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Contrast Sensitivity (contrast + sensitivity)
Terms modified by Contrast Sensitivity Selected AbstractsEvaluation of Melbourne Edge Test contrast sensitivity measures in the visually impairedOPHTHALMIC AND PHYSIOLOGICAL OPTICS, Issue 4 2005James S. Wolffsohn Abstract Aim:, Contrast sensitivity (CS) provides important information on visual function. This study aimed to assess differences in clinical expediency of the CS increment-matched new back-lit and original paper versions of the Melbourne Edge Test (MET) to determine the CS of the visually impaired. Methods:, The back-lit and paper MET were administered to 75 visually impaired subjects (28,97 years). Two versions of the back-lit MET acetates were used to match the CS increments with the paper-based MET. Measures of CS were repeated after 30 min and again in the presence of a focal light source directed onto the MET. Visual acuity was measured with a Bailey,Lovie chart and subjects rated how much difficulty they had with face and vehicle recognition. Results:, The back-lit MET gave a significantly higher CS than the paper-based version (14.2 ± 4.1 dB vs 11.3 ± 4.3 dB, p < 0.001). A significantly higher reading resulted with repetition of the paper-based MET (by 1.0 ± 1.7 dB, p < 0.001), but this was not evident with the back-lit MET (by 0.1 ± 1.4 dB, p = 0.53). The MET readings were increased by a focal light source, in both the back-lit (by 0.3 ± 0.81, p < 0.01) and paper-based (1.2 ± 1.7, p < 0.001) versions. CS as measured by the back-lit and paper-based versions of the MET was significantly correlated to patients' perceived ability to recognise faces (r = 0.71, r = 0.85 respectively; p < 0.001) and vehicles (r = 0.67, r = 0.82 respectively; p < 0.001), and with distance visual acuity (both r = ,0.64; p < 0.001). Conclusions:, The CS increment-matched back-lit MET gives higher CS values than the old paper-based test by approximately 3 dB and is more repeatable and less affected by external light sources. Clinically, the MET score provides information on patient difficulties with visual tasks, such as recognising faces. [source] Vision status of children with oculocutaneous albinismOPHTHALMIC AND PHYSIOLOGICAL OPTICS, Issue 6 2002A. O. Oduntan Purpose:, Black South African children with oculocutaneous (OCA) albinism were examined optometrically to establish the level of vision improvement that could be achieved following optical correction. Methods:, The children (N = 153) (males 50.3%; females 49.7%), aged 7,17 years (mean = 10.76 ± 2.25 years) were examined with a logMAR VA chart, cover tests, retinoscopy (dry), subjective refraction, Vistech contrast sensitivity test, ophthalmoscopy, Randot stereotest, Ishihara and Farnsworth Panel D-15 tests. Results:, Many (34.6%) of the children had strabismus, 2,25 prism dioptres. Uncorrected distance VAs were: OD: Finger counting (FC) to 6/7.5 , 2, OS: 6/7.5 + 2 to 6/7.5 , 3, OU: 6/60 , 1 to 6/7.5. Most (67.6%) of the children had myopia. Others (30.8%) had hyperopia or emmetropia (1.7%). Astigmatism was present in 92.25% of the children. The nearest equivalent spherical powers were: OD: ,12.00 to +2.75 D (mean = ,1.48 ± 2.28 D) and OS: ,8.00 to +5. 75 D (mean = 1.36 ± 2.18 D). Following optical correction, VA improvement ranged from one to three lines in 71.2% of the children. The corrected VAs were, OD FC to 6/6 , 1, OS 6/7.5 + 2 to 6/6 , 1, and OU 6/60 to 6/6. Many (84.3%) of the children had corrected VA worse than 6/18 in the better eye and were therefore classified as partially sighted or blind (VA worse than 3/60). Stereoacuity was poor (500,70 sec arc) in most (89.5%) of the children, whilst others could not perceive the minimum 500 sec arc on the test. Contrast sensitivity was poor, maximum spatial frequency being 18 cpd with peak sensitivity at 3 cpd. Many (83%) of the children, however, had normal colour vision. Conclusion:, These children with OCA had poor VA, which could be improved significantly with optical correction. Their poor contrast sensitivity and depth perception, however, were not improved. Most of the children with OCA had normal colour vision. [source] Spherical and irregular aberrations are important for the optimal performance of the human eyeOPHTHALMIC AND PHYSIOLOGICAL OPTICS, Issue 2 2002Y. K. Nio Contrast sensitivity measured psychophysically at different levels of defocus can be used to evaluate the eye optics. Possible parameters of spherical and irregular aberrations, e.g. relative modulation transfer (RMT), myopic shift, and depth of focus, can be determined from these measurements. The present paper compares measured results of RMT, myopic shift, and depth of focus with the theoretical results found in the two eye models described by Jansonius and Kooijman (1998). The RMT data in the present study agree with those found in other studies, e.g. Campbell and Green (1965) and Jansonius and Kooijman (1997). A new theoretical eye model using a spherical aberration intermediate between those of the eye models described by Jansonius and Kooijman (1998) and an irregular aberration with a typical S.D. of 0.3,0.5 D could adequately explain the measured RMT, myopic shift, and depth of focus data. Both spherical and irregular aberrations increased the depth of focus, but decreased the modulation transfer (MT) at high spatial frequencies at optimum focus. These aberrations, therefore, play an important role in the balance between acuity and depth of focus. [source] Intravitreal bevacizumab (Avastin®) for neovascular age-related macular degeneration in treatment-naive patientsACTA OPHTHALMOLOGICA, Issue 7 2009Karen Bjerg Pedersen Abstract. Purpose:, To report the effects of intravitreal bevacizumab (Avastin®) in treatment-naive patients with exudative age-related macular degeneration (ARMD) assessed by visual acuity (VA), optical coherence tomography (OCT) and contrast sensitivity. Methods:, A prospective, uncontrolled, pilot study of 26 eyes of 26 patients, all previously treatment-naive to photodynamic therapy, argon laser or anti-vascular endothelial growth factor (VEGF), were treated with one or more intravitreal injections of 1.25 mg bevacizumab. Of the 26 patients, 15 (57.7%) had occult choroidal neovascularization (CNV), 6 (23.1%) had predominantly classic CNV and 5 (19.2%) had minimally classic CNV. Ophthalmic outcome measures included changes in standardized Early Treatment Diabetic Research Study (ETDRS) VA, contrast sensitivity and OCT. The patients were examined at baseline and 1 week, 6 weeks, 3 months and 6 months after the first injection. Re-treatment was given on an ,as needed' basis. Results:, Twenty-four