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PubMed2000

Measuring contrast sensitivity with inappropriate optical correction.

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.

Adult↗
PubMed1984

Spatial and temporal contrast sensitivities of neurones in lateral geniculate nucleus of macaque.

The discharges of single neurones in the parvocellular and magnocellular laminae of the macaque's lateral geniculate nucleus (l.g.n.) were recorded with glass-insulated tungsten micro-electrodes. Linearity of spatial summation was examined using the test devised by Hochstein & Shapley (1976). 2 of 272 parvocellular units and 6 of 105 magnocellular units showed clearly non-linear spatial summation. A quantitative index of non-linearity did not suggest the existence of a distinct 'non-linear' class of magnocellular unit. Spatial contrast sensitivity to moving gratings was measured by a tracking procedure in which contrast was adjusted to elicit a reliable modulation of discharge. With the exception of cells that were driven by blue-sensitive cones, measurements of contrast sensitivity did not reveal distinct subgroups of parvocellular units. All had low sensitivity, and those with receptive fields in the fovea could resolve spatial frequencies of up to 40 cycles deg-1. Magnocellular units had substantially higher sensitivity, but poorer spatial resolution. The higher sensitivities of magnocellular units led to their giving saturated responses to stimuli of high contrast. Responses of parvocellular units were rarely saturated by any stimulus. At any one eccentricity the receptive fields of parvocellular units had smaller centres than did those of magnocellular units. Receptive fields of magnocellular units driven by the ipsilateral eye had larger receptive fields than did those driven by the contralateral eye. Parvocellular units were most sensitive to stimuli modulated at temporal frequencies close to 10 Hz; magnocellular units to stimuli modulated at frequencies nearer 20 Hz. The loss of sensitivity as temporal frequency fell below optimum was more marked in magnocellular than parvocellular units. Changes in temporal frequency altered the shapes of the spatial contrast sensitivity curves of both parvocellular and magnocellular units. These changes could be explained by supposing that centre and surround have different temporal properties, and that the surround is relatively less sensitive to higher temporal frequencies.

Action Potentials↗
PubMed1999

Computerized method to measure glare and contrast sensitivity in cataract patients.

PURPOSE: To evaluate computerized methods for measuring glare sensitivity and visual acuity at 3 contrast levels in cataract patients. SETTING: St. Erik's Eye Hospital, Stockholm, Sweden. METHODS: In a prospective study, 25 consecutive cataract patients meeting the inclusion criteria were examined before and 12 weeks after cataract surgery. Measured were glare sensitivity and visual acuity at 3 contrast levels using the Opthimus Y-VA Contrast Sensitivity Test and Glare Test. RESULTS: Preoperatively, all patients had impaired values compared with those in a group of age-matched normal volunteers (control group). Postoperatively, median values were similar to those in the age-matched control group in all parameters except glare sensitivity, which was significantly higher in the pseudophakic group (P = .03). Correlation coefficients between preoperative visual acuity and contrast sensitivity at 90%, 25%, and 10% were 0.50 (P = .01), 0.53 (P = .006), and 0.45 (P = .02), respectively, and between preoperative visual acuity and preoperative glare difference, 0.45 (P = .02). A significant correlation was found between age and visual acuity in the control group at all contrast levels: 90% (r = 0.61, P = .0018), 25% (r = 0.52, P = .01), and 10% (r = 0.42, P = .04). Median differences between Y-VA examinations (repeatability) were 0 LogMAR except between examinations 1 and 2 at the 25% contrast level, where it was 0.3 LogMAR. CONCLUSION: The Ophthimus Y-VA Test and Glare Test were useful in the preoperative evaluation of patients with cataract and mild to moderate visual impairment.

Adult↗
PubMed2002

Covert attention affects the psychometric function of contrast sensitivity.

We examined the effect of transient covert attention on the psychometric function for contrast sensitivity in an orientation discrimination task when the target was presented alone in the absence of distracters and visual masks. Transient covert attention decreased both the threshold (consistent with a contrast gain mechanism) and, less consistently, the slope of the psychometric function. We assessed performance at 8 equidistant locations (4.5 degrees eccentricity) and found that threshold and slope depended on target location-both were higher on the vertical than the horizontal meridian, particularly directly above fixation. All effects were robust across a range of spatial frequencies, and the visual field asymmetries increased with spatial frequency. Notwithstanding the dependence of the psychometric function on target location, attention improved performance to a similar extent across the visual field.Given that, in this study, we excluded all sources of external noise, and that we showed experimentally that spatial uncertainty cannot explain the present results, we conclude that the observed attentional benefit is consistent with signal enhancement.

