Fuensanta A. Vera-Diaz
New England College of Optometry
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Featured researches published by Fuensanta A. Vera-Diaz.
Vision Research | 2005
Ji C. He; Jane Gwiazda; Frank Thorn; Richard Held; Fuensanta A. Vera-Diaz
Accommodative lags, induced by a target at 33 cm (distance-induced condition) and by a -3.0 D lens (lens-induced condition), and wavefront aberrations were measured in 27 young myopic eyes. The accommodative lags and Strehl ratios derived from the wavefront aberrations in myopes were compared with those from 57 emmetropes. Accommodation was measured using a Canon R-1 autorefractor, while aberrations were measured using a psychophysical ray-tracing technique. In accord with previous results, larger accommodative lags were found for the myopes than the emmetropes in both the lens-induced and distance-induced conditions. The mean Strehl ratio was smaller in the myopes (0.079) than the emmetropes (0.091); this difference approached significance (p = 0.055). In addition, for myopes the accommodative lag was significantly correlated with the Strehl ratio in the lens-induced condition (r = -0.45, p < 0.02) and approached significance in the distance-induced condition (r = -0.35, p = 0.07). No significant correlations were found for emmetropes. Possible reasons to account for these results are discussed.
Journal of Vision | 2004
Fuensanta A. Vera-Diaz; Jane Gwiazda; Frank Thorn; Richard Held
Prolonged exposure to blurred images produces perceptual adaptation (M. A. Webster, M. A., Georgeson, & S. M. Webster, 2002). The purpose of this study is to test whether in addition to the reported change in perceived blur there is also a change in accommodation. Young adult (aged 18 to 31 years) myopic (n = 23) and emmetropic (n = 17) subjects participated in the study. Myopes were tested with contact lenses and had corrected monocular visual acuity of 20/20 or better. Accommodation was measured binocularly with a PowerRefractor, an eccentric infrared photorefractor. Accommodation for a near target (high-contrast text at 0.33 m) was measured for 2 min before and immediately after 3 min of blur exposure. Blur was induced using 0.2 Bangerter diffusing filters in front of both eyes. In addition, accommodation was measured for a far target (high-contrast letters at 4.0 m) before and after the near measurements, with each subjects initial far readings used as a baseline for calculating the accommodative responses at near. Compared to the pre-adaptation level, myopes showed a significant (p < .01) increase in the near accommodative response after 3 min of blur adaptation, while accommodation to the near target in emmetropes did not change. In a second experiment using monocular viewing, the increase of accommodation found in myopes was shown to occur during the period of blur exposure. The refractive group differences in the accommodative response may be related to differences in the habitual response to image clarity between myopes and emmetropes under normal viewing conditions.
Vision Research | 2010
Fuensanta A. Vera-Diaz; Russell L. Woods; Eli Peli
We are interested in clinical implications of adaptation to blurred and sharpened images. Therefore, we investigated repeatability, individual variability and characteristics of the adaptation curves of 39 normally-sighted individuals. The point of subjective neutrality (PSN - the slope of the spatial spectrum of the image that appears normal) following adaptation was measured for each adaptation level and was used to derive individual adaptation curves for each subject. Adaptation curves were fitted with a modified Tukey biweight function as the curves were found to be tumbled-S shaped and asymmetrical for blur and sharp in some subjects. The adaptation curve was found to be an individual characteristic as inter-subject variability exceeds test/re-test variability. The existence of individual variability may have implications for the prescription and clinical success of optical devices as well as image enhancement rehabilitation options.
Journal of The Optical Society of America A-optics Image Science and Vision | 2007
Matthew Fullerton; Russell L. Woods; Fuensanta A. Vera-Diaz; Eli Peli
We used a new method to measure the perceived quality of contrast-enhanced motion video. Patients with impaired vision (n=24) and normally sighted subjects (n=6) adjusted the level of MPEG-based enhancement of 8 videos (4 min each) drawn from 4 categories. They selected the level of enhancement that provided the preferred view of the videos, using a decreasing-step-size staircase procedure. Most patients made consistent selections of the preferred level of enhancement, indicating an appreciation of and a perceived benefit from the MPEG-based enhancement. The selections varied between patients and were correlated with letter contrast sensitivity, but the selections were not affected by training, experience, or video category. We measured just noticeable differences directly for videos and mapped the image manipulation (enhancement in our case) onto an approximately linear perceptual space. These tools and approaches will be of value in other evaluations of the image quality of motion video manipulations.