eyes of 24 patients completed 6 months of follow-up. Two patients chose to discontinue the study. Mean ETDRS VA score improved from 55 letters at baseline to 60 letters at 1 week (P < 0.01) and to 61 letters at 6 weeks (P < 0.01). No significant improvement in VA from baseline was found after 3 and 6 months. Patients with pigment epithelial detachment (PED) had a significantly worse outcome in VA at 6 months. Contrast sensitivity improved from baseline to 3 or 6 months, but this improvement was not statistically significant. Mean macular thickness decreased significantly from baseline to all follow-up examinations (P < 0.01). Conclusion:, Mean ETDRS VA improved significantly after 1 and 6 weeks; thereafter, it remained stable throughout the study period. Macular thickness improved significantly at all time points. The results indicate that 1.25 mg intravitreal bevacizumab is associated with functional as well as morphological improvement among treatment-naive ARMD patients. [source] Aberration and contrast sensitivity comparison of aspherical and monofocal and multifocal intraocular lens eyesCLINICAL & EXPERIMENTAL OPHTHALMOLOGY, Issue 4 2007Mingbing Zeng PhD MD Abstract Background:, Higher-order aberrations and contrast sensitivity were evaluated in patients who underwent phacoemulsification cataract extraction followed by implantation of aspherical, monofocal or multifocal intraocular lens (IOL) replacements. Methods:, In this comparative trial, 124 patients with an average age of 66.8 ± 5.2 years and their 124 eyes were randomly divided into three surgical implantation groups to receive one of three types of IOLs in replacement of cataract lenses. The patients of group 1 were given an aspherical IOL Z9001 (AMO, Santa Ana, CA, USA) replacement, and group 2 was implanted a monofocal IOL SA60AT (Alcon, Fort Worth, TX, USA) and group 3 the multifocal IOL SA40N (AMO). Post-surgical best-corrected visual acuity, corneal aberrations, total ocular aberrations, pupil diameters, capsulorhexsis sizes and contrast sensitivity were measured and compared. Results:, There was no statistical difference for mean best-corrected visual acuity, pupil diameter, curvilinear capsulorhexis size and corneal aberration among the three groups. For the spherical aberration, fourth-order higher-order aberration and total ocular higher-order aberration, the SA40N group was higher than the SA60AT group and the SA60AT group was higher than the Z9001 group, and the differences between the three groups were statistically significant for these measurements. Contrast sensitivity was higher for the Z9001 group than the SA60AT group and the SA60AT group was higher than the SA40N group, and the difference was statistically significant in all the spatial frequencies of 3, 6, 12 and 18. Conclusions:, Although the multifocal IOL can provide near vision, it can increase higher-order aberration and negatively influence contrast sensitivity. However, the aspherical IOL can reduce aberration and improve contrast sensitivity as compared with the monofocal IOL. [source] The value of contrast sensitivity in diagnosing central serous chorioretinopathyCLINICAL AND EXPERIMENTAL OPTOMETRY, Issue 4 2007S Plainis MSc PhD A 39-year-old hyperopic male was referred for laser refractive treatment. In the course of the pre-operative evaluation he complained of a recent deterioration of vision. The suspicion of unilateral central serous chorioretinopathy (CSCR) was confirmed by contrast sensitivity testing and by ocular fundus examination. Contrast sensitivity (CS) for six spatial frequencies (1, 2, 4, 8, 12 and 16 c/deg) was evaluated using Gabor patches of gratings projected on a high-resolution display by means of a stimulus generator card. Although VA remained unaltered, the pattern of contrast sensitivity function varied at different stages of CSCR: during the acute stage, performance at all spatial frequencies was depressed, while at two-month follow up, intermediate and high spatial frequencies were mainly affected. It is concluded that the level of visual deficit in CSCR cannot be evaluated by measuring visual acuity. History and contrast sensitivity can play a central role in setting the correct diagnosis and characterising its stage. [source] Voxel-based analysis of MRI detects abnormal visual cortex in children and adults with amblyopiaHUMAN BRAIN MAPPING, Issue 2 2005Janine D. Mendola Abstract Amblyopia, sometimes called "lazy eye," is a relatively common developmental visual disorder well characterized behaviorally; however, the neural substrates associated with amblyopia in humans remain unclear. We hypothesized that abnormalities in the cerebral cortex of subjects with amblyopia exist, possibly as a result of experience-dependent neuronal plasticity. Anatomic magnetic resonance imaging (MRI) and psychophysical vision testing was carried out on 74 subjects divided into two age ranges, 7,12 years and 18,35 years, and three diagnoses, strabismic amblyopia, anisometropic amblyopia, and normal vision. We report a behavioral impairment in contrast sensitivity for subjects with amblyopia, consistent with previous reports. When the high-resolution MRI brain images were analyzed quantitatively with optimized voxel-based morphometry, results indicated that adults and children with amblyopia have decreased gray matter volume in visual cortical regions, including the calcarine sulcus, known to contain primary visual cortex. This finding was confirmed with a separate region-of-interest analysis. For the children with amblyopia, additional gray matter reductions in parietal-occipital areas and ventral temporal cortex were detected, consistent with recent reports that amblyopia can result in spatial location and object processing deficits. These data are the first to provide possible neuroanatomic bases for the loss of binocularity and visual sensitivity in children and adults with amblyopia. Hum Brain Mapp 25:222,236, 2005. © 2005 Wiley-Liss, Inc. [source] Timing of Thyroid Hormone Action in the Developing Brain: Clinical Observations and Experimental FindingsJOURNAL OF NEUROENDOCRINOLOGY, Issue 10 2004R. T. Zoeller Abstract The original concept of the critical period of thyroid hormone (TH) action on brain development was proposed to identify the postnatal period during which TH supplement must be provided to a child with congenital hypothyroidism to prevent mental retardation. As neuropsychological tools have become more sensitive, it has become apparent that even mild TH insufficiency in humans can produce measurable deficits in very specific neuropsychological functions, and that the specific consequences of TH deficiency depends on the precise