Loss Of Contrast Sensitivity Research Articles

Sensitivity to visual motion in amblyopic macaque monkeys

Amblyopia is usually considered to be a deficit in spatial vision. But there is evidence that amblyopes may also suffer specific deficits in motion sensitivity as opposed to losses that can be explained by the known deficits in spatial vision. We measured sensitivity to visual motion in random dot displays for strabismic and anisometropic amblyopic monkeys. We used a wide range of spatial and temporal offsets and compared the performance of the fellow and amblyopic eye for each monkey. The amblyopes were severely impaired at detecting motion at fine spatial and long temporal offsets, corresponding to fine spatial scale and slow speeds. This impairment was also evident for the untreated fellow eyes of strabismic but not anisometropic amblyopes. Motion sensitivity functions for amblyopic eyes were shifted toward large spatial scales for amblyopic compared to fellow eyes, to a degree that was correlated with the shift in scale of the spatial contrast sensitivity function. Amblyopic losses in motion sensitivity, however, were not correlated with losses in spatial contrast sensitivity. This, combined with the specific impairment for detecting long temporal offsets, reveals a deficit in spatiotemporal integration in amblyopia which cannot be explained by the lower spatial resolution of amblyopic vision.

Visual Function in Patients With Choroidal Neovascularization Resulting From Age-Related Macular Degeneration: The Importance of Looking Beyond Visual Acuity

A detailed understanding of overall quality of vision may help primary care physicians, optometrists, and general ophthalmologists to improve the care of patients with choroidal neovascularization (CNV) resulting from age-related macular degeneration (AMD). Published literature was reviewed using Medline searches and the authors' knowledge of the field. Both visual acuity and contrast sensitivity are strongly associated with the ability to perform vision-related activities of daily living. CNV resulting from AMD often leads to scotoma, which is also strongly associated with the ability to perform everyday activities such as reading and driving. Contrast sensitivity and visual field extent may be better predictors of many abilities than visual acuity. Laser photocoagulation, verteporfin therapy, and pegaptanib sodium have been proven to reduce the risk of visual acuity loss in patients with CNV resulting from AMD. Laser photocoagulation frequently causes scotoma, but data on its effects on other aspects of overall quality of vision are scarce. Verteporfin therapy has been shown to also reduce the risk of contrast sensitivity loss and has been associated with stabilization or reduction of scotoma size. Treatment effects beyond visual acuity have not been investigated for pegaptanib. Detailed assessment of overall quality of vision also aids the design of vision rehabilitation programs tailored to the needs of individual patients. Understanding the impact of vision loss on patients with CNV resulting from AMD and assessing treatment benefits requires assessment of overall quality of vision. Primary care physicians and optometrists have an important role in ensuring that patients receive the best possible care, which can be aided by prompt referral to an ophthalmologist or retina specialist and collaboration with low-vision specialists and optometrists who together can make detailed assessments of overall quality of vision, implement appropriate treatment, and design effective rehabilitation strategies.

Visual Processing in Amblyopia: Animal Studies

In the past five years, substantial progress has been made in our knowledge of the neural basis of amblyopia. Recent advances based on animal models are described, along with new psychophysical data showing perceptual deficits in amblyopic animals that are not explained by simple losses in contrast sensitivity. Studies of contour integration and integration of motion and form signals in the presence of noise show that 1) there are fundamental losses in temporal as well as spatial vision, 2) the losses extend to the fellow eye in many cases, 3) amblyopic animals are especially impaired in the presence of background noise, and 4) these losses must depend on a process downstream from area V1 in the extrastriate cortex.

