Monocular Contrast Sensitivity Research Articles

Contrast sensitivity through hybrid diffractive, Fresnel, and refractive prisms

Fresnel and wedge-shaped refractive prisms are used diagnostically and therapeutically in clinical practice. This article extends the study on the effect of prisms on visual acuity to the effect on contrast sensitivity by membrane Fresnel (F), refractive (R), and newly designed hybrid diffractive (C) prisms (ComPrisms), which combine a wedge-shaped refractive prism with a diffractive element. Vistech contrast sensitivity function (CSF) Charts A, B, and C were used to measure the monocular and binocular contrast sensitivity of 21 and 20 subjects, respectively. CSF was measured without prisms (U), through the hybrid diffractive prisms, membrane Fresnel prisms, and acrylic refractive prisms in powers of 20delta, 30delta, and 40delta. Repeated measures analysis of variance calculations resulted in significant main effects in contrast sensitivity across prism types, prism powers, and between monocular and binocular measurements. Results of the Scheffé test for all possible contrast sensitivity comparisons between spatial frequencies are provided. It was found that as prism power increased from 20delta to 40delta, the rate of reduction in area under the CSF curve of ComPrisms became half that of the refractive and Fresnel prisms. Although all three prism types reduced contrast sensitivity with respect to the unaided condition, the ComPrisms at all powers provided significantly better contrast sensitivity than the refractive or Fresnel prisms of equivalent power. Significant binocular summations in contrast sensitivity were found without prisms and across all prism types and powers.

Induced aniseikonia diminishes binocular contrast sensitivity and binocular summation.

To study the effect on binocular contrast sensitivity and binocular summation of aniseikonia induced by size (afocal) lenses. In 18 young emmetropic observers, the monocular and binocular contrast sensitivity function was measured under normal conditions and after inducing different degrees of aniseikonia (2%, 3%, and 5% and for 6 observers, 8%) in the right eye. The spatial frequencies tested were 2.4, 3.7, 6.0, 9.2, 12, 15, 20, and 24 cpd. The results reveal a significant decline in binocular contrast sensitivity and binocular summation for 5% aniseikonia, this decline being more pronounced for intermediate and high spatial frequencies. These results, together with others on different binocular functions, show the importance of aniseikonia in binocular vision. On this basis, we recommend that aniseikonia be considered in surgical processes such as cataract and refractive surgery, whereby aniseikonia could be induced and binocular performance subsequently diminished.

Visual performance with multifocal intraocular lenses: Mesopic contrast sensitivity under distance and near conditions

Objective To evaluate distance and near visual performance under bright (photopic) and dim (mesopic) conditions in patients who had undergone uncomplicated cataract extraction with multifocal or monofocal intraocular lens (IOL) implantation. Design Prospective, nonrandomized, masked, comparative, observational case series. Participants Thirty-two eyes of 32 patients after zonal-progressive multifocal IOL implantation (Allergan Medical Optics Array SA-40N) and 32 eyes of 32 age-matched patients after monofocal IOL implantation (Allergan Medical Optics SI-40NB). Intervention All eyes underwent phacoemulsification and IOL implantation. Main outcome measures At 18 months after surgery, the monocular contrast sensitivity (CS) function was measured with sinusoidal grating charts at distance and near, at one photopic luminance level and 2 mesopic luminance levels (85, 5, and 2.5 candelas per square meter). Results Under bright conditions, CS at distance in the multifocal group was not statistically different ( P>0.01) from that in the monofocal group at any tested grating spatial frequency (1.5, 3, 6, 12, and 18 cycles per degree [cpd]). At low luminances, distance CS for the multifocal group was worse than that for the monofocal group at the highest test spatial frequencies (12 and 18 cpd; P<0.01). At near, photopic CS in the multifocal group was lower than at distance; patients with only a monofocal distance correction, however, could not detect the test gratings, even at the highest available contrast. With optimal near spectacle additions (i.e., using the distance correction of the multifocal IOL), there were no significant differences between the photopic near CS values for the multifocal and monofocal groups. When the luminance was decreased, near CS at all spatial frequencies was reduced in both groups. Contrast sensitivity in the near-corrected, multifocal group was significantly worse than in the near-corrected, monofocal group at high spatial frequencies (12 and 18 cpd). Conclusions This work supports the findings of earlier authors that the Array multifocal IOL, with its center-distance design, is distance biased. Distance CS is within normal limits under bright photopic conditions but shows deficits at higher spatial frequencies (more than approximately 12 cpd) under dim mesopic conditions. Near CS obtained with the multifocal IOL is below that which can be achieved by an appropriate monofocal near correction, for all spatial frequencies and illumination conditions.

