Stephen A. Burns

Indiana University Bloomington, Bloomington, Indiana, United States

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Publications (132)261.64 Total impact

  • [Show abstract] [Hide abstract]
    ABSTRACT: To image and analyze anatomical differences at the temporal raphe between normal and glaucomatous eyes using adaptive optics scanning laser ophthalmoscopy (AOSLO) and optical coherence tomography (OCT), and to relate these differences to visual field measurements. Nine glaucomatous eyes of 9 patients (age 54-78 years, mean deviation of visual field [MD] -5.03 to -0.20 dB) and 10 normal eyes of 10 controls (age 54-81, MD -1.13 to +1.39 dB) were enrolled. All the participants were imaged in a region that was centered approximately 9° temporal to the fovea. The size of imaging region was at least 10° vertically by 4° horizontally. The raphe gap, defined as the distance between the superior and inferior retinal nerve fiber layer (RNFL) bundles, was measured. A bundle index was computed to quantify the relative reflectivity and density of the nerve fiber bundles. We also measured thickness of the ganglion cell complex (GCC) and RNFL. The raphe gap was larger in glaucomatous eyes than control eyes. Specifically, eight glaucomatous eyes with local averaged field loss no worse than -3.5 dB had larger raphe gaps than all control eyes. The bundle index, GCC thickness, and RNFL thickness were on average reduced in glaucomatous eyes, with the first two showing statistically significant differences between the two groups. Structural changes in the temporal raphe were observed and quantified even when local functional loss was mild. These techniques open the possibility of using the raphe as a site for glaucoma research and clinical assessment.
    Investigative ophthalmology & visual science 06/2015; 56(6):3496-3504. DOI:10.1167/iovs.15-16730 · 3.66 Impact Factor
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    ABSTRACT: Purpose:To quantify and compare phase retardation amplitude and regularity associated with the Henle fiber layer between non-exudative age-related macular degeneration (AMD) patients and age-matched controls using scanning laser polarimetry (SLP) imaging. Methods:A scanning laser polarimeter was used to collect 15 x 15 deg macular centered images in 25 patients with non-exudative AMD and 25 age-matched controls. Raw image data were used to compute macular phase retardation maps associated with the Henle fiber layer. Consecutive, annular regions of interest from 0.5 to 3.0 deg eccentricity, centered on the fovea, were used to generate intensity profiles from phase retardation data and analyzed with two complementary techniques: a normalized 2f FFT component analysis and a curve fitting analysis using a 2f sine function. Paired t-tests were used to compare the normalized 2f FFT magnitude at each eccentricity between the two groups, the eccentricity that yielded the maximum normalized 2f FFT between paired individuals across the two groups, and curve fitting RMS error at each eccentricity between the two groups. Results:Normalized 2f FFT components were lower in the AMD group at each eccentricity, with no difference between the two groups in the maximum normalized 2f FFT component eccentricity. The RMS error from curve fitting was significantly higher in the AMD group. Conclusions:Phase retardation changes in the central macula indicate loss and/or structural alterations to central cone photoreceptors in non-exudative AMD patients. SLP imaging is a non-invasive method for quantifying cone photoreceptor changes associated with central macular disease. Copyright © 2014 by Association for Research in Vision and Ophthalmology.
