The cornea is the transparent covering of the front part of the eye. It is made up of several layers: The epithelium, Bowman’s Membrane, the stroma, Dua’s Layer (new research), Descemet’s Membrane, and the endothelium. Both the corneal clarity and the refractive power of the cornea play an important role in the cornea’s contribution to our overall sight.The following information illustrates some of the conditions which can affect the cornea. If you would like to learn more about corneal conditions, corneal surgery, or other aspects of eye and vision care, the experienced eye doctors at Cascadia Eye can answer your questions. Please contact us today for more information, or to schedule a consultation.
Fuchs’ Endothelial Dystrophy
Fuchs’ Endothelial Dystrophy (Fuchs’) is a slowly progressive dystrophy of the cornea that generally does not affect vision until later in life. Signs of Fuchs’ can be observed for years without any symptoms or visual changes noticed by the patient. One of the first signs we notice are guttae, or small changes in one of the inner layers of the cornea. As this layer continues to change and thicken, it can lead to swelling of the cornea. If the most inner layer of the cornea, the endothelium, can no longer efficiently ‘pump’ the normal fluids from the swollen cornea, Fuchs’ patients may begin to notice a decrease in vision. Generally a decrease in vision and any mild eye irritation is most noticeable to Fuchs’ patients in the morning, as the cornea does not pump out as much fluid while we are sleeping. Symptoms typically improve throughout the day. Once a stage of Fuchs’ is reached where it is affecting daily lifestyle activities, medical management is generally recommended. There are hyperosmotic drops to help ‘draw out’ the fluid, and in more severe cases, surgery may be recommended. Dr. Pereira, our corneal surgeon, is specialty trained in this area. There are procedures available, such as DSEK (Descemet’s Stripping Endothelial Keratoplasty) and DMEK (Deep Membrane Endothelial Keratoplasty) to transplant these most inner layers of the cornea if vision cannot be restored with just eye drops.
Keratoconus is an asymmetric, non-inflammatory thinning of the cornea which causes an outward protrusion of the corneal tissue and thus an irregular surface of the cornea. While the exact cause of keratoconus is unknown, genetics is believed to play a factor. Keratoconus is generally managed with rigid gas permeable contact lenses to mask the corneal irregularity. Mild cases may be managed with glasses or soft lenses as the corneal irregularity may not drastically affect the vision. Many cases of mild to moderate keratoconus are able to maintain 20/20 vision with the aid of rigid contact lenses. Surgical intervention such as intrastromal ring inserts (INTACS) can help to reduce some of the corneal irregularity in mild to moderate cases, but generally are not able to resolve all of the corneal irregularity. In severe cases, a corneal transplant (Penetrating Keratoplasty) may be necessary. Transplants are generally reserved for cases where visual acuity cannot be corrected to better than 20/50 (from corneal scarring), or when gas permeable contact lens wear cannot be tolerated.
Corneal Ulcer and Contact Lens Complications
A corneal ulcer is an inflammation, or possibly both an inflammation and infection of the cornea. A corneal edema is the swelling of the cornea caused by retention of tear fluid. Corneal ulcers or edemas can be caused by infections, contact lenses, chemical injury, trauma, and other eye conditions such as dry eye and severe blepharitis. Infectious corneal ulcers can arise from several types of bacteria, viruses, fungi or even protozoa. Corneal ulcers generally affect the most outer layers of the cornea, the epithelium and the anterior stroma, but severe corneal ulcers can penetrate all the way through to the most inner layers of the cornea and leave behind dense scarring. Symptoms of corneal ulcers can range from a mild foreign body sensation and no vision loss, to severe, boring pain and significant vision loss. Knowing the causative nature of the corneal ulcer can be extremely helpful in our treatment plan. Contact lens-related corneal ulcers are most often found in patients who over-wear their contact lenses and/or sleep in their contact lenses. Careful contact lens care and diligent lens replacement is considered preventative in many of these cases. Many contact lens complications such as “tight lens syndrome,” contact lens-related red eye, and a poor fitting contact lens may all mimic the beginning stages of a corneal ulcer, so it is always best to have the cornea evaluated if any eye pain or blurred vision occurs with contact lens wear. Treatment for a corneal ulcer is dependent on the cause and severity of the infection and inflammation. General treatment begins with an antibiotic, but can vary significantly. Healing time for a corneal ulcer can take days for mild ulcers, and weeks to several months for more severe ulcers. If an ulcer has caused significant scarring to the corneal surface, a corneal transplant procedure may be recommended to help restore vision.
Other Corneal Dystrophies and Degenerations
There are several types of corneal dystrophies and degenerations that can be inherited and in turn, may have a detrimental effect on vision and cause eye irritation. These dystrophies and degenerations may affect only one layer of the cornea or several layers of the cornea. One common dystrophy is Anterior Basement Membrane Dystrophy (ABMD). ABMD affects the most outer surface, or epithelial layer, of the cornea. Many degenerations and dystrophies, however, are quite rare. One example of a more rare degeneration is Salzmann’s Nodular Degeneration. Salzmann’s also affects the more outer layers of the cornea, including Bowman’s layer and the stroma.
If you would like more information on corneal conditions and treatments available here at Cascadia Eye, or if you would like to schedule an appointment with one of our eye doctors, please contact us today.