developmental timing of the deficiency. Models of maternal hypothyroidism, hypothyroxinaemia and congential hyperthyroidism have provided these insights. If the TH deficiency occurs early in pregnancy, the offspring display problems in visual attention, visual processing (i.e. acuity and strabismus) and gross motor skills. If it occurs later in pregnancy, children are at additional risk of subnormal visual (i.e. contrast sensitivity) and visuospatial skills, as well as slower response speeds and fine motor deficits. Finally, if TH insufficiency occurs after birth, language and memory skills are most predominantly affected. Although the experimental literature lags behind clinical studies in providing a mechanistic explanation for each of these observations, recent studies confirm that the specific action of TH on brain development depends upon developmental timing, and studies informing us about molecular mechanisms of TH action are generating hypotheses concerning possible mechanisms to account for these pleiotropic actions. [source] Scotopic spatiotemporal sensitivity differences between young and old adultsOPHTHALMIC AND PHYSIOLOGICAL OPTICS, Issue 4 2010Cynthia L. Clark Abstract Background:, Our lab has previously demonstrated losses in contrast sensitivity to low spatial frequencies under scotopic conditions with older adults. It is not clear, however, whether the temporal frequency of a stimulus alters the relation between age and the spatial contrast sensitivity function (sCSF) under scotopic conditions. Methods:, A maximum-likelihood, two-alternative, temporal forced-choice QUEST procedure was used to measure threshold to spatially and temporally modulated stimuli in both young (mean = 26 years) and old (mean = 75 years) adults. Results:, In general, the shapes of the spatial and temporal CSFs were low-pass for both young and old observers; contrast sensitivity decreased at approximately the same rate with increasing spatial frequency and temporal frequency for both age groups, although the overall sensitivity of the old group was lower than that of the young group. The high-frequency resolution limit was lower for the old group compared to the young group. Conclusions:, The differences in contrast sensitivity between the young and old groups suggest a uniform loss in sensitivity of the channels mediating spatial and temporal vision. Because of this loss, the spatial and temporal window of visibility for the older adults is compromised relative to the younger adults. [source] Custom-devised and generic digital enhancement of images for people with maculopathyOPHTHALMIC AND PHYSIOLOGICAL OPTICS, Issue 4 2009Susan J. Leat Abstract Aim:, The purpose of this study was to compare the effectivity, in terms of the potential usefulness, of digital filters based on either contrast sensitivity (CS) or supra-threshold contrast matching (CM) in enhancing pictures images for people with maculopathy and to investigate whether generic filters (not based on an individual's vision loss) are equally as effective. Effectivity is measured by changes in perceived visibility. Methods:, Thirty-five subjects with maculopathy, aged 20,92 years, took part [13 atrophic age-related macular degeneration (ARMD), 14 exudative ARMD, and 8 juvenile macular dystrophy (JMD)]. CS and supra-threshold CM were measured. A range of CS filters (1 or 2-octave wide band-pass filter using a Gabor or polynomial envelope) with different strengths were developed based on the ratio of the individual's contrast threshold and that of a normal age-related group. Similarly filters were developed based on CM at 3.6% and 27.9% contrast. The following generic filters were also applied with different ,strengths': edge enhancement; sharpening; contrast enhancement; Peli's adaptive enhancement; difference of Gaussian; and an equi-emphasis band-pass filter. The filters were applied to images of faces and general scenes. Subjects were asked to rank the perceived visibility of images (to obtain the best version of each filter) and then to rate the perceived visibility of each image filtered with a particular filter. Results:, In general, subjects with atrophic ARMD and JMD preferred the weaker versions of most of the filters, while those with exudative ARMD did not show such a clear preference. Generally, images of faces were preferred with less enhancement than scenes. The filters based on CM were rated as giving significant improvement, while those based on CS and peak emphasis were not preferred. Of the generic filters, the Peli adaptive enhancement filter was most frequently rated as giving a significant improvement (p < 0.05) followed by the contrast enhancement filter. They gave the same perceived enhancement as the custom-devised filters. Conclusions:, Generic filters, which are easier to apply than the custom-devised filters, are appropriate for rehabilitation purposes. [source] Vision screening of older peopleOPHTHALMIC AND PHYSIOLOGICAL OPTICS, Issue 6 2007Zahra Jessa Abstract A recent systematic review found that between 20% and 50% of older people in the UK have undetected reduced vision and in most cases this is caused by refractive error or cataracts, and is correctable. Two approaches to improve the detection of these problems are to better publicise optometric services and to carry out community-based vision screening of older people. Screening programmes should pass the Wilson criteria and a consideration of these highlights three inter-related questions: ,Is vision screening effective at detecting correctable low vision in older people?'; ,Which tests should be included?' and ,Which venues are most appropriate?' We carried out a systematic review to investigate these questions. For the first question, only one study was found which met our selection criteria. The ,gold standard' eye examination in this study lacked several important components, and the vision screening method that was used was not found to be very effective. The review revealed other studies, which, although not meeting our selection criteria, included relevant information. The screening studies highlight the lack of agreement on the content of a gold standard eye examination and of the test(s) that should be used to screen vision. Visual function in older people is not adequately described by high contrast visual acuity (VA), nor by self-reports of visual difficulties. Other tests that may be relevant include visual field testing, low contrast VA, contrast sensitivity and stereo-acuity. The pinhole test has often been used in attempts to detect uncorrected refractive errors, but results from this test can be problematic and possible reasons for this are