In‐vitro characterisation of corneal scatter in rabbit corneas following PRK

Abstract

Abstract Purpose The present work pertains to the measurement of light scatter in rabbit corneas after Excimer laser treatment, to the microscopic characterisation of the corneal irregularities and to the development of a mathematical model of light propagation through the post‐laser treatment cornea, based on the statistical properties of the scattering structures. Methods Fourteen rabbits underwent photorefractive keratectomy (‐6D). Nine to twelve weeks postoperatively, after confocal imaging, animals were sacrificed and the corneas were excised. The intensity and angular distribution of scatter was measured by enclosing the excised rabbit corneas between two glass elements to form a triplet lens. This lens was used with a CCD camera to record images projected on a computer screen. Scatter intensity and distribution was calculated by measuring the intensity in small dark disk concentric with a series of bright disks. After the scatter measurement, the corneas were examined histologically. The structures observed using the confocal microscope ‐corresponding to refractive index (and therefore optical path difference) variation were fitted with a fractal surface band‐pass filtered in the Fourier domain. Results Scattered light is characterised by a narrow forward distribution. Scatter is dominated by the subepithelial structures having sizes of the order of 50‐150 microns. The modelling of scatter by means of a spatially filtered fractal surface corresponding to OPD results to predictions in accordance to the experimental data. Conclusion Forward scatter following PRK can be attributed mainly to the subepithelial irregular layer. The angular distribution of scatter is in accordance to the size of structures observed microscopically in this layer.