The difference in direction and the ratio between the speed of the incident beam and that of its reflection can then be used to estimate the ocular refraction along this meridian. Moving the incident beam along a certain pupillary meridian (indicated by arrows in the figure) will result in a reflected beam that goes in the same or opposite direction as the incident beam. The iTrace’s patented ray-tracing technology makes it the only piece of ophthalmic equipment on the market that can truly separate the visual function of a patient’s cornea from their internal optics. However, in a hyperopic eye the reflection is directed to the opposite side of the pupil. Because the retina can be considered a spherically concave mirror (reflecting about 4% of incident light), the beam is reflected back in more or less the original direction in a myopic eye. It uses focal shift in a different way, starting with the observation that the retinal image of a light beam coming from a superior direction is located below the optical axis in a myopic eye and above the optical axis in a hyperopic eye. The automatic retinoscope is an automated version of the handheld retinoscope and is implemented in an objective, serial, and double-pass fashion. The uncomplicated nature of the technique makes it robust for extreme aberrations. The x-y scanner, comprising 2 separate scanners for the x- and y-directions, repeatedly moves the beam to a new entry position until homogeneously spread measurements are available for the whole pupil area. Several studies have assessed the repeatability or reproducibility of HOA measurements obtained by Topcon KR-1 W and iTrace, respectively 11, 12, 13, 14. Once in the eye, local aberrations in the beam's entry position cause a focal shift of the retinal image with respect to a certain reference position. With ray tracing, the Tracey iTrace dynamically measures and analyzes wavefront aberrometry, or the focusing power of the human. Both the Topcon KR-1 W system (Hartmann-Shack method) and the iTrace system (ray tracing method) are devices composed of an aberrometer and a corneal topographer. Ray tracing uses a narrow laser beam that is directed into the eye parallel to the eye's line of sight by means of an x-y scanner. Trial registration: This is a retrospective. Tracey Technologies holds the patent to a highly advanced technology called ray tracing aberrometry. The combination of OQAS and iTrace analyzer is a valuable complementary measurement in evaluating the optical quality after the refractive surgery. Using a beam splitter and lens, the retinal image is captured on a linear array of photodetectors and is made available for further processing. Practitioners use the aberration information provided by the Tracey devices to test and treat their patients vision. Ray tracing uses a narrow laser beam that is directed into the eye parallel to the eye's line of sight by means of an x-y scanner. The ray tracing principle is a serial, double-pass method using forward projection that can be implemented in both an objective and subjective manner.
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