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The effect of optical blur (defocus) on edge contrast sensitivity was studied. Edge contrast sensitivity detoriates with fairly small amounts of blur (approximately 0.5 D) and is roughly reduced by half for each dioptre of blur. The effect of blur on edge contrast sensitivity equals the effect of blur on sine wave contrast sensitivity for a spatial frequency of approximately 3 cpd.
PURPOSE: To compare the effects on contrast sensitivity of wave front-guided (WFG) versus standard LASIK. DESIGN: Prospective, nonrandomized, comparative clinical study. PARTICIPANTS: Twenty-four eyes of 13 consecutive patients (mean age, 25.2+/-8.4 years; spherical equivalent, -0.5 to -4.25 diopters [D]) treated with WFG LASIK (WaveLight-Allegretto scanning-spot laser and wave front analyzer) and 22 eyes of 12 consecutive patients (mean age, 28.4+/-9.1 years; spherical equivalent, -0.75 to -4.5 D) treated with standard LASIK (WaveLight-Allegretto scanning-spot laser). METHODS: Best-corrected contrast sensitivity was measured before and 1 month after surgery in both the WFG LASIK group and the standard LASIK group. A sine-wave contrast sensitivity test (functional acuity contrast test) was used to measure contrast sensitivity at 5 spatial frequencies (1.5, 3, 6, 12, and 18 cycles/degree). We compared the LASIK-induced changes in contrast sensitivity in each groups at each spatial frequency. MAIN OUTCOME MEASURE: The effect on contrast sensitivity of WFG LASIK versus standard LASIK. RESULTS: Uncorrected visual acuity of 20/20 or better was achieved by 72% of eyes treated with WFG LASIK and by 70% of the eyes treated with standard LASIK. One month after LASIK, 88% of the contrast sensitivity measurements improved in the WFG LASIK group, whereas in the standard LASIK group, only 40% of the contrast sensitivity measurements improved. The contrast sensitivity improvement was significantly larger in the WFG LASIK group at all spatial frequencies (P<0.05). The WFG LASIK patients had a negative correlation between the changes in contrast sensitivity and the preoperative refractive error. CONCLUSIONS: The ability of WFG LASIK to correct optical aberrations results in significantly improved contrast sensitivity compared with standard LASIK 1 month after surgery.
PURPOSE: To evaluate contrast sensitivity under mesopic conditions in patients who had undergone uncomplicated excimer laser photorefractive keratectomy (PRK) for myopia. METHODS: Monocular contrast sensitivity function was measured with the Stereo Optical F.A.C.T. chart in 26 patients who had received PRK using the Nidek EC-5000 excimer laser system. Mean preoperative refractive error was -6.23 +/- 1.69 D (range, -4.00 to -8.25 D); postoperatively, mean refractive error was -0.36 +/- 0.58 D (range, -0.75 to +0.50 D). Contrast sensitivity function was measured 6 months after surgery using four different chart luminances: 85, 5.0, 2.5, and 0.1 cd/m2, the first being a photopic level and the rest mesopic. A control group of eight emmetropic subjects was also studied to allow comparison of results for statistical purposes. RESULTS: Logarithmic values of contrast sensitivity at each spatial frequency were used for statistical analysis and normalized values were used for graphical representation. The results showed a statistically significant reduction (P < .01) in contrast sensitivity for the PRK patients in comparison with the control group under mesopic conditions for each spatial frequency tested (1.5, 3, 6, 12, and 18 c/deg), although no significant contrast sensitivity differences were observed between PRK and control groups at the photopic (85 cd/m2) level (P > .01 for all frequencies). CONCLUSION: Photorefractive keratectomy can induce significant reductions in contrast sensitivity under mesopic conditions, even though the photopic contrast sensitivity function is normal.
Contrast sensitivity for moving and stationary sine grating patterns was determined in central and peripheral parts of the visual field. The method was primarily developed as a possible screening procedure for visual defects in glaucoma. Contrast sensitivity to moving patterns seemed maximal both in central and in 10 degrees of eccentric viewing for square wave reversals of temporal frequencies 0.5-5 Hz. We selected 2Hz for the clinical procedure. Further, we have determined normal central and peripheral contrast sensitivity in 10 subjects 61-71 years-old, to serve as a basis for the glaucoma studies. We used this age group since glaucoma mainly affects elderly people. We confirmed that contrast sensitivity was higher for dynamic than for static presentation of gratings of low spatial frequencies (below 1 c/d) both centrally and peripherally. For patterns of medium or high spatial frequencies, dynamic and static stimuli were equally detectable. The absolute level of contrast sensitivity was higher centrally than peripherally in the interval 0.3-4 c/d. The lower visual hemifield exhibited greater sensitivity, for both static and dynamic gratings, than the upper one.