Visual contrast sensitivity testing: A comparison of two F.A.C.T. test types

Measures of visual contrast sensitivity (VCS), rather than traditional measures of visual acuity using high-contrast stimuli, have been presented as better appraisals of visual dysfunction resulting from chemical exposures. The present study sought to determine if differences exist between two available measures of contrast sensitivity that use similar stimuli, specifically, a hand-held chart and an Optec 1000 vision tester. Monocular contrast sensitivity measures using both tests were obtained from 45 individuals as part of a NIOSH neurobehavioral test-battery appraisal. Test–retest reliability was found to be high for both the hand-held system and the Optec 1000 test ( r=.750 and .773, respectively). In comparison to the automated test, the hand-held version produced statistically significant higher contrast sensitivity scores for lower spatial frequencies (1.5 and 3.0 cycles per degree) and lower scores for a relatively higher spatial frequency (18.0 cycles per degree [cpd]). Consequently, this study documents a difference in spatial frequency scores obtained with the hand-held form and Optec 1000 form of contrast sensitivity test, and attributes these differences to design characteristics affecting viewing. It is concluded that caution should be taken when making absolute comparisons of contrast sensitivity test scores between neurobehavioral studies that have used different forms of VCS testing.

The pattern of visual deficits in amblyopia.

Amblyopia is usually defined as a deficit in optotype (Snellen) acuity with no detectable organic cause. We asked whether this visual abnormality is completely characterized by the deficit in optotype acuity, or whether it has distinct forms that are determined by the conditions associated with the acuity loss, such as strabismus or anisometropia. To decide this issue, we measured optotype acuity, Vernier acuity, grating acuity, contrast sensitivity, and binocular function in 427 adults with amblyopia or with risk factors for amblyopia and in a comparison group of 68 normal observers. Optotype acuity accounts for much of the variance in Vernier and grating acuity, and somewhat less of the variance in contrast sensitivity. Nevertheless, there are differences in the patterns of visual loss among the clinically defined categories, particularly between strabismic and anisometropic categories. We used factor analysis to create a succinct representation of our measurement space. This analysis revealed two main dimensions of variation in the visual performance of our abnormal sample, one related to the visual acuity measures (optotype, Vernier, and grating acuity) and the other related to the contrast sensitivity measures (Pelli-Robson and edge contrast sensitivity). Representing our data in this space reveals distinctive distributions of visual loss for different patient categories, and suggests that two consequences of the associated conditions--reduced resolution and loss of binocularity--determine the pattern of visual deficit. Non-binocular observers with mild-to-moderate acuity deficits have, on average, better monocular contrast sensitivity than do binocular observers with the same acuity loss. Despite their superior contrast sensitivity, non-binocular observers typically have poorer optotype acuity and Vernier acuity, at a given level of grating acuity, than those with residual binocular function.

Mesopic contrast sensitivity function after laser in situ keratomileusis.