discussed. Appropriate venues for vision screening are contingent upon the format of the vision screening programme. There is still uncertainty over the battery of vision tests that are most appropriate. This, and optimum venues for screening, require further research before it can be fully determined whether vision screening of older people meets the Wilson criteria. If a vision screening programme using a battery of vision tests, perhaps computerised, can be established, then this should be tested to determine the sensitivity and specificity for detecting the target conditions. Ultimately, longitudinal studies are necessary to determine whether such a screening programme will lead to improved visual performance and quality of life in older people. [source] Clinical performance of electronic, head-mounted, low-vision devicesOPHTHALMIC AND PHYSIOLOGICAL OPTICS, Issue 4 2004Louise E. Culham Abstract This study compared four electronic head-mounted devices (HMDs) (Jordy, Flipperport, Maxport and NuVision) with conventional optical low-vision aids (LVAs). The aim was to determine any performance differences for laboratory-based clinical measurements and practical visual tasks for patients with macular disease. Possible factors influencing success were explored. Ten patients with early onset macular disease (EOMD) and 10 with age-related macular disease (AMD) used the four HMDs, habitual spectacles and previously prescribed optical LVAs to complete a range of clinical measurements and everyday visual tasks. The clinical measurements were distance, intermediate and near acuities, and contrast sensitivity. The visual tasks were to read text of three sizes, to write a cheque and to identify grocery items on a shelf. Following the initial evaluation, each subject took home two randomly selected HMD devices for 2 weeks, after which performance measures were repeated. No single HMD stood out as being superior overall. Flipperport and Jordy provided significantly better distance and intermediate acuity than the previously prescribed optical LVAs but near acuity and contrast sensitivity were not consistently better with any of the HMDs. Practice at home provided some improvement in performance with HMDs, nevertheless, optical aids remained the best devices for optimum functioning for the majority of tasks. Younger patients and those with better distance acuity were more likely to benefit from HMDs, particularly when reading small print. In low vision clinics, practitioners should continue to show patients conventional optical aids and demonstrate these electronic HMDs only when appropriate for the individual patient. [source] The prospects for super-acuity: limits to visual performance after correction of monochromatic ocular aberrationOPHTHALMIC AND PHYSIOLOGICAL OPTICS, Issue 6 2003W. N. Charman Abstract It has recently been suggested that correction of the monochromatic aberration of the eye could lead to substantial improvements in visual acuity and contrast sensitivity function. After consideration of the best-corrected visual acuity of normal eyes, the optical and neural limits to visual performance are reviewed. It is concluded that, even if current problems with the accuracy of the suggested techniques of aberration correction, through corneal excimer laser ablation or customised contact lenses, can be overcome, changes in monochromatic ocular aberration over time, the continuing presence of chromatic aberration, errors of focus associated with lags and leads in accommodation, and other factors, are likely to result in only minor improvements in the high-contrast acuity performance of most normal eyes being produced by attempted aberration control. Significant gains in contrast sensitivity might, however, be achievable, particularly under mesopic and scotopic conditions when the pupil is large, provided that correct focus can be maintained. In the immediate future, reduction of the high levels of aberration that are currently found in eyes that have undergone refractive surgery and in some abnormal eyes should bring useful benefits. [source] Vision status of children with oculocutaneous albinismOPHTHALMIC AND PHYSIOLOGICAL OPTICS, Issue 6 2002A. O. Oduntan Purpose:, Black South African children with oculocutaneous (OCA) albinism were examined optometrically to establish the level of vision improvement that could be achieved following optical correction. Methods:, The children (N = 153) (males 50.3%; females 49.7%), aged 7,17 years (mean = 10.76 ± 2.25 years) were examined with a logMAR VA chart, cover tests, retinoscopy (dry), subjective refraction, Vistech contrast sensitivity test, ophthalmoscopy, Randot stereotest, Ishihara and Farnsworth Panel D-15 tests. Results:, Many (34.6%) of the children had strabismus, 2,25 prism dioptres. Uncorrected distance VAs were: OD: Finger counting (FC) to 6/7.5 , 2, OS: 6/7.5 + 2 to 6/7.5 , 3, OU: 6/60 , 1 to 6/7.5. Most (67.6%) of the children had myopia. Others (30.8%) had hyperopia or emmetropia (1.7%). Astigmatism was present in 92.25% of the children. The nearest equivalent spherical powers were: OD: ,12.00 to +2.75 D (mean = ,1.48 ± 2.28 D) and OS: ,8.00 to +5. 75 D (mean = 1.36 ± 2.18 D). Following optical correction, VA improvement ranged from one to three lines in 71.2% of the children. The corrected VAs were, OD FC to 6/6 , 1, OS 6/7.5 + 2 to 6/6 , 1, and OU 6/60 to 6/6. Many (84.3%) of the children had corrected VA worse than 6/18 in the better eye and were therefore classified as partially sighted or blind (VA worse than 3/60). Stereoacuity was poor (500,70 sec arc) in most (89.5%) of the children, whilst others could not perceive the minimum 500 sec arc on the test. Contrast sensitivity was poor, maximum spatial frequency being 18 cpd with peak sensitivity at 3 cpd. Many (83%) of the children, however, had normal colour vision. Conclusion:, These children with OCA had poor VA, which could be improved significantly with optical correction. Their poor contrast sensitivity and depth perception, however, were not improved. Most of the children with OCA had normal colour vision. [source] Objective predictors of subjective visual function for different age-related cataract morphologiesOPHTHALMIC AND PHYSIOLOGICAL OPTICS, Issue 6 2002N. Hakim-Banan Purpose:, To find objective chart tests that give a measure of visual function in the different age-related cataract morphological groups and can be applied in a clinical setting. Methods:, Subjects with age-related cataract (N = 33) were recruited to the study from both private optometric practice and a hospital eye department. All subjects underwent LOCS III grading of their cataract and had their functional vision