ORCID Profile
0000-0003-4171-8927
Current Organisations
Canadian Forest Service
,
University of Houston
,
University of Rochester
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Publisher: Association for Research in Vision and Ophthalmology (ARVO)
Date: 05-2010
DOI: 10.1167/IOVS.09-4604
Publisher: Association for Research in Vision and Ophthalmology (ARVO)
Date: 28-03-2010
DOI: 10.1167/3.12.36
Publisher: Ovid Technologies (Wolters Kluwer Health)
Date: 10-2014
Publisher: Ovid Technologies (Wolters Kluwer Health)
Date: 11-2005
DOI: 10.1016/J.JCRS.2005.08.024
Abstract: To determine the amount of static and dynamic pupil decentrations that occur during laser refractive surgery. The Center of Visual Science and the Department of Ophthalmology, University of Rochester, Rochester, New York, USA. The surgeon's accuracy in aligning the pupil center with the laser center axis was measured when engaging the eye-tracker in 17 eyes receiving conventional laser in situ keratomileusis (LASIK) procedures (Technolas 217z Bausch & Lomb). Eye movements were measured subsequently during the treatment in 10 eyes using a pupil camera operating at 50 Hz. Temporal power spectra were calculated from the eye movement measurements. The mean pupil misalignment by the surgeon at the beginning of the procedure was 206.1 microm +/- 80.99 (SD) (with respect to the laser center). The laser center was typically misaligned below (inferiorly) and to the left (nasally and temporally in left and right eyes, respectively) of the pupil [corrected] center. Small amounts of cyclotorsion were observed during the ablation (<2 degrees). The mean magnitude of dynamic pupil decentration from the laser center during treatment was 227.0 +/- 44.07 microm. The mean standard deviation of eye movements was 65.7 +/- 25.64 microm. Temporal power spectra calculated from the horizontal and vertical changes in eye position during the ablation were similar. Ninety-five percent of the total power of the eye movements was contained in temporal frequencies up to 1 Hz, on average, in both directions. Most eye movements during LASIK are slow drifts in fixation. An eye-tracker with a 1.4 Hz closed-loop bandwidth could compensate for most eye movements in conventional or customized ablations.
Publisher: Elsevier BV
Date: 03-2017
Publisher: Optica Publishing Group
Date: 17-11-2022
DOI: 10.1364/BOE.473458
Abstract: In their pioneering work demonstrating measurement and full correction of the eye’s optical aberrations, Liang, Williams and Miller, [ JOSA A 14 , 2884 ( 1997 ) 10.1364/JOSAA.14.002884 ] showed improvement in visual performance using adaptive optics (AO). Since then, AO visual simulators have been developed to explore the spatial limits to human vision and as platforms to test non-invasively optical corrections for presbyopia, myopia, or corneal irregularities. These applications have allowed new psychophysics bypassing the optics of the eye, ranging from studying the impact of the interactions of monochromatic and chromatic aberrations on vision to neural adaptation. Other applications address new paradigms of lens designs and corrections of ocular errors. The current paper describes a series of AO visual simulators developed in laboratories around the world, key applications, and current trends and challenges. As the field moves into its second quarter century, new available technologies and a solid reception by the clinical community promise a vigorous and expanding use of AO simulation in years to come.
