Exfoliative epitheliopathy of bullous keratopathy with breaches in the MUC16 Glycocalyx

Abstract

Purpose: Expression of cellular adhesion molecules is altered in bullous keratopathy. The hypothesis that epithelial alterations in bullous keratopathy compromise the surface of the cornea and its glycocalyx was tested.

Methods: Studies were performed on eight cases each of pseudophakic bullous keratopathy and healthy corneas. The number of epithelial cell layers was determined with a stereological method of point counting. The minimum distance between points was established by estimates of cell size with variable pressure scanning electron microscopy performed in backscatter mode. The mean number of cell layers with mucin expression was identified by immunohistochemistry with mouse monoclonal antibodies for MUC1 and MUC16. Data were analyzed by Student's t-test if values showed a normal distribution or, alternatively, by the Wilcoxon rank-sum test.

Results: Mean numbers of wing cell and superficial cell layers were lower in bullous keratopathy specimens (1.6 vs. 2.0; P < 0.0001) than in controls (1.1 vs. 1.8; P < 0.000001). The number of exfoliated cell layers evident in sections was increased in the bullous keratopathy specimens compared with controls (0.36 vs. 0.03; P < 0.0001). The number of cell layers decorated with antibodies to MUC16 was lower in bullous keratopathy specimens than in controls (0.5 vs. 1.2; P < 0.025). The reduction of layers expressing MUC1 in bullous keratopathy was not statistically significant.

Conclusions: Pseudophakic bullous keratopathy manifests an abnormal corneal ocular surface in which superficial cell layers are exfoliated, leaving breaches in the protective MUC16 glycocalyx. The results provide a morphologic correlate for the surface epithelial abnormalities noted clinically in these patients.

FIGURE 1

Scanning electron micrograph of bullous keratopathy specimen shows an irregular surface with numerous residual polygonal superficial epithelial cells of varying size and shapes after exfoliation (white arrows).

FIGURE 2

Mean numbers of cell layers in bullous keratopathy versus control specimens. A significant reduction is shown in the total epithelial cell layers and in wing cells and superficial cells in bullous keratopathy specimens. The number of exfoliated cells was significantly increased in bullous keratopathy compared with control specimens.

FIGURE 3

Photomicrographs of epithelial thinning in bullous keratopathy. (A) PAS stain shows thinning of the epithelium with loss of superficial cells (black arrow) and microbullae (white arrow). Hydropic change is evident within the epithelium (h). Many of the wing cell nuclei are faded. (B) Hematoxylin and eosin–stained sections show severe thinning of the epithelium with bullae (b) accompanied by attenuation of the Bowman layer (between black arrows). Exfoliated cells are evident (e). Original magnification, ×250.

FIGURE 4

(A) Photomicrographs of bullous keratopathy show numerous exfoliated superficial cells (arrows) producing the appearance of multiple small surface blebs. A wing cell nucleus appears fragmented (w). (B) In some areas, wing cell dropout (arrows) is accompanied by a relatively intact superficial cell layer. Effete nuclei (n) are seen within the basal cell layer (original magnification, ×250; hematoxylin and eosin).

FIGURE 5

PAS stains of bullous keratopathy (original magnification, ×250). (A) Poorly stained superficial cells are partially exfoliated (arrow) with underlying wing cells that stain. (B) Basement membrane thickening is evident beneath the epithelium (arrow), and the thinned epithelium shows variable staining of various layers with PAS. (C) Marked intraepithelial deposition of basement membrane material (arrows) lies beneath and around the detached epithelium (b).

FIGURE 6

Identification of mucin-positive cell layers in bullous keratopathy compared with control specimens. PAS staining was insignificantly decreased in bullous keratopathy specimens. Immunohistochemical staining for MUC16, but not MUC1, showed a significant decrease in the number of cell layers that were positive.

FIGURE 7

Immunohistochemistry for MUC16 (A) in control specimens shows one to two superficial cell layers staining consistently and (B, C) in bullous keratopathy specimen. (B) Exfoliated cells show intense MUC16 staining (black arrow). Some areas underlying shed cells shows faint staining (s). (C) In some cases exfoliated cells (black arrows) and the underlying epithelium show weak to absent reactivity to MUC16. (D) Negative control of normal cornea with deletion of the primary antibody.