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V. Prevalence of refractive error in school children. 49± 2. Background: Uncorrected refractive error is the leading cause of eye problem and the second cause of blindness worldwide. . Only 10. 3. To assess the prevalence of refractive error and related visual impairment in school-aged children in the rural population of the Mahabubnagar district REFRACTIVE ERROR BLINDNESS OF REFRACTIVE ERRORS WORLD-WIDEStudies around the world indicate that refractive errors are common in all ages. 3 billion people worldwide have refractive errors out of The Refractive Error Study in Children (RESC) examined the prevalence of . 9% children were ever A study on the prevalence of refractive errors among school childern of 7-15 years The prevalence of uncorrected refractive error in urban and rural children hyperopia, myopia, presbyope, presbyopia, uncorrected refractive error In southern India, Nirmalan et al (5) found a prevalence of 55 per cent in people aged Dec 3, 2015 Introduction: Uncorrected refractive ...

The factors that influence a normal corneal topography are not well understood. Factors that may change the corneal curvature measured using corneal topography in a normal eye include accommodation and external forces such as those exerted by the eye lid [6]. Suture and muscle placement are the mechanical forces that may alter the corneal curvature. If a muscle is placed too close to the limbus or tied to the sclera under tightly, the corneal curvature might be altered [2]. Although it has been reported that there are changes of the corneal curvature following extraocular muscle surgery, the effect was also known to be transient [2, 7]. This study demonstrated that there are a corneal topography changes following horizontal muscle strabismus correction surgery, however the effect is transient. Corneal topography measurement 6 weeks after the operation was significantly different than that before operation (mean difference = 0.210±0.096, p=0.029). There was a significant difference in corneal ...

TY - JOUR. T1 - Penetrating keratoplasty for keratoconus: the nexus between corneal wavefront aberrations and visual performance. AU - Pesudovs, Konrad. AU - Coster, Douglas. PY - 2006. Y1 - 2006. M3 - Article. VL - 22. SP - 926. EP - 931. JO - Journal of Refractive Surgery. JF - Journal of Refractive Surgery. SN - 1081-597X. IS - 9. ER - ...

Simultaneous intratunnel cross-linking with intrastromal corneal ring segment implantation versus simultaneous epithelium-off cross-linking with intrastromal corneal ring segment implantation for keratoconus management Mohamed Hosny, Moustafa Nour, Sarah Azzam, Mohsen Salem, Esraa El-Mayah Department of Ophthalmology, Cairo University, Giza, Egypt Purpose: The purpose of this study is to compare the efficacy of intratunnel cross-linking combined with intrastromal corneal ring segment (ICRS) implantation versus combined epithelium-off (epi-off) cross-linking and ICRS implantation for the management of keratoconus.Methods: Our study included 20 eyes of 12 patients with moderate-to-severe keratoconus. Group A included 10 eyes that underwent simultaneous ICRS implantation with intratunnel cross-linking. Group B included 10 eyes that underwent simultaneous ICRS implantation with epi-off cross-linking. Uncorrected distance visual acuity (UDVA), corrected distance visual acuity (CDVA), manifest sphere and

ABSTRACT. Aging often results in reduced visual acuity from changes in both the eye and neural circuits [1-4]. In normally aging subjects, primary visual cortex has been shown to have reduced responses to visual stimulation [5]. It is not known, however, to what extent aging affects visual field representations and population receptive sizes in human primary visual cortex. Here we use functional MRI (fMRI) and population receptive field (pRF) modeling [6] to measure angular and eccentric retinotopic representations and population receptive fields in primary visual cortex in healthy aging subjects ages 57 - 70 and in healthy young volunteers ages 24 - 36 (n = 9). Retinotopic stimuli consisted of black and white, drifting checkerboards comprising moving bars 11 deg in radius. Primary visual cortex (V1) was clearly identifiable along the calcarine sulcus in all hemispheres. There was a significant decrease in the surface area of V1 from 0 to 3 deg eccentricity in the aging subjects with respect to ...

This thesis is dedicated to implementing wavefront analysis for studying the peripheral optics of the human eye with an emphasis on its relation to myopia. The aim is to find properties in the peripheral image quality. The work consists of the following main parts: • Literature review and analysis of population data on ocular aberrations of the relaxed eye over the horizontal visual field (Paper B). This paper recommends a method for the peripheral wavefront analysis and presents data for different groups of people: (a) population average, (b) myopic, and (c) emmetropic subjects. • Development of a novel, dual-angle, open field wavefront sensor (Paper D). The device enables recording of real-time, simultaneous fovealperipheral wavefront measurements, while providing a binocular open field of view. • Studying optical quality for myopic and emmetropic subjects under different accommodation demands (Paper F). The novelty of this work is the real-time accommodation state tracking, allowing a ...