Adult↗
PubMed1980

The contrast sensitivity of cat retinal ganglion cells at reduced oxygen tensions.

1. These experiments were done to investigate the effect of various degrees of hypoxia on the function of retinal ganglion cells (recorded in the optic tract) and on retinal oxygen tension. 2. The contrast sensitivity of the centre of X and Y cells, the surround of X cells and the non-linear subunits of Y cells were measured separately by choosing appropriate spatial and temporal parameters of a sinusoidal grating pattern. 3. Retinal oxygen tension was measured with a bipolar polarographic oxygen electrode positioned in the vitreous humor close to the retina. 4. The time course of changes in ganglion cell sensitivity and retinal oxygen tension was similar. However, oxygen tension frequently overshot the prehypoxic value at the end of hypoxia, while sensitivity did not. 5. The cat retina was rather resistant to hypoxia. Contrast sensitivity and mean firing rate did not change provided the arterial oxygen tension was above about 35 mmHg, but usually dropped precipitously at lower arterial values. 6. The apparent reason for this resistance is that retinal oxygen tension was well regulated, falling only 0.14 mmHg per mmHg of arterial oxygen tension for arterial values above about 35 mmHg, which corresponds to a retinal oxygen tension of about 10 mmHg. Retinal oxygen tension decreased more sharply (0.62 mmHg per mmHg) at lower values of arterial oxygen tension, where sensitivity also decreased. 7. The centre, surround and subunits reacted similarly to hypoxia. This suggests that lateral pathways (i.e. surround) and pathways which might be expected to use more synapses than the centre (i.e. surround and subunits) are not more susceptible to hypoxia.

Action Potentials↗
PubMed1990

VISTECH contrast sensitivity and pattern-VEP in multiple sclerosis patients.

In 12 known multiple sclerosis patients with a visual acuity of 7/10 or better in both eyes, optic nerve function was tested by means of contrast sensitivity measurement (VISTECH technique) and pattern-VEP. The results were compared with those of an age related control group. The VISTECH contrast sensitivity measurement is a useful tool in evaluating the remaining visual discomfort after the resolution of an optic neuritis. However, to detect a subclinical optic neuritis, the pattern-VEP is more sensitive.

Adult↗
PubMed1980

Contrast sensitivity in the presence of a glare light. Theoretical concepts and preliminary clinical studies.

A method is presented for quantitative measurements of the glare effect of light scattered in the ocular media. The contrast sensitivity function is measured with a television display system. A bright light source is introduced into the field of vision, and the resultant decrease in contrast sensitivity is mea-ured. It is further used to calculate a scattering factor which is a direct measure of the intraocular light scattering. The scattering factor shows a marked increase in patients with early cataracts even if their visual acuity is not affected.

Adult↗
PubMed2001

[Effect of latanoprost on ocular hemodynamics and contrast sensitivity].

BACKGROUND: Latanoprost effectively lowers intraocular pressure. Because ischemia has gained increasing importance in the pathogenesis of glaucoma, an antiglaucomatous drug should also be investigated with regard to the influence on ocular hemodynamics. METHODS: In a double masked, randomized, clinical trial, Latanoprost eye drops were administered to 15 volunteers once daily for 8 days and 15 further volunteers received placebo eye drops according to the same protocol. IOP, blood pressure, heart rate, ocular pulse amplitudes, pulse volume, pulsatile ocular blood flow and contrast sensitivity were measured before (1T0), 120 min after drop administration (1T120), after 7 days of therapy (8T0) and again 120 min after an acute administration (8T120). For statistical analysis a two-way variance-analysis and the t-test for paired samples were used. RESULTS: IOP was found to be statistically significantly different comparing both groups over the test period (p = 0.036). In Latanoprost-treated subjects the t-test revealed a significant drop in IOP between 1T0 and 8T0 (p = 0.009) and between 1T0 and 8T120 (p < 0.0001). All other above mentioned parameters remained constant. CONCLUSION: In Latanoprost-treated subjects, a significant drop in intraocular pressure was observed after 1 week. However, ocular perfusion and contrast sensitivity did not change during therapy. This might be due to an effective autoregulation in healthy volunteers.