Publisher: Association for Research in Vision and Ophthalmology (ARVO)
Date: 03-2016
DOI: 10.1167/16.5.1
Publisher: CRC Press
Date: 02-10-2015
DOI: 10.1201/B19322
Publisher: Association for Research in Vision and Ophthalmology (ARVO)
Date: 12-2007
DOI: 10.1167/IOVS.07-0661
Publisher: Elsevier BV
Date: 08-2003
DOI: 10.1016/S0002-9394(03)00222-8
Abstract: To study the optical changes induced by the microkeratome cut, the subsequent laser ablation, and the biomechanical healing response of the cornea in normal laser in situ keratomileusis (LASIK) eyes. Prospective randomized clinical trial. A Hansatome microkeratome was used to cut a corneal flap in one eye (study eye) of 17 normal myopic patients and a subsequent laser ablation was performed 2 months after this initial microkeratome incision. Control eyes received conventional LASIK treatments at the latter time point. The wave aberration of both the study and contralateral control eyes were measured over a 6-mm pupil with a Shack-Hartmann wavefront sensor for all preoperative, postflap cut, and postablation visits. The eye's higher order aberrations had a small, but significant increase (P =.03) of approximately 30% 2 months after cutting a flap. No systematic changes were observed in nearly all Zernike coefficients from their preoperative levels at 2 months postflap cut. A significant difference between the study and control eyes was observed for one trefoil mode, Z(3)(3) (P =.04). There was a wide variation in the response of in idual Zernike modes across patients after cutting a flap. The majority of spherical aberration induced by the LASIK procedure seems to be due to the laser ablation and not the microkeratome cut. In addition, the total and higher order root mean square of wavefront errors were nearly identical for both the study and control eyes 3-months after the laser ablation, indicating that a procedure in which the incision and the ablation are separated in time to better control aberrations does not compromise the outcome of a conventional LASIK treatment.
Publisher: eLife Sciences Publications, Ltd
Date: 03-02-2021
Publisher: Cold Spring Harbor Laboratory
Date: 20-02-2020
DOI: 10.1101/2020.02.19.956219
Abstract: How we see is fundamentally limited by the eye’s optics, which determine retinal image quality and constrain neural processing. Elucidating how long-term exposure to optical defects alters visual processing is vital for understanding the human brain’s capacity for and limits of sensory plasticity. Using adaptive optics to bypass the eye’s optical aberrations, we assessed changes in visual processing in neurotypically-developed adults with keratoconus (KC)—a corneal disease causing severe optical aberrations during adulthood that cannot be fully corrected using conventional methods. As a result, KC patients are chronically exposed to degraded retinal images in their everyday life, making them an ideal model to understand how prolonged exposure to poor optical quality alters visual processing. Here, we show that when tested under similar fully-corrected optical conditions as neurotypical observers, KC patients exhibited altered contrast sensitivity, with impaired sensitivity for fine spatial details and better sensitivity for coarse spatial details. Both gains and losses in contrast sensitivity were more pronounced in patients with poorer habitual optical quality. Moreover, using an equivalent noise paradigm and a computational model of visual processing, we show that these alterations in visual processing are mediated by changes in signal enhancement of spatial frequency selective mechanisms. The present findings uncover fundamental properties of neural compensation mechanisms in response to long-term exposure to optical defects, which alter sensory processing and limit the benefits of improved optics. The outcome is a large-scale functional reorganization favoring the processing of sensory information less affected by the eye’s optics. The eye’s optics represent an intrinsic limit to human visual perception, determining the quality of retinal images. Neural adaptation optimizes the brain’s limited sensory processing capacity to the structure of the degraded retinal inputs, providing an exceptional quality of vision given these optical limitations. Here, we show that prolonged exposure to poor optical quality results in a functional reorganization of visual processing that favors sensory information less affected by the eye’s optics. The present study helps elucidate how optical factors shape the way the brain processes visual information. Notably, the resulting adaptive neural plasticity limits the immediate perceptual benefits of optical interventions, a factor that must be taken into consideration when treating the increasing human population affected by optical defects.
Publisher: Elsevier BV
Date: 08-2004
Publisher: Ovid Technologies (Wolters Kluwer Health)
Date: 12-2013
Publisher: Ovid Technologies (Wolters Kluwer Health)
Date: 06-2007
Publisher: Ovid Technologies (Wolters Kluwer Health)
Date: 05-2009
DOI: 10.1016/J.JCRS.2008.12.039
Abstract: To compare wavefront-derived metrics to predict subjective quality of vision after laser in situ keratomileusis (LASIK) for myopia. Department of Ophthalmology, Goethe University, Frankfurt am Main, Germany. One month postoperatively, wavefront sensing was performed and overall subjective quality of vision assessed under 3 lighting conditions (photopic, high mesopic, low mesopic) with a questionnaire. Four wavefront-error representations were computed for a pupil diameter of 6.0 mm and in idual physiological pupil diameters at 0.4 lux: (1) the visual Strehl ratio based on optical transfer function (VSOTF), (2) the root-mean-square (RMS) value of Zernike orders 2 to 5 (total RMS), (3) higher-order aberration (HOA) RMS, and (4) a wavefront-error breakdown into the RMS of lower-order aberrations, coma, spherical aberration, and remaining HOA. The impact of the postoperative wavefront error on subjective quality of vision was calculated using linear regression analysis. Fifty-six eyes (29 patients) were included. The ability of wavefront error-derived metrics to predict subjective quality of vision was limited. The VSOTF, calculated for the best-corrected eye, showed the highest predictability. Calculation of wavefront error for in idual physiological pupil diameters did not improve predictive ability of the metrics. Eyes with a high theoretical retinal-image quality had a high subjective quality of vision, and eyes with a low subjective quality of vision had a low theoretical image quality. Postoperative wavefront error had limited influence on the subjective quality of vision. Postoperative retinal image quality should be kept as high as possible to provide good subjective quality of vision.
