Corneal Ectasia - Types, Causes, Symptoms, Diagnosis, and Treatment

Introduction

Cornea is the curved and clear transparent uppermost tissue layer of the eye. It allows the light to enter and protects the pupil and iris. Thinning of the corneal layer of the eyes is called corneal ectasia. The eye's corneal tissue is very important as it controls the entry of light and focuses it on the retina, making it possible to see things and objects. Damage to these corneal layer disorders of the corneal tissues of the eye can lead to several vision disorders like nearsightedness (myopia) or astigmatism in the long term.

What Are the Types of Corneal Ectasia?

Depending on which portion of the corneal layer is subjected to thinning, corneal ectasias can have different forms. The following are the types:

• Keratoconus - Keratoconus is a type of corneal ectasia in which the central corneal layer gradually becomes thin, and this causes the eye to bulge in the shape of a cone. Posterior keratoconus is characterized by thinning of the cornea's posterior surface (inner surface) but does not lead to cone-shaped bulging of the eye.

• Keratoglobus - Keratoglobus is a degenerative eye disorder in which overall thinning of the corneal layer is observed. It is a rare condition that causes the round-shaped bulging of the eyes (globular).

• Pellucid Marginal Degeneration - This is adegenerative form of corneal ectasia. This type is characterized by thinning of the lower surface (inferior surface) and the cornea tissue's sides (peripheral surface).

• Terrien Marginal Degeneration - This form of corneal ectasia is a slow-progressing eye disease causing thinning of the peripheral corneal tissues only.

• Post Keratorefractive Ectasia - This corneal ectasia forms due to post-surgical complications after LASIK or PRK (eye surgeries).

• Wound Ectasia - Wound ectasia after penetrating keratoplasty is a cornea disorder that develops after a corneal transplant.

What Are the Causes of Corneal Ectasia?

The eye consists of different liquids, and one of the most important functions of the cornea is to keep these fluids in the right place. Thinning of the corneal tissues can cause the fluids from inside to enter the corneal layer. These fluids build up due to excess accumulation. This can lead to swelling and long-term damage to the cornea. The following are the reasons why the corneal layer can get thin.

• Hereditary - Corneal ectasias can be hereditary (it runs in the families and may be passed onto younger generations).

• Corneal Trauma - Factors such as eye surgery, contact lenses, and vigorous rubbing of the eyes can potentially lead to thinning of the corneal layer.

• Age - Studies show thinning of the corneal tissues can be due to increasing age. As age advances, the corneal tissues can get thin over a period of time.

• Congenital Diseases - Diseases such as Down’s syndrome, retinitis pigmentosa, and albinism are associated with corneal ectasia.

• Allergic Conditions - Allergic conditions associated with corneal ectasia are eczema, allergies, and asthma.

• Connective Tissue Disorders - Connective tissue disorders like Marfan’s syndrome, Rubinstein-Taybi syndrome, Ehlers - Danlos syndrome can lead to corneal ectasia.

• Medications - Overuse or chronic use of corticosteroid medications (systemic or topical) may cause thinning of the corneal layer.

What Are the Symptoms of Corneal Ectasia?

A person suffering from thinning of the corneal layer can experience the following:

• Blurred vision at all distances (astigmatism).

• Myopia (nearsightedness).

• Changes in the shape of the corneal layer.

• Seeing halos, glare, or starbursts around the lights.

• Double vision (diplopia).

• Watery eyes.

• Light sensitivity.

• Unclear vision even after wearing glasses or contact lenses.

• Visual disturbances and eye discomfort after LASIK surgery.

How Is Corneal Ectasia Diagnosed?

The ophthalmologist performs a routine eye check-up after a thorough medical history and checks for worsening symptoms of the corneal layer of the eyes. In addition, the doctor checks for any existing eyesight problems, corneal abnormalities, and a history of keratorefractive surgery. Medical and family history of corneal abnormalities are also noted. Eye examinations include:

• Signs and Symptoms - Signs including bulging eyes, floppy eyelids, swollen inner eyelids, and scaly eyelids are checked.

• Visual Impairment - Signs and symptoms of visual impairment are also looked for.

• Changes in the Corneal Tissue - The severity of the corneal thinning, traumatic signs, protrusion, and anatomy of the corneal tissues are checked.

• Intraocular Pressure - Intraocular pressure is usually high in corneal ectasia.

What Are the Diagnostic Tests Done for Corneal Ectasia?

Ophthalmologists usually carry out the following tests to confirm the diagnosis of corneal ectasia:

• Keratometry - This test involves using a keratometer to measure the radius of the corneal curvature. This is also done to diagnose any irregularities in the corneal surface, astigmatism, and corneal steepening.

• Corneal Topography - This test is done to test the abnormalities in the corneal curvature and diagnose the keratoconus, pellucid marginal degeneration, and post-surgical ectasia.

• Corneal Pachymetry - This test measures the thickness of the corneal layer.

• Optical Coherence Tomography - This test involves taking high-resolution images of the corneal layer of the eye. This is done to better understand the cornea's size, thickness, and shape.

How Is Corneal Ectasia Treated?

Once the diagnosis is confirmed, ophthalmologists treat corneal ectasia with the following treatment options:

• Eyeglasses - Studies and cases show that mild cases of corneal ectasia can be treated with eyeglasses as they can improve symptoms or correct unclear vision.

• Contact Lenses - Soft contact lenses, rigid gas permeable lenses, hybrid lenses, piggyback contact lenses, and scleral lenses can be alternatively used to correct vision abnormalities.

• Corneal Cross-Linking - Corneal cross-linking is a minimally invasive surgical procedure that slows down the thinning of the corneal layer. It is done to treat keratoconus and post-surgical corneal ectasia.

• Intracorneal Ring Segment Implantation - This surgical procedure involves placing ring segments (small clear crescent-shaped implants) in the corneal layer to flatten the steep corneal layer.

• Corneal Transplant - Corneal transplant is done to treat severe cases of corneal ectasia when eyeglasses and contact lenses fail as a treatment option. This surgical procedure is done to cure ectasia. There are two types of corneal transplants:

• Penetrating Keratoplasty (the entire cornea is replaced).

• Lamellar Keratoplasty (front and middle layer of the cornea is replaced).

Conclusion

Corneal thinning can contribute to a series of eye diseases and vision abnormalities, which can be quite disturbing and may hamper the socio-psychological aspects. Hence, a person suffering from the symptoms of corneal ectasia should see an ophthalmologist for early diagnosis and treatment to avoid complications of corneal ectasia.