Speckle reduction in double-pass retinal images

Donatus Halpaap,Carlos E García-Guerra,Cristina Masoller,Meritxell Vilaseca

doi:10.1038/s41598-019-41168-3

Donatus Halpaap, Carlos E García-Guerra + Show 2 more

Open Access

https://doi.org/10.1038/s41598-019-41168-3

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Journal: Scientific Reports	Publication Date: Mar 14, 2019
Citations: 6	License type: open-access

Affiliation: Universitat Politècnica de Catalunya

Abstract

The double pass (DP) technique quantifies the optical quality of the eye by measuring its point spread function. The low reflectivity of the retina requires the use of a high-brightness, point-like illumination source, and thus, DP systems use laser diodes (LDs). However, LDs light produces speckle, and a low-cost solution to reduce speckle is to include a vibrating mirror in the beam path. With the goal of finding an all-optical solution, here we perform a comparative study of the amount of speckle produced by three semiconductor light sources: an LD, a light emitting diode (LED), and a superluminescent diode (SLED). We also compare the results with the speckle reduction that is obtained with a vibrating mirror. We find that the SLED is a good alternative to LD illumination, as the amount of speckle in the image is almost as low as that obtained with an LD and a vibrating mirror in the beam path.

Highlights

The double pass (DP) technique quantifies the optical quality of the eye by measuring its point spread function
We have done a comparative study of the amount of speckle in DP images recorded by using a laser diode (LD), a light emitting diode (LED) or a superluminescent LED (SLED) as light sources, with and without vibration of a mirror in the beam path
We have found that, when the mirror vibration is turned on, the three light sources yield very similar amounts of speckle

Summary

Introduction

The double pass (DP) technique quantifies the optical quality of the eye by measuring its point spread function. Alternative speckle-reduction solutions have been proposed in the literature, like acoustic modulation of laser beams[14], superluminescent diodes[15], periodic variation of the vergence of a lens in the beam[16], rotating diffusers[17], and a low-cost one is the use of a vibrating mirror in the optical path[18]. To our knowledge, another typical speckle reduction technique, fiber shaking, has not been used so far in DP imaging. A second disadvantage is the long time needed to perform the measurements, which limits the applicability of the DP technique for real-time dynamic tests, which are needed, for example, for the clinical evaluation of tear film quality and the diagnosis of dry eye syndrome[19]

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