Vision rehabilitation for Canadians with less than 20/40 acuity: the SmartSight model

Traditionally, vision rehabilitation was directed towards patients who were blind or had very low vision.There is increasing evidence that less severe vision loss is associated with increased risk of falls, hip fractures, medication errors, poor nutrition, reduced physical activity, social isolation, clinical depression, longer hospitalizations, and mortality.The American Academy of Ophthalmology (AAO) 2003 SmartSight initiative in low vision rehabilitation outlined a model of graduated low vision interventions.This paper is a review of the AAO SmartSight model and how it can apply in the Canadian setting.All patients with visual acuity less than 20/40, a scotoma, field loss, or loss of contrast sensitivity would be offered information about available low vision rehabilitation. Eye physicians would be encouraged to communicate with other health care providers to coordinate existing services and integrate graduated services. Enhanced communication among caregivers about the consequences of vision loss, such as depression, falls, and visual hallucinations, could help ensure that all patients who would benefit receive appropriate vision rehabilitation.

Intermediate spatial frequency letter contrast sensitivity: its relation to visual resolution before and during amblyopia treatment

We examined the loss of letter contrast sensitivity (LCS) measured using the Pelli-Robson chart, and the extent to which any such loss was modulated by spectacle wear and occlusion therapy in children participating in an amblyopia treatment trial. Their initial mean interocular difference in logMAR acuity was approximately three times that of their LCS (0.45 vs 0.14 log units). Log LCS was weakly though significantly correlated with logMAR visual acuity (VA) for all VAs better than 0.90 (r = -0.19, 95% CI: -0.28 to -0.10) whereas for all VAs of 0.90 or poorer, log LCS was markedly and significantly correlated with VA (r = -0.72, 95% CI: -0.83 to -0.53). LCS in those children with a > or =0.1 log unit interocular difference on this test improved commensurately with VA during treatment. We conjecture that the spatial visual loss in all but the most severe amblyopes occurs in an area of resolution and contrast space that lies beyond that sampled by the Pelli-Robson chart.

NEOVASCULAR AGE-RELATED MACULAR DEGENERATION

This review summarizes the data reported in peer-reviewed literature and presents current knowledge on differentiation, natural history, and therapeutic outcomes of neovascular age-related macular degeneration (AMD). The MEDLINE database was searched to review natural history of neovascular AMD and therapeutic effects of available treatments. The search produced>7,000 articles. Research suggests that fluorescein angiographic characterization of location, composition, and size of neovascular lesions may be important in prognosis and should be considered for evaluation of treatment benefits in conjunction with evidence of recent disease progression for lesions not composed of predominantly classic choroidal neovascularization (CNV). Laser photocoagulation, photodynamic therapy with verteporfin, and administration of pegaptanib sodium reduce the risk of vision loss in selected cases of neovascular AMD, while submacular surgery can reduce the risk of severe visual acuity loss in selected cases of predominantly hemorrhagic CNV; further approaches are under investigation. Visual prognosis of neovascular AMD is variable according to lesion location, composition, and size. Often, lesions have a poor prognosis, resulting in rapid and progressive loss of visual acuity and contrast sensitivity. Such losses have a profound effect on patients' quality of life and ability to perform everyday tasks. Reducing the risk of further loss of visual acuity and contrast sensitivity might enable patients with neovascular AMD to maintain better functional abilities.

Association Between Intensity of Posterior Capsule Opacification and Contrast Sensitivity

To investigate the correlation between change in contrast sensitivity (CS) and difference in objective posterior capsule opacification (PCO) score before and after Nd:YAG laser capsulotomy. Prospective interventional case series. CS (Functional Acuity Contrast Test, or FACT, chart), distance visual acuity (Early Treatment Diabetic Retinopathy Study [ETDRS] chart), and pupil size of 30 pseudophakic eyes with PCO of varying intensity were measured before and after capsulotomy. Digital retroillumination images were taken, and the area corresponding to the pupil size was evaluated with an automated PCO analysis program known as AQUA. The correlation between change in PCO score and change in CS was highest (r = 0.85) for row B on the FACT chart and lowest (r = 0.09) for row E. The correlation with change in ETDRS visual acuity was 0.57. Objective PCO assessment by an automated image analysis system correlates well with PCO-induced loss of CS and is therefore an appropriate method for clinical studies on the development and prevention of PCO.