Purpose: To correlate subjective visual performance responses with through-focus retinal image quality (RIQ) metrics obtained on presbyopic participants fitted with single vision (SV) and multifocal (MF) contact lenses.. Methods: Thirteen presbyopic participants (50.2 ± 3.5 years, SE: +1.38 to -5.50D) who needed adds of +1.00 or +1.25D were fitted bilaterally with AirOptix Aqua™ SV and AirOptix Aqua™ MF lenses [Alcon, USA]. Using the EyeMapper, a global aberrometer, on-axis ocular wavefront aberration profiles with lenses were captured. Five independent repeats were performed under natural pupils. Additionally, participants pupil sizes were measured at different illumination conditions (scotopic (0 Lux), mesopic (80 Lux) and photopic (300 Lux)) using a custom-built instrument. Post-processing routines in Matlab using the 6th order Zernike polynomial (z1 to z28) obtained from the EyeMapper yielded through-focus retinal image quality metrics (visual Strehl Ratio in the Fourier domain) over ...

purpose. To investigate the influence of pupil diameter on the relation between induced changes in ocular higher-order wavefront aberrations and changes in contrast sensitivity by conventional laser in situ keratomileusis (LASIK) for myopia.. methods. In 215 eyes of 117 patients (age, 33.2 ± 8.3 years) undergoing LASIK for myopia of −1.25 to −13.5 D (−5.28 ± 2.55 D), ocular wavefront aberrations and contrast sensitivity function were determined before and 1 month after surgery. Preoperative photopic pupil diameter was measured with a digital camera. Ocular higher-order aberrations were measured for a 4-mm pupil with a Hartmann-Shack wavefront analyzer. The root-mean-square (RMS) of the third- and fourth-order Zernike coefficients was used to represent coma- and spherical-like aberration, respectively. From the contrast-sensitivity data, the area under the log contrast sensitivity function (AULCSF) was calculated.. results. One hundred five eyes had a photopic pupil diameter of 4 mm or ...

TY - JOUR. T1 - Effect of pupil dilation on biometric measurements and intraocular lens power calculations in schoolchildren. AU - Wang, Xiaogang. AU - Dong, Jing. AU - Tang, Maolong. AU - Wang, Xiaoliang. AU - Wang, Haitao. AU - Zhang, Suhua. PY - 2018/9/1. Y1 - 2018/9/1. N2 - Purpose To investigate the effect of pupil dilation on ocular biometric parameters and intraocular lens (IOL) power calculation in schoolchildren using the Lenstar LS 900. Methods One hundred forty eyes of 140 healthy schoolchildren were included in the analysis. Axial length (AL), central corneal thickness (CCT), aqueous depth (AD), anterior chamber depth (ACD), lens thickness (LT), flat keratometry (K), steep K, astigmatism, white-to-white (WTW), and iris/pupil barycenter distance were measured, before and after pupil dilation. Anterior segment length (ASL) was defined as the sum of ACD and LT, and lens position (LP) was defined as ACD plus half of the LT. The relative lens position (RLP) was defined as LP divided by ...

The shift in ocular dominance induced by monocular deprivation is a sensitive index of the synaptic plasticity available in the binocular visual cortex. In juveniles, brief (≤3 d) monocular deprivation induces a rapid depression in the response to stimulation of the deprived eye, followed by a slowly emerging potentiation of the response to stimulation of the nondeprived eye (Frenkel and Bear, 2004). In adults, brief monocular deprivation is ineffective. However, a longer period of monocular deprivation (≥5 d) can induce a shift in ocular dominance, attributable entirely to potentiation of the response to stimulation of the nondeprived eye (Sawtell et al., 2003). Here, we show that persistent, juvenile-like ocular dominance plasticity can be restored in the adult visual cortex by visual deprivation. In visually deprived adults, brief monocular deprivation induces a rapid depression in the response to stimulation of the deprived eye, previously only reported in juveniles, and an acceleration ...

Uncorrected refractive error is the leading cause of visual impairment; 48.9% globally and 62.9% in South Asia (Bhutan is part of this region) as estimated by the Vision Loss Expert Group (VLEG). Recent studies document a wide global variation in the prevalence of refractive error and predict that without control interventions the prevalence of myopia will significantly increase globally, affecting nearly 5 billion people by 2050. Considering its high prevalence and significant socioeconomic impact, refractive error has gained priority as a public health challenge, particularly in children.. Bhutan did not have any authentic evidence on prevalence of visual impairment due to uncorrected refractive error in the country. The WHO Global Action Plan 2014-2019 emphasized evidence generation for blindness and visual impairment and evidence-based planning and intervention. To do so, IAPB SEA, Primary eye care department of Ministry of Health , Royal Government of Bhutan carried out a nation-wide survey ...

In another study, Atchison et al. 30 measured peripheral refraction out to 35° eccentricity in horizontal and vertical meridians of emmetropic and myopic subjects up to −12 D. Relative hyperopic and myopic shifts were reported in horizontal and vertical meridians, respectively, in the myopic group. Moreover, J 180 was found to increase negatively in horizontal, and positively in vertical meridians, relative to the fovea. In addition, Atchison et al. showed that the differences in peripheral refraction between myopic and emmetropic eyes are small when measured along the vertical meridian out to 30° eccentricity compared with those measured along the horizontal meridian. Figure 8 illustrates the comparison of our results with those in previous peripheral refraction studies on the horizontal and vertical meridians. Our data illustrate a relative hyperopic shift which was similar for all measured meridians for the myopic group, and a relatively constant refractive profile for emmetropic eyes ...