Adult↗
PubMed2006

[Correction and induction of high-order aberrations after standard and wavefront-guided LASIK and their influence on the postoperative contrast sensitivity].

BACKGROUND: Wavefront-guided LASIK-treatments should reduce high-order aberrations (HOA). However, both the microkeratome cut as well as the ablation itself induce HOA. The purpose of this study was to investigate the amount of corrected preoperative measured HOA and induction of new HOA. METHODS: In this retrospective study 67 eyes of 45 myopic patients (- 2 to - 8.1 D SE; spherical equivalent) were treated by standard and wavefront-guided LASIK (Keracor 217z). Pre- and postoperative measurements of total aberrations and contrast sensitivity were performed. The follow-up time was 5.7 +/- 0.9 months. RESULTS: Patients with preoperative increased aberrations of 3rd and 4th order and myopia up to 5 D showed a slightly reduction of wavefront deformation. Cases of higher myopic corrections and lower preoperative spherical aberrations developed an increase of spherical aberrations after LASIK. The changes of other HOA showed no correlation with the amount of corrected myopia. Up to - 5 D patients showed the trend to better postoperative contrast sensitivity under 3 and 85 cd/m (2) after wavefront-guided LASIK than after standard LASIK. A significant advantage of wavefront-guided LASIK can be detected under a spatial frequency of 3 CPD (cycles per degree) and 85 cd/m (2). No advantages of any treatment procedure were shown after higher myopic corrections. CONCLUSION: If preoperative aberrations of 3rd and 4th order were increased and the myopia is < 5 D (SE) -- wavefront-guided LASIK can reduce total ocular HOA. Aberrometric findings after wavefront-guided LASIK in patients with lower preoperative HOA and myopia > 5 D (SE) are comparable with the results after standard treatment.

Contrast Sensitivity↗
PubMed2005

[Frankfurt-Freiburg Contrast and Acuity Test System (FF-CATS). A new test to determine contrast sensitivity under variable ambient and glare luminance levels].

BACKGROUND: The purpose of the present study was to evaluate a computerized test for measurement of contrast sensitivity thresholds under variable ambient and glare luminance levels. METHODS: A total of 40 eyes of 40 healthy subjects were examined with the FF-CATS and the Functional Acuity Contrast Test (FACT) at 0.167 cd/m(-2) (mesopic) and 167 cd/m(-2) (photopic). Measurements were performed twice with and without glare in a randomized fashion. Tests were evaluated according to three criteria: (1) repeatability, (2) discriminative ability, and (3) validity. RESULTS: The FF-CATS showed a higher discriminative ability between the two groups compared to the FACT charts. Under photopic conditions, the COR value was 0.39 for the FF-CATS and 0.26 for the FACT charts; under mesopic illumination, the COR value for the FF-CATS was 0.46 and 0.36 for the FACT charts. CONCLUSION: The FF-CATS is a reliable, sensitive, valid, and flexible test system for the determination of visual acuity and contrast sensitivity thresholds under variable ambient and glare luminance conditions.

Adult↗
PubMed2000

Ocular haemodynamics and colour contrast sensitivity in patients with type 1 diabetes.

BACKGROUND: There is evidence that altered ocular blood flow is involved in the development and progression of diabetic retinopathy. However, the nature of these perfusion abnormalities is still a matter of controversy. Ocular haemodynamics were characterised with two recently introduced methods. METHODS: The cross sectional study was performed in 59 patients with type 1 diabetes with a diabetes duration between 12 and 17 years and an age less than 32 years and a group of 25 age matched healthy controls. Scanning laser Doppler flowmetry and laser interferometric measurement of fundus pulsation amplitude were used to assess retinal and pulsatile choroidal blood flow, respectively. In addition, colour contrast sensitivity along the tritan axis was determined. RESULTS: Fundus pulsation amplitude, but not retinal blood flow, increased with the progression of diabetic retinopathy. Retinal blood flow was influenced by plasma glucose levels (r = 0.32), whereas fundus pulsation amplitude was associated with HbA(1c) (r = 0.30). In addition, a negative correlation between the colour contrast sensitivity along the tritan axis and retinal blood flow was observed. CONCLUSIONS: The present study indicates that pulsatile choroidal blood flow increases with the progression of diabetic retinopathy. Increased retinal blood flow appears to be related to loss of colour sensitivity in patents with type 1 diabetes.

Adolescent↗
PubMed1978

Acuity and contrast sensitivity in 1-, 2-, and 3-month-old human infants.

