Imaging of Human Retina using Spectral Optical Coherence Tomography and high sensitive autofluorescence detection

Abstract

 

Purpose

 

To demonstrate the significant reduction of required intensity of AF excitation beam while using modulated excitation source and lock-in detection a device was constructed which combines two methods of imaging of the retina of the human eye in-vivo: autofluorescence (AF) and spectral optical coherence tomography (SOCT).

 

Methods

 

The instrument was designed and constructed in Optical Biomedical Imaging Group laboratory, Institute of Physics, NCU, Torun, Poland. It combines functionality of imaging fundus of human eye by registration autofluorescence signal by Scanning Laser Ophthalmoscope (FAF-SLO mode of work) with Fourier domain OCT (OCT mode of work). Native fluorescence of human fundus was excited with blue diode laser beam (λ = 473 nm) with high frequency amplitude modulation (20 MHz) directed into OCT optical path with fiber coupler. AF signal was detected with photomultiplier tube and lock-in amplifier operating at frequency of blue beam modulation. The setup allows for simultaneous acquisition of OCT and high contrast AF images using fluorescence excitation power of 50 µW without averaging consecutive images. All the test have been conducted for healthy eyes and in compliance with ANSI standards and with approval of the Ethics Committee of the Collegium Medicum in Bydgoszcz, Nicolaus Copernicus University in Torun, Poland. Examinations were conducted after written informed consent was obtained.

 

Results

 

Successful functioning of constructed device have been demonstrated for 10 objects of different age. Exemplary, wide angle, low excitation power AF images as well as high resolution OCT images of the retina are shown in Figure 1 and 2 respectively. Improved detection of AF signal allows for acquiring high contrast images using single scan without averaging and incomparable low excitation power.

 

Conclusions

 

Using modulated excitation source and lock-in detection in fundus autofluorescence imaging significantly improves the sensitivity of the device and allows for using much lower excitation power than used in standard devices. We expect this method to be more comfortable for the patient and safe for his eye.

 

 

OCT image of fundus of left eye of healthy volunteer (left) and indicated B-scans of the same eye (right).

 

 

Fluorescence of the fundus of the left eye of a healthy 32 years old volunteer measured with average power of the exciting beam equal to 56 μW.

 

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