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A relationship has been derived between intraocular pressure and pulsatile blood flow in the eye. Measurements of intraocular pressure show a time variation that is associated with the pulsatile component of arterial pressure. Experimental results provide a means of transforming intraocular pressure changes into ocular volume changes. The eye is represented by a chamber with elastic walls, a pulsatile incoming flow of incompressible fluid (blood), and a steady outgoing flow of blood. Under these conditions, the rate of pulsatile blood flow through the eye can be approximated from the instantaneous intraocular pressure measurements. Data from a healthy human eye are used to illustrate the analysis.

In recent studies other investigatiors have presented traces of "light scattering" versus depth into the cornea. The present investigation demonstrates that these traces do not measure the actual light scatter intensity and that a proper interpretation of such traces shows that most of the scattering is from within the stroma.

Small-angle light-scattering (SALS) measurements of the cornea together with electron micrographs of the corneal stroma suggest that the waviness in the stromal collagen fibrils of corneas fixed at zero pressure is the structural feature responsible for the cross-polarized SALS patterns. This paper derives and discusses a Born approximation to the parallel- and cross-polarized SALS patterns expected from lamellae of long, thin, optically anisotropic wavy fibrils whose axes are parallel to each other and are spatially distributed about one another in a quasi-ordered fashion. The predicted scattered intensity depends on three factors: (1) the fibrils within a given lamella wave in unison, which produces scattering that is characteristic of a wavy sheet (as opposed to that characteristic of an isolated wavy fibril); (2) the undulations lead to a diffraction condition for determining the dependence of scattered intensity on scattering angle; (3) the relative orientations of fibril axes in different lamellae and the intrinsic electric susceptibility of a fibril determine the dependence of scattered intensity on azimuthal angle. The patterns predicted for anisotropic fibrils with a random distribution of lamella orientations or with distributions of lamella orientations that have one or two preferred directions superimposed upon a random background agree with the qualitative features of the experimental patterns observed with rabbit corneas. Experimental evidence in support of the distributions with preferred orientations is discussed.

It is generally assumed that the collagen fibrils in the stroma are the primary scatters of light in the nearly transparent cornea of the eye. We derive a scaling relationship between scattering angle and light wavelength that should hold if this hypothesis is valid. The derivation accounts for the cornea's layered nature and the azimuthal orientations of the fibrils in the different layers. The fibrils are treated as finite-length cylinders, and the scaling relation is obtained in both the far- and the intermediate-field zones. The predicted relationship is verified experimentally for normal-thickness rabbit corneas.

Threshold damage to the cornea from CO2 lasers is confined to the epithelium. Exposures well above the threshold for epithelial damage produce bowl-shaped stromal wounds. Light and electron microscopy and slit-lamp photographs all show a sharp demarcation between the damaged and undamaged regions 48 hr after exposure. The micrographs also show that the damaged region is accellular. Calculations of the expected temperature increases combined with analyses of slit lamp photographs show that the wound boundary corresponds to a surface of equal peak temperature increase. Comparisons with epithelial and endothelial damage conditions suggest that stromal, endothelial and epithelial cells have essentially the same thermal damage mechanism.

The cornea is the clear front covering of the eye through which we see and is composed of collagen fibrils embedded in an optically homogeneous ground substance. It has long been recognized that these fibrils scatter light and that transparency results from interference effects due to an ordering in the spatial arrangement of the fibrils about one another. The nature of this ordering and of its disruption in abnormal corneas is of great current interest. The present study reviews experimental light scattering and electron microscopic evidence relevant to this problem. This evidence suggests that theoretical attempts to model and understand corneal transparency and its loss during swelling, in terms of ultrastructure, must account for a short-ranged ordering of fibrils in normal healthy corneas and for the formation of regions void of fibrils in swollen corneas.

1. A theoretical and experimental analysis of the relationship of the corneal stromal ultrastructure with light transmission has been made in an attempt to resolve recent contradictory explanations of corneal transparency.2. The spatial distribution of collagen fibrils in electronmicrographs of rabbit corneal stroma has been analysed in terms of a radial distribution function. The results indicate the presence of local order extending to at least 200 nm from individual fibrils.3. The observed spatial distribution of the collagen fibrils was used as a basis to compare the theoretically derived and the experimentally determined values of light transmission. It has been found that the transparency of the normal cornea may be explained by the quasi-random structure revealed by the electronmicroscope.4. Histograms of the collagen fibril diameter in normal rabbit corneal stroma revealed the range to be 12.5-32.5 nm and the mean value to be approximately 20 +/- 1.5 nm. Corneal swelling did not change the collagen fibril diameter significantly.5. It is concluded that the size and distribution of collagen fibrils revealed in electronmicrographs are consistent with the observed transparency of normal stromas.6. A marked heterogeneity in the spatial distribution of collagen fibrils was found in the swollen cornea. This is qualitatively consistent with the observed decrease in transparency.

1. The studies described herein involve the use of light scattering measurements to characterize the ultrastructural arrangement of the constituent collagen fibrils in rabbit corneal stromas.2. Theoretical light scattering techniques for calculating the scattering to be expected from the structures revealed by electron micrographs are discussed, and comparison with the experimental light scattering tests the validity of these structures.3. The wave-length dependence of light transmission and of angular light scattering from normal corneas is in agreement with the short range ordering of collagen fibrils depicted in electron micrographs.4. The transmission measurements on oedematous rabbit corneas indicate that transmission decreases linearly with the ratio of thickness to normal thickness.5. The wave-length dependence of transmission through cold swollen corneas indicates that the increased scattering is caused by large inhomogeneities in the ultrastructure. Electron micrographs do, indeed, reveal the presence of such inhomogeneities in the form of large regions completely devoid of fibrils.