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Edward Frederick Ruppel, Manuel Alejandro Ramirez Garcia, Yousuf Khalifa, Mark Buckley; Correlating corneal endothelial cell loss to compressive forces caused by forceps manipulation.. Invest. Ophthalmol. Vis. Sci. 2017;58(8):5697.
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© ARVO (1962-2015); The Authors (2016-present)
Our previous research has identified a relationship between experimentally applied compressive forces and corneal endothelial cell loss. However, it is unknown what instrument contact forces are induced on corneal endothelial cells during eye banking and surgical procedures. In this study, we developed a method to measure the compressive forces that a pair of forceps applies to hold on to a scored Descemet’s membrane (DM). The goal of this work is twofold: 1) determine the magnitude of forces applied on corneal tissue during a simulated eye banking procedure; and 2) estimate the required forceps contact area to prevent stress-induced cell death.
Fresh porcine eyes (n=6) were dissected and the endothelium was isolated. The endothelium was irrigated with a 0.4% Trypan Blue solution in BSS and the DM was scored with a Sinsky Hook. The DM was peeled at the edges using a custom, calibrated, strain gage-instrumented forceps to track the contact forces applied at its tip. This device was made from a 13.5 cm long Dumont SS forceps with 0.2 x 0.12mm tips. The force threshold for successful gripping of the Descemet’s membrane was tested by holding the DM while applying nominal tension to isolate the point at which slipping stops and gripping occurs (n=12 tests/specimen). The contact area was measured using pressure film.
The mean force required to grip the DM was 2.31 N (128.4 MPa), with a range from 1.7 – 3.19 N (94.56 – 177.2 MPa). The contact area of the forceps was 0.018 mm2. In our previous studies, we found that stresses greater than 9.78 kPa kill endothelial cells. Thus, stress-induced cell death is inevitable when gripping the DM with the forceps used in the study. However, given that a compressive force of 2.31 N is sufficient to hold the DM, a surgical tool with a contact area greater than 236.2 mm2 should enable gripping of this tissue without endothelial cell death.
Our results support the hypothesis that any loading of the DM with fine forceps will induce cell death. However, due to the large required contact area of 236 mm2 to enable manipulation of the DM with little cell loss, it is suggested that the finest tipped forceps be used to minimize inevitable cell injury. Future work will focus on instrumenting a more clinically relevant tool and implementing wireless transmission.
This is an abstract that was submitted for the 2017 ARVO Annual Meeting, held in Baltimore, MD, May 7-11, 2017.
Gripping force per specimen
Custom instrumented forceps, calibrated for tip force
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