Contrast sensitivities were determined for sinusoidal gratings of varying spatial frequencies with and without the presence of a random noise pattern superimposed on the gratings. Control subjects with normal binocular vision and observers with amblyopia were tested to determine the relative effects of noise on contrast sensitivity. For both amblyopes and normal subjects, contrast sensitivities are reduced by the presence of noise. Effects are maximal at 4 cycles/degree and are minimal at low and high spatial frequencies. Dichoptic presentation of noise and gratings to opposite eyes is equivalent to monoptic results for both amblyopes and normal subjects. Masking effects are eliminated if gratings are drifted while noise patterns are static. The contrast sensitivity of amblyopes is reduced by relatively similar amounts to that of normal subjects when noise is added to the stimulus. Overall, masking effects are virtually identical for amblyopes and for subjects with normal binocular vision.
PURPOSE: To evaluate the age-related change in contrast sensitivity seen in a middle-aged to elderly Japanese population. METHODS: Contrast sensitivity and visual acuity were measured in subjects aged 40 to 79 years randomly recruited from a community in Aichi prefecture near Nagoya, Japan. Contrast sensitivity tests were performed using the Vistech contrast sensitivity test chart (VCTS 6500). The results were statistically analyzed relative to age. RESULTS: A statistically significant decrease in contrast sensitivity was seen with advancing age at each spatial frequency (Cochran-Mantel-Haenszel: P<.001). This trend was detected even when the subjects were limited to only those having a corrected visual acuity of 1.0 or better (Cochran-Mantel-Haenszel: P<.001). Overall, 9.4% of the eyes with good visual acuity had poor contrast sensitivity at a high spatial frequency, while in the 70-79-year-old group, the percentage with poor contrast sensitivity reached 21.1%. CONCLUSIONS: The age-related decrease in contrast sensitivity was confirmed at all frequencies in our population, even when adjusted for visual acuity. Our results suggest that contrast sensitivity tests, especially at high frequencies, assess aspects of visual function that cannot be determined in the elderly population from visual acuity tests alone.
PURPOSE: To study the effect of posterior chamber intraocular lenses and aphakic spectacles on contrast sensitivity. METHODS: Contrast sensitivity was evaluated in 20 patients in each group of pseudophakics with post chamber IOL (group I), aphakics with spectacle correction (group II), and age and sex-matched normal subjects (group III) using the Pelli-Robson chart. RESULTS: The mean values of log contrast sensitivity in pseudophakics (1.665+/-0.105) and aphakes with spectacle correction (1.5075+/-0.1) were found to be statistically significantly low (t: 5.186, p < 0.001; t: 11.302, p < 0.001, respectively) as compared to the mean value of normal phakic subjects (1.8075+/-0.0576). Further, mean values of log contrast sensitivity in aphakes with spectacles correction were also found to be statistically significantly low (t: 4.727, p < 0.001) when compared to that in pseudophakes. CONCLUSION: From observations of the present study, it can be concluded that posterior chamber IOL implantation offers an added advantage of higher contrast sensitivity, over and above the well documented advantages of increased field of vision, negligible effect on image size and elimination of prismatic effect and spherical aberration of thick glasses.
Contrast sensitivity and grating acuity were measured using the sweep VEP method in a group of 48 infants from 2 to 40 weeks of age and in a group of 10 adults. Sinusoidal gratings were reversed in contrast at 12 alternations per sec at a space-average luminance of 220 cd/m2. During 10 sec trials, either the contrast or the spatial frequency was increased in a series of 19 steps. Thresholds were estimated by extrapolation of the VEP response functions to zero amplitude. The contrast threshold at low spatial frequencies developed rapidly from 7% contrast at 2-3 weeks to an asymptote of 0.5% at 9 weeks. For adults, maximum sensitivity at low spatial frequencies was 0.32-0.22%. The sweep VEP estimate of grating acuity showed a gradual increase in spatial frequency with age, starting at 5 c/deg during the first month and reaching 16.3 c/deg at 8 months. The mean adult acuity was 31.9 c/deg. There appeared to be two phases in the development of contrast sensitivity and acuity. Between 4 and 9 weeks overall contrast sensitivity increased by a factor of 4-5 at all spatial frequencies. Beyond 9 weeks, contrast sensitivity at low spatial frequencies remained constant, while sensitivity increased systematically at higher spatial frequencies.
