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Nicole Sevilla, Ilyas Saytashev, Pedro Lopez, Joseph Chue-Sang, Herbert Wertheim, Jessica Ramella-Roman; Measurements of retinal temperature using Laser Speckle Imaging (LSI). Invest. Ophthalmol. Vis. Sci. 2018;59(9):6202.
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© ARVO (1962-2015); The Authors (2016-present)
Since the eye’s anatomy makes the retina inaccessible for contact temperature measurement techniques, it becomes difficult to monitor and avoid possible irreversible damages in the eye due to heat during procedures like laser eye surgeries. Inverse thermal models, depicting the thermal distribution of the eye, further suggest that local retinal temperature cannot be extrapolated using standard corneal surface temperature measurements. Therefore, a novel approach is necessary to measure temperature at the retina. Here, we propose the use of a laser speckle imaging (LSI) system to demonstrate how micro changes in speckle pattern of an optical phantom can be correlated with temperature changes using an exponential decay model.
Speckle cross-correlation models are used to highlight changes in speckle patterns as the temperature changes. We have developed a LSI system consisting of a 12-bit monochrome camera, a 50mm focal length F# 1.3 lens, a diode laser centered at 640 nm, and a polarized single mode fiber. In the example below, Figure 1 and 2, an optical phantom is attached to a thermal bath whose temperature increased from 36 to 38 degrees oC. The right side of the phantom is thermally isolated. A stack of images is acquired and pixel cross-correlation is acquired at each frame, Figure 1.
The cross-correlation images clearly show a difference between high and low temperature areas, Figure 2. This finding was validated using thermocouples attached to two different zones of the phantom, and they showed a temperature gradient of about 2 degrees oC. The system can be easily integrated to a fundus camera for clinical use.
We have demonstrated that changes in temperature have a significant impact in speckle imagery. Measurement of cross-correlation can be used to follow even minor temperature changes non-invasively.
This is an abstract that was submitted for the 2018 ARVO Annual Meeting, held in Honolulu, Hawaii, April 29 - May 3, 2018.
A time dependent image stack is collected. Pixel cross-correlation is measured from each frame of the image stack over time
Cross correlation of image stack showcasing the difference between a low (right) and high (left) temperature area. The difference in temperature was about 2 degrees oC for the two zones.
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