Corneal anterior basement membrane dystrophy (ABMD) is the most common corneal dystrophy. It is also known as map-dot-fingerprint, mare’s tail, and Cogan’s microcystic dystrophy
Corneal ABMD is most commonly associated with two clinical presentations: Painful corneal erosions and visual compromise. The treatment of one may differ from that of the other.
10% of the adult population in the United States has some manifestation of ABMD with a strong predilection for women.
The inheritance pattern is autosomal dominant.
Histopathologically, a thickened layer of corneal epithelium is recognized together with reduplication of the epithelial basement membrane and entrapment of debris in cyst-like structures.
As with all corneal dystrophies ABMD is genetically coded for, usually appears in the fourth or fifth decades of life and may worsen over time.
COMMONLY ASSOCIATED CONDITIONS
ABMD may be present with other corneal dystrophies such as Fuchs’ endothelial dystrophy and may be exacerbated by chronic blepharitis.
ABMD is associated with two common presentations:
• Awakening with pain, foreign body sensation, photophobia, and tearing (scenario 1)
• Gradual visual compromise sometimes associated with foreign body sensation (scenario 2)
• Scenario 1: If the patient is symptomatic on presentation, they will likely have a well-demarcated area of loose epithelium in one part of the cornea with the rest of the cornea showing the classical manifestations of ABMD described above.
• Scenario 2: Thickened epithelium and redundant basement membrane over the pupillary aperture in the form of map-dot-fingerprint, mare’s tail, microcystic changes, or a combination of the above. This results in an irregular corneal surface over the visual axis.
DIAGNOSTIC TESTS & INTERPRETATION
Visual acuity and slit-lamp biomicroscopy as noted in physical exam
• Computerized corneal topography may be an invaluable tool in evaluating the contribution of corneal ABMD to the patient’s blurred vision. Irregular mires and an increased surface regularity index (SRI) usually imply that the surface is a significant contributor to the visual compromise.
• More recently, anterior segment ocular coherence tomography (OCT) has been employed to further delineate the epithelial and basement membrane changes.
The contribution of the corneal surface to the patient’s visual compromise may be further confirmed with a rigid gas-permeable (RGP) contact lens diagnostic evaluation. If the patient’s vision improves significantly with an RGP lens, then ABMD may be a significant contributor to the patient’s visual compromise.
A keratectomy specimen submitted for pathologic examination will usually show thickened epithelium with a redundant basement membrane (it is not uncommon to see basement membrane structures undulating obliquely through multilayered epithelium) with cystic collections of epithelial debris.
• Scenario 1 (painful presentation): The differential diagnosis includes keratoconjunctivitis sicca, blepharokeratitis, rosacea keratitis, infectious keratitis, chemical keratitis (and other external factors), trauma, embedded foreign body in the cornea or under the lid, and corneal epithelial edema.
• Scenario 2 (visual compromise): The differential diagnosis includes any condition causing a surface keratopathy including chemical and infectious keratitis, keratoconjunctivitis sicca, other causes of epitheliopathy (edema, Meesmann’s dystrophy, and stem cell deficiency), as well as other causes of visual compromise, including other corneal clouding/opacification, cataract, vitreous opacity, maculopathy, and optic neuropathy.
Scenario 1 (Pain)
• Lubrication, lubrication, lubrication! This may include drops, gel, or ointment.
– Encourage patient to open lids slowly upon awakening followed by instillation of lubricant in the eye
• Hypertonic saline especially in ointment form at bedtime:
– Punctal occlusion to create a wetter surface
– Therapeutic bandage contact lens to protect the corneal surface, especially the areas(s) of loose epithelium, from the movement of the lid. A prophylactic antibiotic may be considered in this scenario.
COMPLEMENTARY & ALTERNATIVE THERAPIES
Topical nonsteroidal anti-inflammatory medication to control pain and cyclosporine both as an anti-inflammatory and to increase tear production may be added to the first or second line treatments.
• Scenario 1 (pain): Consideration may be given to mechanical keratectomy with a diamond-dusted burr or phototherapeutic keratectomy with the excimer laser. Both techniques have been shown to be equally effective in decreasing the incidence of recurrent erosions.
• Ethanol epitheliectomy has been shown to be equally effective.
• Scenario 2 (visual compromise): When ABMD is visually significant treatment usually consists of a superficial keratectomy. We favor a dull rounded or crescent knife to remove the central 5–6 mm of corneal epithelium overlying the pupillary aperture. The epithelial layer usually cleaves easily off the basement membrane. It is very important to then deliberately remove the irregular, and frequently redundant, basement membrane until Bowman’s layer is recognized with its characteristic sheen. Importantly, a diamond-dusted burr is not required in this setting. Since eliminating recurrent erosions is not the focus of treatment, roughening up Bowman’s layer to improve adherence is not required (unnecessary diamond-dusted burr polishing of Bowman’s layer may result in some fibrosis and visually significant haze). In the same vein, antifibrosis treatment with mitomycin is not necessary. Moreover, there is no real role for excimer laser phototherapeutic keratectomy in the treatment of ABMD in the absence of recurrent erosions.
• In both scenarios a therapeutic bandage contact lens is placed (e.g. Acuvue Oasys). The patient is started on a topical steroid, nonsteroidal anti-inflammatory agent, and fluoroquinolone antibiotic, as is the custom with most surface procedures. Re-epithelialization usually takes place over the next 3–7 days. The bandage contact lens is then removed, the topical nonsteroidal anti-inflammatory agent and antibiotic discontinued, and the steroid tapered rapidly. A couple of weeks later the patient is reevaluated, her visual acuity remeasured, and computerized corneal topography repeated.
The treatment may be repeated as need.
Excellent in both scenarios
Secondary infection and subepithelial fibrosis/scar formation
• Buxton JN, Fox ML. Superficial epithelial keratectomy in the treatment of epithelial basement membrane dystrophy. A preliminary report. Arch Ophthalmol 1983;101(3):392–395.
• Buxton JN, Constad WH. Superficial epithelial keratectomy in the treatment of epithelial basement membrane dystrophy. Cornea 1987;6(4):292–297.
• Sridhar MS, Rapuano CJ, Cosar CB, et al. Phototherapeutic keratectomy versus diamond burr polishing of Bowman’s membrane in the treatment of recurrent corneal erosions associated with anterior basement membrane dystrophy. Ophthalmology 2003;110(9):1855; author reply 1855.
• Wong VW, Chi SC, Lam DS. Diamond burr polishing for recurrent corneal erosions: results from a prospective randomized controlled trial. Cornea 2009;28(2):152–156.
371.52 Other anterior corneal dystrophies
• Corneal ABMD may present as painful corneal erosions or visual compromise.
• The treatment of painful erosions may involve a stepwise approach from lubrication to keratectomy, while visually significant ABMD can usually only be addressed by removal of the abnormal epithelium and basement membrane.