    Investigative Ophthalmology &amp Visual Science 12/2014; 56(1). DOI:10.1167/iovs.14-14459 · 3.66 Impact Factor
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    ABSTRACT: Purpose:To investigate the association between the size and shape of the foveal avascular zone and retinal thickness in healthy subjects. Methods:In vivo imaging of the foveal microvasculature was performed on 32 subjects using an adaptive optics scanning laser ophthalmoscope (AOSLO). Foveal avascular zone (FAZ) diameters along the horizontal (FAZH) and vertical (FAZV) meridians were measured. An asymmetry index (AI) of the FAZ was then computed as the ratio of the FAZH to FAZV. Retinal thickness was investigated using spectral domain optical coherence tomography (SDOCT). Inner retinal layer (INLFAZ) thickness and outer nuclear layer (ONLFAZ) thickness were measured at the edges of the FAZ on the horizontal and vertical SDOCT scans on the same eye. Results:There was individual variation in the size and shape of the FAZ. Along the horizontal and vertical meridians, the mean±SD (µm) of the FAZ diameter was 607±217 and 574±155, respectively. The INLFAZ thickness was 68±9 and 66±9, and the ONLFAZ thickness was 103±13 and 105±11, respectively. The mean±SD of the AI was 1.03±0.27. The difference between FAZH and FAZV decreases with increasing FAZ area (p=0.004). Mean ONLFAZ was negatively correlated with FAZ effective diameter (p<0.0001). No significant correlation was found between mean INLFAZ and FAZ effective diameter (p=0.16). Conclusions:The INLFAZ has a relatively constant thickness at the margins of the FAZ, suggesting the presence of retinal capillaries is needed to sustain an INLFAZ thickness greater than 60 µm. A smaller FAZ area is associated with a vertically elongated FAZ.
    Investigative Ophthalmology &amp Visual Science 09/2014; 55(10). DOI:10.1167/iovs.14-15446 · 3.66 Impact Factor
  • Gang Huang, Thomas J Gast, Stephen A Burns
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    ABSTRACT: Purpose:To investigate the anatomy of the temporal raphe and its angular relation to the optic disc in the human retina in-vivo. Methods:Adaptive optics scanning laser ophthalmoscope (AOSLO) was used to image the temporal raphe in 11 young subjects. The raphe's angle relative to a horizontal line and the raphe-fovea-disc angle (angle between the raphe and the line connecting the disc and fovea center) were determined. In addition, to investigate the impact of aging on the raphe, we imaged the raphe at 9-degree eccentricity in 10 additional older healthy subjects, and compared between the two age groups the raphe's anatomy. Results:The raphe's in-vivo appearance were generally in agreement with major findings of ex-vivo studies. The raphe angle was -1.67 ± 4.8 degrees. The raphe-fovea-disc angle was 170.3 ± 3.6 degrees. The averaged distance between superior and inferior bundles is significantly different between the two age group with a larger gap measured in the older subjects (1.93 ± 68.73 µm versus 230.83 ± 113.22 µm, p<0.0001). Conclusions:While raphe angles measured across subjects ranges from -9 degrees to 6 degrees, the raphe angle is related to the angle of the foveal depression relative to the disc. The results are not consistent with classic raphe models; Rather there seems to be a systematic relation between the disc, the fovea and the raphe, and this may be useful for individualizing retinal measurement strategies.
    Investigative Ophthalmology &amp Visual Science 08/2014; 55(9). DOI:10.1167/iovs.14-14893 · 3.66 Impact Factor
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    ABSTRACT: We used a confocal adaptive optics scanning laser ophthalmoscope (AOSLO) to image the retina of subjects with non-proliferative diabetic retinopathy (NPDR). To improve visualization of different retinal features, the size and alignment of the confocal aperture were varied. The inner retinal layers contained clearly visualized retinal vessels. In diabetic subjects there was extensive capillary remodeling despite the subjects having only mild or moderate NPDR. Details of the retinal microvasculature were readily imaged with a larger confocal aperture. Hard exudates were observed with the AOSLO in all imaging modes. Photoreceptor layer images showed regions of bright cones and dark areas, corresponding in location to overlying vascular abnormalities and retinal edema. Clinically undetected intraretinal vessel remodeling and varying blood flow patterns were found. Perifoveal capillary diameters were larger in the diabetic subjects (p<0.01), and small arteriolar walls were thickened, based on wall to lumen measurements (p<.05). The results suggest that existing clinical classifications based on lower magnification clinical assessment may not adequately measure key vascular differences among individuals with NPDR.
