Abstract
Conventional optical systems usually provide best image quality on axis, while showing unavoidable gradual decrease in image quality towards the periphery of the field. The optical system of the human eye is not an exception. Within a limiting boundary the image quality can be considered invariant with field angle, and this region is known as the isoplanatic patch. We investigate the isoplanatic patch of eight healthy eyes and measure the wavefront aberration along the pupillary axis compared to the line of sight. The results are used to discuss methods of ocular aberration correction in wide-field retinal imaging with particular application to multi-conjugate adaptive optics systems.
Highlights
Most man-made optical systems employ rotationally symmetric components with the reflecting and refracting surfaces aligned and centered with respect to each other
The aberrometer featuring Hartmann-Shack wavefront sensor allowed us to consecutively measure the field aberrations at 129 field points in the central visual field (14 x 11.6 degrees) for 8 young healthy eyes. This information about the aberration distribution across the field was used to calculate the size of isoplanatic patch using the line of sight as well as pupillary axis as references
We considered two cases: a perfect adaptive optics (AO) correction applied along line of sight (LOS) and pupillary axis (PA)
Summary
Most man-made optical systems employ rotationally symmetric components with the reflecting and refracting surfaces aligned and centered with respect to each other. The pupillary axis (PA) is defined as the line normal to the anterior cornea passing through the center of the entrance pupil (EP) and the anterior corneal center of curvature (C1). Even in the ideal case of perfectly aligned and centered corneal and lenticular surfaces, the optical axis does not coincide with the PA because the pupil of a real eye is usually decentred nasally, often being displaced by up to 0.5 mm relative to the visual axis [10], and the center of the pupil may be shifted up to 0.6 mm in the nasal. Corneal topographers are designed such that the fixation target, the object (the keratometry mires), and the detection/observation systems are all coaxial with each other In this arrangement the videokeratometric (VK) axis aligns the instrument’s axis normal to the anterior cornea ( passing through the corneal center of curvature C1) while the subject is fixating [17]. Mandel et al emphasised the vertex normal is not an intrinsic corneal reference landmark and is distinguished from the apex (region of greatest curvature) and the corneal sighting center (interception of the anterior cornea by the LOS) [1]
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