue or the health of the recipient.
Fuchs dystrophy, also referred to as Fuchs endothelial corneal dystrophy (FECD) 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.
Hyphema is the medical condition of bleeding in the anterior chamber of the eye between the iris and the cornea. People usually first notice a loss or decrease in vision. The eye may also appear to have a reddish tinge, or it may appear as a small pool of blood at the bottom of the iris in the cornea. A traumatic hyphema is caused by a blow to the eye. A hyphema can also occur spontaneously.
Corneal dystrophy is a group of rare hereditary disorders characterised by bilateral abnormal deposition of substances in the transparent front part of the eye called the cornea.
Iridocorneal endothelial (ICE) syndromes are a spectrum of diseases characterized by slowly progressive abnormalities of the corneal endothelium and features including corneal edema, iris distortion, and secondary angle-closure glaucoma. ICE syndromes are predominantly unilateral and nonhereditary. The condition occurs in predominantly middle-aged women.Iridocorneal Endothelial (ICE) syndrome presents a unique set of challenges for both patients and ophthalmologists, and effective treatment of this group of rare ocular diseases requires a combination of diagnostic and therapeutic complexity. It's important to understand.
Axenfeld–Rieger syndrome is a rare autosomal dominant disorder, which affects the development of the teeth, eyes, and abdominal region.
Polycoria is a pathological condition of the eye characterized by more than one pupillary opening in the iris. It may be congenital or result from a disease affecting the iris. It results in decreased function of the iris and pupil, affecting the physical eye and visualization.
Corneal neovascularization (CNV) is the in-growth of new blood vessels from the pericorneal plexus into avascular corneal tissue as a result of oxygen deprivation. Maintaining avascularity of the corneal stroma is an important aspect of healthy corneal physiology as it is required for corneal transparency and optimal vision. A decrease in corneal transparency causes visual acuity deterioration. Corneal tissue is avascular in nature and the presence of vascularization, which can be deep or superficial, is always pathologically related.
Pellucid marginal degeneration (PMD) is a degenerative corneal condition, often confused with keratoconus. It typically presents with painless vision loss affecting both eyes. Rarely, it may cause acute vision loss with severe pain due to perforation of the cornea. It is typically characterized by a clear, bilateral thinning (ectasia) in the inferior and peripheral region of the cornea, although some cases affect only one eye. The cause of the disease remains unclear.
Meesmann corneal dystrophy (MECD) is a rare hereditary autosomal dominant disease that is characterized as a type of corneal dystrophy and a keratin disease. MECD is characterized by the formation of microcysts in the outermost layer of the cornea, known as the anterior corneal epithelium. The anterior corneal epithelium also becomes fragile. This usually affects both eyes rather than a single eye and worsens over time. There are two phenotypes, Meesmann corneal dystrophy 1 (MECD1) and Meesmann corneal dystrophy 2 (MECD2), which affect the genes KRT3 and KRT12, respectively. A heterozygous mutation in either of these genes will lead to a single phenotype. Many with Meesmann corneal dystrophy are asymptomatic or experience mild symptoms.
Macular corneal dystrophy, also known as Fehr corneal dystrophy, is a rare pathological condition affecting the stroma of cornea first described by Arthur Groenouw in 1890. Signs are usually noticed in the first decade of life and progress afterwards, with opacities developing in the cornea and attacks of pain. This gradual opacification leads to visual impairment often requiring keratoplasty in the later decades of life.
Cornea plana 2(CNA2) is a congenital disorder that causes the cornea to flatten and the angle between the sclera and cornea to shrink. This could result in the early development of arcus lipoides, hazy corneal limbus, and hyperopia. There is evidence that cornea plana 2 is caused by mutations in KERA gene encoding keratocan. Cornea plana 2 is an autosomal recessive disorder.
Cornea plana 1(CNA1) is a congenital disorder that causes the cornea to flatten and the angle between the sclera and cornea to shrink. This could result in the early development of arcus lipoides, hazy corneal limbus, and hyperopia. Cornea plana 1 is an autosomal dominant disorder.
Anterior segment mesenchymal dysgenesis, or simply anterior segment dysgenesis (ASD), is a failure of the normal development of the tissues of the anterior segment of the eye. It leads to anomalies in the structure of the mature anterior segment, associated with an increased risk of glaucoma and corneal opacity.
Forkhead box protein E3 (FOXE3) also known as forkhead-related transcription factor 8 (FREAC-8) is a protein that in humans is encoded by the FOXE3 gene located on the short arm of chromosome 1.
Corneal opacification is a term used when the human cornea loses its transparency. The term corneal opacity is used particularly for the loss of transparency of cornea due to scarring. Transparency of the cornea is dependent on the uniform diameter and the regular spacing and arrangement of the collagen fibrils within the stroma. Alterations in the spacing of collagen fibrils in a variety of conditions including corneal edema, scars, and macular corneal dystrophy is clinically manifested as corneal opacity. The term corneal blindness is commonly used to describe blindness due to corneal opacity.
Primary congenital glaucoma is a rare eye condition that is present at birth or develops early in childhood. It occurs due to improper drainage of the eye's fluids, which leads to increased pressure inside the eye, known as intraocular pressure. This elevated pressure can damage the optic nerve which will result permanent vision loss. It is also known as pediatric glaucoma or childhood glaucoma, and was previously known as trabeculodysgenesis or goniodysgenesis.