    Biomedical Optics Express 03/2014; 5(3):961-74. DOI:10.1364/BOE.5.000961 · 3.50 Impact Factor
  • Toco Y P Chui, Thomas J Gast, Stephen A Burns
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    ABSTRACT: Purpose: To improve the ability to image the vascular walls in the living human retina using multiply-scattered light imaging with an adaptive optics scanning laser ophthalmoscope (AOSLO). Methods: In vivo arteriolar wall imaging was performed on 8 healthy subjects using the Indiana AOSLO. Noninvasive imaging of vascular mural cells and wall structure were performed using systematic control of the position of a 10x Airy disk confocal aperture. Retinal arteries and arterioles were divided into 4 groups based on their lumen diameters (Group 1: ≥100 µm; Group 2: 50-99 µm; Group 3: 10-49 µm; Group 4: <10 µm). Results:Fine structure of retinal vasculature and scattering behavior of erythrocytes were clearly visualized in all 8 subjects. In Group 1 vessels the mural cells were flatter and formed the outer layer of regularly spaced cells of a two (or more) layered vascular wall. In Group 2 and 3 vessels, mural cells were visualized as distinct cells lying along the lumen of the blood vessel, resulting in a wall of irregular thickness. Vascular wall components were not readily identified in Group 4 vessels. Conclusions: Our results show that retinal vascular mural cells and wall structure can be readily resolved in normal subjects using AOSLO with multiply scattered light imaging for retinal vessels with a lumen diameter ≥10 µm. Our noninvasive imaging approach allows direct assessment of the cellular structure of the vascular wall in vivo with potential applications in retinal vascular diseases such as diabetes and hypertension.
    Investigative ophthalmology & visual science 09/2013; 54(10). DOI:10.1167/iovs.13-13027 · 3.66 Impact Factor
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    ABSTRACT: Changes with age in the distribution of cone photoreceptors were measured with Adaptive Optics Scanning Laser Ophthalmoscopy. Cones densities for younger subjects were uncorrelated at central vs. more peripheral locations, but correlated for older subjects.
    Frontiers in Optics; 10/2012
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    ABSTRACT: To demonstrate the use of different aperture sizes and degree of confocality of the AOSLO system on papillary and peripapillary capillary imaging in human subjects. Microvasculature was clearly visualized inside and outside the optic disc.
    Frontiers in Optics; 10/2012
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    Toco Y P Chui, Dean A Vannasdale, Stephen A Burns
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    ABSTRACT: Retinal vascular diseases are a leading cause of blindness and visual disability. The advent of adaptive optics retinal imaging has enabled us to image the retinal vascular at cellular resolutions, but imaging of the vasculature can be difficult due to the complex nature of the images, including features of many other retinal structures, such as the nerve fiber layer, glial and other cells. In this paper we show that varying the size and centration of the confocal aperture of an adaptive optics scanning laser ophthalmoscope (AOSLO) can increase sensitivity to multiply scattered light, especially light forward scattered from the vasculature and erythrocytes. The resulting technique was tested by imaging regions with different retinal tissue reflectivities as well as within the optic nerve head.
    Biomedical Optics Express 10/2012; 3(10):2537-49. DOI:10.1364/BOE.3.002537 · 3.50 Impact Factor
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    ABSTRACT: We investigated the effect of localized visual stimulation on human retinal blood velocity using an adaptive optics scanning laser ophthalmoscope (AOSLO). To measure the blood velocity response, the AOSLO scanning raster was moved over the target arteries and red blood cell velocity was measured. Localized visual stimuli were delivered by projecting flicker patterns inside or outside the target artery's downstream region. The blood velocity increased in the presence of a flicker stimulus in the downstream region but not when outside the downstream region. The blood velocity increased more with larger area of stimulation. This increase was significant even when the stimulus was smaller than 600 μm × 600 μm. These findings suggest that when the retina regulates its blood flow to metabolic demands, it regulates blood velocity in the vascular system selectively, according to activity of neurons within its field of influence.
