OSLI Retina

September 2020

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528 Ophthalmic Surgery, Lasers & Imaging Retina | Healio.com/OSLIRetina postoperative period. Although this is an important adjunct, patient compliance with such instructions is often highly variable, and therefore we recommend this is performed in conjunction with gas concentra- tion adjustment to give the greatest chance for surgi- cal success. It is important to note that we used 80% to 85% fill at time of surgery to calculate gas concentrations. We recognize that this figure may vary slightly on a case by case basis, but it is important to note that 100% is not achievable during PPV due to residual anterior vitreous and a small liquid layer. In addi- tion, the mathematical model is based on a sphere, and therefore the anterior chamber and lens volume needs to be included. Based on these assumptions, in normal eyes, we found the optimal concentrations to be 22.6% for SF 6 , 13.9% for C 2 F 6 , and 11.6% for C 3 F 8 . These concentrations are in line with those of- ten used in clinical practice. A limitation of our study and modified mathemati- cal model is that the aqueous humour dynamics flow rates are based on old studies, in which the accuracy of measurement may be suboptimal. However, we were unable to find more up to date information and therefore used these in our calculations. If further re- search altered these figures, they could be easily ad- justed in our calculations. In conclusion, our model further improves our un- derstanding of gas dynamics and now includes the ability to input variables for aqueous inflow, traditional outflow and uveoscleral outflow. This should provide clinicians with adjunctive information when making decisions regarding gas tamponade procedures. REFERENCES 1. Gupta B, Neffendorf JE, Williamson TH. Trends and emerg- ing patterns of practice in vitreoretinal surgery. Acta Ophthal- mol. 2018;96(7):e889-e890. https://doi.org/10.1111/aos.13102 PMID:27213838 2. Neffendorf JE, Gupta B, Williamson TH. The role of intraocular gas tamponade in rhegmatogenous retinal detachment: A Synthe- sis of the Literature. Retina. 2018;38 Suppl 1:S65-S72. https://doi. org/10.1097/iae.0000000000002015 PMID:29280936 3. Abrams GW, Edelhauser HF, Aaberg TM, Hamilton LH. Dy- namics of intravitreal sulfur hexafluoride gas. Invest Ophthalmol. 1974;13(11):863-868. PMID:4431486 4. Lincoff H, Maisel JM, Lincoff A. Intravitreal disappear- ance rates of four perfluorocarbon gases. Arch Ophthal- mol. 1984;102(6):928-929. https://doi.org/10.1001/ar- chopht.1984.01040030748037 PMID:6329150 5. Peters MA, Abrams GW, Hamilton LH, Burke JM, Schrieber TM. The nonexpansile, equilibrated concentration of perfluoropropane gas in the eye. Am J Ophthalmol. 1985;100(6):831-839. https://doi. org/10.1016/S0002-9394(14)73376-8 PMID:3000186 6. Kontos A, Tee J, Stuart A, Shalchi Z, Williamson TH. Duration of intraocular gases following vitreoretinal surgery. Graefes Arch Clin Exp Ophthalmol. 2017;255(2):231-236. https://doi.org/10.1007/s00417- 016-3438-3 PMID:27460279 7. Intraocular Gases SC. Retina. St. Louis, MO: CV Mosby Co; 1989. 8. Hutter J, Luu H, Schroeder L. A biological model of tamponade gases following pneumatic retinopexy. Curr Eye Res. 2002;25(4):197- 206. https://doi.org/10.1076/ceyr.25.4.197.13487 PMID:12658552 9. Hall SK, Williamson TH, Guillemaut JY, Goddard T, Baumann AP, Hutter JC. Modeling the dynamics of tamponade multicomponent gases during retina reattachment surgery. American Institute of Chemi- cal Engineers AIChE Journal. 2017;63(9):3651-3662. https://doi. org/10.1002/aic.15739 10. Williamson TH, Guillemaut JY, Hall SK, Hutter JC, Goddard T. The- oretical gas concentrations achieving 100% fill of the vitreous cavity in the postoperative period: A Gas Eye Model Study. Retina. 2018;38 Suppl 1:S60-S64. https://doi.org/10.1097/iae.0000000000001963 PMID:29232331 11. Toris CB, Koepsell SA, Yablonski ME, Camras CB. Aque- ous humor dynamics in ocular hypertensive patients. J Glau- coma. 2002;11(3):253-258. https://doi.org/10.1097/00061198- 200206000-00015 PMID:12140404 12. Alberti M, la Cour M. Nonsupine positioning in macular hole surgery: A Noninferiority Randomized Clinical Trial. Retina. 2016;36(11):2072-2079. https://doi.org/10.1097/IAE.0000000000 001041 PMID:27046458 13. Toris CB, Tafoya ME, Camras CB, Yablonski ME. Effects of apra- clonidine on aqueous humor dynamics in human eyes. Ophthal- mology. 1995;102(3):456-461. https://doi.org/10.1016/S0161- 6420(95)31000-7 PMID:7891985 14. Jacobs PM, Twomey JM, Leaver PK. Behaviour of intraocular gas- es. Eye (Lond). 1988;2(Pt 6):660-663. https://doi.org/10.1038/ eye.1988.121 PMID:3256505 15. Costarides AP, Alabata P, Bergstrom C. Elevated intraocu- lar pressure following vitreoretinal surgery. Ophthalmol Clin North Am. 2004;17(4):507-512, v. v. https://doi.org/10.1016/j. ohc.2004.06.007 PMID:15533743 16. Lincoff H, Weinberger D, Stergiu P. 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