Modelling corneal transparency with reference to stromal architecture

Abstract

The arrangement of corneal collagen fibrils within lamellae was investigated by comparing fibril positions obtained from electron microscopy with distorted hexagonal, quasi-random and aperiodic arrays. By calculating the wavelength dependence and Fourier transforms of these various arrays it was determined that an aperiodic array based on the sunflower seed head is the most compatible with corneal ultrastructure. An investigation of corneal light scattering away from the central axis was undertaken for the first time. Experimentally it was shown that corneal transmission decreases peripherally, particularly in the far periphery near the limbus. This was shown to be theoretically compatible with calculated positional changes in refractive index and fibril radius, by calculating transmission using the direct summation of scattered fields method. In swollen human corneas, it was determined that there was a notable change in wavelength dependence in the peripheral regions, possibly suggesting an increase in the size and relative number fibril free voids. . Corneal infrared transmission is poorly studied. In this part of the spectrum, the cornea acts as an absorber of incident radiation. It was hypothesised that there should be a systematic variation between corneal hydration and infrared light transmission. Experimentally, by Fourier transform infrared spectroscopy a convenient linear relationship between hydration and transmission was found. Riboflavin-UVA crosslinking is used to treat keratoconus, a degenerative corneal disorder. A swelling experiment was performed on porcine corneas in order to elucidate whether the crosslinking mechanism is intra- or inter-fibrillar. Swelling rates for the treated and untreated tissue were not statistically significant, excluding interfibrillar crosslinking. The penetration depth of the riboflavin molecule into corneal stroma was also examined by visible spectroscopy of thin segments of tissue. It was demonstrated that when riboflavin infiltrates a full thickness cornea, the highest concentration of riboflavin is present in the anterior tissue segment.EThOS - Electronic Theses Online ServiceGBUnited Kingdo