    Journal of Vision 06/2012; 12(6):3. DOI:10.1167/12.6.3 · 2.73 Impact Factor
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    ABSTRACT: We evaluated the relationship between cone photoreceptor packing density and outer nuclear layer (ONL) thickness within the central 15 degrees. Individual differences for healthy subjects in cone packing density and ONL thickness were examined in 8 younger and 8 older subjects, mean age 27.2 versus 56.2 years. Cone packing density was obtained using an adaptive optics scanning laser ophthalmoscope (AOSLO). The ONL thickness measurements included the ONL and the Henle fiber layer (ONL + HFL), and were obtained using spectral domain optical coherence tomography (SDOCT) and custom segmentation software. There were sizeable individual differences in cone packing density and ONL + HFL thickness. Older subjects had on average lower cone packing densities, but thicker ONL + HFL measurements. Cone packing density and ONL + HFL thickness decreased with increasing retinal eccentricity. The ratio of the cone packing density-to-ONL2 was larger for the younger subjects group, and decreased with retinal eccentricity. The individual differences in cone packing density and ONL + HFL thickness are consistent with aging changes, indicating that normative aging data are necessary for fine comparisons in the early stages of disease or response to treatment. Our finding of ONL + HFL thickness increasing with aging is inconsistent with the hypothesis that ONL measurements with SDOCT depend only on the number of functioning cones, since in our older group cones were fewer, but thickness was greater.
    Investigative ophthalmology & visual science 05/2012; 53(7):3545-53. DOI:10.1167/iovs.11-8694 · 3.66 Impact Factor
  • Feng Lei, Stephen A Burns, Liqin Shao, Yabo Yang
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    ABSTRACT: To compare retinal measurements obtained by time domain optical coherence tomography (OCT) devices before and after myopic laser in situ keratomileusis (Lasik) and to assess the interaction of Lasik and retinal structures as measured by time domain OCT. Fifty-three patients randomly selected participated in the study. Only the right eye of each subject was included in the study. Comprehensive ophthalmic examinations including refraction examination, slit lamp examination, dilated fundus examination, corneal topography, corneal thickness, intraocular pressure, and retinal Stratus OCT scans were acquired for each patient before myopic Lasik and 3months after surgery. Total macular volume (TMV) changed significantly between preoperative and postoperative measurements (p=0.003). No statistical differences were found between preoperative and postoperative disc area, rim area, cup/disk vert. ratio, or average foveal thickness (p>0.05). The variation in TMV correlated significantly with the change in spherical refraction equivalent, maximal corneal curvature, minimal corneal curvature, and corneal ablation depth. Most retinal OCT measurements undergo no obvious changes after myopic Lasik. The increased TMV measurements we measured after Lasik seem to be correlated with the alteration in corneal shape. The exact mechanism for this change is not clear, while we examined several possibilities including subclinical macular oedema, magnification changes, errors in OCT analysis and IOP, none of these seem to be a likely cause.
    Ophthalmic and Physiological Optics 05/2012; 32(3):222-7. DOI:10.1111/j.1475-1313.2012.00905.x · 2.66 Impact Factor
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    ABSTRACT: To develop a clinical planning module (CPM) to improve the efficiency of imaging subjects with a steerable wide-field adaptive optics scanning laser ophthalmoscope (AOSLO) and to evaluate the performance of this module by imaging the retina in healthy and diseased eyes. We developed a software-based CPM with two submodules: a navigation module and a montage acquisition module. The navigation module guides the AOSLO to image identified retinal regions from a clinical imaging platform using a matrix-based mapping between the two. The montage acquisition module systematically moves the AOSLO steering mirrors across the retina in predefined patterns. The CPM was calibrated using a model eye and tested on five normal subjects and one patient with a retinal nerve fiber layer defect. Within the central ±7° from the fixation target, the CPM can direct the AOSLO beam to the desired regions with localization errors of <0.3°. The navigation error increases with eccentricity, and larger errors (up to 0.8°) were evident for regions beyond 7°. The repeatability of CPM navigation was tested on the same locations from two subjects. The localization errors between trials on different days did not differ significantly (p > 0.05). The region with a size of approximately 13° × 10° can be imaged in about 30 min. An approximately 12° × 4.5° montage of the diseased region from a patient was imaged in 18 min. We have implemented a clinical planning module to accurately guide the AOSLO imaging beam to desired locations and to quickly acquire high-resolution AOSLO montages. The approach is not only friendly for patients and clinicians but also convenient to relate the imaging data between different imaging platforms.
