We present an analysis of how visually impaired people perform gestures on touch-screen smartphones and report their preferences, explaining the procedure and technical implementation that we followed to collect gesture samples. To that end, we recruited 36 visually impaired participants and divided them into two main groups of low-vision and blind people respectively. We then examined their touch-based gesture preferences in terms of number of strokes, multi-touch, and shape angle, as well as their execution in geometric, kinematic and relative terms. For this purpose, we developed a wireless system to simultaneously record sample gestures from several participants, with the possibility of monitoring the capture process. Our results are consistent with previous research regarding the preference of visually impaired users for simple gestures: with one finger, a single stroke, and in one or two cardinal directions. Of the two groups of participants, blind people are less consistent with multi-stroke gestures. In addition, they are more likely than low-vision people to go outside the bounds of the display in the absence of its physical delimitation of, especially with multi-touch gestures. In the case of more complex gestures, rounded shapes are greatly preferred to angular ones, especially by blind people, who have difficulty performing straight gestures with steep or right angles. Based on these results and on previous related research, we offer suggestions to improve gesture accessibility of handheld touchscreen devices.