Post corneal embryonic ring

Introduction There is a convex white line near the limbus, and a tissue strip extends from the peripheral portion of the iris to the white line. Axenfeld calls it the post-corneal embryonic ring. The post-corneal embryonic ring is a clinical manifestation due to Axenfeld-Rieger abnormalities or syndromes. Axenfeld-Rieger syndrome is a group of developmental diseases with developmental defects in both eyes with or without systemic abnormalities. It is characterized by: 1 binocular developmental defects; 2 may be associated with systemic abnormalities; 3 secondary glaucoma; 4 autosomal dominant inheritance, mostly family history, there are reports of sporadic cases; 5 men and women have the same incidence.

Cause

(1) Causes of the disease

The Aksenfeld-Rigger abnormality or syndrome is autosomal dominant, and the male and female have equal chances of having a familial history, but there are also reports of sporadic cases. The cause of the disease is that Axenfeld-Rieger syndrome is a type of disease that develops malformations. Reese believes that the iridocorneal angle is incompletely differentiated and causes abnormal development of the anterior segment of the anterior segment of the eye. It is suggested that the keratoconus keratosis syndrome includes three types of diseases: Axenfeld abnormality, Rieger abnormality and Peter abnormality. The anterior chamber forms and differentiates into the iris corneal horn structure at 4 to 6 months of the embryo. At this time, if the mesoderm tissue between the cornea and the iris is stagnant, and the cells and tissues remain, it will cause abnormalities in the anterior segment of the eye. Recent studies have revealed that neural crest cells are the most likely primary tissues involved in Aksenfeld-Rigger or syndrome. The development of the anterior segment of the eye from the neural crest cells is blocked at the end of the embryo, leading to abnormalities in the original endothelial cells of the iris and iris cornea, and variations in the aqueous drainage system.

(two) pathogenesis

Based on clinical and histopathological observations and modern understanding of normal anterior segment development, there is a theory that some anterior ocular structures originating from neural crest cells stop developing in the third trimester, causing eye syndrome in patients with AR syndrome. Damage, including abnormalities in the original endothelial cell layer of the iris and iris cornea, and variations in the aqueous drainage structure.

Iris change

In front of the iris, the tissue strip of the iris cornea and the abnormal Schwalbe line, there is an abnormal membrane tissue that represents the residual island of the original endothelial cell layer. Membrane contraction on the iris surface may be related to pupillary ectopic, pigmented valgus, iris atrophy and rupture formation. Of course, atrophy and rupture may also be associated with other factors such as ischemia. Residual primitive endothelial cells are associated with iris and corneal adhesions. During normal embryonic development, this primitive endothelial cell layer should disappear, but patients with AR syndrome remain, and extend from the edge of the corneal endothelium to the periphery of the iris, and some pigmented tissue contacts the membrane to form an iris corneal tissue strip. band.

2. Post-corneal embryonic ring

The abnormal development of the primitive endothelial cell layer of the iris corneal endothelium causes the junction of the corneal endothelium and the trabecular endothelial layer to shift forward. Due to the metabolic abnormality of the endothelial cell layer, the posterior elastic membrane abnormality or the posterior elastic membrane-like structure is covered. In the trabecular meshwork, a large number of abnormally active cells occur at this junction, and the Schwalbe line is formed to thicken and advance.

3. Abnormal water discharge structure

The developmental stagnation at the end of the third trimester of pregnancy blocked the anterior pigmentary tissue from retreating completely, causing the iris to adhere to the posterior part of the trabecular meshwork at a high level; developmental stagnation may also result in incomplete formation of the trabecular meshwork and the Schlemm's canal. Anyone can make the drainage of the water affected and increase the intraocular pressure.

4. Other

The forebrain, pituitary gland, maxillary bone, and most of the cartilage and teeth are derived from neural crest cells. Therefore, abnormal development of the neural crest can also explain the abnormal development of the pituitary, facial bone and teeth. In addition, pigment cells of the iris matrix, choroid, skin and hair are derived from the melanocytes of the neural crest. However, abnormal development of neural crest cells can not explain all the clinical manifestations of the intrinsic, such as excessive skin wrinkles around the umbilical cord and abnormalities of the genitourinary system. AR syndrome also involves the original outer embryonic layer other than the neural crest.

an examination

Related inspection

Corneal examination and CT examination of the temporal region

It is not difficult to diagnose according to the clinical features of this disease. Mainly based on the following:

