Hydrogel contact lens-corneal interactions: a new mechanism for deposit formation and corneal injury.

PURPOSE: In this study, we examined the interactions between hydrogel contact lenses and the cornea, and the role of these interactions in the pathogenesis of interfacial debris formation and the complications of contact lens use. METHODS: We used a corneal abrasion device to simulate the motion of contact lenses on the cornea and the ensuing abrasive interactions. We examined lens and corneal surfaces by Atomic Force Microscopy (AFM), Low Voltage Scanning Electron Microscopy (LVSEM), and optical microscopy (with vital staining of corneas) for unused hydrogel contact lenses, lenses tested in the corneal abrasion device, and worn contact lenses. Young's modulus of hydrogel contact lenses was also measured and compared with the modulus of the human cornea, as reported in the literature. RESULTS: We observed patterns of abrasive damage to the rabbit cornea in vitro caused by corneal interaction with hydrogel contact lenses. Comparison of AFM and SEM of unused lens surfaces with the surfaces of lenses tested in the abrasion device showed dramatic alterations of the contact lens surfaces. Damage to the lenses was also evident by AFM for lenses worn by volunteers. The modulus of hydrogel contact lenses was lower than the modulus of the human cornea. CONCLUSIONS: The surface morphology of hydrogel contact lenses is significantly altered during use. The Young's modulus of the cornea is higher than the modulus of hydrogel contact lenses. These observations suggest a new mechanism for contact lens complications; namely, damage to the contact lens by the cornea as an initial event that produces lens particles and deposits at the lens-cornea interface, followed by corneal abrasion and the onset of other complications.