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K. Nakashima, O. Roche, N. Massamba, B. Lamory, F. Harms, G. Soubrane, J.-L. Dufier; Assessment of Cone Mosaic Imaging Performance Using Flood-Illumination Adaptive Optics in Ametropia. Invest. Ophthalmol. Vis. Sci. 2009;50(13):1066.
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© ARVO (1962-2015); The Authors (2016-present)
To evaluate the ability of a flood-illumination adaptive optics (AO) system to image the cone mosaic with a field size of 3 degrees in presence of significant refractive errors.
Cone photoreceptor images were acquired in the left eyes of 36 healthy subjects presenting various amounts of spherical ametropia and astigmatism, at retinal horizontal eccentricities of at 4, -2, 0, +2 and +4 degrees. The eye pupils were dilated using 0.5% tropicamide. Ocular wavefront errors (OWE) were corrected using a compact AO system operating in closed-loop at 10 Hz, based on a 52-actuator electromagnetic deformable mirror, a 1024 lenslet Shack-Hartmann sensor (both Imagine Eyes, France) and an superluminescent diode emitting at 750 nm. A square 3° x 3° retinal area was flood-illuminated by a pulsed LED emitting at 850 nm and its optical image through the deformable mirror was detected a low-noise CCD camera (Roper Scientific, USA). Every acquisition consisted in a series of 20 consecutive images, out of which 10 were numerically selected and averaged to produce an enhanced final image. The root-mean-square (RMS) residual wavefront error (RWE) was recorded throughout the acquisitions. A quality mesure of each final image was computed as the ratio between the Sobel filter output and the image mean (RSFM). The possible relations between image eccentricity, OWE, RWE and RSFM were analyzed using descriptive statistics, linear regression and ANOVA.
The subjects' spherical ametropia, astigmatism and higher-order OWE ranged between -8.75 and 0.5D, -1.25 and 5D, 0.3 and 1.2µm respectively. Mean and standard deviation of RWE and RSFM were 0.14 ± 0.05µm RMS and 0.09 ± 0.013 respectively. Cone photoreceptors were clearly discernible in 31%, 47% and 72% of the images centered at eccentricities of 0, 2 and 4 degrees respectively. Statistical analysis confirmed the significant effect of eccentricity on RSFM (p<0.05), however no significant relation was found between RSFM and initial OWE. A RWE of less than 0.2µm RMS appeared to be a necessary, yet not sufficient, condition for resolving the cones.
The cone mosaic could be sharply imaged over a three-degree field at eccentricities of 2 and 4 degrees even in cases of large myopia and astigmatism. When aberrations are systematically reduced to less than 0.2µm RMS, the refinement of retinal image quality may depend on critical experimental factors other than optical aberrations.
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