To evaluate contrast sensitivity under mesopic conditions in patients who have undergone uncomplicated bilateral laser in situ keratomileusis (LASIK) for myopia. Best-corrected monocular contrast sensitivity was measured with the Stereo Optical F.A.C.T. chart at 1.5, 3, 6, 12, and 18 c/deg in 20 patients (20 left eyes) before and after bilateral LASIK (with the Nidek EC-5000 excimer laser and the Automated Corneal Shaper). Mean preoperative refractive error was -6.40 +/- 1.28 D (range -4.00 to -8.00 D) and postoperative mean refractive error was -0.41 +/- 0.45 D (range -0.75 to +0.50 D). Contrast sensitivity function was measured before and 6 months after surgery using four different chart luminances: 85, 5, 2.5, and 0.1 cd/m2, the first being a photopic level and the rest mesopic. Log contrast sensitivity values at each spatial frequency were used for statistical analysis and normalized values for graphical representation. Contrast sensitivity of postoperative LASIK eyes did not differ from preoperative values at a photopic level (85 cd/m2). However, under mesopic conditions (5 cd/m2 or less) a statistically significant reduction (P<.01) in contrast sensitivity was found at high spatial frequencies (12 and 18 c/deg), although no significant contrast sensitivity differences were observed at low and middle spatial frequencies (P>.01 for 1.5, 3 and 6 c/deg). LASIK induced significant reductions in contrast sensitivity under mesopic conditions only at high spatial frequencies, even though the photopic contrast sensitivity function was normal.

Binocular contrast inhibition in subjects with age-related macular degeneration.

In subjects with normal vision, binocular contrast sensitivity is generally higher than monocular sensitivity, indicating summation of contrast in the two eyes. We have compared monocular and binocular contrast sensitivity and acuity for a group of 13 subjects with age-related macular degeneration (AMD). Relative to a normal control group, many of the AMD subjects showed reduced binocular contrast summation, and binocular inhibition was found for eight subjects for a narrow or an extended frequency band. A better monocular than binocular function may have practical implications for reading and orientation in AMD.

Mesopic contrast sensitivity function after excimer laser photorefractive keratectomy.

To evaluate contrast sensitivity under mesopic conditions in patients who had undergone uncomplicated excimer laser photorefractive keratectomy (PRK) for myopia. 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. 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). Photorefractive keratectomy can induce significant reductions in contrast sensitivity under mesopic conditions, even though the photopic contrast sensitivity function is normal.

Contrast sensitivity and reading in subjects with age-related macular degeneration

Thirteen subjects with age-related macular degeneration (AMD) participated in a study designed to investigate the predictive value of acuity and contrast sensitivity for reading. Compared with the normally sighted individuals, the spatial contrast sensitivity of all these AMD subjects was markedly reduced, particularly at the higher spatial frequencies. The difference was smaller at frequencies below 1 c/deg. For about half the subjects, maximum monocular contrast sensitivity was better than or equal to binocular sensitivity, indicating binocular inhibition or failure of summation. For the 11 subjects who were able to read at a luminance of 40cd/m², reading speed was correlated with various measures of contrast sensitivity and acuity. Of all the visual functions tested, maximum monocular contrast sensitivity and integrated monocular contrast sensitivity showed the best correlation with monocular reading speed. Binocular contrast sensitivity functions, monocular grating acuity, and monocular letter acuity ...

Binocular vision in older people with adventitious visual impairment: sometimes one eye is better than two.

To determine the effect of adventitious visual impairment (low vision) on monocular and binocular spatial contrast sensitivity of older people. A between-within repeated measures design. Fifty-nine older adults between the ages of 50 and 96; 49 of the observers had age-related macular degeneration (AMD). Visual acuity screening and spatial contrast sensitivity. In almost half of the population with AMD, the sensitivity to spatial information, as measured by spatial contrast sensitivity, is worse when both eyes are used than when the stimuli are viewed with only one eye. This "binocular inhibition" is not related to the contrast sensitivity of the better eye or to acuities. Furthermore, this inhibition process is reflected primarily in images with medium to low spatial frequency components (medium to large size bars). These results have important implications for understanding the functional impact of low vision in older people. They suggest that almost one-half of older people with AMD view the world best using only one of their eyes, whereas for the other half, there is an advantage to using binocular vision for certain visual tasks.

