Three-Dimensional Light Field Fundus Imaging: Automatic Determination of Diagnostically Relevant Optic Nerve Head Parameters.

Purpose: Morphological changes to the optic nerve head (ONH) can be detected at the early stages of glaucoma. Three-dimensional imaging and analysis may aid in the diagnosis. Light field (LF) fundus cameras can generate three-dimensional (3D) images of optic disc topography from a single shot and are less susceptible to motion artifacts. Here, we introduce a processing method to determine diagnostically relevant ONH parameters automatically and present the results of a subject study performed to validate this method. Methods: The ONHs of 17 healthy subjects were examined and images were acquired with both an LF fundus camera and by optical coherence tomography (OCT). The LF data were analyzed with a novel algorithm and compared with the results of the OCT study. Depth information was reconstructed, and a model with radial basis functions was used for processing of the 3D point cloud and to provide a finite surface. The peripapillary rising and falling edges were evaluated to determine optic disc and cup contours and finally calculate the parameters. Results: Nine of the 17 subjects exhibited prominent optic cups. The contours and ONH parameters determined by an analysis of LF 3D imaging largely agreed with the data obtained from OCT. The median disc areas, cup areas, and cup depths differed by 0.17 mm², -0.04 mm², and -0.07 mm, respectively. Conclusions: The findings presented here suggest the possibility of using LF data to evaluate the ONH. Translational Relevance: LF data can be used to determine geometric parameters of the ONH and thus may be suitable for future use in glaucoma diagnostics.

3D retinal imaging and measurement using light field technology.

SIGNIFICANCE: Light-field fundus photography has the potential to be a new milestone in ophthalmology. Up-to-date publications show only unsatisfactory image quality, preventing the use of depth measurements. We show that good image quality and, consequently, reliable depth measurements are possible, and we investigate the current challenges of this novel technology. AIM: We investigated whether light field (LF) imaging of the retina provides depth information, on which structures the depth is estimated, which illumination wavelength should be used, whether deeper layers are measurable, and what kinds of artifacts occur. APPROACH: The technical setup, a mydriatic fundus camera with an LF imager, and depth estimation were validated by an eye model and in vivo measurements of three healthy subjects and three subjects with suspected glaucoma. Comparisons between subjects and the corresponding optical coherence tomography (OCT) measurements were used for verification of the depth estimation. RESULTS: This LF setup allowed for three-dimensional one-shot imaging and depth estimation of the optic disc with green light. In addition, a linear relationship was found between the depth estimates of the OCT and those of the setup developed here. This result is supported by the eye model study. Deeper layers were not measurable. CONCLUSIONS: If image artifacts can be handled, LF technology has the potential to help diagnose and monitor glaucoma risk at an early stage through a rapid, cost-effective one-shot technology.

Repeatability of autofluorescence lifetime imaging at the human fundus in healthy volunteers.

PURPOSE: We aim to evaluate the repeatability of a new fluorescence lifetime imaging (FLIM) technique which measures time-resolved autofluorescence to assess metabolism of the retina. MATERIALS AND METHODS: We performed FLIM with two spectral channels (channel 1: 490-560 nm and channel 2: 560-700 nm) on 10 healthy volunteers, with 10 replicates per volunteer. From the 30° fundus FLIM images, we selected three regions: the fovea, the optic disc and the papillo-macular bundle. For each channel in these regions, we determined an average multi-exponential approximation with three components, and the six resulting parameters, α1-α3 (amplitudes) and τ1-τ3 (fluorescence lifetimes), were analyzed in terms of the coefficient of variation (CV). RESULTS: Repeatability was highest in the papillo-macular bundle, followed by the fovea and the optic disc. Repeatability was higher in channel 1 (mean CV of 7.9%) than in channel 2 (mean CV of 17.7%). The average CV for the diagnostically most relevant channel 1 and the most relevant parameters was as follows: τ1 (5.5%) and τ2 (4.7%) in the papillo-macular bundle, and τ1 (6.8%) and τ2 (6.9%) in the fovea. CONCLUSIONS: We demonstrated repeatability of FLIM measurement results within acceptable ranges of variation. Based on the detailed coefficients of variation, we derived recommendations for parameter ranges suitable for diagnostic applications.

Bioelectric and biomagnetic measurements are differentially sensitive to spiral currents.

Observations indicate that different information is contained in electrocardiograms and magnetocardiograms in both patients and healthy volunteers. Closed loop currents could explain this phenomenon. We hypothesized that open loops, such as the spirally shaped currents in the heart, also contribute to these differences. We modeled two types of open spiral-shaped loops, based on the heart geometry, using 12 artificial current dipoles in a physical torso phantom. The electric potentials and magnetic fields were measured simultaneously with increasing numbers of active dipoles in the spiral source geometries. We found a continuous increase in the measured amplitudes of the magnetic fields, up to a plateau value when 10 active dipoles were enabled. For the electric potentials, we found that the amplitudes increased when up to six or eight active dipoles had been enabled, and then decreased thereafter. We conclude that open loop currents also contribute to the experimentally observed differences in magnetocardiograms and electrocardiograms in both patients and healthy volunteers. Combined bioelectric and biomagnetic measurements should provide greater insight into heart activity than do single modality measurements.