[Reasons to reconsider interpretation of densitometry for corneal transparency]

To assess the effect of light scattering in the corneal epithelium on densitometric brightness of the stroma through mathematical modeling of the interaction between a light beam and the two-layer epithelium-stroma system.

In order to study the scattering behavior of a plane-parallel non-coherent beam at the epithelium-stroma interface, a multi-age group was formed (87 patients, 174 eyes) that comprised two subgroups with equal number of assign participants: healthy patients with no systemic changes and mixed patients with undisturbed corneal transparency that, nevertheless, were under instillation therapy. In the first subgroup, the assessment of light scattering was done at random times, while in the second subgroup - within the first 200 seconds after the instillation in order to avoid a reaction of the ocular surface structures, including epithelium (rapid response of epithelial cells to instillations). Light scattering intensity was measured with Pentacam (USA). The densitometric curve and brightness maxima of the epithelium and neighboring stroma as well as the mid and upper stroma were recorded for each patient.

A physico-mathematical model of the interaction between a light beam and the two-layer epithelium-stroma system was created. The study confirmed our theoretical CONCLUSION: on the effect size of light scattering intensity on the apparent densitometric brightness of the stroma.

Direct densitometry of multilayered spherical objects, of which each layer possesses its own optical properties, has been proved inaccurate. Complex optical interactions in a multilayered model cause a false increase in brightness of more transparent layers that lie behind those with pronounced light scattering properties. The function that describes the false increase in scattering ability of the layer that is more transparent rises sharply at the border between the layers.