An interferometric method for the dynamic evaluation of the tear film

Abstract

This study describes a non-invasive method for the in vivo assessment of precorneal tear film stability. A lateral shearing interferometer (LSI) is used for the measurement. The interference fringes obtained from the tear film layer are analysed using the fast Fourier transform (FFT) technique. The method is based on evaluating the degree of fringe disturbance by calculation of the second momentum of Fourier spectra on the interferogram pattern. This method points to the occurrence of dynamic changes in the tear film surface over time. We propose four different parameters. One of them is presented here. The less smooth the tear film, the more disturbed the interference fringes and the higher the value of the calculation parameters. Clear differences were discerned between tear film quality in healthy eyes, dry eyes and eyes with various contact lenses. The benefits of artificial tears used by patients with dry eye or contact lenses were also noted. Examination of dry eyes before and after applying fluorescein revealed significant differences in tear film stability. Lateral shearing interferometry is a suitable method for assessing the stability of the tear film on the cornea and on contact lenses. Evident differences can be demonstrated in tear film quality between normal eyes and dry eyes or eyes with soft contact lenses.