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Matthew T. Sheehan, Maciej Nowakowski, Daniel R. Neal, Alexander V. Goncharov; Measurement of the Isoplanatic Patch for Human Eyes. Invest. Ophthalmol. Vis. Sci. 2012;53(14):160.
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© ARVO (1962-2015); The Authors (2016-present)
Conventional optical systems usually provide best image quality on axis with unavoidable gradual decrease in image quality towards the periphery of the field. Image quality can be considered invariant within a limiting field region known as the isoplanatic patch. Measuring the isoplanatic patch of the eye is complicated by the fact that the eye is a non-centered and non-rotationally symmetric system without a uniquely defined optical axis. It is known that the field-dependent component of lower-order aberrations (defocus and astigmatism) account for the largest contribution to the total wavefront error for each field point. However, the basis and choice of an optimal ocular axis that maximizes the size of the isoplanatic patch after correction with an Adaptive Optics (AO) system has not been established yet.
The wavefront aberration was consecutively measured at 129 field points over the central visual field (14 x 11.6 degrees) for 8 young healthy cyclopleged eyes. A combined corneal topographer and aberrometer was used to perform measurements as it allowed the orientation of the pupillary axis (PA) with respect to the line of sight (LOS) to be estabilished. The aberration distribution across the field was used to simulate the size of isoplanatic patch considering two cases: a perfect AO correction applied along LOS and PA. In both cases a single adaptive element conjugated to the pupil was simulated.
The shape of the isoplanatic region applying the LOS reference is typically larger and more regular than that by applying the PA reference. Suggesting that for a single corrector AO system, it may be better to use the LOS as a reference as is the norm. The dominace of the lower order aberrations regarding variation in the total wavefront aberration across the field emphasizes the importance of utilizing variable optics to reduce the field curvature and field astigmatism in ocular AO systems.
Maximizing the size of the isoplanatic patch is important for ocular AO systems to achieve high-resolution retinal images over a wider field. Observations indicate the LOS reference provides wavefront aberrations that are closer to the median wavefront aberrations over the central field in most eyes, however, significant inter-subject variability exists and aberration correction methodologies may benefit from consideration of individual aberration pattern across the field.
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