Publisher: Elsevier BV
Date: 03-2017
Publisher: Elsevier BV
Date: 03-2022
Publisher: eLife Sciences Publications, Ltd
Date: 22-02-2021
DOI: 10.7554/ELIFE.58734
Abstract: The eye’s optics are a major determinant of visual perception. Elucidating how long-term exposure to optical defects affects visual processing is key to understanding the capacity for, and limits of, sensory plasticity. Here, we show evidence of functional reallocation of sensory processing resources following long-term exposure to poor optical quality. Using adaptive optics to bypass all optical defects, we assessed visual processing in neurotypically-developed adults with healthy eyes and with keratoconus – a corneal disease causing severe optical aberrations. Under fully-corrected optical conditions, keratoconus patients showed altered contrast sensitivity, with impaired sensitivity for fine spatial details and better-than-typical sensitivity for coarse spatial details. Both gains and losses in sensitivity were more pronounced in patients experiencing poorer optical quality in their daily life and mediated by changes in signal enhancement mechanisms. These findings show that adult neural processing adapts to better match the changes in sensory inputs caused by long-term exposure to altered optics.
Publisher: SLACK, Inc.
Date: 03-09-2004
DOI: 10.3928/1081-597X-20040901-22
Abstract: ABSTRACT PURPOSE: To psychophysical^ demonstrate vision improvement when correcting higher-order aberrations with phase plates in normal eyes. METHODS: The wavefront aberrations of three nonsurgical normal eyes were measured with a Shack-Hartmann wavefront sensor. With these measured aberrations, phase plates were fabricated using a lathing technique. Theoretical improvement in retinal image quality was estimated by calculating the optical modulation transfer functions under the white light condition. Visual acuity measurements were also conducted to demonstrate improvement in visual performance after correcting higher-order aberrations with the phase plate. In this visual acuity measurement, a tumbling "E" with high (100%) and low (10%) contrast was used. RESULTS: The phase plate reduced the higherorder root mean square (RMS) wavefront error from 0.39 ? 0.09 to 0.15 ? 0.02 µm (mean ? standard deviation from three eyes) for a 6 -mm pupil. With the phase plate, retinal image quality based on the volume of modulation transfer function under 60 cycles per degree (c/deg) was improved by a factor of 1.8 ? 0.4 over that of the eyes with spherocylindrical correction only. Average improvement in visual acuity achieved by correcting the higherorder aberration was 0.23 lines with high-contrast letters and 1.12 lines with low-contrast letters. All subjects reported subjective improvement in image quality of the letter with the phase plate. CONCLUSION: The phase plate effectively corrected the higher-order aberrations in normal eyes. As a result, both retinal image quality and visual acuity especially with the low -contrast letters were improved. This study demonstrated the feasibility of correcting higher-order aberrations and improving vision with customized optics. [J Refract Surg 2004 :S523-S527]
Publisher: SLACK, Inc.
