Optical characteristics of the cornea and sclera and their alterations under the effect of nondestructive 1.56-μm laser radiation

Abstract

Optical properties of cornea and sclera of the eye and their alterations under the effect of 1.56-μm laser radiation are studied. The laser settings corresponded to the laser treatment regimens used (1) to correct the shape of the cornea and change the refraction of the eye and (2) to improve the hydraulic permeability of the sclera in glaucoma cases. A fiber-optical system to investigate the dynamics of the reflected and transmitted scattered laser radiation and a setup with a double integrating sphere to determine the optical properties of the ocular tissues on the basis of the Monte-Carlo simulation of the propagation of light was used. When the radiation characteristics corresponded to the treatment regimens for correcting the shape of the cornea, no noticeable changes were detected in its optical properties. When irradiating the sclera in conditions corresponding to the treatment regimens for improving its hydraulic permeability, the optical characteristics of the tissue showed definite changes. The results obtained as to the dynamics of the optical signals during the course of laser irradiation of the cornea and sclera create prerequisites for designing test systems to be used with novel medical laser techniques for correcting visual abnormalities.

Microstructural changes in sclera under thermo‐mechanical effect of 1.56 µm laser radiation increasing transscleral humor outflow

“…The results presented in this paper demonstrated for the first time that laser irradiation of sclera with laser settings increasing water permeability really results in formation of submicron pores in sclera. These results correspond well to the data of optical measurements showing that laser‐induced structural alterations in sclera lead to pronounced changes in its optical characteristics . As it was shown in Yuzhakov et al , the laser irradiation of the mini‐pig sclera in conditions corresponding to the therapeutic laser effect in normalizing the IOP gives rise to some changes in the optical characteristics of the tissue (increase in absorption coefficient, and decrease in scattering coefficient).…”

“…These results correspond well to the data of optical measurements showing that laser‐induced structural alterations in sclera lead to pronounced changes in its optical characteristics . As it was shown in Yuzhakov et al , the laser irradiation of the mini‐pig sclera in conditions corresponding to the therapeutic laser effect in normalizing the IOP gives rise to some changes in the optical characteristics of the tissue (increase in absorption coefficient, and decrease in scattering coefficient). These changes were attributed to the laser‐stimulated formation of a porous structure that improves the hydraulic permeability of the sclera and accordingly raises (locally) the concentration of the interstitial fluid, which increases somewhat the effective absorption coefficient.…”

“…In our experiments, we used 1.56 µm laser radiation which is mainly absorbed by the tissue layer of thickness H = 1/ µ eff where is an effective absorption coefficient including absorption coefficient µ a and scattering coefficient µ s . According to the paper for 1.56 µm laser radiation affecting sclera, µ a = 9.7 cm −1 , µ s = 33.2 cm −1 , µ eff = 34 cm −1 , and therefore H ∼ 300 µm. The last value corresponds well to the typical thickness of rabbit's sclera.…”

Optical coherence elastography for strain dynamics measurements in laser correction of cornea shape

“…The threshold “inflexion temperatures” marked in Figure are significantly lower than temperatures causing damage of the tissue's biological functionality (coagulation, etc. ); furthermore, such moderate heating does not significantly alter the optical properties (transparency and scattering coefficients) of cornea . It is known that the denaturation‐induced decrease in cornea transparency depends on the heating duration (e. g., 50 % transparency decrease for 30 s heating at 65 °C, or a few seconds at ∼80–90 °C .…”

Optical properties of mouse brain tissue after optical clearing with FocusClear™

“…[18][19][20][21] We first collected a standard reflectance measurement, which consisted of no sample in the beam path and the 99% diffuse reflectance standard at the reflectance port. We then mounted a brain slice in the tissue holder and measured the thickness of the glass-tissue preparation with a micrometer (Mitutoyo Corp., Kawasaki, Japan).…”