TY - JOUR. T1 - Morphological variation of layer III pyramidal neurones in the occipitotemporal pathway of the macaque monkey visual cortex. AU - Elston, Guy N.. AU - Rosa, Marcello G.P.. PY - 1998/5/28. Y1 - 1998/5/28. N2 - We compared the morphological characteristics of layer III pyramidal neurones in different visual areas of the occipitotemporal cortical 'stream', which processes information related to object recognition in the visual field (including shape, colour and texture). Pyramidal cells were intracellularly injected with Lucifer Yellow in cortical slices cut tangential to the cortical layers, allowing quantitative comparisons of dendritic field morphology, spine density and cell body size between the blobs and interblobs of the primary visual area (V1), the interstripe compartments of the second visual area (V2), the fourth visual area (V4) and cytoarchitectonic area TEO. We found that the tangential dimension of basal dendritic fields of layer III pyramidal neurones increases from ...

Purpose.: To characterize refractive error, presbyopia, and spectacle correction among adults aged ≥40 years in Timor-Leste in 2010 and examine the impact of the National Spectacle Program by comparing results to those obtained 5 years earlier. Methods.: A population-based, cross-sectional survey sampled 50 clusters of 45 people each. Participants with uncorrected and undercorrected refractive error (presenting visual acuity ,6/18, but ≥6/18 in the better eye with pinhole), uncorrected and undercorrected presbyopia (,N8 binocular), corrected refractive error (≥6/18 in the better eye with presenting spectacles), and corrected presbyopia (binocular ≥N8 with presenting spectacles) were identified. Willingness to wear and to pay for spectacles was elicited. Data were adjusted for sex, age, and urban/rural domicile, to compare results from 2005 and 2010. Results.: A participation rate of 89.5% (n = 2014) was achieved. The 2010 sex-age-domicile-adjusted parameters were as follows: 3.7% (95% ...

In the Journal of Refractive Surgery from the August of 2018 issue, the article written by Rohit Shetty M.D. Et. al titled "Wavefront-Guided LASIK Has Comparable Ocular and Corneal Aberrometric Outcomes but Better Visual Acuity Outcomes Than SMILE in Myopic Eyes" compares Wavefront Guided LASIK (WFG) with small incision lenticule extraction (SMILE).. In this study, 48 SMILE eyes were completed and 58 WFG LASIK eyes were completed. The eyes were re-tested at the one month and 3 month post-operative periods using corneal topography and anterior aberration assessment. Both WFG LASIK and SMILE had comparable safety and efficacy. However, it was noticed that more WFG LASIK eyes had achieved an uncorrected distance vision of 20/16 after surgery than SMILE eyes. WFG LASIK and SMILE had similar aberrometric outcomes but WFG has better postoperative visual acuity. The experience was small pupil size, internal aberrations and wound healing can enable similar outcomes with both procedures.. Here at ...

DISCUSSION. Over the last few years, the impact of higher order aberrations on visual development and emmetropization has been the source of much debate. Brunette et al. described significant levels of higher order aberrations in children, but these higher order aberrations tended to decrease with growth, possibly as part of emmetropization(8). Studies have shown that lower order aberrations are responsible for about 90% of the quality of retinal images and that the remaining 10% is a combination of the effects of various higher order aberrations(9). However, higher order aberrations do not interact with each other in a linear algebraic manner(10,11); in fact, the effects of the different aberrations tend to compensate for each other(4,12). According to the work of Kelly et al., corneal optical aberrations are often compensated by internal ocular aberrations; therefore, the measurement of corneal wavefront aberrometry alone may produce inaccurate information about the retinal image quality(12). ...

Both Kerarings and Intacs have been shown to be an effective method of improving vision when used in isolation for patients with keratoconus. In 2014 Torquetti et al. [17] published data showing that Kerarings could effectively improve UDVA and CDVA in patients with keratoconus. Fahd et al. [18] showed Intacs to be safe and effective when used to treat eyes with moderate to severe keratoconus. However, recent data has suggested that there is regression in visual, refractive and topographic measures 5 years after ISCRS implantation [19]. This regression is to be expected as although the ISCRS flatten the cornea, they do not prevent the progression of the disease itself. CXL has therefore been used in combination with ISCRS to address this and provide the maximal visual improvement for the patient [20-22]. Our data shows ISCRS (INTACS and Kerarings) combined with CXL treatment to be a safe and effective treatment for keratoconus. We found both INTACS and Kerarings combined with CXL to produce a ...

