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Editor,—Wettability1 of the corneal epithelial surface and properties of tear fluids2 have been regarded as principal factors in the determination of precorneal tear film stability. However, there is no direct evidence indicating which factor is the key to this stability. The role of wettability of corneal epithelial surface in tear film stability can be elucidated in cases where damage occurs only to the corneal epithelium, not to the tear fluid itself. Therefore, we report an unusual case with sudden burning of the superficial layer of the corneal epithelium which clearly shows the relation between corneal surface epithelial integrity and tear film stability.
A 59 year old man with no history of ocular disease came to our hospital as an emergency patient for treatment of a corneal burn. The patient was working at his desk when he quickly turned his head and his eye accidentally contacted a hot incandescent bulb. His chief complaint was decreased vision without pain. On the first day, his left corrected visual acuity was decreased to finger counting. By slit lamp biomicroscopic examination, the eye did not show any inflammation or apparent reflex tearing; there was, however, an oval whitish necrotised area approximately 6 mm in diameter on the superficial layer of the central corneal epithelium (Fig 1). This lesion stained with fluorescein and rose bengal; the remaining portion of the ocular surface epithelium was intact without fluorescein or rose bengal staining. A previously reported system,3 which can be used for the screening and the evaluation of the severity of dry eye and is now commercially available in Japan (DR-1, Kowa Co Ltd, Tokyo, Japan), was used for further observing the tear film in this case. The system disclosed that, outside the lesion, the tear film was stable and the precorneal tear film lipid layer moved easily with blinking. However, the tear film on the lesion was discontinuous and the lesion did not change in appearance with blinking (Fig 2A). A combination of 0.1% fluorometholone, 0.3% ofloxacin, and preservative-free artificial tears was applied to the eye four times a day. By 4 days after the first visit, the corneal epithelium in the burned region had recovered completely to normal without any resultant epithelial abnormalities. Thus, it is likely that only the superficial layer was involved in the lesion. The appearance of tear lipid layer interference returned to show a greyish colour with striped pattern in conjunction with blinking (Fig 2B) and this pattern corresponded to that in normal healthy eyes.3 The corrected visual acuity returned to 20/20.
The present case clearly demonstrated that tear film stability was completely lost, when the corneal surface epithelium was damaged. In contrast, outside the lesion, the tear film was normal in appearance and seemed to have an intimate relation with the corneal epithelium. In this case, as it is reasonable to presume that there was no continuous damage to the tear film itself, this observation suggests that tear film stability may be supported much more by corneal surface epithelial integrity (wettability) than by the properties of tear themselves. Factors which contribute to this mechanism probably include intact expression of glycocalyx4 and the recently demonstrated MUC 15 (epithelial cell derived mucin). Given these observations, it is reasonable to postulate that various corneal epithelial diseases may be accompanied by some tear film instability due to superficial epithelial abnormalities. Thus, in such cases, therapy should be targeted to treat the loss of tear film interaction with the epithelium.
Supported in part by a research fund from Kyoto Foundation for the Promotion of Medical Science, and the intramural research fund of Kyoto Prefectural University of Medicine.