Abstract
Aims: Mare’s tail lines are uncommon, grey, parallel, tapering epithelial lines, which may give rise to discomfort or to visual symptoms. The authors report the clinical and ultrastructural findings in two patients Methods: Therapeutic debridement was performed in two patients suffering from mare’s tail disorder. The loosely attached epithelium was removed and fixed in glutaraldehyde containing cuprolinic blue and processed in a standard fashion for electron microscopy. Results: Ultrastructural studies showed an avascular, collagenous pannus extending under the whole of the excised epithelium in each case and separated from it by a thickened basal lamina like zone. The basal laminar material extended into the epithelium in folds, in keeping with the clinical features. Interesting ultrastructural features included: (1) a lack of hemidesmosomes in relation to the basal laminar material; (2) trapping of degenerate keratocytes within the invaginating basal laminar folds; (3) an unusual regularity and fine dimensions of the collagen fibrils and proteoglycans making up the subepithelial pannus. The basal laminar material contained proteoglycans and small fibres similar in appearance to long spacing collagen. Conclusions: Mare’s tail lines are caused by basal laminar material, assumed to be chiefly of epithelial origin, which invaginates the corneal epithelium. The presence of occasional keratocytes within the invaginating folds suggests that there may be a stromal contribution to the disorder. The visibility of mare’s tail lines in the focal beam of the slit lamp is likely to be related to the thickness and light scattering properties of the invaginations and of the subepithelial deposits. Tractional forces, imposed by lid action, could explain their horizontal disposition.