Handheld Simultaneous True Color SLO-OCT System

Abstract

 

Purpose

 

Unlike clinical color fundus photography, scanning laser ophthalmoscopes (SLOs) typically use monochromatic illumination. Prior research-oriented color SLO systems described in the literature have utilized multiple lasers for illumination, and are therefore not capable of generating “true color” fundus images [Bartsch D et al. 2002]. We present a handheld, simultaneous operation, true color SLO and optical coherence tomography (OCT) system utilizing a supercontinuum white light source.

 

Methods

 

The handheld device contains independently controlled SLO and OCT systems with separate scanners and wavelengths (584 ± 111 and 840 ± 35 nm, respectively). For the SLO spectrum, separate wavelength division multiplexers and 3 variable optical attenuators were used to optimize the visible spectrum uniformity. SLO reflectance was collected confocally (2.8 times diffraction limited) using a multimode fiber, then split into three different color channels (430-495, 495-580, and 580-770 nm) for photomultiplier tube (PMT) detection. Each SLO color channel was corrected for illumination differences, PMT gain, and PMT spectral sensitivity and then combined to create true color images.

 

Results

 

Sample imaging results from the color SLO-OCT handheld system are shown in Fig.1. All three color channels of the SLO and the OCT channel were acquired simultaneously with a 20° field of view at 16 and 40 frames per second, respectively. The SNR, axial resolution, and 6 dB falloff range of the OCT system were 100 dB, 7 μm, and 1.1 mm, respectively. SLO and OCT image pixel dimensions were 530 x 580 and 1024 x 500, respectively. The radiant flux incident on the eye for the color-SLO and OCT were under the ANSI limit at 75 µW and 300 µW, respectively, which comprised 56% and 41% of the maximum permissible exposure limit.

 

Conclusions

 

We have demonstrated a handheld color SLO-OCT system for simultaneous acquisition of color SLO and OCT images of the retina. The use of this technology may provide a compact, multi-modal solution for imaging of patients that are supine or under anesthesia, and should also be suitable for use with children.

 

 

Imaging results of the color SLO-OCT handheld probe. A) Color SLO image. B) Red channel SLO image. C) Green channel SLO image. D) Blue channel SLO image. Each SLO image is a 100 frame average and all three channels were combined to produce the color image in A). E) OCT B-scan (single frame) taken simultaneously with color-SLO.

 

Keywords: 551 imaging/image analysis: non-clinical • 552 imaging methods (CT, FA, ICG, MRI, OCT, RTA, SLO, ultrasound)