Optometry and Vision Science | 2011
Bradley E. Dougherty; K. Bradley Kehler; Richard Jamara; Nicole Patterson; Denise Valenti; Fuensanta A. Vera-Diaz
Purpose. To investigate abandonment rate of prescribed low-vision devices for near tasks and factors associated with abandonment in a U.S. outpatient population. Methods. A telephone survey was administered to 88 patients with low vision from four clinical sites about 1 year after examination and prescription of devices. Patients were surveyed on timing and frequency of use and reasons for abandonment of devices. The main outcome measure (abandonment) was defined as patient report of no use of prescribed device in the previous 3 months. Multivariate logistic regression was used to investigate significant vision and demographic factors related to abandonment. Results. Of 119 prescribed devices, 19% (95% CI, 12 to 26) had not been used within the previous 3 months. Mean (±SD) better eye visual acuity at examination was 0.61 ± 0.29 logMAR, and mean age was 77 ± 17 years. Mean time between device prescription and survey was 11 ± 3 months. Device abandonment was not associated with age (p = 0.863), time since prescription (p = 0.125), visual acuity (p = 0.804), or category of magnification device (spectacle, handheld, stand, or video) (p = 0.412). There was a significant association between documented non-central visual field loss and abandonment of magnification device (p = 0.046). Repeat administration of the survey resulted in the same abandonment classification in 15 of 15 patients (100%). Conclusions. Abandonment rate was similar for this outpatient population to those previously reported in the U.S. veteran inpatient population and in other countries. Patients with visual field loss may be more likely to abandon prescribed devices.
Ophthalmic and Physiological Optics | 2003
Charlotte A. Hazel; Niall C. Strang; Fuensanta A. Vera-Diaz
Post‐near task accommodation regressions have been measured in a number of studies to investigate the association between myopia and nearwork. The slow nature of the regression found when measuring both open‐ and closed‐loop regressions in some subjects has been hypothesised to be associated with myopia development and progression. However, it is not known whether the speed and characteristics of the regression for an individual is the same under open‐ and closed‐loop conditions. In this study we measured post‐near task accommodation regression functions under open‐ and closed‐loop conditions for myopic and emmetropic subjects. We compared the responses of each subject under the two conditions and found that some subjects responded differently depending on the condition (i.e. a fast regression under one condition and a slow regression under the other condition). When compared as a group, the myopic subjects showed significantly more prolonged open‐loop regressions than closed‐loop regressions. In terms of the effect on the post‐task accommodation, the myopes appear to be more affected by the measurement conditions than the emmetropes in this study. The results highlight the importance of the type of accommodation stimulus when investigating the accommodation response.
Journal of Vision | 2017
Guido Maiello; Lenna E. Walker; Peter J. Bex; Fuensanta A. Vera-Diaz
We evaluated the ability of emmetropic and myopic observers to detect and discriminate blur across the retina under monocular or binocular viewing conditions. We recruited 39 young (23–30 years) healthy adults (n = 19 myopes) with best-corrected visual acuity 0.0 LogMAR (20/20) or better in each eye and no binocular or accommodative dysfunction. Monocular and binocular blur discrimination thresholds were measured as a function of pedestal blur using naturalistic stimuli with an adaptive 4AFC procedure. Stimuli were presented in a 46° diameter window at 40 cm. Gaussian blur pedestals were confined to an annulus at either 0°, 4°, 8°, or 12° eccentricity, with a blur increment applied to only one quadrant of the image. The adaptive procedure efficiently estimated a dipper shaped blur discrimination threshold function with two parameters: intrinsic blur and blur sensitivity. The amount of intrinsic blur increased for retinal eccentricities beyond 4° (p < 0.001) and was lower in binocular than monocular conditions (p < 0.001), but was similar across refractive groups (p = 0.47). Blur sensitivity decreased with retinal eccentricity (p < 0.001) and was highest for binocular viewing, but only for central vision (p < 0.05). Myopes showed worse blur sensitivity than emmetropes monocularly (p < 0.05) but not binocularly (p = 0.66). As expected, blur perception worsens in the visual periphery and binocular summation is most evident in central vision. Furthermore, myopes exhibit a monocular impairment in blur sensitivity that improves under binocular conditions. Implications for the development of myopia are discussed.
