The human eye has aberrations that degrade the quality of vision. Adaptive Optics visual simulators allow closed-loop correction of the eye’s wave aberrations to produce diffraction-limited retinal image quality, or to manipulate the optics of the eye to probe the spatial limits of vision and neural adaptation. On the other hand, the wave aberrations can be controlled to expand depth-of-focus or provide multiple foci in eyes that have lost the ability to accommodate (presbyopia) and more recently to slow down myopia progression. We will present different wavefront control strategies (deformable mirrors, spatial light modulators and opto-tunable lenses) in visual simulators, and measured effects of correction and induction of wave aberrations and multifocal phase maps on visual function and perception.
SimVis Gekko is a novel see-through binocular visual simulator that is based on liquid-membrane tunable lenses (TLs) projected onto the pupil of the eye using a twisted miniaturized 4-f system. Following a temporal multiplexing approach that introduces periodic defocus variations in optical power at 50Hz, the TL generates multifocal images on the retina of the observer, that look static. In this study, the image quality of different tentative designs of SimVis Gekko was evaluated for different optical powers. The full optical system of SimVis Gekko was computer simulated to get the spot size, prismatic shift, angular magnification, and field curvature up to 20° of field of view. An image quality bench was developed to capture and process images through the SimVis Gekko simulator. The system comprises a grayscale camera and a 19- mm focal-length lens with an adjustable diaphragm. A high-resolution screen was placed at one meter with two different targets: (1) a checkerboard, imaged through a 1-mm diaphragm, to measure optical quality, prismatic shift, magnification, and optical distortion; (2) a binary noise, imaged through a 5-mm diaphragm, used to measure the local field curvature and image quality. Images were obtained from 1 to 3D of the TL and automatically analyzed. Theoretical simulations and experimental measurements showed good agreement. Magnification and curvature were the major differences across designs. The last version measured was free of optical distortions with a central curvature-free area with high optical quality. The developed system could guide the assembly and fine adjustment of active afocal optical systems.
As a large variety of intraocular lens (IOL) designs is commercially available in a growing market, selecting the best IOL for each patient has become a crucial task for a positive surgical outcome. Information about the measured or estimated performance of commercial lenses, as the through-focus modulation transfer function (TF-MTF) at a given frequency and pupil diameter, is routinely published. SimVis Gekko, a see-through simultaneous vision simulator based on temporal multiplexing, allows patients to experience the real world through different multifocal corrections prior to surgery. Implementing the maximum number of commercially available IOL designs into the portfolio of SimVis Gekko simulations is needed to provide a complete experience for the patients. We developed a new method to visually simulate IOL designs using temporal multiplexing, based only on publicly available information (mainly scientific literature or regulatory information), using the TF-MTF at 15cpd as input data to estimate the temporal coefficients that provide the best approximation to the real lens design. We validated the method with synthetic phase maps of equal area segmented bifocal and trifocal multifocal corrections for three pupil diameters of 3mm, 3.75mm and 4.5mm and applied it to three commercially available IOLs (trifocal or extended-depth-of-focus lenses). Through-focus visual acuity (TF-VA) curves were measured in seven patients using the SimVis simulations in the SimVis Gekko and matched, on average, the through-focus VA measurements in patients with implanted IOLs, reported in the scientific literature (on average logMAR RMS error=0.05, corresponding to less than 3 letters of visual acuity charts).
Adaptive Optics (AO) is of growing importance for understanding the impact of retinal and systemic diseases on the retina. While AO retinal imaging in healthy eyes is now routine, AO imaging in older eyes and eyes with optical changes to the anterior eye can be difficult and requires a control and an imaging system that is resilient when there is scattering and occlusion from the cornea and lens, as well as in the presence of irregular and small pupils. Our AO retinal imaging system combines evaluation of local image quality of the pupil, with spatially programmable detection. The wavefront control system uses a woofer tweeter approach, combining an electromagnetic mirror and a MEMS mirror and a single Shack Hartmann sensor. The SH sensor samples an 8 mm exit pupil and the subject is aligned to a region within this larger system pupil using a chin and forehead rest. A spot quality metric is calculated in real time for each lenslet. Individual lenslets that do not meet the quality metric are eliminated from the processing. Mirror shapes are smoothed outside the region of wavefront control when pupils are small. The system allows imaging even with smaller irregular pupils, however because the depth of field increases under these conditions, sectioning performance decreases. A retinal conjugate micromirror array selectively directs mid-range scatter to additional detectors. This improves detection of retinal capillaries even when the confocal image has poorer image quality that includes both photoreceptors and blood vessels.
We imaged the retina using the Indiana Adaptive Optics Scanning Laser Ophthalmoscope (AOSLO). Our system uses two deformable mirrors to provide en face, high-resolution images of retinal structures at a 28 Hz frame rate. The wavelength of the sensor light was 850 nm and the imaging wavelength was 820 nm at 50 and 120 W respectively. The confocal pinhole was located in a position conjugate with the retina allowed us to segment one retina plane. Two different confocal apertures of 75 m and 100 m (1.5 and 2 times the Airy disk size) were used to provide different amounts of confocal or scattered light. The imaging area was 1.4 x 1.2 deg which corresponds roughly to 400 x 350 m.
Using the large stroke deformable mirror, which provides the focusing capability of the confocal system, we imaged the same location at different planes. We moved from superficial layers to the retinal pigment epithelium in 0.3 D increments. The range of adjustments included the subjectively best overall image, and focal planes anterior and posterior to this.
We imaged 10 subjects at approximately 7.5 deg temporal from the fovea. A video of individual frames was taken, and the individual frames were dewarped, aligned, and averaged. We measured 10 bright and 10 dim cones for each subject at the 10 depths, with brightness groupings based subjectively on the most superficial location. The function for amount of light reflected differed for the two groups of cones. Reflectivity varied as a function of depth.
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