Image quality degradation by light scattering in display devices.
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Veiling glare and ambient light reflection can significantly degrade the quality of an image on a display device. Veiling glare is primarily associated with the diffuse spread of image signal caused by multiple light scattering in the emissive structure of the device. The glare ratio associated with a test image with a 1-cm-diameter black spot is reported as 555 for film, 89 for a monochrome monitor, and 25 for a color monitor. Diffuse light reflection results from ambient light entering the display surface and returning at random emission angles. The diffuse reflection coefficient (luminance/illuminance, 1/sr) is reported as 0.026 for film, 0.058 for a monochrome monitor, and 0.025 for a color monitor with an antireflective surface coating. Both processes increase the luminance in black regions and cause contrast reduction. Specular reflections interfere with detail in the displayed scene. The specular reflection coefficient (luminance/luminance) is reported as 0.011 for film, 0.041 for a monochrome monitor, and 0.021 for a color monitor with an antireflective coating. (+info)
Use of vision tests in clinical decision making about cataract surgery: results of a national survey.
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AIM: To provide information on the use of vision tests in clinical decision making about cataract surgery in the UK. METHOD: A questionnaire survey was mailed to 703 consultant ophthalmologists. RESULTS: A response rate of 70% was obtained. Monocular distance visual acuity was the only visual function that was tested routinely by all surgeons. Supplementary use of contrast sensitivity and glare testing was low. Many surgeons (35%) were willing to consider surgery at acuity levels better than 6/9 and a small but substantial number (12%) indicated that they did not use an acuity criterion. Being prepared to consider surgery at relatively good levels of acuity was not associated with more common use of other tests of vision. CONCLUSION: Many UK surgeons are prepared to consider cataract extraction at relatively good levels of visual acuity and use other vision tests infrequently. (+info)
Contrast and glare sensitivity in epilepsy patients treated with vigabatrin or carbamazepine monotherapy compared with healthy volunteers.
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BACKGROUND/AIM: Many antiepileptic drugs have influence on visual functions. The aim of this study was to investigate possible changes in contrast sensitivity, macular photostress, and brightness acuity (glare) tests in patients with epilepsy undergoing vigabatrin (VGB) or carbamazepine (CBZ) monotherapy compared with healthy volunteers. METHODS: 32 patients undergoing VGB therapy, 18 patients undergoing CBZ therapy, and 35 healthy volunteers were asked to participate in an ophthalmological examination. In the previous study, visual field constrictions were reported in 40% of the patients treated with VGB monotherapy. In the present study, these VGB and CBZ monotherapy patients were examined for photopic contrast sensitivity with the Pelli-Robson letter chart and brightness acuity and macular photostress with the Mentor BAT brightness acuity tester. RESULTS: Contrast sensitivity with the Pelli-Robson letter chart showed no difference between these groups and normal subjects (ANOVA: p= 0.534 in the right eye, p= 0.692 in the left eye) but the VGB therapy patients showed a positive correlation between the contrast sensitivity values and the extents of the visual fields in linear regression (R = 0.498, p = 0.05 in the right eye, R = 0.476, p = 0. 06 in the left eye). Macular photostress and glare tests were equal in both groups and did not differ from normal values. CONCLUSION: The results of this study indicate that carbamazepine therapy has no effect on contrast sensitivity. Vigabatrin seems to impair contrast sensitivity in those patients who have concentrically constricted in their visual fields. Neither GBZ nor VGB affect glare sensitivity. (+info)
Contrast sensitivity and glare disability by halogen light after monofocal and multifocal lens implantation.
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BACKGROUND: Standard examination of contrast sensitivity under conditions of glare disability is performed with incandescent light. A new halogen glare test that simulates glare as seen with oncoming vehicle headlights was used to measure glare disability in patients implanted with multifocal and monofocal intraocular lenses (IOLs). METHODS: 28 patients with an average age of 69 years (SD 12 years) were implanted with a monofocal IOL (SI-40NB, Allergan) and 28 patients with an average of 66 years (12 years) were implanted with a refractive multifocal IOL (Array-SA-40N, Allergan). All patients were followed for 5 months postoperatively. Contrast sensitivity at four spatial frequencies (3, 6, 12, and 18 cycles per degree, cpd) with and without a glare source were measured using the halogen glare test (CSV-1000 HGT). Statistical analysis was performed using the two sample Wilcoxon test. The local significance level was set at 0.05. RESULTS: When tested at the lowest spatial frequency (3 cpd) without halogen glare, contrast sensitivity was lower in the multifocal group than in the monofocal group (p=0.0292). With additional glare, there was no difference between both groups. At all other spatial frequencies (6, 12, and 18 cpd), when tested without halogen glare (6 cpd, p=0.5250; 12 cpd, p=0.8483; 18 cpd, p=0.9496) and with moderate (3 cpd, p=0.7993; 6 cpd, p=0.4639; 12 cpd, p=0.7456; 18 cpd, p=1.0) and high halogen glare (3 cpd, p=0. 1513; 6 cpd, p=0.2016; 12 cpd, p=0.3069; 18 cpd, p=0.9933), there was no statistically significant difference between groups. Patients in both groups of age 70 or older had reduced contrast sensitivity without halogen glare and with moderate and strong glare. When monofocal and multifocal patients older than 70 years of age were analysed separately, there was no statistically significant difference in contrast sensitivity with and without glare. Astigmatism >1 dioptre had no significant influence on contrast sensitivity and glare disability when monofocal and multifocal eyes were compared. CONCLUSION: Reduced contrast sensitivity was found in the multifocal group only at the lowest spatial frequency without halogen glare. The monofocal and multifocal groups had no statistically significant differences in contrast sensitivity with moderate and strong glare. These results suggest no difference in glare disability induced by halogen light similar to oncoming vehicle headlights for patients implanted with monofocal and multifocal IOLs. (+info)
The association of multiple visual impairments with self-reported visual disability: SEE project.
