Endogenous fluorescence can differentiate the keratoconic cornea

The purpose of the study was to investigate the endogenous fluorescence of the keratoconic cornea in order to analyze changes in the spectra due to the keratoconic stroma abnormalities. Twenty-two corneal buttons obtained from patients with keratoconus (KC, N = 22) at the time of penetrating keratoplasty were used. As a reference, twelve normal corneas (N = 12): ten from the Eye Bank and two from enucleated eyes due to choroidal melanoma were used. The fluorescence excitation/emission matrices (EEM) in the ranges of 250-400/260-600 nm were recorded. Healthy cornea, keratoconic cornea and sclera showed three main EEM bands, which correspond to the following fluorophores: tryptophan residues in the proteoglycan fraction of corneal/scleral stromas, naturally occurring collagen cross-links and the NAD(P)H fraction present in the metabolically active cells. Relative intensity factors S₁, S₂ and S₃ describing the contribution of each kind of fluorophore to the total fluorescence of the tissue were calculated. Normal and keratoconic corneas show qualitatively similar fluorescence matrices, but the statistically significant differences in the mean values of the S₁, S₂ and S₃ parameters for the KC and normal corneas were observed indicating changes in contribution of different fluorophores to the whole fluorescence of the tissue. Moreover, differences between multidimensional distribution of the relative intensity factors S₁, S₂ and S₃ between these groups were demonstrated (p < 0.001). In conclusions: Differences in the relative intensity factors calculated on a basis of the fluorescence spectra can correspond to the changes found in the KC stroma regarding natural collagen cross-links and the proteoglycan fraction. These parameters well differentiate the KC and normal corneas that could serve as an additional tool for the keratoconus characterization.

[Contemporary applications of wavefront aberrometry in ophthalmology practice]

The aim of the article is to present and summarize the current knowledge of wavefront aberrations, methods and applications of aberrations measurement. Ideal optical system is stygmatic, which means that object point is imaged by optical system into the image point without deformation. Optical system of the eye is not ideal, it has aberrations. Aberrations limitate and determine visual quality. Wavefront aberrometers measure manochromatic low and high order aberrations. Wavefront aberrations are described by Zernike polinomials. More important wavefront sensor types are described in the article. In their practice authors use KR1W Topcon aberrometer. Authors also present difficulties in taking aberrometric measurements. In recent years quality of vision becomes the point of interest for vision scientists. Correction of high order aberrations is the future of optics.