Disclosing disease mechanisms with a spatio-temporal summation paradigm

We develop the logic for a stimulus that can evaluate cone-dependent spatial summation and detail the modelling and interpretation of thresholds obtained with this stimulus. Fifteen observers participated, including two young normals tested extensively in control experiments, and a clinical trial based on four observers with age-related macular degeneration (AMD), four age-similar controls and five young observers. Monocular spatial summation functions were measured with contrast-modulated Gabor targets that approximated the optimal visual contrast detector. Thresholds were returned from a yes/no adaptive psychophysical algorithm. By fine titration along the size domain it was demonstrated that the spatial summation of normal observers can be adequately described by a two-component model. A reduced set of variables are proposed for clinical applications and the model was applied to data derived using these variables in persons with AMD and age-similar controls. We do not find a significant age-related loss of contrast sensitivity in our normal group. On the other hand, persons with early AMD exhibited a 0.41 log unit loss of sensitivity (P=0.04) from age-similar controls, without any change in their maximum summation area (A(max)). The nature of the spatial summation is consistent with the interpretation that early AMD produces a decrease in cone input to post-receptoral mechanisms in the absence of neural remodelling.

Retentissement à long terme de la plongée sous-marine sur le champ visuel, la vision des couleurs et la sensibilité au contraste du plongeur professionnel

To assess long-term functional effects of iterative diving, we studied visual field, color vision, and contrast sensitivity in 21 French Navy professional divers and 21 controls. This retrospective study investigated a population of 21 divers and 21 controls. All subjects were male. The inclusion criterion for divers was a total number of dives greater or equal to 1,000. Exclusion criteria for the two groups were glaucoma, ocular hypertension, smoking, and vasospastic risks. Additional exclusion criteria for controls were any history of diving practice and of hyperbaric oxygen therapy. The visual field was examined with a Humphrey Central 30-2 threshold test. Moreover, we explored spatial contrast sensitivity using Metrovision Moniteur Ophtalmologique "STAT" program and color vision with desaturated 15 hue test. None of the divers had any loss of spatial contrast sensitivity. There was a high frequency of yellow-blue axis color vision defects (45.2%) in the diver group. Regarding visual field, corrected pattern standard deviation was significantly higher in divers (p<0.01). These findings suggest that iterative diving may cause subclinical functional effects on vision. Further studies will be needed to determine the exact setting of this repercussion upon macula and/or the optic nerve.

Measures of Visual Function and Time to Driving Cessation in Older Adults

Older adults may place restrictions on their driving once their visual function has become compromised, presumably in an effort to ensure their safety. It is important to identify the types of visual function loss that lead to driving cessation to better understand the relationship between vision and driving. Data were used from the Salisbury Eye Evaluation project, a cohort study of 2520 older adults followed for 8 years with four rounds of data collection. Multiple measures of visual function were objectively assessed and driving information was collected through self-report from subjects or proxies. Cox regression was used to examine whether those with worse baseline and 2-year change scores in acuity, contrast sensitivity, visual fields, and glare sensitivity were more likely to stop driving after baseline after adjusting for demographic and health variables. Those with worse baseline scores in acuity, contrast sensitivity, central or lower peripheral visual fields were more likely to stop driving (trend p values < 0.05). Also, those who experienced 2-year losses in acuity, contrast sensitivity, or lower peripheral visual fields were more likely to stop driving (trend p values < 0.05). With the vision variables entered into the same model, baseline acuity and 2-year acuity loss were no longer statistically significant. Those with worse baseline scores in contrast sensitivity, central and lower peripheral visual fields were more likely to stop driving (trend p values < 0.05), and those who had 2-year losses in contrast sensitivity and lower peripheral visual fields were more likely to stop driving (trend p values < 0.05). Interactions with gender, other drivers in the house, or cognitive impairment were not detected. We present prospective data that indicate that older adults with worse scores in multiple measures of vision are more likely to stop driving and that contrast sensitivity and visual fields are most associated with driving cessation.

