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Monday, October 31, 2011

Epithelial Basement Membrane Dystrophy (EBMD)

SIGNS AND SYMPTOMS
EBMDs are bilateral, often asymmetrical corneal basement membrane disorders usually occurring in individuals over 30. Symptoms vary, ranging from nothing at all to mild, short-lived corneal irritation upon waking with photophobia or glare.

Approximately 10 percent of affected individuals develop transient blurred vision with painful recurrent epithelial erosions. Most patients experience fluctuating visual acuity without discomfort. Signs of EBMD include corneal epithelial microcysts, whorling defects known as "fingerprints" or "mare's tails," and positive and negative sodium fluorescein staining.


PATHOPHYSIOLOGY
A dystrophy is a non-infectious, non-inflammatory defect secondary to malnutrition or faulty metabolism. There are four principle classes of corneal dystrophies:

anterior dystrophies
dystrophies of Bowman's layer
stromal dystrophies
endothelial dystrophies

Anterior EBMDs are variants of one cardinal pathophysiology. They are diagnosed and named principally by their appearance. In EBMD disorders, the basal epithelial cells manufacture abnormal finger-like projections that protrude from the abnormally thickened basement membrane. These projections reduce adherence of the overlying epithelium, and produce the characteristic changes. Fibrogranular ridges associated with, and adjacent to, these extensions form the fingerprint patterns. These protuberances bend in the epithelium, trapping cells and intercellular debris to mold microcysts. When a series of microcysts become grouped together and migrate forward, corneal surface abnormalities and RCE occur.

MANAGEMENT
The corneal changes of EBMD patients can be monitored closely with keratometry (paying specific attention to mire quality) and biomicroscopy. Carefully assess the tear film and wetting stability of the corneal surface to determine if keratitis sicca is present.

As opposed to the end of day symptoms of dry eye, the symptoms of EBMD are most severe in the morning. Sodium fluorescein staining reveals surface irregularities and illuminates areas of positive staining (bright green: missing epithelium) and negative staining (free of fluorescein: heaped epithelium). As an option, use rose bengal or lissamine green to reveal areas of devitalized corneal cells.

Treat asymptomatic patients with prophylactic supportive therapies. Artificial tear drops QID PRN, ointments HS-TID, punctal plugs, blindfolds during sleep and goggles or spectacles that prevent dust exposure and add ocular moisture retention support are helpful. Moderate presentations may require hypertonic drops and ointments (NaCl 5%), Q3H to QID, for a minimum of six months. You can prescribe soft contact lenses to smooth surface disturbances when intolerable levels of acuity exist in severe presentations.

Patients with acute recurrent corneal erosion may require debridement of the loose epithelium, topical cycloplegia (cyclopentolate 1% TID or homatropine 5% BID), topical prophylactic antibiotic drops QID (tobramycin, ofloxacin), or ointments and topical hypertonic drops and/or ointment. Manage pain with cold compresses, oral analgesics or topical nonsteroidal anti-inflammatory preparations (Voltaren, BID to QID, or Acular, BID to QID).

The long-term management of RCE follows the same course as EBMD. Cases of RCE that resist medical management may require surgical procedures. Anterior stromal puncture (ASP) under topical anesthesia involves the use of a 25g needle to place 0.1mm deep perforations, breaching Bowmans's membrane, at 0.25mm intervals in a chronic RCE zone in an attempt to initiate scar formation and healing. ASP can also be achieved using the Nd:Yag laser. Dispense appropriate topical cycloplegic, antibiotic, steroidal and hypertonic medications following the procedure. Pressure patching is also an option. Excimer photorefractive therapeutic keratectomy (PTK) to smooth the corneal surface is an effective alternative modality.

CLINICAL PEARLS

The use of the pressure patch remains controversial. While it is still considered acceptable, many clinicians are electing not to patch, citing inability to medicate topically and inconvenience to the patient. While contact lenses may be valuable for smoothing corneal surface irregularities, many practitioners avoid them as bandage devices to keep therapy simple.

There is no evidence suggesting topical nonsteroidal anti-inflammatory medicines increase healing time.

Since many sources suggest an autosomal dominant inheritance pattern, clinicians should closely examine the family members of any EBMD patient.

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