The present results suggest a nonlinear pressure-volume relation in the living human eye characterized by an increase in rigidity at higher IOP levels. The increased OPA and decreased pulse volume relate to the decreased POBF and the increased mechanical resistance of the ocular wall at high IOP levels.

We present an instrument based on Purkinje imaging that permits the objective measurement of the amount of scattering associated with the eye's anterior segment, avoiding the contribution from the retina. The experimental system records the fourth Purkinje image, and adequate processing is used to compute a parameter that quantifies the scattering. The method was first tested in an artificial eye and later in normal young eyes wearing customized contact lenses that induced different amounts of scatter. We were able to detect scattering increments, which indicates that this technique may be used as an objective tool to quantify the level of scattering in the anterior segment of the living human eye. The future use of this technique in clinical environments might help to estimate the level of corneal haze in eyes undergoing refractive surgery or/and scattering within the lens during cataract development.

Corneal light scatter associated with the increased amount of haze after excimer laser ablation has a narrowly forward distribution that can be attributed to the subepithelial structures observed in treated corneas.

Corneal haze following excimer laser ablation is an adverse after-effect of photorefractive keratectomy (PRK) and is associated with the development of subepithelial opacities. The present work pertains to the measurement of light scattering in rabbit corneas following excimer laser treatment; to the microscopic analysis of the light-scattering corneal structures; and to the development of a mathematical model of light propagation through the post-laser treatment cornea. Photorefractive keratectomy (PRK-6D, 6 mm optical zone) followed by standard postoperative pharmaceutical treatment was performed on rabbit eyes. Animals were examined clinically on a weekly basis and sacrificed after the tenth postoperative week. Confocal microscope image sequences were acquired immediately before animal sacrifice. After the scatter measurement, the corneas were prepared for histopathological evaluation. The subepithelial structures observed using the confocal microscope correspond to refractive index (and therefore optical path difference (OPD) variation. This OPD distribution can be approximated with a fractal surface, band-pass filtered in the Fourier domain. The angular distribution of scattered light is characterised by a narrow forward peak of the order of 0.5 degrees full-width at half maximum (FWHM) in accordance with the sizes of the subepithelial structures (5-150 microm).The intensity of scattered light is correlated with the thickness of the subepithelial scar-tissue layer.

Purpose The intraocular pressure (IOP) is the primary mechanical load to several ocular structures. It fluctuates over time as a result of a dynamic equilibrium between the systems of aqueous and blood flow. The purpose of this study is to characterize the eye’s pressure volume relationship and quantify hydro and haemodynamic parameters in the living human eye. Methods An invasive manometric dynamic measurement procedure was developed and used in a series of healthy and pathological eyes measured intraoperatively before cataract surgery. Different measurement protocols involving injection of predetermined doses of saline and monitoring the IOP in a time‐resolved manner, allow the measurement of ocular rigidity, outflow facility and pulsatile ocular blood flow. In addition, a new non‐invasive ultrasound based technique enabled us to visualize and define the elastic properties of the ocular globe and periocular structures. Results Measurements in humans indicate that the above techniques are safe and effective. A non‐linear pressure‐volume relationship is established. The ocular pulse amplitude (and therefore pulsatile ocular blood flow) is shown to correlate with IOP. Conclusion A model that incorporates ocular rigidity is proposed in order to describe and quantify the relationship between hydrodynamic and hemodynamic parameters of the human eye. These measurements along with the use of new non invasive techniques may improve our understanding of the relationship between these parameters and their significance in health and disease.