Confocal microscopic observations of the human cornea following overnight contact lens wear

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Abstract
Striae and folds are observed with a slitlamp biomicroscope in the cornea following overnight contact lens wear. These phenomena are poorly understood. The aim of this study is to employ confocal microscopy to observe and document these and other morphological changes in the human cornea following overnight contact lens wear. Slitlamp biomicroscopy, slit-scanning confocal microscopy and ultrasonic pachometry were performed on both eyes of 13 subjects (3M, 10F, age 24 +/- 3 years) before and after eight hours overnight wear of a -3.00 D Bausch & Lomb one day disposable soft contact lens (Dk/t = 15.1 x 10(-9) [cm/sec] x [ml O2/ml x mmHg]) in one eye; the other non-lens-wearing eye acted as a control. Following sleep, both corneas were swollen (lens-wearing eye 11.8 +/- 3.8 per cent; control eye 2.1 +/- 1.9 per cent) and the stroma of both corneas displayed an apparent reduction in keratocyte density (lens-wearing eye 21 per cent; control eye 10 per cent). Folds were observed with the slitlamp biomicroscope and long, straight, dark, orthogonal lines were observed with the confocal microscope, in the posterior stroma of the oedematous lens-wearing eyes. Such features were not observed in the control eyes. The keratocytes appeared less distinct with greater levels of corneal oedema. The apparent loss of keratocytes following overnight lens wear is an optical artefact that can be explained in terms of corneal oedema causing volumetric tissue expansion and a loss of optical clarity, which hampers keratocyte detection. These findings place the onus on researchers postulating a loss of stromal keratocytes following clinical interventions, such as contact lens wear, to account for the effects of oedema.