Henle’s fiber layer investigated by polarization-sensitive optical coherence tomography in healthy and glaucoma eyes

Abstract

Purpose : Henle’s fiber layer shows poor contrast in conventional optical coherence tomography (OCT) images. However, the fibril composition of Henle fibers (HF) introduces form birefringence, a physical property that can be exploited by polarization-sensitive (PS-) OCT to gain additional information on this tissue. We investigate the capability of PS-OCT to determine the presence and extension of HF in the macula area and to quantify the polarization properties of HF.

Methods : A PS-OCT instrument incorporating a retinal tracker and operating in the 840nm wavelength range was used for imaging. The PS information was compensated for influences from other birefringent structures that lie anterior to HF layer such as the anterior segment and the retinal nerve fiber layer. From each of the 156 healthy subjects and 64 early glaucoma patients, one eye was randomly selected to be enrolled into this study. To detect the presence of HF, we introduce a new method that is based on the measured axis orientation as this polarization parameter is very sensitive to the presence of birefringent structures.

Results : The extension of HF from the fovea is on average 8°. Figure 1 A shows the measured extension for all subjects and reveals a small age dependency of this parameter (slope = -0.0266 °/year) for healthy eyes. In the glaucoma sub-group the age dependency is slightly changed to -0.0316°/year. The retardation pattern posterior to HF layer shows a slight asymmetric donut shape with increased retardation temporal and nasal from the fovea (cf. Fig. 1B) which possibly corresponds to the asymmetric cone density in this area. The maximum retardation of the donut was found at 2° eccentricity from the fovea and reached in average values of 9° (cf. Fig. 1C).

Conclusions : PS-OCT is a powerful tool to detect the presence of fibril structures such as HF. There seems to be a weak dependency of HF extension on age that possibly is correlated with the natural loss of photoreceptors with age. There was no difference between healthy subjects and early glaucoma patients indicating that the neuronal tissue of HF is not affected in this disease at this stage.

This abstract was presented at the 2023 ARVO Annual Meeting, held in New Orleans, LA, April 23-27, 2023.

 

Fig. 1. A) Extension of HF and dependence on age. B) Retardation measured posterior to HF layer averaged over all healthy volunteers (color bar: 0° to 25°). C) Quantitative evaluation of retardation introduced by HFL averaged circumferentially around the fovea.