Vision Research | 2016
Kristen L. Kerber; Frank Thorn; Peter J. Bex; Fuensanta A. Vera-Diaz
Disruption of normal visual experience or changes in the normal interaction between central and peripheral retinal input may lead to the development of myopia. In order to examine the relationship between peripheral contrast sensitivity and myopia, we manipulated attentional load for foveal vision in emmetropes and myopes while observers detected targets with peripheral vision. Peripheral contrast detection thresholds were measured binocularly using vertical Gabor stimuli presented at three eccentricities (±8°, 17°, 30°) in a spatial 2 alternative forced choice task. Contrast thresholds were measured in young adult (mean age 24.5±2.6years) emmetropes (n=17; group SE: +0.19±0.32D) and myopes (n=25; group SE: -3.74±1.99D). Attention at central fixation was manipulated with: (1) a low attention task, requiring simple fixation; or (2) a high attention task, which required subjects to perform a mathematical task. We found that at 30° all subjects exhibited lower contrast sensitivity (higher thresholds). In addition, myopes (Wilcoxon, p<0.01), but not emmetropes (Wilcoxon, p=0.1), had a significant decrease in sensitivity at 30° during the high attention task. However, the attention dependent threshold increase for myopes was not significantly greater than for emmetropes (Wilcoxon, p=0.27). Attentional load did not increase thresholds at 8° or 17° for either refractive group. These data indicate that myopes experience a greater decrease in contrast sensitivity in the far periphery than emmetropes when attention is deployed in central vision.
Journal of Vision | 2015
Guido Maiello; William Harrison; Fuensanta A. Vera-Diaz; Peter J. Bex
Myopic eyes are elongated compared to the eyes of normally-sighted, emmetropic observers. This simple observation gives rise to an empirical question: what are the physiological and perceptual consequences of an elongated retinal surface? To address this question, we developed a geometric model of emmetropic and myopic retinae, based on magnetic resonance imaging (MRI) data [Atchison et al. (2005)], from which we derived psychophysically-testable predictions about visual function. We input range image data of natural scenes [Howe and Purves (2002)] to the geometric model to statistically estimate where in the visual periphery perception may be altered due to the different shapes of myopic and emmetropic eyes. The model predicts that central visual function should be similar for the two eye types, but myopic peripheral vision should differ regardless of optical correction. We tested this hypothesis by measuring the fall-off in contrast sensitivity with retinal eccentricity in emmetropes and best-corrected myopes. The full contrast sensitivity function (CSF) was assessed at 5, 10 and 15 degrees eccentricity using an adaptive testing procedure [Vul et al. (2010)]. Consistent with our model predictions, the area under the log CSF decreases in the periphery at a faster rate in best-corrected myopic observers than in emmetropes. Our modeling also revealed that a target at a given eccentricity projects onto a larger area of peripheral retinal for myopic than emmetropic eyes. This raises the possibility that crowding zones - the area over which features are integrated - may differ between eye types. We measured crowding zones at 5, 10 and 15 degrees of eccentricity using a 26 AFC letter identification task and found no significant differences between myopic and emmetropic observers. This suggests that crowding depends on spatial rather than retinal feature separation, which implies differences in the retino-cortical transformations in myopes and emmetropes. Meeting abstract presented at VSS 2015.
Archive | 2012
Fuensanta A. Vera-Diaz; Nathan Doble
Scientists have rapidly taken advantage of adaptive optics (AO) technology for the study of the human visual system. Vision, the primary human sense, begins with light entering the eye and the formation of an image on the retina (Fig 1), where light is transformed into electro-chemical impulses that travel towards the brain. The eye provides the only direct view of the central nervous system and is, therefore, the subject of intense interest as a means for the early detection of a host of retinal and possibly systemic diseases. However, ocular aberrations limit the optical quality of the human eye, thus reducing image contrast and resolution. With the use of AO it is now routinely possible to compensate for these ocular aberrations and image cellular level structures such as retinal cone and rod photoreceptors (Liang et al, 1997; Doble et al, 2011), the smaller foveal cones (Putnam et al, 2010), retinal pigment epithelium (RPE) cells (Roorda et al, 2007), leukocyte blood cells (Martin & Roorda, 2005) and the smallest retinal blood vessels (Tam et al, 2010; Wang et al, 2011), in vivo and without the aid of contrast enhancing agents.