Contrast sensitivity functions were measured with five light filters and without a filter, in the presence of a glare source, in 12 retinal degeneration subjects and 9 normal subjects. The light filters included yellow-tinted, CPF 527, NoIR 111, 0.6 neutral density and sunglasses with a 95% UV filter. Retinal degeneration subjects showed a mild improvement in contrast sensitivity at the higher spatial frequencies and maintained mean log contrast sensitivity with light filters which reduced photopic light transmission up to 75%. Normal subjects exhibited a systematic decrease of contrast sensitivity at higher spatial frequencies with all light filters and overall mean log contrast sensitivity was significantly correlated (r = 0.86, P < 0.025) with photopic light transmission of the filters. It is concluded that, when in the presence of a glare source, the benefits of certain light filters to retinal degeneration subjects is related to the reduction of overall photopic luminance.
I measured contrast sensitivity and glare in 51 cataract patients who had Snellen visual acuities of 20/60 or better. The VCTS contrast sensitivity plates, the Miller-Nadler glare tester, Baylor visual function tester, and the Stereo Optical glare tester were used. Patients indicated that the Baylor visual function tester most closely reproduced their daytime glare symptoms and that the Stereo Optical glare tester most closely reproduced their nighttime glare symptoms. Scores on the Stereo Optical glare tester and VCTS contrast sensitivity chart statistically were most strongly correlated with patients' complaints and the severity of their lens opacities. Contrast sensitivity and glare testing are important adjuncts in evaluating patients who have visual complaints and yet have good Snellen acuities.
Contrast sensitivity is a useful measure of the ability of an observer to distinguish contrast signals from noise. Although usually applied to human observers, contrast sensitivity can also be defined operationally for individual visual neurons. In a model linear neuron consisting of a filter and noise source, this operational measure is a function of filter gain, noise power spectrum, signal duration, and a performance criterion. This definition allows one to relate the sensitivities of linear neurons at different levels in the visual pathway. Mathematical formulae describing these relationships are derived, and the general model is applied to the specific problem of relating the sensitivities of parvocellular LGN neurons and cortical simple cells in the primate.
Contrast sensitivity testing is a powerful tool for determining the capability of the visual system to process spatial and temporal information about the everyday objects we see. The current gold standard in the assessment of vision, visual acuity, provides only a limited amount of information, obtained under artificial conditions. Contrast sensitivity testing measures a range of visual performance under real-life conditions. It measures the least amount of contrast needed to detect a visual stimulus and gives us a more complete quantitization of patients' visual capabilities. Many instances in which losses in contrast sensitivity were detected when visual acuity (one point on the contrast sensitivity function) was normal have been reported. These include amblyopia, neuro-ophthalmology, retina, anterior segment disease, and glaucoma. Therefore, contrast sensitivity testing enables the clinician to diagnose selective deficits in visual processing at an earlier stage than is possible with conventional testing methods.
We measured the contrast sensitivity function in a 16-year-old boy with cystic fibrosis, before and during vitamin A supplementation. Before vitamin A supplementation, serum levels of vitamin A were abnormally low, the electroretinogram was reduced, and contrast sensitivity was abnormally low at all spatial frequencies. During vitamin A supplementation (25,000 IU/day), serum levels of vitamin A became low normal, the electroretinogram returned to normal, and the overall contrast sensitivity function improved by 94%. We propose that the contrast sensitivity function may be abnormal in patients with cystic fibrosis who have reduced retinal function secondary to vitamin A deficiency.
Contrast sensitivity in 64 patients aged from 50 to 69 years with an intraocular lens (IOL) was studied. There were 23 eyes with a silicone and 31 eyes with a polymethylmethacrylate (PMMA) IOL. Ten patients had a silicone IOL in one eye and a PMMA IOL in the other. Contrast sensitivity was examined with the Vistech far vision VCTS 6500 test. The contrast sensitivity test results in silicone and PMMA IOL eyes were in all cpd (cycles per degree) lines significantly worse than in normal eyes except in the 60-year-old group in the 18-cpd line. The contrast sensitivity test results were in all cpd lines better in the silicone IOL eyes than in the PMMA IOL eyes, but it reached significantly only in the 3-cpd line. In the 10 patients with the silicone lens in one and the PMMA lens in the other eye, the test results were also better in the silicone IOL eye; it also reached significance only in the 3-cpd line.
Temporal contrast sensitivity was measured in 1.5- and 3-month-old infants using the FPL procedure. Stimuli were 0.1 c/deg counterphase-flickering sinewave gratings. Temporal rates ranged from 1 to 20 Hz. Because the spatial sinewave underwent phase shifts of 180 degrees, the target could not be seen unless the observer was able to resolve it temporally. Adults were tested with the same temporal stimuli using a 2-alternative forced-choice procedure and a spatial frequency of 0.5 c/deg. Adult temporal CSFs were bandpass with peak sensitivity at 10 Hz. Infant temporal CSFs were lowpass at 1.5 months and bandpass at 3 months. The infants' contrast sensitivity was over a log-unit lower than adults'. Unlike spatial CSFs, infant sensitivity was closest to adult sensitivity at the highest flicker rate.