APEDS was a population based study representative of the population of the Indian state of Andhra Pradesh with a good participation rate.. We have previously reported data on moderate visual impairment from the urban area of APEDS using two definitions of moderate visual impairment.7 In the previous report, the prevalence of moderate visual impairment in the urban area was estimated at 7.2% with definition one (presenting distance visual acuity ,6/12-6/60 or equivalent visual field loss), and 4.8% with the other more conservative definition two (presenting distance visual acuity ,6/18-6/60 or equivalent visual field loss).7 These estimates were adjusted for the population distribution of India available from the year 1991 census.7 For this report, we have adjusted the estimates for the most recent data for the estimated population distribution of India in the year 2000.3,13 On adjusting the urban area estimates for the estimated population distribution of India in the year 2000, the prevalence ...

Enrolled children were 6 to 11 years of age at baseline. Children had between −0.75 D and −4.50 D of myopia in each meridian of each eye, ,2.00 D astigmatism, and ,2.00 D anisometropia as measured by cycloplegic autorefraction. Enrolled children had no history of bifocal or contact lens wear, strabismus, or diabetes mellitus. All children had best-corrected Snellen visual acuity of at least 20/30 in each eye and weighed at least 1250 g at birth by parental report. Eligible children had a lag of accommodation of at least 1.30 D to a 4-D Badal letter stimulus (before correction for lens effectivity). The lag value of 1.30 D was chosen based on a median split of data from myopic children in the Collaborative Longitudinal Evaluation of Ethnicity and Refractive Error (CLEERE) Study because the CLEERE protocol for measuring lag was used in STAMP. 23 If a child's spherical equivalent refractive error was more myopic than −2.25 D, he or she had to be esophoric at near while wearing full ...

One-year evaluation of the performance of the Trulign toric intraocular lens implanted in eyes using intraoperative aberrometry to determine sphere, cylinder and position., P Dee G

The aim of this study was to use a Shack-Hartmann clinical aberrometer (COAS, Wavefront Sciences Ltd) to evaluate the variability of low- and higher-order aberration measurement of the eye. Using the wave aberration polynomial determined for a full-size pupil we compared the Zernike expansion coefficients for a smaller, 3 mm pupil derived by two methods: first, by re-calculating the wave aberration coefficients to the reduced sampled points corresponding to that pupil ("direct" method), and, second, by using a matrix method to reconstruct a new set of coefficients appropriate for the reduced pupil ("scaling" method) (see figure 1).. Our results suggest that, for full-size pupil, the efficiency of the measurements varies across x and y pupil position: where the wavefront is larger, measurement variance is higher, especially near the margins of the pupil, where increased standard deviation results to higher wave-aberration error. Some of this increased variance may have been due to poorer image ...

Results The overall prevalence of SE and cylindrical anisometropia ≥1.0 D were 2.7% and 3.0%, for the overall sample and in children of European-Caucasian ethnicity, 3.2%, 1.9%; East-Asian 1.7%, 5.2%; South-Asian 2.5%, 3.6%; Middle-Eastern ethnicities 2.2%, 3.3%, respectively. Anisometropia prevalence was lower or similar to that in the Baltimore Pediatric Eye Disease Study, Multi-Ethnic Pediatric Eye Disease Study and the Strabismus, Amblyopia and Refractive error in Singapore study. Risk (OR) of anisometropic amblyopia with ≥1.0 D of SE and cylindrical anisometropia was 12.4 (CI 4.0 to 38.4) and 6.5 (CI 2.3 to 18.7), respectively. We found an increasing risk of anisometropia with higher myopia ≥−1.0 D, OR 61.6 (CI 21.3 to 308), hyperopia , +2.0 D, OR 13.6 (CI 2.9 to 63.6) and astigmatism ≥1.5 D, OR 30.0 (CI 14.5 to 58.1).. ...

Purpose: To assess reproducibility of central corneal thickness (CCT) measurement by means of ultrasonic pachymetry.. Methods: Fifty one volunteers underwent three sessions of CCT measurements, each consisting of three CCT measurements, performed by each of three different observers. Intra- and interobserver reproducibility was calculated by means of intraclass correlation coefficient (ICC). The expected range of variability between two independent evaluations was calculated using scatter plots of each test-retest difference against their mean. The standard deviation of the mean differences in the test-retest scores was used to describe the differences in the score spread.. Results: The ICC ranges of the intra- and interobserver evaluations were 0.95-0.97 and 0.89-0.95 respectively; the expected variability was ⩽±1% and ⩽± 2% respectively (95% confidence interval).. Conclusions: The measurement of CCT by means of ultrasonic pachymetry is highly reproducible.. ...

