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Sebastian Bohn, Karsten Sperlich, Heinrich Stolz, Rudolf F Guthoff, Oliver Stachs; Applanation force monitoring during in vivo corneal confocal laser scanning microscopy. Invest. Ophthalmol. Vis. Sci. 2019;60(9):2131. doi: https://doi.org/.
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© ARVO (1962-2015); The Authors (2016-present)
In vivo confocal laser scanning microscopy images of the subbasal nerve plexus (SNP) are often impaired by compression artifacts in form of ridge-like deformations due to an increased applanation force. They inhibit a gapless SNP imaging, which is mandatory for its assessment in terms of early diagnoses of different diseases. However, increasing the applanation force advantageously reduces involuntary eye movements during imaging. The aim of this work is to develop an applanation force monitoring tool in order to identify the compression artifact threshold.
A customized objective lens module  adapted to a confocal laser scanning ophthalmoscope was used as an imaging system. We implemented a force sensor into this system to enable applanation force monitoring without shifting the focal plane. As proof of concept, SNP images of a healthy human eye were repeatedly captured at series of different applanation forces of up to 0.6 N for a planar and a concave contact cap, whereas the latter was originally designed to constrain eye movements while imaging . Based on these images the individual force threshold of first deformation occurrence was estimated.
Fig. 1a shows the schematic setup including the implemented force sensor. The force sensor calibration is depicted in Fig. 1b. Exemplary measurements on a human eye revealed a reproducible threshold force of 0.203 ± 0.022 N using the planar contact cap. Contrary, we did not observe deformation artifacts at any force using the concave contact cap.
Applanation force monitoring provides a new tool to identify the tradeoff between applanation force and compression artifact avoidance. It is subject to future work, whether this tradeoff can be generalized to a larger population in order to support the clinical examination process. This would increase the accuracy of SNP assessments and hence the specifity. Furthermore, this method provides a possibility to evaluate different contact cap designs with regard to the formation and magnitude of deformation artifacts. Bohn et al. Biomed Opt Express. 2018
This abstract was presented at the 2019 ARVO Annual Meeting, held in Vancouver, Canada, April 28 - May 2, 2019.
Fig. 1: Customized objective lens module with the integrated force sensor (a) and the force sensor calibration curve (b).
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