assessed using the VF-14 questionnaire. High (96%) and low (16%) contrast logMAR visual acuity were measured together with Pelli,Robson contrast sensitivity. A stepwise linear regression was then performed on the data to find significant predictors for VF-14 in the three age-related cataract morphological groups as well as in a mixed group. Results:, Low contrast logMAR visual acuity was a significant predictor of VF-14 in the cortical (p = 0.014) and nuclear (p = 0.024) subgroups. For the mixed morphological group both high and low contrast visual acuity were significant predictors (p < 0.03). There were only three subjects with pure posterior subcapsular cataract and so no meaningful analysis could be performed. Conclusions:, Low contrast logMAR visual acuity may be a better predictor of visual function in cortical and nuclear cataract compared with high contrast logMAR visual acuity or Pelli,Robson contrast sensitivity. [source] Perceived blur in amblyopiaOPHTHALMIC AND PHYSIOLOGICAL OPTICS, Issue 6 2002A. J. Simmers Purpose:, It is well documented that visual acuity and contrast sensitivity in amblyopia are attenuated at high spatial frequencies: this would predict that amblyopes should perceive objects as blurred because they lack high spatial frequency information necessary to adequately represent sharp edges. In a series of experiments, we explored the representation of blur in amblyopia with blur discrimination and blur matching tasks. Methods:, Monocular blur discrimination thresholds were measured in a spatial 2-Alternative Force Choice procedure. The luminance profiles of the blurred edge were cumulative Gaussians with the standard deviation of the reference blurred edge being fixed at 1.88, 3.75, 7.5, 15, 30, or 60 min arc. Observers were required to discriminate which edge (right or left) appeared to be the less blurred. Observers also interocularly matched edges which were identical to those employed in the blur discrimination tasks, with the exception that they were viewed dichoptically at all times. Results:, Blur discriminination thresholds were elevated in both the amblyopic and fellow fixing eye but were within the normal range for interocular matching thresholds. Our results suggest that blur is veridically represented in the amblyopic visual system. Conclusions:, The surprising result here is that all amblyopes, even those with the most severe visual loss, veridically matched all blurred edges, including the sharpest ones. This implies that amblyopes are able to represent levels of blur that are defined by spatial structure beyond their resolution limit. These results also raise interesting questions about the mechanism by which blur is represented in the visual system. [source] The contrast sensitivity function for detection and resolution of blue-on-yellow gratings in foveal and peripheral visionOPHTHALMIC AND PHYSIOLOGICAL OPTICS, Issue 5 2002R. S. Anderson Abstract Previous studies using polychromatic gratings have shown that the peripheral grating contrast sensitivity function is significantly different when the task is resolution rather than detection. Specifically, in the middle frequency range, while resolution acuity drops suddenly to zero, detection performance continues up to much higher frequencies, accompanied by observations of aliasing. We wanted to determine if the same holds true for blue-cone isolating gratings in either foveal or peripheral vision. Contrast sensitivity function (CSFs) were measured at the fovea and 20 degrees eccentricity in the temporal retina under conditions of short-wavelength-sensitive (SWS)-cone pathway isolation using a two-alternative forced choice paradigm. The detection and resolution CSF were identical at the low frequency end but at higher frequencies resolution sensitivity falls abruptly while contrast detection remained possible till higher frequencies [cut-off frequencies: fovea detection 6.0 cycles (degree),1, resolution 4.6 cycles (degree),1; periphery detection 1.6 cycles (degree),1, resolution 1.05 cycles (degree),1]. Aliasing was observable when spatial frequency exceeded the resolution limit. Medium/high contrast blue-cone-mediated resolution acuity is sampling limited in both the fovea and periphery. Previous studies of blue-cone contrast sensitivity which employed a detection task do not reflect the true resolution limit. [source] Measuring contrast sensitivity with inappropriate optical correction*OPHTHALMIC AND PHYSIOLOGICAL OPTICS, Issue 6 2000Russell L. Woods Summary Spatial frequency-selective minima (notches) in the contrast sensitivity function (CSF) because of defocus can mimic those that occur with ocular disease. We examined the influence of measurement conditions on CSF shape in simulated clinical testing. CSF notches occurred with almost all levels of defocus for all subjects. Multiple notches were found under some conditions. Notches were found with defocus as small as 0.50 D. Effects of induced astigmatism depended on the orientation of the target. Notches were apparent in defocus conditions after stimulus size and room illuminance were modified and when subjects had insufficient accommodation to compensate for hypermetropic defocus. The equivalent of notches was not noted with the Pelli-Robson chart. As defocus-induced CSF notches may be mistaken for functional loss, careful refractive correction should be conducted prior to clinical or experimental CSF measurement, even at low spatial frequencies. [source] The practical near acuity chart (PNAC) and prediction of visual ability at near,OPHTHALMIC AND PHYSIOLOGICAL OPTICS, Issue 2 2000James S. Wolffsohn Summary Objective: To improve on present reading chart designs, providing a quick and accurate method to measure the near acuity threshold, of particular importance with low vision patients. Design: The Practical Near Acuity Chart (PNAC) uses a single paragraph with 3 simple related words on each line (12 lower case letters). The line print size decreases in a logMAR progression (N80-N5). Methods: The time taken to measure near acuity of 53 subjects aged 9,91 years with the PNAC and Bailey,Lovie near chart was recorded and compared to their distance acuity (Bailey,Lovie chart), contrast sensitivity (Melbourne Edge Test) and ability to read extracts of newsprint. Results: There was no difference in near acuity threshold using related or un-related words. There was a high correlation (r=0.97) between near acuity measured with the PNAC and Bailey,Lovie charts. However, the time taken to measure near acuity was significantly faster with the PNAC (32±2 s vs 76±4 s, p<0.001). Near acuity measured with either chart was highly correlated (p<0.001) to distance