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PURPOSE: This report examines the relationship between psychophysical measures of visual impairment and self-reported difficulty with everyday visual tasks in a population-based sample of individuals 65 years of age and older. METHODS: Community-dwelling residents (n = 2520) of Salisbury, MD, between the ages of 65 and 84 were recruited for the study. Visual acuity under normal and low luminance, contrast and glare sensitivity, stereoacuity, and visual fields were measured. Subjective physical disability was assessed with the Activities of Daily Vision Scale (ADVS). RESULTS: In multiple regression analyses adjusted for demographic factors, cognitive status, depression, and number of comorbid medical conditions, each of the vision tests except low luminance acuity was independently associated with lower ADVS scores. The analyses indicate that a factor of 2 reduction in visual acuity or contrast sensitivity, comparable with that observed in mild to moderate lens opacity, was associated with a three- to fivefold odds of reporting difficulty with daily tasks. Although age alone was a significant risk factor for disability, it was not associated with overall ADVS score, once visual impairment and other chronic medical conditions were taken into account. CONCLUSIONS: Visual acuity, contrast and glare sensitivity, stereoacuity, and visual fields are significant independent risk factors for self-reported visual disability in an older population. Visual impairment defined by acuity alone is not the only dimension of the association with subjective disability. Additional vision measures are required to understand the impact of vision loss on everyday life. (+info)
The time course of the lower threshold of motion during rapid events of adaptation.
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To examine how the time course of rapid events of adaptation affect motion vision, the lower threshold of motion (LTM) was measured for suprathreshold sinusoidal gratings in presence of transient and steady glare. In the case of the transient condition, glare and stimulus were presented separated in time by a variable extent (SOA: 50-450 ms). A two alternative forced choice paradigm using the method of constant stimuli was adopted to measure the LTM. It was found that LTM follows the characteristic Crawford's time course of adaptation. Results are similar for two stimulus duration (300 and 500 ms). It was proposed that the increment of contrast threshold for displacing gratings (C(tq)) due to the loss of sensitivity produced by the sudden onset of the glare source can explain the results. (+info)
Contrast and glare testing in keratoconus and after penetrating keratoplasty.
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AIM: To compare the performance of keratoconus, penetrating keratoplasty (PK), and control subjects on clinical tests of contrast and glare vision, to determine whether differences in vision were independent of visual acuity (VA), and thereby establish which vision tests are the most useful for outcome studies of PK for keratoconus. METHODS: All PK subjects had keratoconus before grafting and no subjects had any other eye disease. The keratoconus (n = 11, age 35.0 (SD 11.1) years), forme fruste keratoconus (n = 6, 33.0 (13.0)), PK (n = 21, 41.2 (7.9)), and control (n = 24, 33.7 (8.6)) groups were similar in age. Vision testing, conducted with optimal refractive correction in place, included low contrast visual acuity (LCVA) and Pelli-Robson contrast sensitivity (PRCS) both with and without glare, as well as VA. RESULTS: Normal subjects saw better than PK subjects who in turn saw better than keratoconus subjects on all raw measures. However, when adjusted for VA, the normal group only saw significantly better than the keratoconus group on LCVA (low contrast loss 0.05 (0.04) v 0.15 (0.12), F(2,48) = 6.16; p<0.01, post hoc Sheffe p<0.05), and the decrements to glare were no worse than for normals. The forme fruste keratoconus group were indistinguishable from normals on all measures. CONCLUSIONS: PK subjects have superior vision to keratoconus subjects, but not as good as normal subjects. Including mild keratoconus subjects within a keratoconus group could confound these differences in vision. While VA is an excellent test for comparing normal, keratoconus and PK groups, additional information can be provided by LCVA and PRCS, but not by glare testing. Outcomes research into keratoconus management should include a measure in the contrast domain. (+info)
Methods of assessment of patients for Nd:YAG laser capsulotomy that correlate with final visual improvement.
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BACKGROUND: This paper attempts to clarify the usefulness of various simple pre-operative measures in estimating the potential for a visually successful capsulotomy. METHODS: 24 patients attending for capsulotomy had pre-operative measures of glare with BAT tester, visibility of posterior pole and grading of posterior capsular pearls and fibrosis seen at slit lamp. Visual function was measured before and after standardised capsulotomy. Correlations of the various preoperative measures with eventual visual function improvements were calculated. RESULTS: Pearls at slit lamp and poor posterior pole visualisation were all correlated with improvements in visual acuity and contrast sensitivity after capsulotomy. Amount of fibrosis visible at slit lamp and glare assessment were not correlated with vision improvements after laser. CONCLUSION: Of the various measures that are taken prior to Nd : YAG capsulotomy, some correlate with eventual visual improvement but for others no clinical utility was found. Practitioners should note these findings as they are especially of use in more questionable or high-risk cases to help determine whether referral for PCO treatment by Nd: YAG capsulotomy is likely to benefit the patient. (+info)