Anterior Basement Membrane Dystrophy: An Overview for Patients

Anterior Basement Membrane Dystrophy: An Overview for Patients
David G. Hwang, MD, FACS
Professor and Vice Chair
Director, Cornea Service
Director, Refractive Surgery Service
Department of Ophthalmology
University of California, San Francisco

Note: The information provided in this text is current as of the date above and provided for educational purposes. The information is not intended for the management of an individual case or to substitute for the advice of a treating physician

OVERVIEW
Anterior Basement Membrane Dystrophy
(ABMD; also known as Map-Dot-Fingerprint Corneal Dystrophy, Cogan’s Microcystic Dystrophy, or Epithelial Basement Membrane Dystrophy [EBMD]) is an inherited disorder of the cornea that may present with a variety of symptoms, including recurrent corneal erosions and/or blurred vision. Due to abnormal buildup of a microscopic amount of substance under the surface layer of the cornea over the course of many years, the surface cell layer of the cornea, known as the corneal epithelium, can become irregularly elevated from the underlying stromal layer of the cornea. This build-up of abnormal material can result in reduced adherence of the epithelium to the underlying stromal layer of the cornea, predisposing to spontaneous “erosions” of the cornea, as well as distorted or blurred vision.

Recurrent erosions typically occur upon awakening in the morning, resulting in pain, tearing, light sensitivity, and blurred vision upon awakening. Since the natural tear production subsides during sleep, the eye dries somewhat and the upper lid may become slightly adherent to the cornea. Thus in patients with ABMD, due to reduced adherence of the corneal epithelium to the underlying corneal stroma, the sudden retraction of the upper eyelid upon awakening may precipitate a tear in the corneal epithelium.Depending on the severity of the erosion, symptoms of pain and blurred vision may last for an hour or several days until the epithelium spontaneously heals.

ABMD is the most common corneal dystrophy, affecting an estimated 2-3% of the population. Patients of all ages and both genders can be affected, although the most common age range at time of presentation is 25 to 75 years of age. The onset may be spontaneous or may be triggered by a traumatic injury to the cornea (e.g., fingernail scratch, paper cut) or recent ocular surgery (e.g., cataract surgery, LASIK, or blepharoplasty [eyelid tuck]). Although the inheritance pattern is autosomal dominant, meaning that 50% of passing along the gene to offspring of either gender, not all individuals will be symptomatic. Accordingly, the absence of a known family history of this disorder does not exclude the diagnosis.

DIAGNOSIS
The diagnosis is made by eliciting a typical history as well as careful examination of the cornea to identify the characteristic signs of the disorder, which can include transparent lmicrocysts, grayish dots, and;or “fingerprint lines” in the corneal epithelium. These findings can be subtle, transient, and even absent. The absence of findings is more common in younger patients and can prompt to the incorrect diagnosis of “traumatic recurrent corneal erosion.” Blurred vision associated with ABMD will generally result in an irregular corneal contour that can be diagnosed with the aid of corneal topography, a noninvasive diagnostic test that measures the smoothness and contour of the corneal surface.

INITIAL MANAGEMENT
First-line treatment for erosions includes topical antibiotic eye drops and in some cases, patching, placement of a soft contact lens, and/or debridement of loose corneal epithelium. In some cases, a therapeutic soft contact lens may be prescribed to be worn continuously for a period of several weeks, to allow the underlying cornea to heal. To prevent recurrences, nighttime lubricants can be applied; bland nondedicated ointments are typically used. In some cases, artificial tears during the day may help, as well as adjuvant therapies to address any associated lid margin disease (e.g., doxycycline oral therapy).

It should be noted that medical therapy is generally ineffective for management of blurred vision associated with anterior basement membrane dystrophy. Such cases generally will require surgical management with superficial keratectomy (see below), although spectacles (glasses) or contact lenses may help to some degree.

ADDITIONAL MANAGEMENT
individuals who continue to have symptoms of recurrent erosions despite medical management, or those with ABMD associated with blurred vision, may benefit from a staged surgical approach, including options such as superficial keratectomy, phototherapeutic keratectomy, and/or anterior stromal puncture. The efficacy of these treatments is high and complication rates are low. Superficial keratectomy is a brief and effective outpatient procedure in which the epithelial layer is removed and the underlying abnormal basement membrane material gently scraped and removed. After the new epithelium regrows in a few days, the attachment is generally stronger than before. Mechanical (manual) removal is generally recommended for first-line surgical therapy and can result in improvement in recurrent erosion symptoms and/or improved vision.

The response rate to superficial keratectomy is very good, with the majority of patients experiencing sustained reduction in frequency and/or severity of their symptomatology without risk of reduction of vision that can occur in a minority of cases associated with other surgical options. Accordingly, superficial keratectomy is a natural choice for first-line surgical management of ABMD. In some cases, repeat superficial keratectomy may be necessitated after a number of year after initial treatment, due to gradual recurrent build-up of abnormal basement membrane material.

Some practitioners prefer to use the laser to perform this procedure, called phototherapeutic keratectomy (PTK). This procedure differs slightly from superficial keratectomy in that the excimer laser, in addition to removing the epithelium and underlying abnormal basement membrane material, also removes a thin, superficial layer of the underlying cornea. The resulting adhesion can be somewhat stronger than that afforded by superficial keratectomy alone, but on the other hand, PTK can result in a modest change in vision. Accordingly, some practitioners prefer to reserve PTK for cases in which superficial keratectomy fails.

In the small subset of patients that are refractory to superficial keratectomy and/or phototherapeutic keratectomy, anterior stromal puncture may provide definitive relief. This brief, well tolerated procedure is generally performed in the office at the slit lamp microscope, in which a tiny bent needle is used to make multiple small, evenly spaced micro punctures in the surface of the anesthetized cornea. After the punctures heal, focal microscars result that act to increase the adherence of the corneal epithelium to the underlying corneal stroma.

While some cases can be treated by applying the micrpunctures only to a limited area of the cornea, many others will require application of the treatment to a broader sector of the cornea, or even to the entire cornea. Doing so has the potential to cause a slight change in vision, so application of anterior stromal puncture to the central cornea overlying the pupil should generally be reserved for severe, recalcitrant cases. However, when properly applied to appropriately selected patients, this approach can provide lasting relief for even the most severe cases of ABMD with recurrent corneal erosion.

CONCLUSION
Although there is presently no “cure” for ABMD or proven approach the preventing the development of symptoms, a well-designed management algorithm should allow almost all affected patients to experience sustained and substantial relief from their recurrent corneal erosions and/or improvement of associated blurred vision. Most straightforward cases can be managed by a primary eye care specialist, but in difficult or uncertain cases, consultation with a corneal specialist may be helpful and appropriate.

Prepared 1 November, 2017

© 2017 David G. Hwang MD, FACS