1 The presence of the post-corneal embryonic ring: a typical feature of the disease, which is characterized by thickening and advancement of the Schwalbe line. But the intrinsic is not manifested in every patient. Individual patients may have no post-corneal embryonic rings, but have other typical manifestations of the eye and body. It is worth noting that this post-corneal embryonic ring can also occur in normal eyes, with an incidence of 8% to 15%, which is manifested by the isolated Schwalbe line protruding forward without any other eye changes. In addition, the posterior corneal embryonic ring is occasionally seen in patients with primary congenital glaucoma and iris corneal endothelial syndrome.

2 iris corneal angle abnormality: its main feature is that the thick tissue band from the surrounding iris across the angle crypt, connected with the prominent Schwalbe line, and the angle of the corner is open, but the iris root is attached to the high position, the sclera tendon is often Cover, the iris root is attached to the back of the trabecular meshwork.

3 iris abnormalities: mainly manifested as thinning of the iris, loss of normal texture, pigmentation epithelial eversion, pupillary deformation, multiple pupils and pupillary membrane closure.

4 may be associated with systemic abnormalities: mainly for tooth and facial developmental defects; such as tooth defects, small teeth, no teeth; flat middle face, maxillary dysplasia. There are also other systemic abnormalities.

5 Secondary glaucoma: More than 50% of patients have secondary glaucoma, which is more common in childhood and adolescents, but also in infants or middle-aged.

6 eyes on the onset: the vast majority of the incidence of both eyes, very few single eye disease.

7 No gender differences.

8 The disease has a family history.

According to the above characteristics, the disease can be diagnosed. But be aware that not every variation is fully expressed in one person. Even if several members of a family are ill, the ocular and systemic abnormalities of each patient can vary. Therefore, you should pay attention to the identification of other diseases before making a diagnosis.

Differential diagnosis

1. Iridocorneal endothelial syndrome (ICE): In ICE syndrome, abnormalities of iris and iris cornea angle are very similar to AR syndrome in clinical and histopathological terms, which makes some scholars think that two Syndrome is a part of a series of common abnormalities, but clinical manifestations can be distinguished as ICE including corneal endothelium abnormalities, monocular disease, no family history, and adolescent onset. In histopathology, the two syndromes are characterized by a membrane on the anterior chamber and the iris surface, which can form many different lesions when the membrane contracts. However, the membrane of AR syndrome represents a remnant of the original endothelial cell layer, while the ICE syndrome is caused by abnormal corneal endothelial proliferation.

2. Posterior corneal polymorphic dystrophy (PPD): PPD is similar to Aksenfeld-Rigger syndrome, both congenital, binocular, autosomal dominant, mostly symptomatic in adulthood It can be expressed as iris atrophy and abnormal iris corneal angle. However, the difference between PPD is that the corneal endothelium and the posterior elastic layer are abnormal. Under the slit lamp microscope, there is a vesicular or saclike appearance behind the cornea, which is arranged in a line or cluster shape, surrounded by a gray fuzzy halo, and partially visible corneal stroma. And epithelial edema.

3. Peter anomaly: The disease is a series of abnormalities, including the center of the cornea, the iris, and the lens. Because of some similarities with the Aksenfeld-Rigger syndrome, they were included in the same dysplasia classification, but the developmental abnormalities of the two diseases were different.

4. Aniridia: In this dysplasia, residual iris and anterior chamber abnormalities with glaucoma may confuse some patients with the Aksenfeld-Rigger syndrome.

5. Congenital iris dysplasia (congenital irishypoplasia): only iris dysplasia, no axenfeld-Rigger syndrome corner or any other abnormalities. But it can be accompanied by adolescent glaucoma and autosomal dominant inheritance.

6. Ocular dysplasia (oculodentodigitaldysplasia): In this disease, the dysplasia of the teeth is the same as the Aksenfeld-Rigger syndrome, even mild iris matrix dysplasia, corneal defects, small eyeballs and glaucoma.

7. The lens and ectopic ectopia (ectopia lentis etpupillae): is an autosomal recessive genetic disease. The binocular lens and the pupil ectopic, both of which are typically displaced in the contralateral direction. The pupil ectopic is similar to the Aksenfeld-Rigger syndrome, but the developmental defects of the iris-free corneal angle are different.

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