The cornea is the clear domed window of the eye. You don’t see it, but it is what is overlying the pupil and colored part of the eye called the iris. It maintains 2/3 of the refractive power of the eye (the other 1/3 being the crystalline lens).
It is made of 3 basic layers along with borders called membranes or layers. The 3 layers are the epithelium (‘outer skin layer’), the stroma (bulk of the cornea) and the endothelium (‘inner layer’).
- The epithelium is the protective layer of the cornea. This is vitally protected by the tear film (more on that later) and thus, is where dryness occurs. Other conditions of the epithelium include: Anterior basement membrane dystrophy, recurrent corneal erosions and pterygium.
- The stroma is where most of the visually detrimental scars form. This is where viruses can affect vision along with many corneal dystrophies.
- The endothelium contains cells that are the ‘workhorses’ of the cornea. They pump out the fluid and keep the cornea clear. When this layer is affected, the cornea becomes bogged with fluid and becomes opaque like the white part of the eye called the sclera.
What is a corneal transplant and when do I need one?
Typically, a transplant is necessary at the final stages of your disease process. For many, this occurs because of genetic diseases such as Fuchs dystrophy (the most common reason for corneal transplant in the US) or keratoconus. Other causes include herpes keratitis, scars, infectious and non-infectious ulcers, post cataract surgery edema and perforations.
In our modern era, we are able to transplant very selectively. This means that we remove only the diseased layer of the cornea. For Fuchs dystrophy, we replace the endothelium (inner layer) with a partial thickness-transplant called a DMEK.
For conditions such as keratoconus, we will try to replace only the outer layers of the cornea with a transplant known as a DALK.
Our tissue is supplied by CorneaGen out of Seattle, WA.
Common conditions and treatments:
This condition is an inherited disease of the endothelium (inner layer of the cornea). It is inherited in roughly a 50% inheritance pattern. So approximately 2 of 4 siblings will acquire this disease. It usually presents itself in the 50s. Symptoms can be staved off with topical medications, such as hypertonic saline solution (Muro 128), but ultimately needs a partial-thickness corneal transplant, such as a DMEK or DSEK.
Anterior basement membrane dystrophy (ABMD) & Recurrent Corneal Erosions
A dystrophy means that this is an inherited condition. However, this corneal dystrophy is unique in that it has a strong acquired component and doesn’t always express itself symptomatically. What this means is that many patients will be told they have this condition, but not feel any different. However, many will be affected by painful corneal erosions with the telltale sign being that they occur upon waking. The condition can also blur your vision.
Fortunately, we have many treatments for this condition.
- Nightly hyperconcentrated saline ointment (Muro 128)
- Treating dry eye if present
- Topical steroid + oral tetracycline
- Corneal debridement (in office procedure to ‘resurface’ the cornea by removing just the outer layer (‘epithelium’) followed by a polish of the underlying membrane and allowing a normal layer to grow in it’s place
- Anterior stromal micropuncture
- Phototherapeutic keratectomy (PTK) – uses the same excimer laser that is used in LASIK
Fortunately, this corneal dystrophy does not require a corneal transplant.
This is a condition that causing ‘warpage’ or ‘bulging’ of the cornea. It is thought to be strongly associated with eye rubbing and thus, many underlying conditions are linked to keratoconus, including: atopic disease, sleep apnea, floppy eyelid syndrome, Down syndrome, connective tissue disorders.
Fortunately, we have treatments that can stave off a corneal transplant. One of the major preventative treatments includes corneal crosslinking, where a riboflavin (vitamin B2) solution is coupled with a specific UV light source in order to ‘stiffen’ the cornea and keep it from progressing further.
This is a benign, degenerative growth that is associated with environmental exposure, such as wind, dust, sun. It is more prevalent is people who work outdoors and who live closer to the equator.
Having this condition doesn’t always mean that it needs treated. Often, we can just monitor it. At times, we can treat it medically with drops. In severe cases when it affects vision or causes recurrent inflammation, we elect to remove the growth surgically.
Herpes simplex keratitis (‘history of cold sore’)
Patients are usually shocked when we tell them that they have a herpes infection in the eye. Part of this has to do with the stigma surrounding its cause of genital ulcers as an STD. There are 2 types of herpes simplex virus (HSV): HSV-1 and HSV-2. HSV-1 typically affects the oropharynx and HSV-2 the genitals, but there can be cross-contamination. It is estimated that worldwide, nearly 90% of people have one or both viruses! The problem with these viruses is that they lay dormant in our bodies. When our immune system weakens, they can reactivate and cause problems. One of these problems is herpes simplex keratitis along with other manifestations in and around the eye.
Fortunately, we have great antiviral therapies and topical steroids to combat the multiple manifestations of herpes keratitis. If you have a history of this condition, please give us a call and request a consult with our cornea specialist.
Herpes zoster ophthalmicus (‘Shingles’)
Herpes zoster is caused by reactivation of the varicella-zoster virus, the same virus that causes varicella (chickenpox). Most people are familiar with shingles as a condition, but most don’t realize it can affect the eye in the way that it does. Typically, this happens after shingles has affected the face and more specifically, on the tip of the nose. An estimated one million cases of herpes zoster occur annually in the United States. The incidence among people 60 years and older is about 1 case per 100 U.S. population annually. About 1 in 10 adults with herpes zoster develop postherpetic neuralgia (severe pain that lingers in the area of the shingles outbreak).
The most important thing that you can do to combat this disease is to get your shingles vaccine. Two doses of Shingrix is more than 90% effective at preventing shingles and postherpetic neuralgia. Protection stays above 85% for at least the first four years after you get vaccinated.
Contact lens-related issues
Contact lenses are an amazing convenience for many people. Just like most things, there are potential problems that can occur. Many of these problems have to do with over wear and bad contact lens hygiene. Some are simply a consequence of exposure to the contact lens or solution.
All of these complications should prompt a visit to the ophthalmologist and in some cases, a corneal specialist. Some can become chronic and irreversible.
- Microbial keratitis (i.e. infectious corneal ulcer) – this can be one of the most devastating complications of contact lenses. The best way to prevent this condition is by maintaining adequate contact lens hygiene (never use homemade solution or tap water; never reuse solution) and not sleeping in your contact lenses regardless of lens type or design
- Corneal edema – usually self-limiting
- Corneal de-epithelialization – usually temporary
- Corneal distortion – we see this commonly in patients preparing for cataract and refractive surgery. We ask ALL patients in the preop testing phase to stay out of their contacts for 2-4 weeks prior to testing as the contact lenses can make the results of your calculations inaccurate.
- Sterile infiltrates – treatable & usually reversible
- Neovascularization – a somewhat common occurrence, but can also be devastating to vision and comfort if left unchecked
- Acquired limbal stem cell deficiency – usually requires cessation of contact lens wear
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