embryotoxon

Embryotoxon is a descriptive term for a congenital anomaly of the anterior segment of the eye. It is characterized by a prominent, thickened, and often white or yellowish ring within the corneal periphery. This ring is a result of a developmental abnormality of the limbus, the border between the cornea and the sclera. Specifically, it represents a thickened and often opaque Descemet's membrane and endothelium in this region.

This condition is typically bilateral, meaning it affects both eyes, although asymmetry can occur. Embryotoxon is often asymptomatic and is usually discovered during a routine eye examination. It does not typically affect visual acuity unless it is associated with other ocular anomalies. In some cases, it can be mistaken for other peripheral corneal opacities.

The most common form, posterior embryotoxon, is a prominent Schwalbe's line, which is a ring-like thickening at the termination of Descemet's membrane. Anterior embryotoxon is a rarer form where the entire limbal conjunctiva and anterior sclera appear thickened and pale.

While embryotoxon itself is benign, it can sometimes be associated with other congenital syndromes, such as Axenfeld-Rieger syndrome. This syndrome is characterized by a spectrum of anterior segment abnormalities including iridial dysgenesis, glaucoma, and tooth and facial anomalies. Therefore, when embryotoxon is diagnosed, a thorough ocular and systemic examination is often recommended to rule out associated conditions. Management is generally supportive and focuses on monitoring for any potential complications like glaucoma.