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Comparison of central corneal thickness measurements in corneal edema using ultrasound pachymetry, Visante anterior-segment optical coherence tomography, Cirrus optical coherence tomography, and Pentacam Scheimpflug camera tomography Nida Wongchaisuwat,1,2 Ankana Metheetrairat,1 Pratuangsri Chonpimai,1 Waree Nujoi,1 Pinnita Prabhasawat1 1Department of Ophthalmology, Faculty of Medicine, Siriraj Hospital, Mahidol University, Bangkok, Thailand; 2Department of Ophthalmology, Golden Jubilee Medical Center, Mahidol University, Nakhon Pathom, Thailand Purpose: To compare the central corneal thickness (CCT) measurements in subjects with corneal edema using ultrasound pachymetry, Visante anterior-segment optical coherence tomography (OCT), Cirrus OCT, and Pentacam Scheimpflug camera tomography.Methods: This prospective cross-sectional study included 46 eyes of 33 patients with corneal edema and a CCT exceeding 550 μm evaluated by ultrasound pachymetry, Visante OCT, Cirrus OCT, and Pentacam. Two observers

Purpose: : To compare visual acuity and refractive outcomes with lamellar DSAEK graft thickness over time. Methods: : We retrospectively analyzed eyes that underwent DSAEK surgery and had anterior segment optical coherence tomography (AS-OCT) measurements. We compared postoperative logMAR best-corrected visual acuity (BCVA) and manifest refraction to AS-OCT graft thickness at 1, 3, 6, 12, and 24 months. Comparisons were made using paired T-tests and Pearson correlation coefficients. Results: : Forty-three eyes underwent DSAEK surgery and had AS-OCT imaging post-operatively. The average patient age was 66 ± 12 years old (range: 40-86 years old). Mean logMAR BCVA at 1, 3, 6, 12, and 24 months were 0.58, 0.39, 0.24, 0.22, and 0.33, respectively. Further analysis was performed in patients who had both visual acuity and AS-OCT measured at the same visit. There were no significant correlations of logMAR BCVA, spherical equivalent, or amount of cylinder with graft thickness by AS-OCT at any time ...

Purpose: : Anisometropia is associated with increased risk for accommodative esotropia (ET) in hyperopic children (Weakley & Birch, 2000). The aim of this study was to evaluate longitudinal changes in anisometropia and its association with visual deficits in children with accommodative ET. Methods: : Retrospective cohort study of children with accommodative ET. Eligibility criteria included: initial visit after 1 year and before 4 years of age and final visit after 7 years of age; with full cycloplegic refraction correction on first follow-up examination. Cycloplegic refractions culled from medical records were converted into power vector components: M (spherical equivalent), J0 (positive J0 indicates with-the-rule astigmatism) and J45 (oblique astigmatism) in diopters (D). Unilateral amblyopia was defined interocular visual acuity difference ≥0.2 logMAR (2 lines); bilateral amblyopia was defined as visual acuity worse than 0.30 logMAR (20/40) in both eyes. Results: : The study included 87 ...

Abstract: Purpose: To compare the accuracy of the Hoffer Q and Haigis formulae according to the anterior chamber depth (ACD) in cases of short axial length (AL).Design: Retrospective cross-sectional studyMethods: A total of 75 eyes from 75 patients with an AL of less than 22.0 mm implanted with an Acrysof IQ intraocular lens (IOL) were enrolled. The median absolute errors (MedAEs) predicted by the Hoffer Q and Haigis formulae were compared. The correlations between ACD and the predicted refractive error calculated using the two formulae were analyzed.Results: There were no significant differences in the MedAEs predicted by the Hoffer Q (Read more...) Full Story →. ...

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Purpose: To compare refraction and ocular biometry in European Caucasian children aged 6-7 years and 12-13 years living in Sydney, Australia and Northern Ireland. Methods: All children had a comprehensive eye examination, including cycloplegic (cyclopentolate 1%) autorefraction (Sydney; Canon RK-F1, Northern Ireland; Shin-Nippon SRW-5000) and ocular biometry (IOLMaster, Carl Ziess). Hyperopia was defined as a right spherical equivalent refraction (SER) of ≥+2.00 dioptres (D), myopia as ≤-0.50D and astigmatism as a cylindrical error of ≥1.00D.Results: The mean SER was similar at age 6-7 yrs (p=0.9), however, at 12-13 yrs, children in Northern Ireland had a significantly less hyperopic mean SER (+0.66D) than children in Sydney (+0.83D, p=0.008). The prevalence of myopia, hyperopia and astigmatism was significantly greater in Northern Ireland than Sydney at both ages (all p ,0.03). The distribution of refraction was highly leptokurtic in both samples, but less so in Northern Ireland ...

Efficacy and safety of fluticasone furoate nasal spray, administered using a unique side-actuated device, were evaluated in patients ≥12 years of age with seasonal allergic rhinitis to determine the optimal dose. A randomized, double-blind, parallel-group, placebo-controlled, dose-ranging study was performed on 641 patients who received placebo (n = 128) or fluticasone furoate, 55 g (n = 127), 110 g (n = 127), 220 g (n = 129), or 440 g (n = 130), once daily for 2 weeks. Fluticasone furoate was significantly more effective than placebo for mean changes from baseline over the 2-week treatment period in daily reflective total nasal symptom score (primary end point; p < 0.001 each dose vs. placebo), morning predose instantaneous total nasal symptom score (p < 0.001 each dose versus placebo), daily reflective total ocular symptom score (p ≤ 0.013 each dose versus placebo), and morning predose instantaneous total ocular symptom score (p ≤ 0.019 for three highest doses versus ...

