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Georg Schuele, David Dewey, Phillip Gooding, Mike Simoneau, Alexander Vankov; Intra-lenticular femtosecond laser cavitation threshold variations. Invest. Ophthalmol. Vis. Sci. 2015;56(7 ):1909.
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© ARVO (1962-2015); The Authors (2016-present)
Femtosecond laser-assisted laser cataract surgery has gained a significant interest due to its ability to create perfectly sized capsulotomies as well pre-fragment the lens to facilitate easy removal of the lens during cataract surgery. In this paper we present measurements of intra-lenticular variation of cavitation threshold using fresh porcine lenses and compare it to optical modeling result.
A water-filled cuvette with embedded hydrophone was connected and synchronized with a standard CATALYS ® System to allow synchronized exposure and reading of cavitation events. Specialized software was developed to probe full fields within the cuvette volume for cavitation thresholds. Initially the cavitation threshold variation of water was measured and acted as a system specific baseline. Fresh porcine lenses were placed in the cuvette and the same fields retested for cavitation thresholds.<br /> <br /> An optical model of the CATALYS ® System in ZEMAX software along with a standard lens model was used to calculate Strehl-ratios of different field points within the porcine lens. These data are compared to the variations seen in experiments.
Even for very fresh and clear porcine lenses cavitation thresholds varied greatly throughout the different locations of the lens. Within the center 3 mm radius mean threshold was increased 2.5 fold while the three star suture areas of the lens increased the threshold up to 4 fold. Beyond the 3mm radius thresholds increased even further to 6-8 fold threshold relative to water.<br /> <br /> Optical simulations showed only minor variation of strehl-ratio of 0.2 which did not correspond to the significant higher variations in threshold using porcine lenses.
We could demonstrate that significant variation of cavitation threshold using femtosecond lasers exist even in clear fresh porcine lenses. Optical modeling of the strehl-ratio does not predict the measured variations. This might indicate that other tissue related effects like the grin-lens effect or other tissue specific refractive index variations will lead to focus distortions and with that to increased cavitation threshold
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