Abstract
Abstract: :
Purpose: Spectral imaging provides indirect insight into chemical processes in a number of scientific disciplines e.g. astronomy, microscopy, and remote sensing by military and civilian agencies. Application of these spectral imaging techniques may allow non-invasive, in vivo investigation of retinal and optic nerve head chemistry, including tissue oxygenation. Method: Development of a retinal camera to allow imaging of the retina at different narrow spectral bands is described. Use of a liquid crystal tuneable filter and supplementary interference filters to modulate the light source, together with a cooled, low-noise CCD detector has allowed in vivo retinal imaging between 400 and 1100nm. In comparison to other techniques, such as Fourier-transform spectral imaging, this method enables higher signal-to-noise ratios to be obtained with lower retinal light levels whilst providing wide-field imaging and random access to specific spectral bands. Images at each spectral band were captured using a 'snapshot' whole-field approach, and then subsequently co-registered. Results: Images of normal volunteers show marked changes in the visibility of small retinal venules and arterioles, reflecting the spectral absorption characteristics of haemoglobin in oxygenated and deoxygenated states. Markedly reduced visibility of arterioles was found between 633 and 700nm, venules were less prominent beyond 700nm. Choroidal vasculature patterns were most prominent at 550nm, and difficult to detect at other imaged spectral bands. Enhanced visibility of the optic disc scleral ring, and lamina cribrosa pattern, reflecting the absorption characteristics of collagen, was seen beyond 700nm. Examples of spectral imaging of the retina using this technique in patients with diabetic retinal disease, and optic disc imaging in glaucomatous eyes are demonstrated. Calibration methods to enable accurate determination of retinal albedo will be discussed as well as ongoing refinement of the instrumentation to allow simultaneous 'snapshot' imaging at several spectral bands. This will reduce co-registration difficulties, and enhance sub-pixel feature detection. Conclusion: A novel spectral imaging technique to examine the human retina in vivo is described. This non-invasive approach enables characterisation of ocular blood flow and other chemical processes in the retina and optic nerve head.
Keywords: 432 imaging methods (CT, FA, ICG, MRI, OCT, RTA, SLO, ultrasound) • 430 imaging/image analysis: clinical • 331 blood supply