LASIK which is customised according to the patient's own optical (eye) aberrations is called custom-vue LASIK or wavefront guided LASIK.. What are optical aberration?. Optical aberration are the natural defects in the refractive state/mechanism of the eye due to which the patient cannot focus and see objects clearly. There are different types of optical aberrations. Lower order aberrations are rectified in a normal LASIK but for significant higher order aberrations, wavefront guided LASIK is required.. What is done in custom-vue LASIK or wavefront guided LASIK?. Firstly, the patient's eyes are scanned to find out its optical aberrations. Then, this data is fed into the LASIK machine, where the computer generates the laser for rectifying these errors, according to the individual optical aberrations, during LASIK surgery.. Do all cases require custom-vue LASIK or wavefront guided LASIK?. This depends upon the type of optical aberrations present in one's eye. For lower order aberrations normal ...

We studied the age dependence of the relative contributions of the aberrations of the cornea and the internal ocular surfaces to the total aberrations of the eye. We measured the wave-front aberration of the eye with a Hartmann-Shack sensor and the aberrations of the anterior corneal surface from the elevation data provided by a corneal topography system. The aberrations of the internal surfaces were obtained by direct subtraction of the ocular and corneal wave-front data. Measurements were obtained for normal healthy subjects with ages ranging from 20 to 70 years. The magnitude of the RMS wave-front aberration (excluding defocus and astigmatism) of the eye increases more than threefold within the age range considered. However, the aberrations of the anterior corneal surface increase only slightly with age. In most of the younger subjects, total ocular aberrations are lower than corneal aberrations, while in the older subjects the reverse condition occurs. Astigmatism, coma, and spherical ...

Stereoscopic depth perception is based on binocular disparities. Although neurons in primary visual cortex (V1) are selective for binocular disparity, their responses do not explicitly code perceived depth. The stereoscopic pathway must therefore include additional processing beyond V1. We used functional magnetic resonance imaging (fMRI) to examine stereo processing in V1 and other areas of visual cortex. We created stereoscopic stimuli that portrayed two planes of dots in depth, placed symmetrically about the plane of fixation, or else asymmetrically with both planes either nearer or farther than fixation. The interplane disparity was varied parametrically to determine the stereoacuity threshold (the smallest detectable disparity) and the upper depth limit (largest detectable disparity). fMRI was then used to quantify cortical activity across the entire range of detectable interplane disparities. Measured cortical activity covaried with psychophysical measures of stereoscopic depth perception.

TY - JOUR. T1 - Specificity in the axonal connections of layer VI neurons in tree shrew striate cortex. T2 - Evidence for distinct granular and supragranular systems. AU - Usrey, William Martin. AU - Fitzpatrick, David. PY - 1996/2/1. Y1 - 1996/2/1. N2 - Pyramidal neurons in layer VI of striate cortex are the source of descending projections to the lateral geniculate nucleus (LGN) as well as a major source of axon terminals in the layers of striate cortex that receive LGN projections. This study examines how the connections of layer VI neurons are arranged with respect to the functionally distinct classes of neurons that compose their cortical and subcortical targets. By placing injections of biocytin into layer VI of tree shrew striate cortex, we identified two sublayers that differ in their intracortical and thalamic connections. Neurons in the upper part of layer VI, layer VIa, terminate in cortical layer IV, whereas those in the lower part of layer VI, layer VIb, terminate throughout the ...

Patients with myopia, hyperopia and astigmatism can now reduce or eliminate their dependence on contact lenses and eyeglasses through refractive surgery that includes radial keratotomy (RK), photorefractive keratectomy (PRK), laser-assisted in situ keratomileusis (LASIK), laser thermal keratoplasty (LTK) and intrastromal corneal rings (ICR). Since the approval of the excimer laser in 1995, the popularity of RK has declined because of the superior outcomes from PRK and LASIK. In patients with low-to-moderate myopia, PRK produces stable and predictable results with an excellent safety profile. LASIK is also efficacious, predictable and safe, with the additional advantages of rapid vision recovery and minimal pain. LASIK has rapidly become the most widely performed refractive surgery, with high patient and surgeon satisfaction. Noncontact Holium: YAG LTK provides satisfactory correction in patients with low hyperopia. ICR offers patients with low myopia the potential advantage of removal if the vision

The distribution of local preferred directions and motion sensitivities within the receptive fields of so-called tangential neurons in the fly visual system was previously found to match optic flow fields as induced by certain self-motions. The complex receptive-field organization of the tangential neurons and the recent evidence showing that the orderly development of the fly's peripheral visual system depends on visual experience led us to investigate whether or not early visual input is required to establish the functional receptive field properties of such tangential neurons. In electrophysiological investigations of two identified tangential neurons, it turned out that dark-hatched flies which were kept in complete darkness for 2 days develop basically the same receptive-field organization as flies which were raised under seasonal light/dark conditions and were free to move in their cages. We did not find any evidence that the development of the sophisticated receptive-field organization of ...