Contrast Response Properties of Magnocellular and Parvocellular Pathways in Retinitis Pigmentosa Assessed by the Visual Evoked Potential

To evaluate the contrast response of the visual system in retinitis pigmentosa (RP) under conditions designed to emphasize the parvocellular (PC) and magnocellular (MC) pathways. Visual evoked potentials (VEPs) were measured in 10 patients with RP and in 10 age-equivalent control subjects with normal visual acuity and color vision, by using an array of isolated checks that were presented against a steady yellow background. The checks were modulated sinusoidally, either in isoluminant chromatic contrast (5.6 Hz), to favor the chromatic PC pathway, or in luminance contrast (5.6 and 11.2 Hz), to favor the MC pathway. Response amplitude and phase at the stimulus (fundamental) frequency were derived from Fourier analysis, and contrast response functions were fit with a Michaelis-Menten equation to derive R(max), the maximum response amplitude, and sigma, the contrast necessary to produce R(max)/2. In the control subjects, the mean amplitude function for chromatic modulation increased approximately linearly with increasing contrast, whereas the function for luminance modulation increased sharply at low contrasts and saturated at contrasts above approximately 30% for both temporal frequencies, as expected. The patients with RP showed primarily a reduction in R(max) with little change in sigma in all testing conditions. The reduction in R(max) was equivalent for chromatic modulation and luminance modulation at 5.6 Hz, but was substantially lower for luminance modulation at 11.2 Hz. Contrast processing was impaired within both the MC and PC pathways in these patients with RP, but the degree of impairment within the MC pathway depended on temporal frequency. These VEP results are in general agreement with recent psychophysical studies of contrast sensitivity losses in patients with RP, and further they characterize contrast processing deficits in these patients at suprathreshold levels.

Long‐term macular function in eyes with central serous chorioretinopathy

This study aimed to investigate the long-term effects of central serous chorioretinopathy (CSCR) on macular function. Sixty-two eyes of 31 patients were included in this study. All patients were diagnosed with unilateral CSCR at the Retina Unit of the Ophthalmology Department, Trakya University Medical Faculty, and had a post-attack bilateral visual acuity of 6/6 and a follow-up period of a minimum of 6 months. Visual function was assessed using the Amsler grid, 40-hue colour discrimination test, visual field examination by means of Octopus automatic perimeter and Cambridge contrast sensitivity tests. Of the 31 patients, 71% were men and 29% were women, with a mean age of 39.3 +/- 7.6 years. The patients had a mean follow-up period of 50.6 +/- 40.5 months after the acute attack. Metamorphopsia was observed in 67.7% of the cases with CSCR. A colour discrimination defect was found in 48.4% of the CSCR eyes and in 54.8% of the fellow eyes. As compared with the fellow eyes, the mean deviation in the central 10 degrees of visual field was significantly higher (t = 2.9, P = 0.007) and the mean contrast sensitivity score was significantly lower (t = -3.2, P = 0.004) in the CSCR eyes. Patients with unilateral CSCR were observed to have long-term bilateral colour discrimination defects, and eyes with clinical CSCR were determined to have central relative scotoma and loss of contrast sensitivity.

Surface Roughness After Excimer Laser Ablation Using a PMMA Model: Profilometry and Effects on Vision

To show that the limited quality of surfaces produced by one model of excimer laser systems can degrade visual performance with a polymethylmethacrylate (PMMA) model. A range of lenses of different powers was ablated in PMMA sheets using five DOS-based Nidek EC-5000 laser systems (Nidek Technologies, Gamagori, Japan) from different clinics. Surface quality was objectively assessed using profilometry. Contrast sensitivity and visual acuity were measured through the lenses when their powers were neutralized with suitable spectacle trial lenses. Average surface roughness was found to increase with lens power, roughness values being higher for negative lenses than for positive lenses. Losses in visual contrast sensitivity and acuity measured in two subjects were found to follow a similar pattern. Findings are similar to those previously published with other excimer laser systems. Levels of surface roughness produced by some laser systems may be sufficient to degrade visual performance under some circumstances.

