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Editor,—Map-dot epithelial dystrophy, also called Cogan’s microcystic dystrophy,1 is a well known and relatively frequent clinical entity. The microscopic basis for the biomicroscopic appearance of the typical superficial corneal opacities and epithelial erosions are intraepithelial cysts and a multilaminated or bilaminated aberrant epithelial basement membrane.1-5Therefore, the term epithelial basement membrane dystrophy has been introduced by some authors.5
We report a patient with Cogan’s corneal dystrophy with histologically proved erythrocyte inclusions in the intraepithelial cysts and a conspicuous clinical appearance not before described.
In March 1995 a 48-year-old white man reported to our clinic with typical symptoms of recurrent epithelial microerosions mainly on his right eye. He complained of early morning pain and reduced vision for a few weeks but could not recall an earlier ocular trauma. He did not wear contact lenses. Biomicroscopically, bright red intraepithelial inclusions in the corneal epithelium were found in the right eye (Fig1A); there was no fluorescein staining. The left eye showed a few whitish, map-dot-like epithelial opacities. There was no corneal or limbal neovascularisation and only a slight ciliary flush. The corneal stroma, the endothelium, and the anterior chamber were without peculiarities. The eyelid margins showed signs of mild chronic blepharitis, and the tear film was unstable. The visual acuities were 6/6 left eye and 6/7 right eye.
As the clinical appearance on the right eye was unknown to us and to exclude, for example, a bacterial infection, bacterial cultures, conjunctival scrapings, and focal superficial stripping of the corneal epithelium in some of the areas of the red alterations were performed by means of a hockey knife. The bacterial cultures were negative. Therefore, we only prescribed artificial tears.
After a few weeks treatment was stopped because the patient no longer had any symptoms. Biomicroscopically, the red inclusions had completely disappeared without leaving scars. However, there were still typical map-dot epithelial opacities in both eyes. The visual acuity of the right eye had normalised to 6/6.
The light microscopic examination of the stripped corneal epithelium revealed intraepithelial microcysts containing entrapped cellular debris, keratin, and numerous red blood cells (Fig 1B and C). In addition, a thickened bilaminar aberrant basement membrane with folds was found intraepithelially, visible with periodic acid Schiff staining (Fig 2A). Electron microscopy again displayed a redundant, bilaminar basement membrane of the epithelial cells with folds (Fig 2B). On microscopy there was no hint of a bacterial infection.
We are not aware of any case of map-dot epithelial dystrophy or other corneal disease published previously with intraepithelial blood inclusions. It is useful to know of this corneal alteration because of the differential diagnosis of bacterial infection. It is also interesting because this case shows that blood cells can be included intraepithelially in the cornea under special circumstances despite regular blinking and washing of the ocular surface by the tear film.
The microscopic findings are compatible with previous histological reports on map-dot epithelial dystrophy.1-5 The aberrant intraepithelial basement membrane may obstruct the normal migration of maturing epithelial cells leading to the disintegration of these cells and the formation of microcysts which may rupture eventually and form corneal erosions.1-4
In our case, initially there must have been temporary microerosions, presumably due to ruptured epithelial microcysts to which erythrocytes were attached, which were then incorporated into the epithelial microcysts when the corneal epithelium closed again. The site of origin of the erythrocytes within the intraepithelial cysts is unknown, although haemorrhage from the eyelid is a possibility. After a few weeks the red inclusions were no longer visible, probably because the entrapped erythrocytes had been phagocytised by macrophages.