The importance of assessing infant visual function is indicated by recent demonstrations that early visual experience in part determines the eventual state of adult visual function. It is argued that the contrast sensitivity function (CSF) could be a valuable index in the assessment of infant vision because it provides information concerning several aspects of vision. CSF's were measured in 1-, 2-, and 3-month-old infants. The "cut-off" spatial frequencies, which are estimates of visual acuity, were 2.4 cy/deg for 1-month-olds, 2.8 cy/deg for 2-month-olds, and 4.0 cy/deg for 3-month-olds. Sensitivity to contrast was shown to increase between 1 and 3 months of age. The CSF's measured also provide evidence for the presence of a low-frequency fall-off at 2 and 3 months.

Age Factors↗
PubMed2003

Letter contrast sensitivity changes in early diabetic retinopathy.

PURPOSE: To investigate the discriminative ability of letter contrast sensitivity (CS) and visual acuity (VA) in detecting functional losses in participants with type 2 diabetes. METHODS: LogMAR VA and letter CS were measured on 20 type 2 diabetic and 24 age-matched control participants. The diabetic participants were sub-grouped according to the level of retinopathy present. RESULTS: Letter CS was able to distinguish those participants with and without macular oedema and those with no or minimal diabetic retinopathy from the control group, whereas VA was not. CONCLUSION: Letter CS may be used as an effective screening tool to assess damage to the visual pathway of diabetic participants both with and without clinically detectable signs.

Adult↗
PubMed1984

The effects of field size and luminance on contrast sensitivity differences between specifically reading disabled and normal children.

Contrast sensitivity functions were measured for normal and specifically disabled readers in experiments which varied either field size or luminance level. The nature of the differences between groups was unaffected by field size, implying that spatial summation in specifically disabled readers is normal. Increasing luminance, however, increased the range over which disabled readers are less sensitive than normal readers. The results are discussed in terms of possible differences in underlying mechanisms.

Animals↗
PubMed1983

Evoked potential contrast sensitivity in the parafovea: spatial organization.

Visual evoked potential contrast sensitivity functions (VEP/CSFs) were determined for counterphase flickered sine-wave gratings in circular fields up to 8 degrees in diameter centered on the fovea. VEP sources responding to 16 c/deg gratings appeared to be concentrated in the central 2 degrees of the visual field while sources responding to lower spatial frequencies appeared to be distributed over progressively wider areas of the visual field as spatial frequency decreased. It was also found that independently determined VEP/CSFs for non-overlapping annular regions of the visual field centered on the fovea summed to equal the VEP/CSF obtained when both regions were stimulated simultaneously.

Evoked Potentials, Visual↗
PubMed1988

[How good are the correlations between contrast sensitivity and differential light sensitivity in the visual field center in optic neuropathies?].

Contrast sensitivity (CS) and differential light sensitivity (LUE) tend to deteriorate with increasing severity of the neuropathy. However, the correlation between the two psychophysical functions is low for the total number of optic neuropathies as well as for groups with different visual acuities. This fact is mainly explained by the range of scatter in LUE values. Moreover, visual acuity is much better correlated with CS than with LUE. CS and LUE represent different visual functions that may be processed by separate neural structures.

Adult↗
PubMed1994

A theoretical model to predict contrast sensitivity with bifocal intraocular lenses.

Bifocal intraocular lenses (BIOLs) cause a reduction in image contrast. However, the clinically measurable reduction is much lower than that predicted by experimental results. We therefore compared monofocal IOLs, the True Vista BIOL, and the diffractive BIOL. We measured the modulation transfer function (MTF) of all IOLs in a model eye. Clinically, we determined the contrast sensitivity (CS). For a comparison of the results, the MTF was converted into the theoretical CS of the eye using the age-corrected values of retinal CS. The calculated CS of the BIOLs was similar to the values measured clinically. However, the calculated CS of monofocal IOLs was considerably higher than the clinical values. This difference should be due to the MTF of the normal eye; the MTF of monofocal IOLs was considerably higher than that of the normal eye, whereas the MTF of the BIOLs was lower. Thus, the MTF of the normal eye becomes the limiting factor of this system. The proposed model takes into account the retinal CS and the MTF of the normal eye. Using the MTF of an IOL, the clinical CS can be calculated, and the clinical performance of new IOL designs may be predicted before clinical trials commence.

Adult↗