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Marcel Pfister, Jawchyng Lormen Lue, Michael J Koss, Francisco Rosa Stefanini, Paulo Falabella, Mark S Humayun, ; Comparison of reaction response time between hand and foot controlled devices in simulated microsurgical testing. Invest. Ophthalmol. Vis. Sci. 2014;55(13):2332.
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The cut and vacuum rates of most modern vitreous cutters are controlled by foot-paddle. We hypothesized that reaction times (RT) for the switch release are faster for hand- than for foot-controlled switches for physiological, anatomical (e.g. nerve conduction speed) and ergonomic reasons. The risk of accidental trauma to eye (e.g. sucking retina into the vitreous cutter) could be reduced if the surgeon reacted quicker to reduce vacuum power and to improve the surgical outcome.
The study included 47 medical students and ophthalmic surgeons at USC. Age, dominant/non-dominant hand/foot, gender and experience level were recorded. Under a microscope, a red light emitting diode (LED) was shown as a START indicator. After the start signal, participants expected a green LED signal to trigger their release of a hand- or footswitch. The duration between start time and the green LED signal was randomized as was the order of the four extremities tested. The RT is the time between the green LED signal and the break in the switch circuitry. Each extremity of each individual was tested 5 times. A subjective questionnaire was also administered addressing ergonomic preferences.
The mean RT: hands 318.24ms±51.13; feet 328.69ms±48.70. Comparison: Hand vs. Foot: mean (SD) = -10.45ms (30.86), p= 0.025. Male subjects' responses (291ms±9) were statistically significantly faster than females' (339ms±10, p = 0.001). The analysis and comparison of each extremity for the different experience level groups (years of microscopic surgery (YMS): 0 years to 8 or more years / microscopic surgeries per week (MPW): 0 to 10 or more) showed partially significant differences between the groups (YMS p=0.01-0.003/ MPW p=0.57-0.002) but no statistically significant trend toward shorter RTs with more years of practice (p=0.81-0.4) or more surgeries per week (p=0.8-0.28). According to the results of the subjective questionnaire, 89% (n=42) of test subjects prefer to use hand-controls for the vitreous cutter.
Our data show that the RT for hands is faster than feet. Similarly the subjective questionnaire showed a greater preference for hand actuation than foot actuation of switch. This data suggest a hand-controlled ophthalmic instrument might have distinct advantages than a foot-controlled unit; however, clinical correlation is required to confirm these findings.
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