Binocular function and patient satisfactionafter monovision induced by myopic photorefractive keratectomy

Purpose: To measure binocular function and patient satisfaction with monovisioninduced by photorefract ve keratectomy (PRK) in myopic presbyopic patients. Setting: Refractive Department; Cleveland Clinic; Cleveland, Ohio, USA. Methods: This study comprised 21 myopic presbyopic patients with monovisioninduced by PRK. Sixteen emmetropic patients who had PRK served as a control group. Monovision was induced by undercorrecting the nondominant eye by 1.25 diopters for near vision and correcting, the dominant eye with emmetropia for distance vision. Monocular and binocular uncorrected Snellen visual acuities at 20 feet and 13 inches, manifest refraction, ocular dominance, stereopsis at 20 feet and 13 inches, Monocular and binocular contrast sensitivities, Worth-4-Dot test at 20 feet and ⅓ of a meter, and fusional convergence amplitudes were examined in each patient. Results: In the monovision group at near and distance, 20 patients (95.3%) had binocular visual acuity of 20/25 or better. No patient in the monovision group used reading glasses postoperatively; 4 of 16 patients (25.0%) in the control group used such glasses. All patients maintained binocular fusion and stereo acuity ranging from 40 to 800 seconds of arc. Mean patient satisfaction was 86% (range 40% to 100%). In the control group, 12 patients (75.0%) had binocular distance visual acuity of 20/25 or better and 11 (68.8%) had binocular near visual, acuity of 20/25 or better. Conclusion: Monovision PRK patients had better near vision than control PRKpatients, with minimal compromise in stereo acuity and overall high patient satisfaction.

Orientation anisotropy and strabismus.

Monocular contrast sensitivity (CS) measurements were obtained in the two principal meridians of eight constant unilateral strabismic subjects and four subjects diagnosed with alternating strabismus. The results indicated that: (1) the CS of both the fellow and deviating eyes of patients with a constant unilateral deviation is significantly less than that of visually normal eyes at high spatial frequencies; (2) both the fellow and deviating eyes reveal a significant reduction in CS to vertically oriented gratings. This effect is frequency-specific, occurring only at the highest spatial frequencies; (3) the magnitude of the orientation anisotropy did not vary systematically with the degree of amblyopia; and (4) a mild orientation anisotropy was observed in only three of the eight alternating strabismic eyes tested. The etiology of the vertical effect is examined with respect to the role of anomalous binocular competition, suppression and abnormal eye movements.

Binocular Function in Early Glaucoma

This study investigated whether certain binocular mechanisms are disrupted in early glaucoma. Glaucoma patients, suspects, and normals were tested on a battery of psychophysical tests consisting of flicker sensitivity (5 and 34 Hz), temporal cut-off frequency (CFF), contrast sensitivity (Pelli-Robson chart), and stereoacuity. Monocular channels were evaluated with tests of monocular flicker performance and spatial contrast sensitivity. Binocular summation on spatial and temporal tests was used to reflect integrity of binocular neural interactions. Stereoacuity was taken as a measure of performance of disparity processing mechanisms. The groups differed in terms of binocular flicker sensitivity at both temporal rates, binocular and monocular peak contrast sensitivity, and stereoacuity. Binocular summation of both spatial and temporal sensitivity was normal. The glaucoma suspect group was distinguishable from the age-matched normal group on binocular contrast sensitivity and stereoacuity. The binocular mechanisms that mediate stereoacuity appear to be heavily disrupted, whereas the binocular mechanisms that mediate central neural interaction of monocular inputs are normal. Although monocular spatiotemporal abilities are disrupted, the binocular processes combine the monocular input normally. In addition, our results suggest a benefit of binocular testing for routine assessment of glaucoma patients. The profound disruption of stereoacuity appears to result from disorder in the spatial sampling array at the ganglion-cell level similar to the disorder reported in the normal periphery and the central retina of strabismic amblyopes. These and previous findings were reviewed to evaluate the supposition of preferential M-pathway disruption in early glaucoma. Such a model can not be reconciled with the present findings. We conclude that measurements of temporal modulation sensitivity fit well with such a model, but that the current evidence of spatiotemporal contrast sensitivity disruption is less supportive of such a model.