    Optometry and vision science: official publication of the American Academy of Optometry 04/2012; 89(5):593-601. DOI:10.1097/OPX.0b013e318253e081 · 2.04 Impact Factor
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    Weiyao Zou, Stephen A Burns
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    ABSTRACT: A Lagrange multiplier-based damped least-squares control algorithm for woofer-tweeter (W-T) dual deformable-mirror (DM) adaptive optics (AO) is tested with a breadboard system. We show that the algorithm can complementarily command the two DMs to correct wavefront aberrations within a single optimization process: the woofer DM correcting the high-stroke, low-order aberrations, and the tweeter DM correcting the low-stroke, high-order aberrations. The optimal damping factor for a DM is found to be the median of the eigenvalue spectrum of the influence matrix of that DM. Wavefront control accuracy is maximized with the optimized control parameters. For the breadboard system, the residual wavefront error can be controlled to the precision of 0.03 μm in root mean square. The W-T dual-DM AO has applications in both ophthalmology and astronomy.
    Applied Optics 03/2012; 51(9):1198-208. DOI:10.1364/AO.51.001198 · 1.78 Impact Factor
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    ABSTRACT: To investigate the retinal microvasculature at the fovea and peripheral retina in humans using an adaptive optics scanning laser ophthalmoscope (AOSLO) and to examine the association of foveal avascular zone (FAZ) and foveal pit morphology. Retinal imaging of the foveal capillary network was performed on 11 subjects (15 eyes; age range 20 to 54 years) with an AOSLO. Standard deviation maps of the AOSLO images were generated from ∼10 to 30 frames, producing high-resolution maps delineating the complete capillary distribution of the retina. Foveal pit morphology was investigated in the same subjects by using a spectral domain optical coherence tomography. In an additional subject, only a relatively large retinal vasculature map was obtained using AOSLO. A well-demarcated FAZ was seen in 11 subjects tested with foveal capillary imaging. There was considerable individual variation in the size and shape of the FAZ. The mean FAZ area and mean FAZ effective diameter were 0.33 mm(2) and 622 μm, respectively. Foveal thickness was found to be negatively correlated with the FAZ effective diameter. The structure of the capillary network could be evaluated in the fovea and parafovea using our approach. We find that a smaller FAZ is associated with a narrower foveal pit opening and a thicker fovea.
    Optometry and vision science: official publication of the American Academy of Optometry 03/2012; 89(5):602-10. DOI:10.1097/OPX.0b013e3182504227 · 2.04 Impact Factor
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    Weiyao Zou, Xiaofeng Qi, Gang Huang, Stephen A Burns
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    ABSTRACT: An ophthalmic adaptive optics (AO) imaging system is especially affected by pupil edge effects due to the higher noise and aberration level at the edge of the human pupil as well as the impact of head and eye motions on the pupil. In this paper, a two-step approach was proposed and implemented for reducing the edge effects and improving wavefront slope boundary condition. First, given an imaging pupil, a smaller size of sampling aperture can be adopted to avoid the noisy boundary slope data. To do this, we calibrated a set of influence matrices for different aperture sizes to accommodate pupil variations within the population. In step two, the slope data was extrapolated from the less noisy slope data inside the pupil towards the outside such that we had reasonable slope data over a larger aperture to stabilize the impact of eye pupil dynamics. This technique is applicable to any Neumann boundary-based active /adaptive modality but it is especially useful in the eye for improving AO retinal image quality where the boundary positions fluctuate.
    Biomedical Optics Express 12/2011; 2(12):3309-20. DOI:10.1364/BOE.2.003309 · 3.50 Impact Factor
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    ABSTRACT: Global changes with age in the density of photoreceptors were investigated by using novel software to compute the thickness of the outer nuclear layer seen with Optical Coherence Tomography.
    Frontiers in Optics; 10/2011
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    Gang Huang, Zhangyi Zhong, Weiyao Zou, Stephen A Burns
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    ABSTRACT: Adaptive optics (AO) has greatly improved retinal image resolution. However, even with AO, temporal and spatial variations in image quality still occur due to wavefront fluctuations, intraframe focus shifts, and other factors. As a result, aligning and averaging images can produce a mean image that has lower resolution or contrast than the best images within a sequence. To address this, we propose an image postprocessing scheme called "lucky averaging," analogous to lucky imaging [J. Opt. Soc. Am. 68, 1651 (1978)] based on computing the best local contrast over time. Results from eye data demonstrate improvements in image quality.
