Dr Ben Wild
Overview |
The cornea is the outermost layer of the eye in front of the iris. It is a clear tissue, void of any blood vessels, and is one of the main optical components responsible for focusing light on the retina.
Corneal ectasia refers to the progressive thinning and subsequent bulging outwards of a specific part of the cornea. Keratoconus occurs when the central, or just off central, area of the cornea thins and balloons outwards, pellucid marginal degeneration occurs when the very bottom of the cornea thins and protrudes, keratoglobus refers to the entire cornea thinning and protruding, and post-keratorefractive ectasia refers to thinning and protruding of the cornea after laser eye surgery.
A sagittal view of an eye depicting a healthy cornea (top left), keratoconus (top middle), pellucid marginal degeneration (top right), keratoglobus (bottom left) and a depiction of a hard contact lens doming over the cornea to produce good vision (bottom right).
Corneal ectasias occur bilaterally, although affect one eye more than the other, present usually in teenage years to early 20s, and progression leads to large changes in nearsightedness and astigmatism over a short period of time.
Signs and Symptoms |
Signs
Iron ring within cornea, scarring of the cornea, wrinkling of the cornea, protrusion of the cornea, swelling of the cornea, eye redness.
Symptoms
Blurry vision, poor vision even with an up-to-date glasses prescription, eye pain.
Causes and Risk Factors |
Causes
Progressive thinning and protruding of the cornea.
Risk Factors
Most prominent risk factor is eye rubbing. This is followed by laser eye surgery, connective tissue disorders (Down syndrome, Ehlers Danlos, Marfan, osteogenesis imperfecta), genetics, conditions that cause itchy eyes such as allergic conjunctivitis, chronic blepharitis, etc.
Prevention and Treatment |
Prevention
Avoid eye rubbing at all costs.
Treatments
1. Hard contact lenses for best vision (rigid gas permeable, scleral, or hybrid).
2. Corneal cross-linking surgery to slow progression.
3. Corneal Intacs insertion to flatten the cornea and allow better contact lens fitting.
4. Corneal transplant (either full thickness or a certain layer).
Prognosis |
Usually, corneal ectasias start with increasingly difficult to obtain eyeglass prescriptions that deliver adequate vision at best. Eventually, vision deteriorates to the point where hard contacts are needed. Unfortunately, there is no cure for most types of corneal ectasia. If detected early, corneal cross-linking surgery has been shown to dramatically slow or even stop progression of keratoconus. Otherwise, vision can continue to decrease until a corneal transplant is necessary.
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