Monocular Contrast Sensitivity in 3- to 36-Month-Old Human Infants

A recently developed psychophysical "card" technique was used to evaluate monocular contrast sensitivity in ninety 3-, 6-, 12-, 24-, and 36-month-old human infants. Results showed that for 3-, 6-, 24-, and 36-month-olds, monocular contrast sensitivity functions were very similar to binocular contrast sensitivity functions estimated in a previous experiment. However, at 12-months, monocular contrast sensitivity functions were significantly lower (about 1 octave) than binocular contrast sensitivity functions, a trend also observed in developmental studies of visual acuity. This asymmetry suggests that the neural substrate underlying the development of monocular and binocular spatial vision undergoes different rates of development, at least during the months surrounding the end of the first postnatal year.

The effect of glare upon visual performance in keratoconus

Purpose: The irregular optics of keratoconus produce visual deficits not revealed by standard visual acuity measurements. Non‐standard tests, such as low contrast visual acuity, contrast sensitivity measurement and glare sensitivity may provide a fuller description of the visual deficit in keratoconus. The present study investigates the effect of glare upon visual performance in keratoconus using a variety of clinical tests.Methods: One keratoconic subject (aged 28 years), and one visually normal subject (aged 27 years) participated in the study. Monocular log MAR acuities (high and low contrast) and contrast sensitivities (Pelli‐Robson) were measured in the presence and absence of a glare source (Mentor BAT).Results: (1) High contrast acuity was unaffected by glare in the normal subject, but was reduced by 0.20 log units in the keratoconic subject. (2) Glare reduced low contrast acuity by 0.15 log units in the normal subject, and by 0.70 log units in the keratoconic subject. (3) Contrast sensitivity was reduced by 0.30 log units due to glare in the normal subject, and by 0.50 log units in the keratoconic subject.Conclusions: Glare is a significant factor in reducing visual performance in keratoconus. The effects of glare are most pronounced for low contrast visual acuity.

Diurnal Visual Changes in Radial Keratotomy: Implications for Visual Standards

Diurnal variations in vision have been reported in radial keratotomy (RK) patients. Applicants to certain professions may meet an uncorrected vision standard at the time of testing but fail to meet that standard at another time. Ten firefighter applicants who had undergone RK and nine normal subjects attended for two morning visits, and two afternoon visits. At each visit subjective refraction, uncorrected visual acuity, best-corrected visual acuity, automated refraction, and keratometry were measured for each eye. Monocular contrast sensitivity was measured using the Pelli-Robson chart with and without a glare source (brightness acuity tester, BAT) and for both natural and dilated pupils. The RK group showed a significant myopic shift from morning to afternoon (mean = -0.41 +/- 0.33 D; t = 3.92, p = 0.004), which was well correlated (r = -0.86) with significant steepening of the corneal curvature (mean = +0.41 +/- 0.36 D; t = -3.65, p = 0.005). The controls showed no change in either refractive error (mean change = +0.06 +/- 0.42 D) or corneal curvature (mean change = +0.05 +/- 0.08 D). No significant difference in corrected visual acuity or contrast sensitivity was found between the RK and control groups for natural pupils. For dilated pupils, the RK patients showed significantly poorer log contrast sensitivity both with and without glare (RK mean = 1.49 +/- 0.11; control mean = 1.67 +/- 0.11; t = 3.21, p = 0.005). All RK subjects met the firefighter visual acuity standard on the initial visit, three subjects did not meet the standard at an afternoon examination. We propose that, if RK applicants are to be considered for employment, existing visual standards be amended to include visual acuity testing in both the early morning and late afternoon. Clinicians and agencies should also be aware that contrast sensitivity may be reduced at low light levels.

