Corneal Surface Changes in Thygeson's Superficial Punctate Keratitis: A Clinical and Noncontact Photomicrographic in Vivo Study in the Human Cornea

Abstract

Purpose To elucidate mechanisms behind the morphology of Thygeson's superficial punctate keratitis (TSPK). METHODS Sixteen patients were examined with the slit lamp and photographed by noncontact photomicrography. The results were compared with morphology of epithelial keratitis in herpes simplex type 1 (HSV1), varicella zoster (VZV), and adenovirus type 8 (Ad8) infections, all previously studied by the same method, and with published histologic findings in TSPK. Results In the photographs, the corneal epithelium showed various numbers of abnormal subsurface cells measuring about 10 μm in diameter, present individually, in small groups, or aggregated in larger lesions (coarse lesions with the slit lamp). The surface epithelium was well preserved, except in larger lesions, which showed surface debris. The morphology was unlike HSV1 and VZV epithelial keratitis, but strongly resembled epithelial changes occurring in Ad8 infections on day 5, and later, after the onset of symptoms. CONCLUSIONS TSPK shows a more widespread epithelial involvement than suspected with the slit lamp. Its morphology seems to reflect an action of a noxious agent targeted at the deeper epithelial layers, with the appearance of abnormal cells as a result. These might represent invading inflammatory cells, damaged intraepithelial ones, or both. The coarse lesions visualize areas of major involvement showing discernible signs of cell destruction. The similarity to Ad8 keratitis suggests that the source of the noxious agent might be located outside the cornea. The morphology, in conjunction with clinical features, is compatible with an immunologically mediated injury. The etiology remains unknown.