The Laser Ray Tracing aberrometer (LRT) measures the optical aberrations of the eye by delivering narrow laser beams sequentially through different pupil positions, and simultaneously collecting the light reflected off the retina corresponding to each entry position. The beam from a laser diode is rapidly deflected using a scanning system and the aerial images are captured on a highly sensitive CCD camera conjugated with the retina. Additionnal channels are a pupil monitoring system (pupillary images are captured simultaneously to retinal images) and a fixation channel. The local ray aberration (proportional to the local derivative of the wave aberration) is obtained from the corresponding aerial as the deviation of the centroid position from the reference (position corresponding to chief ray). The wave aberration for each position is then estimated by integration from ray aberrations.
Some advantages of this device are: continuous defocus correction using a Focusing Block, flexible pupil sampling pattern changed by software, continuous pupil monitoring and recording (passive eye-tracking). The system is automatically controlled by custom developed software, which manages the settings, data collection and storage.
Details of the system can be found in Llorente et al. 2004, Lourdes Llorente PhD thesis and Carlos Dorronsoro PhD thesis.