This study confirms the positive therapeutic effect of contact lenses in some patients with congenital nystagmus for whom few treatments are available. Much of the clinical improvement observed in our patients may result from a better optical correction of their refractive error with contact lenses than with spectacles, rather than a true damping effect of the nystagmus by contact lens wear. It is also possible that contact lenses had a placebo effect on our patients who strongly believed contact lenses helped them with daily activities. Visual acuity was slightly improved in all patients, and their contrast sensitivity was better with contact lens wear.. All patients had an important refractive error that was most likely better corrected with contact lenses than with spectacles. Indeed refractive disorders are more common in patients with congenital nystagmus than in the general population, and accurate refraction is the best way to improve visual acuity in patients with nystagmus.9 However, ...

Purpose: : To investigate the effect of correcting ocular aberrations on visual acuity (VA), both for white-on-black (WoB) and black-on-white (BoW) letters at various luminances. To assess the relative contribution of optical and neural factors to the visual acuity measured in those conditions. Methods: : We measured VA with natural aberrations and under static aberration correction with adaptive optics (AO). The custom-made instrument included a Hartmann-Shack wavefront sensor, a magnetic deformable mirror with 52 actuators (MIRAO, Imagine Eyes), a motorized Badal system, a pupil monitoring CCD, and a high brightness minidisplay. VA was measured using a four alternative choice procedure with tumbling Snellen E letters (Quest algorithm with 50 trials presented during 0.5 s, programmed in Psychotoolbox). VA was measured as a function of luminance (0.8, 1.6, 2.5, 5, 16, 25 and 50 cd/m2), starting with the dimmest test, and allowing for adaptation. Three conditions were measured: WoB letters under ...

The cortical area called frontal eye field (FEF) plays an important role in the control of visual attention and eye movements.[3] Electrical stimulation in the FEF elicits saccadic eye movements. The FEF have a topographic structure and represents saccade targets in retinotopic coordinates.[4]. The frontal eye field is reported to be activated during the initiation of eye movements, such as voluntary saccades[5] and pursuit eye movements.[6] There is also evidence that it plays a role in purely sensory processing and that it belongs to a "fast brain" system through a superior colliculus - medial dorsal nucleus - FEF ascending pathway.[7]. In humans, its earliest activations in regard to visual stimuli occur at 45 ms with activations related to changes in visual stimuli within 45-60 ms (these are comparable with response times in the primary visual cortex).[7] This fast brain pathway also provides auditory input at even shorter times starting at 24 ms and being affected by auditory ...

Horizontal disparity tuning for dynamic random-dot stereograms was investigated for a large population of neurons (n = 787) in V1 of the awake macaque. Disparity sensitivity was quantified using a measure of the discriminability of the maximum and minimum points on the disparity tuning curve. This measure and others revealed a continuum of selectivity rather than separate populations of disparity- and nondisparity-sensitive neurons. Although disparity sensitivity was correlated with the degree of direction tuning, it was not correlated with other significant neuronal properties, including preferred orientation and ocular dominance. In accordance with the Gabor energy model, tuning curves for horizontal disparity were adequately described by Gabor functions when the neuron's orientation preference was near vertical. For neurons with orientation preferences near to horizontal, a Gaussian function was more frequently sufficient. The spatial frequency of the Gabor function that described the disparity

TY - JOUR. T1 - Laser vision correction in treating myopia. AU - Ehlke, Germano Leal. AU - Krueger, Ronald R.. PY - 2016/1/1. Y1 - 2016/1/1. N2 - Myopia is a generally benign refractive error with an increasing prevalence worldwide. It can be corrected temporarily with glasses and contact lenses and permanently with laser vision correction. The 2 main procedures currently being performed formyopia correction are photorefractive keratectomy and laser-assisted in situ keratomileusis. Each technique has its advantages, but they appear to yield similar visual outcomes 1 year after surgery. Laser vision correction for myopia was considered a paradigm shift because healthy eyes could now undergo a surgical procedure to permanently and safely correct the error by altering the center of the cornea, which was previously off limits because of the potential for loss of transparency. Customized ablation using wavefront aberrometry and its optimized profiles were created to correct higher-order aberrations ...

An in vitro model-blink cell that mimics break-up of the tear lipid layer Peng et al. developed an in vitro model-blink cell that closely represents how the tear lipid layer breaks up over the contact lens during a blink.3 Their model-blink cell works by first placing a soft contact lens in a Teflon mold that leaves the anterior surface of the contact lens exposed to the treatment conditions.3 The investigators then add an aqueous layer with a mixture of proteins to the chamber, which is followed by a layer of artificial-tear lipid solution.3 The blink is then simulated by removing the aqueous layer until there is a break in the aqueous layer, which results in the lipid layer making contact with the contact lens.3 The aqueous solution is then replaced, and the process repeated to simulate normal contact lens wear.3. Validation of their apparatus demonstrated that the device was able to produce lipid deposition patterns similar to that of human worn contact lenses.3 Peng et al.'s apparatus and ...

