ABSTRACT
BACKGROUND: Computer-controlled video keratoscopy is being employed ever more frequently and for various indications. PATIENTS: We have studied the effects of high-viscosity and low-viscosity tear substitutes on the corneal topography, one and five minutes after application to 14 normal eyes of 7 subjects, and compared the results. RESULTS: In contrast to low-viscosity preparations, high-viscosity preparations cause an appreciable increase in astigmatism and an alteration of the axis shortly after application. The variations caused by low-viscosity tear substitutes lie within the normal range of variation between several measurements. CONCLUSIONS: At least in the case of the normal eye, gels should not be applied immediately before keratometry. In the case of patients who have undergone keratoplasty, however, it can be helpful before fitting contact lenses. In addition keratometry can be helpful to determine the residence time of ophthalmic preparations being different in viscosity.