PURPOSE: To study the utility of measurements of contrast sensitivity at different spatial frequencies as an index of visual recovery following refractive surgery. METHODS: Contrast sensitivity at 1.5, 3, 6, 12, and 18 c/deg was measured with the Stereo Optical FACT chart in 20 patients after photorefractive keratectomy (PRK) using the Nidek EC-5000 excimer laser system, and in 18 patients following laser in situ keratomileusis (LASIK). Contrast sensitivity was measured preoperatively and 1, 3, 6, and 12 months after surgery. RESULTS: Results showed a statistically significant reduction (P<.01) in contrast sensitivity at all spatial frequencies in PRK patients during the first and third month, but contrast sensitivity recovered to preoperative values by 6 months after surgery (P>.1). In LASIK patients, decreased contrast sensitivity values 1 month after surgery were also obtained at all spatial frequencies. After 3 months, contrast sensitivity at 1.5 and 3 c/deg had recovered and did not differ significantly from preoperative values (P>.1), although contrast sensitivity at other frequencies remained reduced (P<.01). At 6 and 12 months, contrast sensitivity at all spatial frequencies did not differ from that obtained preoperatively (P>.1). CONCLUSIONS: Contrast sensitivity measurements at 6 and 12 c/deg appear to be most useful in the assessment of patients who have undergone laser refractive surgery because defocus and optical aberrations primarily affect the higher spatial frequencies.
PURPOSE: The exponential increase of patients having refractive surgery has increased the number of patients with night vision disturbances, such as decreased contrast sensitivity. However, there are no standard contrast sensitivity scales in normal persons in the mesopic range. We describe Pelli-Robson contrast sensitivity under photopic and mesopic luminance conditions in a large Spanish population over a wide range of age groups to provide normal values. A further aim was to evaluate the effect of photopic visual acuity on photopic and mesopic contrast sensitivity. METHODS: A cross-sectional study was performed on 292 participants stratified by age into six groups. Binocular contrast sensitivity was determined with best spectacle correction using the Pelli-Robson letter chart at 1 m under photopic (85 cd/m2) and mesopic (0.15 cd/m2) luminance conditions. RESULTS: Phototopic letter contrast sensitivity began to decrease gradually from the 61 to 70-year-old age group onward, and for mesopic conditions, from the 51 to 60-year-old age group onward. The reduction in mean contrast sensitivity between the oldest and the youngest age groups was 0.20 log units (photopic) and 0.33 log units (mesopic). Loss in contrast sensitivity due to luminance (two successive triplets) increased slightly with age. Both photopic and mesopic letter contrast sensitivity significantly improved as photopic visual acuity increased. CONCLUSIONS: Under mesopic conditions, Pelli-Robson contrast sensitivity began to decline 1 decade earlier than under photopic conditions and was affected by visual acuity. Normal values for mesopic contrast sensitivity could be of help in deciding whether mesopic function is normal or a decrease in contrast sensitivity is pathologic in nature.
OBJECTIVE: Contrast sensitivity involves distinguishing threshold luminance differences and is usually assessed using static sine-wave gratings over a range of different spatial frequencies. The purpose of this study was to determine the effects of various levels of acute alcohol intoxication on contrast sensitivity to stationary and moving sine-wave gratings. Moving gratings required the subjects to make pursuit eye movements. A secondary goal was to investigate whether any alcohol-related effects were associated with any measures of intoxication. METHOD: Male volunteers (N = 8) participated in three counterbalanced, double-blind, testing sessions (low alcohol, moderate alcohol and placebo) plus a control session with no beverage. Breath alcohol concentration and two subjective measures of intoxication were measured for each subject. Static and dynamic contrast sensitivity were determined for electronically generated sine-wave gratings that were either stationary or traveled in a circular path with a diameter of 9 cm (3.7 degrees) at 51.7 rpm, thus requiring the subject to make smooth pursuit eye movements. RESULTS: The mean blood alcohol concentration measured in the moderate alcohol condition was 0.043% and in the low alcohol condition 0.011%. Moderate dose alcohol consumption significantly impaired both static and dynamic contrast with a greater effect for moving targets. CONCLUSIONS: Objective and subjective measures of intoxication were unrelated to the alcohol-related losses in contrast sensitivity. Although most states currently prohibit driving with BACs of 0.08-0.10%, the present data indicate reliable visual impairment at approximately half of that level (.44%).