Corneal thinning disorders

http://www.revophth.com/index.asp?page=1_14448.htm

Thinning in the ‘Quiet’ Eye

• Dellen. In the absence of inflammation, one of the more likely causes of the thinning is a dell, or an area of non-wetting that thins and then breaks down. The treatment is lubrication, maybe punctal occlusion, and a bandage contact lens, a temporary tarsorraphy.
• Furrow degeneration. This is a variety of peripheral thinning, typically between the limbus and the arcus senilis, that usually occurs in elderly patients. The hallmark signs of furrow degeneration are that the thinning, if it’s present at all, is very shallow, non-progressive and isn’t visually significant; the eye is white and quiet, there’s no vascularization and there’s no possibility for perforation.No actual treatment is necessary.
• Pellucid marginal degeneration. This is a cousin to keratoconus, however, where keratoconus tends to mean central or paracentral thinning, pellucid is peripheral. Some patients with pellucid can have severe thinning, usually inferiorly, within a couple of millimeters of the limbus. Though there’s no redness, pain or inflammation, it causes significant irregular astigmatism, so the patient tends to complain of a slow, progressive worsening of vision. On topography, PMD will have an area of inferior steepening that resembles a crab claw. Glasses sometimes help, though the management typically involves a rigid gas permeable contact lens or a hybrid lens like the Synergize. Rarely, you’ll need to do a corneal transplant.
• Terrien’s marginal degeneration. This presents as a marginal furrow, usually bilateral, and is most common in men between 20 and 40 years of age. It starts as a non-ulcerated area of thinning located superiorly, and it slowly progresses from there. You’ll see vascularization in addition to the thinning, often with a leading edge of lipid. However, the epithelium is also intact with this condition. The thinning can be progressive, and can progress circumferentially or centrally. And, since it starts superiorly, the patient usually gets against-the-rule astigmatism. You can manage the astigmatism with glasses or, failing that, RGPs or hybrid lenses.

Thinning in the ‘Hot’ Eye

• Patients can also present with peripheral thinning accompanied by ulceration and general inflammation. These are the presentations are more concerning since actual tissue is being lost. Since several of the ulcerative conditions have similar appearances, it takes more diagnostic detective work to narrow down the cause in these cases.
• If the eye is red and painful, and there’s peripheral thinning with an epithelial defect, then you first assess the defect’s size, location and whether it’s associated with a hypopyon.
• None of the immune conditions cause a hypopyon, while the bacterial ones do. If there’s a hypopyon, corneal specialists say to proceed as if it’s a bacterial infection until proven otherwise. Scrape it, culture it and put the patient on antibiotics.
• When presented with a non-infectious peripheral ulcerative keratitis, however, first suspect rheumatoid arthritis or another autoimmune condition. If a patient doesn’t already have a diagnosis of rheumatoid, physicians also suspect Wegener’s granulomatosus, a serious vasculitis; or Mooren’s ulcer, which is peripheral ulcerative keratitis of unknown etiology. Unfortunately, all three ulcerative conditions have similar characteristics, and serologic testing is often the key to making the diagnosis. Corneal specialists say many patients who present with PUK often have already been diagnosed with rheumatoid disease and are on some type of systemic medication for it already, which aids the diagnosis.
• If the patient doesn’t already have a diagnosis of a systemic disease associated with peripheral corneal thinning with ulceration, order a panel of blood work: check for rheumatoid factor, erythrocyte sedimentation rate, an antinuclear antibody test, an anti-neutrophil cytoplasmic antibody test, a complete blood count, check for hepatitis-C, (because there’s one form of peripheral thinning that looks like peripheral ulcerative keratitis or Mooren’s ulcer but which is actually associated with hepatitis-C and is very responsive to interferon therapy).
• If autoimmune disease isn’t the cause, the other two frequent diagnoses, Wegener’s granulomatosus and Mooren’s ulcer
• Wegener’s is one of the main differentials in PUK because, if it’s missed, it can kill someone. Wegener’s is a vasculitis that manifests with peripheral corneal ulcers that mimic a Mooren’s ulcer, in which there’s a nasal or temporal immune-looking ulcer—in other words, there’s no hypopyon in the anterior chamber. The patient needs a chest X-Ray or a CAT scan of the chest because the Wegener’s patient will have a classic diagnostic picture in that region. If a mass is observed, a biopsy is necessary in some cases. With Wegener’s in mind, an ANCA is needed in all cases of PUK. If a patient’s ulceration involves the sclera as well as the cornea, suspect Wegener’s.
• If the PUK isn’t from an autoimmune condition like RA, Wegener’s or hepatitis, it’s classified as Mooren’s ulcer, or a peripheral ulcerative keratitis of unknown etiology.
• Mooren’s is typically more chronic, progressive and very painful. It will begin in the periphery and spread both circumferentially and centripetally. The key sign is that there will be a leading, undermined edge of de-epithelialized tissue. There will also usually be blood vessels crossing the edge. There’s also a milder form of Mooren’s ulcer that’s more limited and actually responds well to medical therapy consisting of lubrication and low-dose steroids and tarsorraphy, if necessary.
• There are also less common causes that need to be kept in mind, as well: Corneal melting can occur in the setting of the neurotrophic cornea or from the frequent use of topical anesthetics or topical non-steroidal anti-inflammatories like Acular, Xibrom and Nevanac. Another cause, which was more common when we did more scleral surgery, is surgically induced necrotizing scleritis, in which there’s melting of the sclera from an old cataract wound. This was rare to begin with, and it still is, but it’s worth being aware of.
• The cause may also be just staph marginal hypersensitivity, a relatively mild condition. In blepharitis and other lid disease, patients can get small white infiltrates at the limbus. Those infiltrates can be associated with some thinning and, when they heal, they can result in some scarring and thinning, but they’re not that serious.