Abstract
Speckle arises in double-pass images when coherent light is scattered by the retina. Since this noise degrades the images that are used to characterize the eye, there is special attention in reducing speckle when working with instruments based on retina reflections. In this work, we present a method for speckle reduction in double-pass retinal images by producing minor periodic variations in the vergence of the beam entering the eye with a variable-focus lens during image recording. Measurements in an artificial and a real eye following the implementation of the method corroborate the speckle reduction.
Highlights
The ability of the human visual system to process information from our surrounding is crucial to our daily activities
Double-pass retinal images are affected by speckle because they rely on reflections of coherent light in the retina, a rough surface composed of photoreceptors that scatter light back with a random phase [4]
The observed values of speckle contrast suggest that variations in the vergence of the beam during image recording led to speckle reduction
Summary
The ability of the human visual system to process information from our surrounding is crucial to our daily activities. The optical components of the eye are not perfect and present aberrations and intraocular scattering [1], which degrade the image of external objects formed on the retina In this sense, the double-pass technique [2] is an excellent tool currently used in clinical environments to obtain an overall estimation of retinal optical quality [3]. Similar to the use of broadband lasers where the speckle decorrelation is partially ruled by the defocus effect of the wavelength bandwidth [11], the induced vergence variations shift longitudinally the focal position of the beam in relation to the retina and change the optical path of reflected light [12] This space diversity allows the generation of uncorrelated speckle patterns during the integration time of the recording device, permitting in this manner the speckle reduction. When image acquisition is requested, six consecutive images are recorded with an integration time of 40 ms and post-processed in Matlab (MathWorks, 2010) following the procedure described in Section 4 of this document
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