Modelling contrast sensitivity as a function of retinal illuminance and grating area

We extended the contrast detection model of human vision [Rovamo, Luntinen & Näsänen (1993b) Vision Research, 33, 2773-2788] to low light levels by taking into account the effect of light-dependent quantal noise. The extended model comprises (i) low-pass filtering due to the optical modulation transfer function of the eye, (ii) addition of light-dependent noise at the event of quantal absorption, (iii) high-pass filtering of neural origin (lateral inhibition), (iv) addition of internal neural noise, and (v) detection by a local matched filter whose efficiency decreases with increasing grating area. To test the model we measured foveal contrast sensitivity as a function of retinal illuminance and grating area at spatial frequencies of 0.125-32 c/deg. In agreement with the model, monocular contrast sensitivity at all grating areas increased in proportion to I when retinal illuminance (I) was smaller than critical illuminance. Thereafter the increase saturated and contrast sensitivity became independent of retinal illuminance. Similarly, at all levels of retinal illuminance contrast sensitivity increased in proportion to A when grating area (A) was smaller than critical area. Thereafter the increase saturated and contrast sensitivity became independent of area. Critical level of retinal illuminance increased in proportion to the spatial frequency squared. Critical area marking the saturation of spatial integration was constant at low spatial frequencies but decreased in inverse proportion to spatial frequency squared at medium and high spatial frequencies. The maximum contrast sensitivity obtainable by spatial integration in bright light increased at low spatial frequencies in proportion to spatial frequency, was constant at medium spatial frequencies, and decreased in inverse proportion to spatial frequency cubed at high spatial frequencies. The increase was due to the neural modulation transfer function of the visual pathways whereas the decrease was due to the optical modulation transfer function of the eye. The model explained 91-99% of the total variance of our contrast sensitivity data at various spatial frequencies.

Binocular contrast summation and inhibition in amblyopia. The influence of the interocular difference on binocular contrast sensitivity.

The monocular contrast sensitivity loss in amblyopia is well documented. We investigated the influence of interocular sensitivity difference on binocular contrast sensitivity in amblyopia. Monocular and binocular contrast sensitivity functions of six amblyopes (three strabismic and three anisometropic) were measured. The monocular contrast sensitivity loss depended on the type of amblyope. Anisometropic amblyopes generally showed high frequency losses. Strabismic amblyopes showed losses at both low and high spatial frequencies. Binocular performance was assessed in terms of binocular ratios (binocular/non-amblyopic). A binocular ratio greater than 1 indicates binocular summation (binocular > monocular) while a ratio less than 1 shows binocular inhibition (binocular < monocular). In all subjects, the binocular ratio depended on the difference between the amblyopic and the non-amblyopic eye. Minimal interocular difference produced binocular summation, the magnitude of which decreased as the difference between the two eyes increased. Further increases in the monocular difference produced binocular inhibition. Anisometropic amblyopes showed a greater degree of binocular summation at low spatial frequencies compared to strabismic amblyopes. Both types of amblyopes showed binocular inhibition at high spatial frequencies. Clinical implications of binocular summation and inhibition in amblyopia are discussed.

Visual acuity and contrast sensitivity in cataract: Summation and inhibition of visual performance

Patients exhibiting uniocular cataract often report an improvement in vision on closing their cataractous eye. Such qualitative evidence suggests the presence of binocular inhibition--the converse of binocular summation (that is the normal superiority of binocular over monocular vision). To quantify the extent of inhibition in cataract, binocular and monocular visual acuity and contrast sensitivity were measured in 28 patients. Twelve patients showed binocular inhibition for visual acuity whilst 11 showed inhibition for contrast sensitivity measured at four cycles per degree (c.deg-1). Contrast sensitivity for 8 c.deg-1 targets was further recorded in a subset of 14 patients in whom seven showed inhibition. In patients who demonstrated inhibition, the mean decrement in performance for visual acuity was 13%. For contrast sensitivity at 4 and 8 c.deg-1 the mean decrement was 25% and 32% respectively. The clinical significance of these findings is discussed with respect to the assessment of visual function and management of the cataract patient.

Inhibition of Binocular Contrast Sensitivity in Hypermetropic Anisometropia

Binocular contrast inhibition can occur when the monocular contrast sensitivities are not equal. It has been reported in cases of monocular cataracts. Our case is an 18-year-old female with 3.50 D of hypermetropic anisometropia. She was not amblyopic but showed a typical binocular contrast inhibition.