Psychophysical measurements of luminance and chromatic spatial and temporal contrast sensitivity in Duchenne muscular dystrophy

In children with Duchenne muscular dystrophy, color vision losses have been related to dystrophin deletions downstream of exon 30, which affect a dystrophin isoform, Dp260, present in the retina. To further evaluate visual function in DMD children, we measured spatial, temporal, and chromatic red-green and blue-yellow contrast sensitivity in two groups of DMD children with gene deletion downstream and upstream of exon 30. Psychophysical spatial contrast sensitivity was measured for low, middle, and high spatial frequencies with achromatic gratings and for low and middle frequencies with red-green and blue-yellow chromatic gratings. Temporal contrast sensitivity was also measured with achromatic stimuli. A reduction in sensitivity at all spatial luminance contrasts was found for the DMD patients with deletion downstream of exon 30. Similar results were found for temporal luminance contrast sensitivity. Red-green chromatic contrast sensitivity was reduced in DMD children with deletion downstream of exon 30, whereas blue-yellow chromatic contrast sensitivity showed no significant differences. We conclude that visual function is impaired in DMD children. Furthermore, we report a genotype-phenotype relationship because the visual impairment occurred in children with deletion downstream but not upstream of exon 30, affecting the retinal isoform of dystrophin Dp260.

Visual contrast sensitivity in tonic-clonic epileptic patients

We measured the effects of epilepsy on visual contrast sensitivity to linear and vertical sine-wave gratings. Sixteen female adults, aged 21 to 50 years, comprised the sample in this study, including eight adults with generalized tonic-clonic seizure-type epilepsy and eight age-matched controls without epilepsy. Contrast threshold was measured using a temporal two-alternative forced-choice binocular psychophysical method at a distance of 150 cm from the stimuli, with a mean luminance of 40.1 cd/m². A one-way analysis of variance (ANOVA) applied to the linear contrast threshold showed significant differences between groups (F[3,188] = 14.829; p < .05). Adults with epilepsy had higher contrast thresholds (1.45, 1.04, and 1.18 times for frequencies of 0.25, 2.0, and 8.0 cycles per degree of visual angle, respectively). The Tukey Honestly Significant Difference post hoc test showed significant differences (p < .05) for all of the tested spatial frequencies. The largest difference between groups was in the lowest spatial frequency. Therefore, epilepsy may cause more damage to the neural pathways that process low spatial frequencies. However, epilepsy probably alters both the magnocellular visual pathway, which processes low spatial frequencies, and the parvocellular visual pathway, which processes high spatial frequencies. The experimental group had lower visual contrast sensitivity to all tested spatial frequencies.

Wavefront Analysis, Contrast Sensitivity, and Depth of Focus After Cataract Surgery With Aspherical Intraocular Lens Implantation

PURPOSE: To determine whether implantation of an aspherical intraocular lens (IOL) results in reduced ocular aberrations and improved contrast sensitivity after cataract surgery without critical reduction of depth of focus. DESIGN: Double-blinded, randomized, prospective study. METHODS: In an intraindividual study of 25 patients with bilateral cataract, an aspherical IOL (Akreos Advanced Optic [AO]; Bausch & Lomb, Inc., Rochester, New York, USA) was implanted in one eye and a spherical IOL (Akreos Fit; Bausch & Lomb, Inc) in the fellow eye. Higher-order aberrations with a 5- and 6-mm pupil were measured with a dynamic retinoscopy aberrometer at 1 and 3 months after surgery. Uncorrected and best-corrected visual acuity and contrast sensitivity under mesopic and photopic conditions also were measured. Distance-corrected near and intermediate visual acuity were studied as a measurement of depth of focus. RESULTS: There was no statistically significant difference between eyes in uncorrected and best-corrected visual acuity at I and 3 months after surgery. There was a statistically significant between-group difference in contrast sensitivity under photopic conditions at 12 cycles per degree and under mesopic conditions at all spatial frequencies. The Akreos AO group obtained statistically significant lower values of higher-order aberrations and spherical aberration with 5- and 6-mm pupils compared with the Akreos Fit group (P < .05). There was no significant difference in distance-corrected near and intermediate visual acuity between both groups. CONCLUSIONS: Aspherical aberration-free Akreos AO IOL induced significantly less higher-order aberrations and spherical aberration than the Akreos Fit. Contrast sensitivity was better under mesopic conditions with the Akreos AO with similar results of depth of focus. (Am J Ophthalmol 2010;149:383-389. (C) 2010 by Elsevier Inc. All rights reserved.)