Characteristics of contrast processing deficits in X-linked retinoschisis

Contrast sensitivity and contrast discrimination were evaluated in six males with X-linked retinoschisis (XLRS), a form of early-onset macular degeneration, using testing paradigms designed to favor either the magnocellular (MC) or parvocellular (PC) pathway. Compared to a group of age-similar control observers, the patients with XLRS showed a pronounced loss of contrast sensitivity at high spatial frequencies, consistent with their reduced visual acuities. At low spatial frequencies, the patients’ deficits were greater under conditions favoring the MC pathway, for both contrast sensitivity and contrast discrimination. The pattern of contrast sensitivity loss shown by the patients with XLRS could be simulated in control observers by testing at a parafoveal locus, although by optical coherence tomography, none of the patients with XLRS had eccentric fixation. The pattern of findings indicates that the foveas of patients with XLRS functionally resemble the normal parafoveal retina.

Generic and customised digital image enhancement filters for the visually impaired

This study compares the effectiveness of various image enhancement filters for improving the perceived visibility of coloured digital natural images for people with visual impairment. Generic filters were compared with Peli’s adaptive enhancement and adaptive thresholding and custom-devised filters based on each subject’s contrast sensitivity loss. Subjects with low vision made within filter rankings followed by between filter ratings. In general, subjects preferred filters with lower gains. Unsharp masking resulted in a significant increase in perceived visibility for some image types ( p ⩽ 0.05) while Peli’s adaptive enhancement, edge enhancement and histogram equalization resulted in borderline improvements. Adaptive thresholding and the custom devised filter did not result in overall improvements in perceived visibility.

Colour vision and contrast sensitivity losses of mercury intoxicated industry workers in Brazil

We evaluated vision loss in workers from fluorescent lamp industries ( n = 39) who had retired due to intoxication with mercury vapour and had been away from the work situation for several years (mean = 6.32 years). An age-matched control group was submitted to the same tests for comparison. The luminance contrast sensitivity (CSF) was measured psychophysically and with the sweep visual evoked potential (sVEP) method. Chromatic red–green and blue–yellow CSFs were measured psychophysically. Colour discrimination was assessed with the Farnsworth–Munsell 100-hue test, Lanthony D-15d test and Cambridge Colour Vision Test. Patient data showed significantly lower scores in all colour tests compared to controls ( p < .001). The behavioural luminance CSF of the patients was lower than that of controls ( p < .001 at all frequencies tested). This result was confirmed by the electrophysiologically measured sweep VEP luminance CSF except at the highest frequencies—a difference that might be related to stimulus differences in the two situations. Chromatic CSFs were also statistically significantly lower for the patients than for the controls, for both chromatic equiluminant stimuli: red–green ( p < .005) and blue–yellow ( p < .04 for all frequencies, except 2 cycles per degree (cpd), the highest spatial frequency tested) spatial gratings. We conclude that exposure to elemental mercury vapour is associated with profound and lasting losses in achromatic and chromatic visual functions, affecting the magno-, parvo- and koniocellular visual pathways.

Senescence of spatial chromatic contrast sensitivity I Detection under conditions controlling for optical factors

Chromatic contrast thresholds for spatially varying patterns of various spatial frequencies (0.5, 1, 2, and 4 cycles per degree) were measured for ten older (65-77 yr of age) and ten younger (18-30 yr of age) observers. The stimuli were Gabor patches modulated along S-varying or (L - M)-varying chromatic axes. Thresholds were determined for two sets of stimuli. For one set of stimuli, the mean chromaticity and luminance were equated at the cornea for all observers. The second set of stimuli was corrected for ocular media density differences to equate stimulation of each of the three cone types at the retina for each individual. Chromatic contrast thresholds were higher for older observers for all stimuli tested. The magnitude of this difference showed little dependence on spatial frequency. When stimuli were equated at the cornea, this difference was greater for S-varying stimuli. When stimuli were equated at the retina, the age-related difference in thresholds for S-varying stimuli was reduced. Both optical and neural factors contribute to these age-related losses in spatial chromatic contrast sensitivity.

