1A, 1C, 1D), potentially compromising subsequent quantitative analysis of retinal structures. However, even an AOSLO image that appears distortionless may contain residual distortion ( Figs.
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1) can be mitigated by registration 22, 23 and eye tracking 24, 25 methods, in conjunction with the selection of a minimally distorted reference (or template) image. In AOSLO, distortions from eye motion ( Fig. Given the relatively low frame rate (<30 Hz) and the high magnification of current AO scanning ophthalmoscopes (∼1°), even the involuntary eye motion of subjects with good fixation can cause substantial image distortion (local shear and compression/expansion). 6, 7, 10, 20, 21 However, in (point or line) scanning ophthalmoscopes, the image pixels are recorded sequentially, rather than simultaneously as in fundus ophthalmoscopes. Regardless of the AO imaging modality used, analysis of images of the photoreceptor mosaic often includes extraction of measurements that describe the geometry of the cone mosaic.
The existence of these artifacts emphasizes the need for caution when interpreting results derived from scanning instruments. It may be possible to use multiple images from the same retinal area to approximate a “distortionless” image, though more work is needed to evaluate the feasibility of this approach.Įven in subjects with good fixation, images from AOSLOs contain intraframe distortions due to eye motion during scanning. Our data demonstrate that the intraframe distortion found in AOSLO images can affect the accuracy and repeatability of cone mosaic metrics. The average of all metrics extracted from AOSLO images (with the exception of VCAR) was not significantly different than those derived from AO-fundus images, though there was variability between individual images. We observed substantial variation across subjects in the repeatability of density (1.2%–8.7%), inter-cell distance (0.8%–4.6%), percentage of six-sided Voronoi cells (0.8%–10.6%), and Voronoi cell area regularity (VCAR) (1.2%–13.2%). In nine additional subjects, we compared AOSLO-derived measurements to those from adaptive optics (AO)-fundus images, which do not contain system-imposed intraframe distortions. Cone mosaic geometry was measured in all registered images ( n = 600) using multiple metrics, and the repeatability of these metrics was used to assess the impact of the distortions from each reference frame. An expert grader manually selected 10 minimally distorted reference frames from each 150-frame sequence for subsequent registration. We acquired AOSLO image sequences from 20 subjects at 1.0, 2.0, and 5.0° temporal from fixation.
To characterize the effects of intraframe distortion due to involuntary eye motion on measures of cone mosaic geometry derived from adaptive optics scanning light ophthalmoscope (AOSLO) images.
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