Date: 03-2010
DOI: 10.3928/1081597X-20100224-04
Abstract: To simulate the simultaneous contribution of optical zone decentration and pupil dilation on retinal image quality using wavefront error data from a myopic photorefractive keratectomy (PRK) cat model. Wavefront error differences were obtained from five cat eyes 19±7 weeks (range: 12 to 24 weeks) after spherical myopic PRK for −6.00 diopters (D) (three eyes) and −10.00 D (two eyes). A computer model was used to simulate decentration of a 6-mm sub-aperture relative to the measured wavefront error difference. Changes in image quality (visual Strehl ratio based on the optical transfer function [VSOTF]) were computed for simulated decentrations from 0 to 1500 µ m over pupil diameters of 3.5 to 6.0 mm in 0.5-mm steps. For each eye, a bivariate regression model was applied to calculate the simultaneous contribution of pupil dilation and decentration on the pre- to postoperative change of the log VSOTF. Pupil diameter and decentration explained up to 95% of the variance of VSOTF change (adjusted R 2 =0.95). Pupil diameter had a higher impact on VSOTF (median β= −0.88, P .001) than decentration (median β=−0.45, P .001). If decentration-induced lower order aberrations were corrected, the impact of decentration further decreased (β= −0.26) compared to the influence of pupil dilation (β= −0.95). Both pupil dilation and decentration of the optical zone affected the change of retinal image quality (VSOTF) after myopic PRK with decentration exerting a lower impact on VSOTF change. Thus, under physiological conditions pupil dilation is likely to have more effect on VSOTF change after PRK than optical zone decentration. [ J Refract Surg. 2010 :183–190.]
Publisher: Optica Publishing Group
Date: 19-03-2007
DOI: 10.1364/OL.32.001000
Abstract: Higher-order aberration correction in abnormal eyes can result in significant vision improvement, especially in eyes with abnormal corneas. Customized optics such as phase plates and customized contact lenses are one of the most practical, nonsurgical ways to correct these ocular higher-order aberrations. We demonstrate the feasibility of correcting higher-order aberrations and improving visual performance with customized soft contact lenses in keratoconic eyes while compensating for the static decentration and rotation of the lens. A reduction of higher-order aberrations by a factor of 3 on average was obtained in these eyes. The higher-order aberration correction resulted in an average improvement of 2.1 lines in visual acuity over the conventional correction of defocus and astigmatism alone.
Publisher: Ovid Technologies (Wolters Kluwer Health)
Date: 2005
DOI: 10.1016/J.JCRS.2004.10.046
Abstract: To develop a corneal model to better explain how refractive surgery procedures induce spherical aberration. Department of Ophthalmology and Center for Visual Science, University of Rochester, Rochester, New York, USA. The preoperative cornea was modeled as a rotationally symmetric surface with various radii of curvature and asphericities. The postoperative cornea was defined as the difference between the preoperative cornea and an ablation thickness profile computed based on the Munnerlyn equation. A ray-tracing program and Zernike polynomial fitting were used to calculate the induced amount of spherical aberration assuming a fixed ablation depth per pulse or a variable ablation depth depending on the incidence angle of each pulse on the cornea. A biological eye model of the corneal surface change after laser refractive surgery was also developed to explain the induced spherical aberrations after myopic and hyperopic treatments. The clinical data showed that positive spherical aberration was induced after myopic correction and negative spherical aberration increased after hyperopic correction. In contrast, assuming a fixed ablation depth per pulse, the theoretical prediction was that negative spherical aberration with myopic treatment and positive spherical aberration with hyperopic treatment would increase. However, when assuming a variable ablation depth per pulse caused by non-normal incidence of laser spot on the cornea, the theoretically predicted induction of spherical aberration tends to fit better with the myopic and hyperopic clinical data. The effect of a variable ablation depth accounted for approximately half the clinically observed amount of spherical aberration. The biological model of the corneal surface change used to explain this remaining discrepancy showed the magnitude of the biological response in myopic correction is 3 times smaller than in hyperopic correction and that the direction of the biological response in hyperopic treatment is opposite that in myopic treatment. This nontoric eye model, which separates the effects of differences in ablation efficiency and biological corneal surface change quantitatively, explains how spherical aberration is induced after myopic and hyperopic laser refractive surgery. With the corneal topographic data, this model can be incorporated into the ablation algorithm to decrease induced spherical aberrations, improving the outcomes of conventional and customized treatments.
Location: Korea, Republic of
No related grants have been discovered for Geunyoung Yoon.