acuity (r=0.74), contrast sensitivity (r=0.62) and ability to read newsprint (r=0.87). The PNAC was shown to have high test-reliable (r=0.99). Conclusions: The PNAC offers a quick but accurate way to measure near acuity and shows a high degree of correlation with distance acuity, contrast sensitivity and the ability to read newsprint. [source] Visual function of police officers who have undergone refractive surgeryAMERICAN JOURNAL OF INDUSTRIAL MEDICINE, Issue 11 2006Jeffery K. Hovis OD Abstract Introduction The visual acuity and contrast sensitivity of police recruits and officers was evaluated in both normal and dim illumination conditions to determine whether officers who have had refractive surgery have compromised night vision. Methods The control group consisted of 76 officers and recruits who have not had refractive surgery and the refractive surgery group consisted of 22 officers and recruits who had refractive surgery. Visual acuity and contrast sensitivity were measured under both room illumination and dim illumination. The room illumination test series included high contrast acuity, low contrast acuity and Pelli-Robson contrast sensitivity. The dim illumination test series included high contrast acuity, low contrast acuity, Pelli-Robson contrast sensitivity, license plate number acuity (with and without glare) and the Mesotest. Results The general findings were that the refractive surgery group had lower acuity scores on low contrast targets in both room and dim light levels along with a reduction in the Mesotest scores with a glare source compared to the control group. Conclusions Although refractive surgery police recruits and officers had reduced performance on some vision tests, these reductions were small and it is unlikely that their performance on vision related tasks would be compromised, on average. The major concern is the small number of refractive surgery candidates whose results were well outside the range of the non-surgical candidates. Their vision may be unacceptable for policing. Am. J. Ind. Med. 49:885,894, 2006. © 2006 Wiley-Liss, Inc. [source] Chromatic and spatial properties of parvocellular cells in the lateral geniculate nucleus of the marmoset (Callithrix jacchus)THE JOURNAL OF PHYSIOLOGY, Issue 1 2004Esther M. Blessing The parvocellular (PC) division of the afferent visual pathway is considered to carry neuronal signals which underlie the red,green dimension of colour vision as well as high-resolution spatial vision. In order to understand the origin of these signals, and the way in which they are combined, the responses of PC cells in dichromatic (,red,green colour-blind') and trichromatic marmosets were compared. Visual stimuli included coloured and achromatic gratings, and spatially uniform red and green lights presented at varying temporal phases and frequencies. The sensitivity of PC cells to red,green chromatic modulation was found to depend primarily on the spectral separation between the medium- and long-wavelength-sensitive cone pigments (20 or 7 nm) in the two trichromatic marmoset phenotypes studied. The temporal frequency dependence of chromatic sensitivity was consistent with centre,surround interactions. Some evidence for chromatic selectivity was seen in peripheral PC cells. The receptive field dimensions of parvocellular cells were similar in dichromatic and trichromatic animals, but the achromatic contrast sensitivity of cells was slightly higher (by about 30%) in dichromats than in trichromats. These data support the hypothesis that the primary role of the PC is to transmit high-acuity spatial signals, with red,green opponent signals appearing as an additional response dimension in trichromatic animals. [source] 3421: Straylight and visionACTA OPHTHALMOLOGICA, Issue 2010TJTP VAN DEN BERG Purpose Straylight is considered an important source of patient complaints. They can be voiced like halos, glare, hazy vision and blinding at night. With visual acuity, contrast sensitivity and slit lamp examination little may be found. Yet increased large angle light scattering in the eye media not detected by common tests, may degrade the image projected on the retina, thus decreasing the quality of vision. Aging changes to the crystalline lens and cataract are the most common causes of increased straylight. This study aimed to quantify the importance of straylight for daily life on the basis of patient complaint scores. Methods In a duocenter setting questionnaires were administered before and after cataract surgery. The 37 questions VFQ as well as a self developed 5 question straylight questionnaire were used. A comparison was made between the importance of visual acuity and of straylight to explain the questionnaire outcomes. Results A total of 214 patients were included in the study. For the comparison correlation coefficients were calculated between a weighted average of the 2 functional measures visual acuity and straylight on the one hand, and the questionnaire outcomes on the other. In all 4 cases (2 questionnaires x 2 visits) correlation was lowest for both visual acuity and straylight used in isolation. When visual acuity and straylight were combined to one combined score, correlation improved. Maximum correlation was found when visual acuity and straylight were combined 1:1 (preop) to 2:1 (postop), for both questionnaires. Conclusion For cataract patients, straylight is of about equal importance compared to visual acuity for their appreciation of daily function. In this comparison both were quantified as logarithms (logMAR and log(s)). [source] 3425: Influence of cataract morphology on retinal straylight and straylight changes due to cataract surgery using the Morcher 89A Bag in the LensTMACTA OPHTHALMOLOGICA, Issue 2010MJ TASSIGNON Purpose To evaluate straylight and contrast sensitivity (CS) in eyes with various cataract morphologies, to determine which type of cataract presents a higher impairment of visual function with respect to proposed norms car driver safety and to compare retinal straylight and CS before and after implantation of a Morcher 89A IOL. Methods BCVA, CS and straylight were measured in 97 cataractous eyes using respectively a Snellen chart, a Pelli-Robson chart and the C-Quant. Cataracts were graded using the LOCS III scale and divided into four groups: nuclear, cortical, nuclear-cortical and posterior subcapsular cataract. These results were compared to data from 38 cataract-free control subjects. A separate group of 71 eyes had their straylight measured before and after cataract surgery. Results CS was reduced and straylight increased in all cataract patients, most notably in posterior subcapsular and nuclear-cortical