Spatio‐temporal selectivity of loss of colour and luminance contrast sensitivity with multiple sclerosis and optic neuritis

Colour and luminance-contrast thresholds were measured in the presence of dynamic Random Luminance-contrast Masking (RLM) in individuals who had had past diagnoses of optic neuritis (ON) some of whom have progressed to a diagnosis of multiple sclerosis (MS). To explore the spatio-temporal selectivity of chromatic and luminance losses in MS/ON, thresholds were measured using three different sizes and modulation rates of the RLM displays: small checks modulating slowly, medium-sized checks with moderate modulation and large checks modulating rapidly. The colour of the chromatic stimuli used were specified in a cone-excitation space to measure relative impairments in red-green and blue-yellow chromatic channels. These observers showed chromatic thresholds along the L/(L+M) axis that were higher than those along the S-cone axis for all display sizes/modulation rates and both red-green and blue-yellow colour thresholds were higher than luminance-contrast thresholds. The principal change in thresholds with spatio-temporal changes in the display was a reduction in thresholds for L/(L+M) and S-cones with increasing check size and modulation rate. However, luminance contrast thresholds did not change with display size/rate. These results are consistent with MS/ON selectively affecting processing in colour pathways rather than in the magnocellular pathway, and that within the colour pathways neurones with opposed L- and M-cone inputs are more damaged than colour-opponent neurons with input from S-cones.

The spatial localization deficit in visually deprived kittens

We measured the spatial localization abilities (alignment accuracy) of visually deprived kittens by use of similar spatially bandpass stimuli (Gaussian blobs) to those employed for the assessment of human amblyopes. The tests of vision were conducted on kittens reared with either strabismus or following different periods of monocular deprivation. As with amblyopic humans, the deficits in alignment accuracy were scaled in proportion to blob size and were not only considerably larger than those of grating acuity but also were not correlated with either the acuity or contrast sensitivity losses. Tests with stimuli of various contrast revealed that the deficits could not be explained in terms of the contrast sensitivity loss in this eye. The positional deficits that arise from anomalous visual development are independent of the contrast sensitivity loss and profound.

Contrast Sensitivity Deficits in Inferred Magnocellular and Parvocellular Pathways in Retinitis Pigmentosa

To define the contrast sensitivity deficits of patients with retinitis pigmentosa (RP) under testing conditions designed to emphasize threshold mediation by either the magnocellular (MC) or parvocellular (PC) pathway. Contrast sensitivity was measured with spatially localized, narrow-band test patterns at peak spatial frequencies ranging from 0.25 to 8 cycles per degree (cpd), using a steady-pedestal paradigm (brief presentation of the test stimulus against a continuously presented luminance pedestal) and a pulsed-pedestal paradigm (simultaneous brief presentation of the test stimulus and luminance pedestal) to favor the MC and PC pathways, respectively. The contrast sensitivity functions of 12 patients with RP who had visual acuities ranging between 20/12.5 and 20/40 were compared to those of 10 visually normal, age-equivalent control observers. Five of the patients with RP who had Snellen visual acuities better than 20/25 had contrast sensitivity functions that were within the normal limits at all spatial frequencies for both testing paradigms. The other seven patients with RP had reduced contrast sensitivities for both paradigms, with the greatest reduction in sensitivity occurring at the highest spatial frequency. Their contrast sensitivity deficits were equivalent for the steady- and pulsed-pedestal paradigms. As observed in previous studies, the degree of contrast sensitivity loss shown by the patients with RP was greatest at the highest stimulus spatial frequency. However, in comparison to prior studies of contrast discrimination in patients with RP, there was no evidence of a preferential contrast sensitivity loss within the MC pathway. This apparent discrepancy is attributed to differences in the test targets and psychophysical judgments that were used in the studies, which emphasizes the importance of task characteristics in evaluating relative deficits within the MC and PC processing streams in visual disorders.