Abstract
Purpose :
Computational simulation of light scattering in ocular tissue would aid interpretation of image artifacts and enable optimization of existing and new imaging modalities. However, development of an accurate light scattering simulation that incorporates the distinct retinal layers has been held back by a lack of empirical data. That retinal layers are visible in Optical Coherence Tomography demonstrates that the back scattering from these layers varies dramatically, but in order to develop computational simulations, total scattering coefficient and scattering anisotropy coefficients must be determined. There is a need to measure and map the complete optical scattering properties of each layer of the retina, choroid, and sclera.
Methods :
To map the optical scattering properties of the retina, a light scattering goniometer was developed that measures the light scattered as a function of angle from a tissue section. A tunable supercontinuum laser with is collimated by the objective and illuminates a 50μm spot at the sample. The scattered light is collected at the pupil planes of the forward and backward objectives and imaged onto cameras enabling a direct image of the angular scattering profile. A galvonometer mirror scans the illumination angle enabling measurement of scattered light profile over 4π steradians. From this data, all relevant scattering properties can be determined including absorption coefficient, scattering coefficient, and scattering anisotropy. Fixed tissue from a thirteen lined ground squirrel was cryosectioned 30μm thick and mounted in PBS between #1.5 coverslips.
Results :
Measured scattering properties are shown in the figure that includes an H&E stained section of the same tissue labeled and aligned to the measured properties for reference. Error bars on the data indicate the standard deviation. The scattering coefficient is much lower in the retina and higher in the choroid and sclera. In most cases, the scattering decreases with wavelength as expected. Absorption is negligible in all but the RPE and choroid. Anisotropy is high in the retina and drops dramatically in the RPE, choroid, rebounding but remaining lower in the sclera.
Conclusions :
These initial measurement provide a starting point for developing a more accurate model for light scattering simulations that will enable interpretation and optimization of imaging modalities including OCT and emerging methods such as split detection used in AOSLO.
This abstract was presented at the 2019 ARVO Annual Meeting, held in Vancouver, Canada, April 28 - May 2, 2019.