cataract. CS and BCVA were correlated (r=0.44), whereas straylight and BCVA were not. Applying cut-off values as proposed by European drivers studies of l.25 log CS and 1.4 log straylight as safe margins for driving, 31% would be considered unfit to drive on the basis of CS and 78% on the basis of straylight although their visual acuity was still above the current European visual acuity requirement for driving. Retinal straylight reduced significantly from 1.560.26 to 1.250.22logunits (P<0.001) after IOL implantation . Conclusion Straylight and, to a lesser extent, CS are complementary to BCVA and should be taken into account when considering driving eligibility. After IOL implantation straylight reduces significantly, resulting in a significant increase in driving eligibility. [source] 4432: Comparison of the two domains of visual optics: the aberrometric domain and the straylight domainACTA OPHTHALMOLOGICA, Issue 2010TJTP VAN DEN BERG Purpose The ocular point-spread-function defines the functional problem originating from optical defects in the eye. Aberrations as well as scatter degrade the psf. How do these two types of defect differ with respect to their effect on the psf, and on functional measures? Methods Literature models for different aspects of the optical irregularities in the eye media, in particular Thibos et al. JOSA A 2002 for the aberration structure and Van den Berg et al. VR 1999 for small particle scattering, were used to delineate their effects on the psf. The Thibos et al. model was extrapolated to allow inclusion of the high orders of aberration not normally included in aberrometry, but potentially visible with double pass. With respect to the visual function counterparts, straylight (C-Quant from Oculus) outcomes were compared to visual acuity and contrast sensitivity in 2400 subjects. Results As a reference the full scale psf standard model of Vos et al. CIE 1999 was used. The modeled aberration structures of the eye proved to predict the central part of the psf up till about 0.3 degrees if extreme high orders were included. For angles >1 degree predicted values were far below the actual values of the psf. Small particle scattering was essential to predict the psf for angles above 1 degree. Conclusion In the assessment of disturbances to the optical media two domains must be discriminated: the aberration domain and the small particle domain, with corresponding parts (small angle vs large angle) to the psf. Straylight typically originates from irregularities of size 10 micrometer and below, as opposed to aberrations originating from refractile humps and bumps extending over 100 micrometer and more. Straylight has independent value. [source] 4241: Optical characterization of PCOACTA OPHTHALMOLOGICA, Issue 2010TJTP VAN DEN BERG Purpose Opacification of the posterior capsule (PCO) is known to degrade visual function on both counts: small angle resolution (visual acuity and contrast sensitivity) as well as large angle light scatter (straylight). No studies have been performed to delineate the optical characteristics of PCO as a basis for explanation of these visual function defects. Methods Preparations of IOL-capsule combinations were harvested from donor eyes after removal of the cornea. They were mounted submersed in saline in an optical set-up, used earlier to characterize the optics of the crystalline lens (van den Berg et al. VR 1999). Illuminated by monochromatic beams of light, the light spreading originating from different areas of the preparation was measured as function of wavelength for different angles. Based on physical optics theory, the optical characteristics of PCO was derived. The data will be presented translated into the straylight parameter, directly comparable to the figures obtained in vivo using the clinical straylight meter (C-Quant from Oculus). Results Twenty successful preparations were harvested with at least some PCO areas. PCO grades varied from severe to slight. Two physically different types of light spreading could be discriminated. One type corresponding to pearl-like appearance, characterized by little wavelenght dependence and smal angle dominance. The other type corresponding to diffuse scatter, characterized by strong wavelength dependence and large angle dominance. The scatter values measured corresponded to clinical measures of straylight in PCO patients using the C-Quant. Conclusion The light scattering characteristics of PCO show two types of optical disturbance: a refractile type, probably dominated by pearl-like structures, and a diffuse type of scattering of yet unclear origin. [source] 4243: Capsular peeling in premium IOLs to improve visual outcomeACTA OPHTHALMOLOGICA, Issue 2010MJ TASSIGNON Purpose To demonstrate that capsular peeling may improve quality of vision of patients who experienced reduced vision in the short postoperative period after premium IOL implantation due to decentration of the IOL secondary to PCO. Methods Patients who were refered to our centre because of unsatisfactory quality of vision after premium IOL implantation (more specifically after multifocal IOLs) were scheduled for surgery aiming at peeling the capsular bag. The conditions which the patient needed to meet were: increased higher order aberrations, evidence of tilt or decentration of the IOL, important fibrotic proliferation in the capsular bag, no YAG laser capsulotomy performed. Results After capsular peeling, it was possible to demonstrate that the quality of vision of the patient improved, the higher order aberrations reduced and it was often unnecessary to explant the premium IOL. Although there was an obvious improvement of the quality of vision, this improvement still did not reached the high standard of vision as measured after monofcal IOLs. Conclusion This paper shows how important the role is of PCO on quality of vision. Because contrast sensitivity is already reduced after premium IOL implantation, patients will be very sensitive to an additional reduction as it appears after PCO. [source] 2126: Retinal and cortical functions in adult mice lacking cannabinoid receptorsACTA OPHTHALMOLOGICA, Issue 2010C CASANOVA Purpose Cannabinoid receptor type 1 (CB1R) has been localized in the adult retina of rodents. It is expressed in cones, horizontal, bipolar, some amacrine and ganglion cells. The expression of the cannabinoid receptor type 2 (CB2R) mRNA in the retina of adult rats was also reported. The goal of the present study was to investigate the functional roles of CB1R and CB2R in the retina by comparing retinal electrophysiological responses and cortical optical signals in normal and genetically modified mice. Methods Experiments were