Purpose:
Fundus imaging has become an essential clinical diagnostic tool in ophthalmology. However, common implementations of SLO, such as the confocal scanning laser ophthalmoscope (CSLO) and line-scanning laser ophthalmoscope (LSLO), require imaging or multidimensional scanning elements which are typically implemented in bulk optics placed close to the subject eye. Here, we apply a spectral encoding technique in one dimension combined with single-axis lateral scanning to create a spectrally encoded confocal scanning laser ophthalmoscope (SECSLO) which is fully confocal. This novel implementation of the SLO allows for high contrast, high resolution in vivo human retinal imaging with image transmission through a single-mode optical fiber. Furthermore, the scanning optics are similar and the detection engine is identical to that of current-generation spectral domain optical coherence tomography (SDOCT) systems, potentially allowing for a simple implementation of a joint SECSLO-SDOCT imaging system.
Methods:
SECSLO was implemented on a modified slit lamp base for human fundus imaging. An SLD, with a center wavelength of 840 nm and bandwidth of 49 nm, was used as the illumination source. The source was input into a single-mode fiber-optic circulator and the output was collimated, laterally dispersed using a grating, and scanned across the retina. The back-reflected signal, after transmission back through the circulator, was detected using a custom spectrometer with a 1024 pixel linear array. Modified SDOCT software (Bioptigen, Inc.) allowed for real-time imaging at 20 Hz frame rate and ImageJ was employed for image registration and averaging.
Results:
In vivo human macula was imaged with 1024 x 1024 pixels (spectral x lateral) at a line-rate of 52 kHz with 700 µW illumination power at the pupil. Real time imaging permitted rapid scanner alignment and live monitoring of retinal features. An example of improved SNR and speckle reduction resulting from registration and averaging of ten sequential image frames (with an effective frame rate of 5 Hz) is illustrated in Fig. 1.
Conclusions:
We have demonstrated SECSLO as a novel method for video-rate high resolution, high contrast fiber-based retinovitreal imaging.
Keywords: imaging/image analysis: non-clinical • retina • macula/fovea