En Face Snapshot Spectral Imaging of the Retina

Abstract

Purpose:: There is increasing interest in the application of spectral imaging for biochemical functional mapping of the retina. The solution to recording the required three-dimensional data cube using a two-dimensional detector array is normally to record images in time sequence in a way that scans one of the cube dimensions; typically either a sequence of narrow-band images are recorded and subsequently coregistered or a hyperspectral line image is scanned across the retina. In both cases the time sequential nature is undesirable: the increased time required to record the data combined with the infirmity that is common of patients with eye disease is problematic - both for the patient and in the impact on image quality; spectral calibration and image coregistration can be highly problematic and it is not possible to record en face time-resolved spectral images. Unfortunately a putative two-dimensional spectral camera; the spectral imaging equivalent of conventional RGB colour camera has been notable by its absence. We report here on the development of a new snapshot spectral retinal camera and its first use for blood oximetry.

Methods:: The key component of this unique retinal camera is a novel image replicating imaging spectrometer (IRIS) that employs polarising interferometry and Wollaston prism polarising beam splitters to simultaneously replicate images of the retina in multiple spectral bands onto a single detector array. In principle the technique is 100% optically efficient enabling the intensity of light at the retina to be minimised. An IRIS system has been integrated into a conventional fundus camera by simply locating its input object plane so as to intercept the output image plane of the fundus camera.

Results:: Eight bands in the range of 580-600 nm are recorded in a single snapshot and spectral processing yields a map of retinal blood oxygenation in real time. The results of early clinical trials will be reported.

Conclusions:: A new spectral imaging instrument suitable for clinical applications allows performing oxygen saturation measurements in the retina by erradicating calibration and misregistration problems associated with time-sequential techniques.

Keywords: imaging/image analysis: clinical • hypoxia • retina