    Optics Letters 10/2011; 36(19):3786-8. DOI:10.1364/OL.36.003786 · 3.18 Impact Factor
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    ABSTRACT: This study quantified normal age-related changes to the photoreceptor axons in the central macula using the birefringent properties of the Henle fiber layer. A scanning laser polarimeter was used to acquire 15° × 15° macular images in 120 clinically normal subjects, ranging in age from the third decade to the eighth. Raw image data of the macular cross were used to compute phase retardation maps associated with Henle fiber layer. Annular regions of interest ranging from 0.25° to 3° eccentricity and centered on the fovea were used to generate intensity profiles from the phase retardation data, which were then analyzed using sine curve fitting and Fast Fourier Transform (FFT). The amplitude of a 2f sine curve was used as a measure of macular phase retardation magnitude. For FFT analysis, the 2f amplitude, as well as the 4f, were normalized by the remaining FFT components. The amplitude component of the 2f curve fit and the normalized 2f FFT component decreased as a function of age, while the eccentricity of the maximum value for the normalized 2f FFT component increased. The phase retardation changes in the central macula indicate structural alterations in the cone photoreceptor axons near the fovea as a function of age. These changes result in either fewer cone photoreceptors in the central macula, or a change in the orientation of their axons. This large sample size demonstrates systematic changes to the central cone photoreceptor morphology using scanning laser polarimetry.
    Vision research 08/2011; 51(21-22):2263-72. DOI:10.1016/j.visres.2011.08.017 · 2.38 Impact Factor
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    Toco Y.P. Chui, Zhangyi Zhong, Stephen A Burns
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    ABSTRACT: We evaluated the relationship between the size of the peripapillary crescent and the axial length (AL) of the eye as well as the fine structure of the peripapillary crescent in selected eyes. Infrared fundus imaging and spectral domain optical coherence tomography (SDOCT) (Spectralis HRA+OCT, Heidelberg Engineering, Germany) centered at the fovea were performed on 72 healthy adults. On the infrared fundus images, we measured (a) the distance between the foveola and the temporal edge of the optic disc (FOD) and (b) the distance between the foveola and the temporal edge of the peripapillary crescent (FOC) (if present). A peripapillary crescent presented at the nasal margin of the disc in 64% of the subjects. The FOD and FOC were 4.22mm±0.46 and 3.97mm±0.25, respectively. Only the FOD was significantly correlated with axial length. As AL increased by 10%, the FOD increased by 13%, the outer neural retina only expanded by 4% (as indicated by the FOC). This result emphasizes that retinal stretching may not mirror scleral growth, and the existence in some eyes of a difference between the photoreceptor margin and retinal pigment epithelium (RPE) margin suggests that within the retina there could be slippage during eye growth.
    Vision research 08/2011; 51(19):2132-8. DOI:10.1016/j.visres.2011.08.008 · 2.38 Impact Factor

Publication Stats

3k Citations
261.64 Total Impact Points

Institutions

  • 2006–2014
    • Indiana University Bloomington
      • School of Optometry
      Bloomington, Indiana, United States
  • 1991–2007
    • Schepens Eye Research Institute
      Boston, Massachusetts, United States
  • 2000–2006
    • Harvard Medical School
      Boston, Massachusetts, United States
  • 2001–2004
    • Harvard University
      Cambridge, Massachusetts, United States
    • Spanish National Research Council
      • Institute of Optics "Daza de Valdés"
      Madrid, Madrid, Spain
  • 1996
    • Northeastern University
      • Department of Psychology
      Boston, Massachusetts, United States
  • 1987
    • University of Illinois at Chicago
      • Survey Research Laboratory
      Chicago, Illinois, United States
  • 1984–1986
    • University of Chicago
      Chicago, Illinois, United States
  • 1985
    • University of Pittsburgh
      • Department of Ophthalmology
      Pittsburgh, Pennsylvania, United States