1. A method, for treating a structure in an eye, comprising: engaging, with an eye holder, an outer surface of an eye during a treatment period to maintain the eye in substantially a fixed position during the treatment period; emitting an x-ray beam from an x-ray source toward the structure based on a determination of whether the eye is in substantially the fixed position during the treatment period; acquiring optical data indicative of eye motion; determining, from the optical data, whether the eye is in a different position than the fixed position; and when the eye is determined to be in a different position than the fixed position: (i) aligning the eye, with the eye holder, to be in substantially an aligned position, or (ii) ceasing or reducing emitting of the x-ray beam from the x-ray source .