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B. Thurin, L. Diaz-Santana; Dynamic Ocular Speckle Interferometry for the Study of Microscopic Retinal Structures. Invest. Ophthalmol. Vis. Sci. 2007;48(13):4250.
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© ARVO (1962-2015); The Authors (2016-present)
Ocular Speckle Interferometry was the first technique to allow assessing microscopic retinal structures in vivo. At the time the technique suffered from several drawbacks. A slow data collection scheme, meant that a small number of frames was collected limiting the technique's potential benefits. Here we demonstrate the feasibility of a fast recording ocular speckle interferometer that could be suitable for further studies, including retinal pathologies.
An Ocular Speckle Interferometer with a Membrane Deformable Mirror as a random phase screen (RPS) conjugated with the pupil plane was implemented. The system can record up to 100fps. The acquisition camera is synchronised with the RPS. Coherent Laser illumination at two wavelengths (543nm, 633nm) is used (power <10 microwatts). The spatial resolution of the system is around 200 cycles per degree. A CCD detector, conjugated with the retina, collects a speckle pattern. The power spectrum of each individual speckle pattern is calculated. The power spectra are averaged to retrieve spatial frequencies up to the diffraction limit imposed by the eye. 5 subjects with no known ocular pathology took part in this study. Speckle patterns were collected for 2 seconds time intervals under non-mydriaticly viewing conditions and relaxed accommodation at 0 deg eccentricity. Additionally, for one subject, data were collected over a period of 20 seconds, with his pupil reflex inhibited with one drop of tropicamide (0.5%).
Data from the 5 subjects was used to calculate the power spectra of the speckle patterns. Results showed a spatial frequency content of up to 120 cycles/deg. Data from the 20 seconds data set showed the dynamic evolution of the power spectrum. As the eye moved the retinal patch illuminated changed producing a different power spectra unique to that retinal patch. The observed changes in orientation of the power spectrum correspond with spatial changes of the retinal mosaic.
Our rapid data collection scheme (100 images collected per second) with a low illumination power (possibility of recording for a few seconds) is an important step towards using the technique to study retinal diseases.
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