We found rhythmic oscillations in visual contrast sensitivity time locked to the execution of a voluntary reaching action. Three aspects appear particularly relevant. First, the oscillations emerge a long time before the action onset. Second, the action was not visually guided, all visual information being completely irrelevant for motor planning and execution. Third, oscillations were found for targets presented in both the left and right visual hemifields. The present results strongly suggest an automatic nonspecific coupling between early motor planning and early visual processing, possibly mediated by transient synchronization of motor and visual neuronal activities.. The observed rhythmicity in visual contrast sensitivity is the likely behavioral signature of oscillatory activity in visual areas within the theta band. Previous studies have established a firm relationship between the probability of perceiving a near-threshold visual stimulus and the prestimulus phase of ongoing cortical ...

This thesis is about our peripheral vision. Peripheral vision is poor compared to central vision, due to both neural and optical factors. The optical factors include astigmatism, defocus and higher order aberrations consisting mainly of coma. Neurally, the density of ganglion cells decreases towards the periphery, which limits the sampling density. The questions that this thesis attempts to answer are how much and under which circumstances correction of optical errors can improve peripheral vision. For this, an adaptive optics system has been constructed with a wavefront sensor and a deformable mirror working in closed loop to perform real-time correction of optical errors. To investigate vision, psychophysical routines utilizing Bayesian methods have been evaluated and modified for peripheral vision to handle the presence of aliasing, fixation instability and rapid fatigue.. We found that correcting both refractive errors and higher order aberrations improved peripheral low-contrast resolution ...

Advanced computerized optical diagnostic equipment is revolutionizing eye care in the 21st century. Refraction is no exception. Traditionally, the refraction of the eye was given with spherical and cylindrical lens powers assumed to be valid across the entire pupil. However, using wavefront sensing, adaptive optics, and new treatment technologies, higher-order aberrations can be measured across the pupil and then modified or eliminated. Research has clearly shown that there are many applications involving these aberrations with diagnosis, treatment, and management of disorders, such as myopia, corneal disorders, presbyopia, cataract, and intraocular lens application and the dynamic changes in refractive state and retinal image quality produced by tear film thinning and accommodation. There are also many related questions that need to be answered regarding the natural stimulus for focusing, the patients' perception of the aberrations and their correction, and vision simulation with computational ...

Optical Phase Conjugation is a non-linear optical phenomenon that generates a phase conjugate replica of an incident beam. It has been widely used to suppress the effects of aberrations in optical systems such as resonators or imagetransmitting optical fibers. In this work, the possibility of using optical phase conjugation as a means of suppressing the effect of scattering in turbid media is analyzed, with the final aim to apply it to biological tissues. Firstly, light propagation through a slab representing a turbid sample was calculated by solving Maxwell's equations with the Finite-Difference Time-Domain method, in order to preserve all the information about the phase and coherence of the wavefront. The non-linear process that takes place within the phase conjugation mirror is described by coupledwave theory. A set of simulations was performed, and the results confirm the feasibility of using this effect to compensate the effect of scattering in turbid media. Subsequently, an experimental ...

Irreversible ischemic myocardial cell injury developes in an increasing number of cells as the duration of coronary occlusion is prolonged. The present study quantitates myocardial necrosis produced by 40 minutes, 3 hours, or 6 hours of temporary circumflex coronary occlusion (CO) followed by 2 to 4 days of reperfusion, or by 24 or 96 hours of permanent circumflex ligation in pentobarbital anesthetized open chest dogs. After 40 minutes of ischemia, myocyte necrosis was subendocardial but with increasing duration of coronary occlusion, irreversible injury progressed as a wavefront toward the subepicardium. Transmural necrosis was 38 +/- 4% after 40 min, 57 +/- 7% after 3 hours, 71 +/- 7% after 6 hours and 85 +/- 2% after 24 hours of ischemic injury. These results document the presence of a subepicardial zone of ischemic but viable myocardium which is available for pharmacologic or surgical salvage for at least three and perhaps six hours following circumflex occlusion in the dog. ...

The Q value, which reflects corneal asphericity, is negative for most eyes and not related to the degree of myopia [3]. However, conventional surgery could make the cornea undergo a pathological topographical change, from its initially prolate shape (Q , 0) with a steeper central area and flat peripheral area to an oblate shape (Q , 0) with a flat center and steep periphery [4-6]. Q value guided surgery aimed to minimize changes of the corneal anterior surface asphericity in order to reduce the spherical aberration, which impacts mostly on visual quality.. Most of previous papers about Q value guided ablation were focused on short or medium-term study, correcting low myopia or medium myopia, or comparing aspheric and conventional spheric ablation. Then what about correcting high myopic astigmatism? How the parameters of the anterior corneal surface changed following Q value guided LASIK and LASEK?In the present study, Q value guided LASIK and LASEK showed good efficacy, safety, and ...