Flat cornea, also known as cornea plana, is a rare eye condition present from birth. It involves an unusual flattening of the clear front part of the eye, which significantly impacts how light enters and focuses within the eye. This anomaly can lead to various vision challenges for affected individuals.
Understanding the Cornea’s Role
The cornea is the transparent, dome-shaped outer layer at the front of the eye, covering the iris, pupil, and anterior chamber. It plays a significant role in vision by bending, or refracting, incoming light and directing it onto the retina at the back of the eye to produce a clear image. Normally, the cornea has a distinct curved shape, typically described as an ellipsoid with an approximate radius of curvature around 7.8 millimeters.
In individuals with cornea plana, this natural curvature is greatly reduced, causing the cornea to appear much flatter. This reduction diminishes the eye’s ability to refract light effectively. As a result, light does not focus properly on the retina, leading to visual disturbances. The primary consequence is often severe farsightedness (hypermetropia), where distant objects appear clearer than close ones.
Genetic Basis and Clinical Types
Cornea plana is a congenital condition with a genetic origin. Several genes are implicated in its development, with mutations in the KERA (keratocan) gene being a common cause, particularly for the autosomal recessive form. This gene is responsible for producing a protein that maintains the cornea’s hydration, transparency, and structural organization.
Disruptions in the KERA gene can impair the proper formation of collagen, a protein contributing to the cornea’s normal curvature. There are two clinical types: autosomal recessive cornea plana (CNA2) and autosomal dominant cornea plana (CNA1). The autosomal recessive form is generally more severe, occurring when an individual inherits two copies of the mutated gene, one from each parent.
In contrast, the autosomal dominant form usually presents with milder symptoms, caused by inheriting just one copy of the mutated gene from a parent. Individuals with autosomal dominant cornea plana tend to have fewer associated eye abnormalities. The more severe autosomal recessive form is frequently linked to additional ocular conditions like sclerocornea or microcornea.
Recognizing Symptoms and Related Eye Issues
The specific symptoms of cornea plana can vary considerably, depending on the severity of the condition and its underlying genetic cause. A common visual symptom is severe farsightedness, often accompanied by reduced clarity of vision. Some individuals may also experience nystagmus, which involves involuntary, repetitive eye movements.
Cornea plana can also be associated with other eye abnormalities. These include conditions such as glaucoma, an eye disease that can damage the optic nerve, and cataracts, which cause clouding of the eye’s lens. Retinal detachment, microcornea (an unusually small cornea), and a hazy corneal limbus (the border between the cornea and the white of the eye) have also been observed.
The angle between the cornea and the sclera (the white outer layer of the eye) may be decreased, leading to an indistinct border between them. Patients may also present with shallow anterior chamber depth. These associated conditions can significantly impact vision.
Diagnosis, Management, and Outlook
Diagnosing cornea plana typically involves a thorough eye examination performed by an eye care professional. This examination includes precise measurements of the corneal curvature using specialized equipment like a keratometer or a corneal topographer. An assessment of the eye’s refractive error is also conducted to determine the degree of farsightedness.
Genetic testing can further aid in confirming the diagnosis, especially when there is a family history of the condition, by identifying specific gene mutations. Management strategies primarily focus on improving visual acuity and addressing any associated complications. This often involves prescribing glasses or contact lenses to correct the refractive error caused by the flat cornea.
For severe cases, surgical interventions such as corneal transplantation or refractive surgery may be considered. Regular monitoring and follow-up appointments are important to manage potential complications and preserve vision. While some individuals may achieve good visual acuity with appropriate management, the prognosis can vary depending on the condition’s severity and the presence of other eye issues.