Effect of+3.00 diopter and+4.00 diopter additions in multifocal intraocular lenses on defocus profiles, patient satisfaction, and contrast sensitivity

PURPOSE: To evaluate the advantages and disadvantages of the new low-addition (add) (+3.00 diopter [D]) ReSTOR multifocal IOL compared with the preceding ReSTOR model with +4.00 D add. SETTING: University Eye Hospital, Tuebingen, Germany. DESIGN: Comparative case series. METHODS: Patients with a +3.00 D or +4.00 D add multifocal IOL were examined for uncorrected and distance-corrected visual acuity at distance, intermediate, and near. A defocus profile was assessed, individual reading distance and the distance for lowest intermediate visual acuity were determined. Patient satisfaction was evaluated with a standardized questionnaire. Contrast sensitivity was tested under mesopic and photopic conditions. RESULTS: Uncorrected and distance-corrected intermediate visual acuities were statistically significantly better in the +3.00 D add group (24 eyes) than in the +4.00 D add group (30 eyes); distance and near visual acuities were not different between groups. The defocus profile significantly varied between groups. The +4.00 D add group had a closer reading distance (33.0 cm) than the +3.00 D add group (43.5 cm), a closer point of lowest intermediate visual acuity (65.8 cm versus 86.9 cm) and worse lowest intermediate visual acuity (20/59 +/- 4.5 letters [SD] versus 20/48 +/- 5.5 letters). Thus, patients in the +3.00 D add group reported being more satisfied with intermediate visual acuity. The +3.00 D add group reported more glare but less halos than the +4.00 D add group; contrast sensitivity was not different. CONCLUSION: The lower addition resulted in a narrower defocus profile, a farther reading distance, and better intermediate visual acuity and thus increased patient satisfaction.

Intraocular Straylight And Contrast Sensitivity Two Months After Lasik: Intraocular Straylight Measurement As A New Parameter In Visual Quality Assessment

PROPÒSIT: Estudiar l'efecte de la cirurgia LASIK en la llum dispersa i la sensibilitat al contrast. MÈTODES: Vint-i-vuit pacients van ser tractats amb LASIK. La qualitat visual es va avaluar abans de l'operació i dos mesos després. RESULTATS: La mitjana de llum dispersa i la sensibilitat al contrast abans de l'operació no va canviar en dos mesos després. Només un ull tenia un marcat augment en la llum dispersa. Nou ulls van presentar una lleugera disminució en la sensibilitat al contrast. S'han trobat dues complicacions. CONCLUSIÓ: Després de LASIK la majoria dels pacients (80%) no van tenir complicacions i van mantenir la seva qualitat visual. Uns pocs pacients (16%) van tenir una mica de qualitat visual disminuïda. Molt pocs (4%) van tenir complicacions clíniques amb disminució en la qualitat visual.

Contrast sensitivity to angular frequency stimuli is higher than that for sinewave gratings in the respective middle range

This study compares contrast thresholds for sinewave gratings, or spatial frequencies (1/CSF) with contrast thresholds for angular frequencies (1/aCSF) and for radial frequencies, or J0 targets (1/rCSF). Observers had to differentiate between one of these frequency stimuli and a stimulus at mean luminance within a forced-choice procedure. All measurements were made with the same equipment, methods and subjects. Our results show higher sensitivity to, or lower thresholds for, angular frequencies when compared to either sinewave gratings or J0 targets. Contrast values in arbitrary units, in the lower threshold range for angular frequencies, were about half those required to differentiate sinewave gratings from mean luminance in its most sensitive range

Contrast sensitivity to radial frequencies modulated by Jn and j n Bessel profiles

We measured human contrast sensitivity to radial frequencies modulated by cylindrical (Jo) and spherical (j o) Bessel profiles. We also measured responses to profiles of j o, j1, j2, j4, j8, and j16. Functions were measured three times by at least three of eight observers using a forced-choice method. The results conform to our expectations that sensitivity would be higher for cylindrical profiles. We also observed that contrast sensitivity is increased with the j n order for n greater than zero, having distinct orderly effects at the low and high frequency ends. For n = 0, 1, 2, and 4 sensitivity tended to occur around 0.8-1.0 cpd while for n = 8 and 16 it seemed to shift gradually to 0.8-3.0 cpd. We interpret these results as being consistent with the possibility that spatial frequency processing by the human visual system can be defined a priori in terms of polar coordinates and discuss its application to study face perception.

