Spectral imaging of the retina

Abstract

Introduction The work described here involved the use of a modified fundus camera to obtain sequential hyperspectral images of the retina in 14 normal volunteers and in 1 illustrative patient with a retinal vascular occlusion. Methods The paper describes analysis techniques, which allow oximetry within retinal vessels; these results are presented as retinal oximetry maps. Results Using spectral images, with wavelengths between 556 and 650 nm, the mean oxygen saturation (OS) value in temporal retinal arterioles in normal volunteers was 104.3 ( ± 16.7), and in normal temporal retinal venules was 34.8 (±17.8). These values are comparable to those quoted in the literature, although, the venular saturations are slightly lower than those values found by other authors; explanations are offered for these differences. Discussion The described imaging and analysis techniques produce a clinically useful map of retinal oximetric values. The results from normal volunteers and from one illustrative patient are presented. Further developments, including the recent development of a 'snapshot' spectral camera, promises enhanced non-invasive retinal vessel oximetry mapping.

Multispectral retinal image analysis: a novel non-invasive tool for retinal imaging

“…Other groups have used multispectral imaging for the quantification of retinal haemoglobins (for example, see Mordant et al 23 ), but MRIA offers a completely different approach in that it interprets the images by means of a comparison of the images with a computer-generated reflectance model of the fundus and it reconstructs 'parametric maps' from the data available, potentially providing the clinician with pixel-by-pixel concentration values.…”

Light path-length distributions within the retina

“…The measurement of oxygen saturation in retinal vessels is useful as a diagnostic aid in a number of ocular vascular disorders such as glaucoma, 1 diabetic retinopathy, 2 and central retinal vein occlusion, 3 where hypoxia of the retina and optic-nerve head [4][5][6] are believed to contribute. Spectral imaging is also potentially a useful tool for making reliable measurements of oxygen saturation in the human ocular fundus; however, a deeper understanding of light propagation from the illumination source through the various layers of the retina and to the detector is needed to enable these measurements to be made accurately.…”

“…10,11 In retinal imaging, it is often assumed that images obtained in reflection geometry can be used to estimate transmission measurements through a blood vessel. 6 A proportion of the illuminating light is scattered by tissues underneath the vessel and then illuminates the vessel from the underside. This effectively results in a transmission geometry between the "back-illuminating" light and the imaging camera.…”

A multi-object spectral imaging instrument

“…They have applications in astronomy and microscopy [13] and also in opthalmology [14,15]. Snapshot imaging spectrometers generally require a trade-off between spatial and spectral resolution and hence the spectral resolution is normally limited.…”