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Dipesh Bhattarai, Marwan Suheimat, Andrew J. Lambert, David A. Atchison; Fixation stability with Bessel beams. Invest. Ophthalmol. Vis. Sci. 2018;59(9):5791.
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Shapes such as bull’s eye extended target and Gaussian beams have been used as fixation targets during ophthalmic procedures. Bessel beams, with non-diffracting and self-reconstructing properties, have imaging advantages over Gaussian beams. Improved fixation stability, using Bessel beams as fixation targets, during the procedures could further improve quality. We investigated whether Bessel beam fixation targets improve fixation stability over that achieved with conventional targets.
Right eyes of 16 healthy participants were presented with seven fixation targets: a monitor-based bull’s eye with a cross hair shape (target A), a monitor-based Gaussian beam (target B), monitor-based Bessel beam with 4 rings (target C), monitor-based Bessel beam with 3 rings (target D), laser Gaussian beam (target E), laser Bessel beam with 4 rings (target F), and laser Bessel beam with 3 rings (target G). Participants fixated the target centres for five runs, in which each run presented the seven targets in random order for 20 seconds each. An EyeTribe tracker recorded eye positions at 30 Hz sampling rate. Standard deviations (SDs) of fixation positions and the area of bivariate contour ellipse (BCEAs), encompassing 68.2% of the highest density eye position samples for each target, were calculated and statistical significances of the differences between the targets were determined.
The average SDs of fixation positions between targets ranged from 0.31 degree (target D) to 0.60 degree (target E), but target differences were not statistically significant (χ2 (6) = 11.0, p = 0.09). The average BCEAs of fixation positions between targets ranged from 1.03 degree2 (target D) to 2.84 degree2 (target E), and target differences were statistically significant (χ2 (6) = 16.9, p = 0.01). The Gaussian beam (target E) had significantly greater BCEAs than the monitored-based bull’s eye and a cross hair shape (target A) and two of the Bessel targets (D and F). There were no significant differences between other fixation target combinations.
Bessel beams provide better fixation targets, whether monitor-based images or laser beams, than laser Gaussian beams, and are as good as a monitor-based bull’s eye with a cross hair shape. Ophthalmic imaging instruments can benefit by using Bessel beams for both illumination and fixation targets.
This is an abstract that was submitted for the 2018 ARVO Annual Meeting, held in Honolulu, Hawaii, April 29 - May 3, 2018.
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