Contrast sensitivity to angular frequency gratings is not higher than to Cartesian gratings

When contrast sensitivity functions to Cartesian and angular gratings were compared in previous studies the peak sensitivity to angular stimuli was reported to be 0.21 log units higher. In experiments carried out to repeat this result, we used the same two-alternative forced-choice paradigm, but improved experimental control and precision by increasing contrast resolution from 8 to 12 bits, increasing the screen refresh rate from 30 Hz interlaced to 85 Hz non-interlaced, linearizing the voltage-luminance relation, modulating luminance in frequencies that minimize pixel aliasing, and improving control of the subject's exposure to the stimuli. The contrast sensitivity functions to Cartesian and angular gratings were similar in form and peak sensitivity (2.4 cycles per visual degree (c/deg) and 32 c/360º, respectively) to those reported in a previous study (3 c/deg and 32 c/360º, respectively), but peak sensitivity to angular stimuli was 0.13 log units lower than that to Cartesian stimuli. When the experiment was repeated, this time simulating the experimental control level used in the previous study, no difference between the peak sensitivity to Cartesian and angular stimuli was found. This result agrees with most current models that assume Cartesian filtering at the first visual processing stage. The discrepancy in the results is explained in part by differences in the degree of experimental control.

Comparison of angular frequency contrast sensitivity in young and older adults

The aim of the present study was to measure contrast sensitivity curves for angular frequencies in the range between 2 and 96 cycles/360º in older human adult volunteers and to compare these measurements with the more usual contrast sensitivity functions for sine-wave gratings. All subjects were free of identifiable ocular disease and had normal acuity. We measured the contrast thresholds for young adults (N = 6; age range, 20-26 years) and older adults (N = 6; age range, 60-67 years) using the psychophysical forced-choice method. In this paradigm the volunteers had to choose the stimulus containing a test frequency at low contrast (e.g., either a sine-wave grating or an angular frequency stimulus), or another neutral stimulus at mean luminance (without any contrast). Older adults presented a loss in contrast sensitivity at high and medium angular frequencies compared to the young adults (i.e., from 8 to 96 cycles/360º). Contrary to expectation, contrast sensitivity at low angular frequencies, i.e., 2 and 4 cycles/360º, was better for the older group than for the younger group. On the other hand, contrast sensitivity for sine-wave gratings at 3 and 4 cpd was higher for young adults as expected. These results suggest age-related changes in the contrast sensitivity function for angular frequencies.

Contrast sensitivity threshold measured by sweep-visual evoked potential in term and preterm infants at 3 and 10 months of age

Although healthy preterm infants frequently seem to be more attentive to visual stimuli and to fix on them longer than full-term infants, no difference in visual acuity has been reported compared to term infants. We evaluated the contrast sensitivity (CS) function of term (N = 5) and healthy preterm (N = 11) infants at 3 and 10 months of life using sweep-visual evoked potentials. Two spatial frequencies were studied: low (0.2 cycles per degrees, cpd) and medium (4.0 cpd). The mean contrast sensitivity (expressed in percentage of contrast) of the preterm infants at 3 months was 55.4 for the low spatial frequency (0.2 cpd) and 43.4 for the medium spatial frequency (4.0 cpd). At 10 months the low spatial CS was 52.7 and the medium spatial CS was 9.9. The results for the term infants at 3 months were 55.1 for the low spatial frequency and 34.5 for the medium spatial frequency. At 10 months the equivalent values were 54.3 and 14.4, respectively. No difference was found using the Mann-Whitney rank sum T-test between term and preterm infants for the low frequency at 3 or 10 months or for the medium spatial frequency at 3 or 10 months. The development of CS for the medium spatial frequency was equally fast for term and preterm infants. As also observed for visual acuity, CS was equivalent among term and preterm infants, suggesting that visual experience does not modify the development of the primary visual pathway. An earlier development of synapses in higher cortical visual areas of preterm infants could explain the better use of visual information observed behaviorally in these infants.