conducted on four different groups of C57BL/6 mice: CB1R wild type (WT), CB1R knockout (KO), CB2R WT and KO. Scotopic electroretinograms (ERG) luminance-response functions and photopic ERGs were recorded. In a subset of CB1 groups, intrinsic signals acquired by optical brain imaging were used to determine spatial frequency, contrast sensitivity and retinotopic maps in the visual cortex. Results The CB1R KO retina showed a stronger photopic response. No differences were observed for scotopic responses. For the CB2R groups, the scotopic b-wave response was stronger in the KO mice. No differences could be seen between visual cortices maps with respect to SF and contrast sensitivity. Retinotopic maps differed only along the azimuth. Significant differences were observed between hemodynamic response functions. Conclusion These results indicate that CB receptors can play a regulatory effect on the neurovascular coupling at the retinal and cortical levels and on the functional organization of the mice visual cortex along the azimuth Axis.(NSERC) [source] Intravitreal bevacizumab (Avastin®) for neovascular age-related macular degeneration in treatment-naive patientsACTA OPHTHALMOLOGICA, Issue 7 2009Karen Bjerg Pedersen Abstract. Purpose:, To report the effects of intravitreal bevacizumab (Avastin®) in treatment-naive patients with exudative age-related macular degeneration (ARMD) assessed by visual acuity (VA), optical coherence tomography (OCT) and contrast sensitivity. Methods:, A prospective, uncontrolled, pilot study of 26 eyes of 26 patients, all previously treatment-naive to photodynamic therapy, argon laser or anti-vascular endothelial growth factor (VEGF), were treated with one or more intravitreal injections of 1.25 mg bevacizumab. Of the 26 patients, 15 (57.7%) had occult choroidal neovascularization (CNV), 6 (23.1%) had predominantly classic CNV and 5 (19.2%) had minimally classic CNV. Ophthalmic outcome measures included changes in standardized Early Treatment Diabetic Research Study (ETDRS) VA, contrast sensitivity and OCT. The patients were examined at baseline and 1 week, 6 weeks, 3 months and 6 months after the first injection. Re-treatment was given on an ,as needed' basis. Results:, Twenty-four eyes of 24 patients completed 6 months of follow-up. Two patients chose to discontinue the study. Mean ETDRS VA score improved from 55 letters at baseline to 60 letters at 1 week (P < 0.01) and to 61 letters at 6 weeks (P < 0.01). No significant improvement in VA from baseline was found after 3 and 6 months. Patients with pigment epithelial detachment (PED) had a significantly worse outcome in VA at 6 months. Contrast sensitivity improved from baseline to 3 or 6 months, but this improvement was not statistically significant. Mean macular thickness decreased significantly from baseline to all follow-up examinations (P < 0.01). Conclusion:, Mean ETDRS VA improved significantly after 1 and 6 weeks; thereafter, it remained stable throughout the study period. Macular thickness improved significantly at all time points. The results indicate that 1.25 mg intravitreal bevacizumab is associated with functional as well as morphological improvement among treatment-naive ARMD patients. [source] Ocular wavefront analysis and contrast sensitivity in eyes implanted with AcrySof IQ or AcrySof Natural intraocular lensesACTA OPHTHALMOLOGICA, Issue 7 2009Tamer Takmaz Abstract. Purpose:, This study aimed to compare ocular wavefront aberrations for pupil diameters of 4 mm and 6 mm, and contrast sensitivity, in eyes with AcrySof IQ and AcrySof Natural intraocular lenses (IOLs). Methods:, Sixty eyes of 60 patients were enrolled in this prospective randomized study. After phacoemulsification the eyes received either AcrySof IQ SN60WF or AcrySof Natural SN60AT IOLs. One month after surgery, all patients underwent complete ophthalmological examination including corneal topography, wavefront analysis for pupil diameters of 4 mm and 6 mm, and contrast sensitivity measurements with the CSV 1000E instrument under photopic and mesopic conditions with and without glare. Results:, There was no statistically significant difference between groups in age, sex or other preoperative ocular characteristics (p > 0.05). Patients with AcrySof IQ IOLs had higher contrast sensitivity at 6 c.p.d. under photopic conditions, at 6 c.p.d. and 18 c.p.d. under mesopic conditions, and at 6 c.p.d., 12 c.p.d. and 18 c.p.d. under mesopic conditions with glare (p < 0.05). Corneal spherical aberration was 0.273 ± 0.074 ,m in the AcrySof Natural group and 0.294 ± 0.086 ,m in the AcrySof IQ group (p = 0489). Ocular spherical aberration was 0.362 ± 0.141 ,m and 0.069 ± 0.043 ,m (p < 0.001) for 6-mm diameter pupils and 0.143 ± 0.091 ,m and 0.017 ± 0.016 ,m (p < 0.001) for 4-mm diameter pupils, with AcrySof Natural and AcrySof IQ IOLs, respectively. There were no significant differences in other higher-order aberrations between the groups (p > 0.05). Conclusions:, Aspherical AcrySof IQ IOLs significantly reduced spherical aberration for pupil diameters of both 4 mm and 6 mm and also improved contrast sensitivity more than spherical AcrySof Natural IOLs, especially in mesopic conditions. [source] Association of lens opacities, intraocular straylight, contrast sensitivity and visual acuity in European driversACTA OPHTHALMOLOGICA, Issue 6 2009Ralph Michael Abstract. Purpose:, To study the relationship between lens opacity and intraocular straylight, visual acuity and contrast sensitivity. Methods:, We investigated 2422 drivers in five clinics in different European Union (EU) member states aged between 20 and 89 years as part of a European study into the prevalence of visual function disorders in drivers. We measured visual acuity [Early Treatment Diabetic Retinopathy Study (ETDRS) chart], contrast sensitivity (Pelli,Robson chart) and intraocular straylight (computerized straylight meter). Lens opacities were graded with the Lens Opacities Classification System III (LOCS) without pupillary dilation. Participants answered the National Eye Institute Visual Functioning Questionnaire , 25. Results:, Intraocular straylight was related more strongly to LOCS score than to both visual acuity and contrast sensitivity. Visual acuity and contrast sensitivity were correlated to each other well, but to intraocular straylight to a much lesser extent. Self-reported visual quality was best related to contrast sensitivity; night driving difficulty was best related to visual acuity. Conclusion:, Straylight is found to have added value for visual function assessment in drivers, whereas if visual acuity is known contrast sensitivity has limited added value. [source] | |||||||||||||