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Katja Schlichting, Muzammil A. Arain, Tilman Schmoll, Jochen Straub; Use of Focus-Tunable Lenses for Flexible Focusing in OCT Systems. Invest. Ophthalmol. Vis. Sci. 2017;58(8):3134.
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© ARVO (1962-2015); The Authors (2016-present)
To compensate for a patient’s refractive error or to switch between posterior and anterior segment imaging modes, a change in focus of the OCT sample beam is required. Tunable lenses make it possible to change the focus quickly, precisely, and without moving any mechanical parts. We demonstrate the use of such focus-tunable lenses in ophthalmic OCT systems.
A swept-source OCT prototype setup (ZEISS, Dublin, CA) is used to show the focusing accuracy of a focus-tunable lens prototype developed by Optotune (Optotune Switzerland AG, Switzerland). Optotune’s focus-tunable lenses are shape-changing lenses based on a combination of optical fluids and a polymer membrane. The system uses a 100 kHz swept source at 1050 nm central wavelength. The tunable lens is inserted in the sample arm of the interferometer after the collimator. We defocus the sample beam by placing various trial lenses in front of the sample to simulate refractive errors from -15 D to +15 D. The variable power of the focus-tunable lens is used to re-focus the beam. As samples, we used a model eye simulating different retinal layers as well as a lateral resolution test target. In order to prove the accuracy of the tunable lens, we evaluate the image quality and signal strength of the OCT B-scans and enface scans.
The focus-tunable lens was able to correct refractive errors of ±15 D. Images of a model eye and a resolution test target were obtained before and after defocus correction. Comparing the refocused images to images of the same sample acquired in focus, showed that the same signal strength and lateral resolution could be achieved after refocusing. Fig. 1 shows example images where the focus-tunable lens was used to correct a defocus of +10 D. We further demonstrated that the same tunable lens can be used to switch between an anterior segment and posterior segment imaging mode within 2 ms.
Tunable lenses allow quick and precise focus change in an OCT system. This lens technology enables fast and accurate correction of large refractive errors as well as switching the sample beam focus between anterior and posterior segments.
This is an abstract that was submitted for the 2017 ARVO Annual Meeting, held in Baltimore, MD, May 7-11, 2017.
Figure 1: Image showing B-scans for various configurations. Left: B-Scan with a focused OCT System without the tunable-lens. Center: defocused B-scan via trial lens of +10 D. Right: refocused B-Scan using the tunable lens.
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