Mesopic radial frequency contrast sensitivity function for young and older adults

The objective of the present study was to determine contrast sensitivity curves of concentric circular patterns with radial frequencies of 0.25, 0.5, 1.0, 2.0, and 4.0 cycles per degree in young and older adult volunteers. These parameters were also compared with sensitivity contrasts for sine-wave gratings. All participants had normal acuity vision and were free of identifiable ocular illness. Contrast sensitivity was measured in 6 young adults aged 19 to 23 years and 6 older adults aged 60 to 69 years using the psychophysical forced-choice method. In this paradigm the volunteers had to decide which of two stimuli contained the above radial frequencies at low contrast levels. The other neutral stimulus was gray with homogeneous luminance. We detected a decline in contrast sensitivity for older adults at all radial frequencies compared to young adults. Also, contrast sensitivity for sine-wave gratings at all measured frequencies was better, as predicted, for all young adults. Maximum sensitivities in the radial frequency contrast sensitivity function and contrast sensitivity function occurred at 0.25 and 0.5 cycles per degree, respectively, for both young and older adults. These results suggest age-related changes in the contrast sensitivity function for concentric symmetrical stimuli.

Mercury toxicity in the Amazon: contrast sensitivity and color discrimination of subjects exposed to mercury

We measured visual performance in achromatic and chromatic spatial tasks of mercury-exposed subjects and compared the results with norms obtained from healthy individuals of similar age. Data were obtained for a group of 28 mercury-exposed subjects, comprising 20 Amazonian gold miners, 2 inhabitants of Amazonian riverside communities, and 6 laboratory technicians, who asked for medical care. Statistical norms were generated by testing healthy control subjects divided into three age groups. The performance of a substantial proportion of the mercury-exposed subjects was below the norms in all of these tasks. Eleven of 20 subjects (55%) performed below the norms in the achromatic contrast sensitivity task. The mercury-exposed subjects also had lower red-green contrast sensitivity deficits at all tested spatial frequencies (9/11 subjects; 81%). Three gold miners and 1 riverine (4/19 subjects, 21%) performed worse than normal subjects making more mistakes in the color arrangement test. Five of 10 subjects tested (50%), comprising 2 gold miners, 2 technicians, and 1 riverine, performed worse than normal in the color discrimination test, having areas of one or more MacAdam ellipse larger than normal subjects and high color discrimination thresholds at least in one color locus. These data indicate that psychophysical assessment can be used to quantify the degree of visual impairment of mercury-exposed subjects. They also suggest that some spatial tests such as the measurement of red-green chromatic contrast are sufficiently sensitive to detect visual dysfunction caused by mercury toxicity.

Chromatic spatial contrast sensitivity estimated by visual evoked cortical potential and psychophysics

The purpose of the present study was to measure contrast sensitivity to equiluminant gratings using steady-state visual evoked cortical potential (ssVECP) and psychophysics. Six healthy volunteers were evaluated with ssVECPs and psychophysics. The visual stimuli were red-green or blue-yellow horizontal sinusoidal gratings, 5° × 5°, 34.3 cd/m2 mean luminance, presented at 6 Hz. Eight spatial frequencies from 0.2 to 8 cpd were used, each presented at 8 contrast levels. Contrast threshold was obtained by extrapolating second harmonic amplitude values to zero. Psychophysical contrast thresholds were measured using stimuli at 6 Hz and static presentation. Contrast sensitivity was calculated as the inverse function of the pooled cone contrast threshold. ssVECP and both psychophysical contrast sensitivity functions (CSFs) were low-pass functions for red-green gratings. For electrophysiology, the highest contrast sensitivity values were found at 0.4 cpd (1.95 ± 0.15). ssVECP CSF was similar to dynamic psychophysical CSF, while static CSF had higher values ranging from 0.4 to 6 cpd (P < 0.05, ANOVA). Blue-yellow chromatic functions showed no specific tuning shape; however, at high spatial frequencies the evoked potentials showed higher contrast sensitivity than the psychophysical methods (P < 0.05, ANOVA). Evoked potentials can be used reliably to evaluate chromatic red-green CSFs in agreement with psychophysical thresholds, mainly if the same temporal properties are applied to the stimulus. For blue-yellow CSF, correlation between electrophysiology and psychophysics was poor at high spatial frequency, possibly due to a greater effect of chromatic aberration on this kind of stimulus.