The application of low coherence interferometry to the micron scale imaging of the living human retina

Current optical and ultrasound techniques for high resolution in vivo retinal imaging cannot provide the depth accuracy required to enable sensitive ophthalmologic diagnosis to be carried out on the basis of images of retinal microstructures. The axial depth resolution of one of the recently introduced retinal imaging instruments, the scanning laser ophthalmoscope, is restricted by the combined effect of the depth of focus achievable through the eye pupil and aberrations to about 300 pm. A new imaging technique, based on low coherence interferometry, providing improved depth resolution figures of the order of a few microns, is demonstrated here. Non-invasive topographic and tomographic measurements can be performed with an instrument based on this technique. A novel path modulation procedure, the Newton rings sampling function, is presented together with experimental results obtained in its application to the imaging of various objects including human in vivo retina. The advantages and disadvantages of novel and more conventional imaging modes, their associated techniques and the overall importance and likely impact of the novel Newton rings modulation method are considered. The measurement of 3-dimensional profiles of various targets, including tomographic images of in vivo human retinas from volunteers’ eyes, is presented. The utility of OCT measurements in the high-resolution mapping of in vivo tissue and its potential usage alongside scanning laser ophthalmoscopy in identifying features in the human eye are discussed.