Contrast Sensitivity Function Measurements Research Articles

Impact of Keratoconus on Contrast Sensitivity

Objective: Keratoconus (KC) disrupts corneal shape, leading to irregular astigmatism and increased higher-order aberrations (HOA), ultimately affecting visual quality. While visual acuity (VA) remains the standard, its limitations in early KC diagnosis are recognized. This study aimed to evaluate the impact of KC on contrast sensitivity function (CSF), a potentially more sensitive measure of visual performance.Material and Methods: A case-control design compared CSF in KC patients (n=7) to healthy controls (n=16). All subjects achieved the best-corrected visual acuity (BCVA) of 6/9 or better (logMAR ≤0.10). Corneal topography was measured using Tomey TMS-5 to confirm KC diagnosis. CSF was assessed with the Functional Acuity Contrast Test (FACT).Results: KC eyes exhibited significantly reduced CSF across all spatial frequencies compared to controls (p-value<0.05). Row A of the FACT chart (representing the lowest spatial frequency, 1.5 cpd) demonstrated the most prominent difference (t (21)=-3.073, p-value=0.003).Conclusion: Our findings reveal that KC patients, despite achieving good BCVA, demonstrate measurable deficits in CSF. This suggests CSF measurement with FACT may be a valuable tool for the early diagnosis and monitoring of KC, potentially offering a more sensitive and comprehensive assessment of visual function compared to BCVA alone.

The Measurement of Contrast Sensitivity in Near Vision: The Use of a Digital System vs. a Conventional Printed Test

In recent years, there has been intense development of digital diagnostic tests for vision. All of these tests must be validated for clinical use. The current study enrolled 51 healthy individuals (age 19–72 years) in which achromatic contrast sensitivity function (CSF) in near vision was measured with the printed Vistech VCTS test (Stereo Optical Co., Inc., Chicago, IL, USA) and the Optopad-CSF (developed by our research group to be used on an iPad). Likewise, chromatic CSF was evaluated with a digital test. Statistically significant differences between tests were only found for the two higher spatial frequencies evaluated (p = 0.012 and <0.001, respectively). The mean achromatic index of contrast sensitivity (ICS) was 0.02 ± 1.07 and −0.76 ± 1.63 for the Vistech VCTS and Optopad tests, respectively (p < 0.001). The ranges of agreement between tests were 0.55, 0.76, 0.78, and 0.69 log units for the spatial frequencies of 1.5, 3, 6, and 12 cpd, respectively. The mean chromatic ICS values were −20.56 ± 0.96 and −0.16 ± 0.99 for the CSF-T and CSF-D plates, respectively (p < 0.001). Furthermore, better achromatic, red–green, and blue–yellow CSF values were found in the youngest groups. The digital test allows the fast measurement of near-achromatic and chromatic CSF using a colorimetrically calibrated iPad, but the achromatic measures cannot be used interchangeably with those obtained with a conventional printed test.

Association between contrast sensitivity function and structural damage in primary open-angle glaucoma

AimsTo evaluate the association between contrast sensitivity function (CSF) and glaucomatous structural damage in primary open-angle glaucoma (POAG).MethodsA cross-sectional study was performed with 103 patients (103 eyes) aged 25–50 years...

Visual perception alterations in COVID-19: a preliminary study.

To compare the visual perception (color and chromatic-achromatic contrast vision) of a small cohort of COVID-19 patients at the time of infection and after 6mo with that of a healthy population matched for sex and age. A total of 25 patients (9 females, 16 males, mean age: 54±10y) with COVID-19 hospitalized in the COVID-19 Unit of the University Clinical Hospital of Valladolid were recruited for this preliminary study. Visual perception, as determined by monocular measurement of contrast sensitivity function (CSF) and color vision was assessed in each patient using the Optopad test. The results obtained were then compared with those of a sample of 16 age- and sex-matched healthy controls (5 females, 11 males, mean age: 50±6y) in which the same measurement procedure was repeated. Statistically significant differences between groups were assessed using the Mann-Whitney U test. Measurements were repeated after a minimum follow-up period of 6mo and statistically significant differences between the two time points in each group were assessed using the Wilcoxon signed rank test. Discrimination thresholds (color and chromatic-achromatic contrast vision) and their corresponding sensitivity, calculated as the inverse of the discrimination threshold, were evaluated. Analysis of the data revealed higher contrast threshold results (i.e., worse contrast sensitivity) in the COVID-19 group than in the control group for all spatial frequencies studied in the Optopad-CSF achromatic test and most of the spatial frequencies studied in the Optopad-CSF chromatic test for the red-green and blue-yellow mechanisms. In addition, color threshold results in the COVID-19 group were also significantly higher (i.e., worse color sensitivity) for almost all color mechanisms studied in the Optopad-Color test. At 6mo, most of the differences found between the groups were maintained despite COVID-19 recovery. The present results provide preliminary evidence that visual perception may be impaired in COVID-19, even when the infection has passed. Although further research is needed to determine the precise causes of this finding, analysis of CSF and color vision could provide valuable information on the visual impact of COVID-19.

Vitrectomy Improves Contrast Sensitivity in Multifocal Pseudophakia With Vision Degrading Myodesopsia

Multifocal intraocular lenses (MFIOL) are associated with degradation in contrast sensitivity function (CSF); yet the contribution of vitreous is not known, nor is the benefit of vitrectomy. Prospective, nonrandomized clinical study. A total of 180 eyes of 180 patients (55 MFIOL, 60 monofocal intraocular lenses [MIOL], 65 phakic) with symptomatic vitreous opacities were enrolled. Vitreous structure was assessed with quantitative ultrasonography (QUS). Vision was evaluated with visual acuity and CSF measurements. Vitreous echodensity was the same in all lens cohorts, yet CSF was worse in MFIOL eyes (P < .001). In 86 patients who elected vitrectomy, there was 68% greater vitreous echodensity and 31% worse CSF than in observation controls (P < .0001 for each). Preoperatively, CSF was 25% worse in MFIOL than in MIOL (P=.014). Postoperatively, vitreous echodensity decreased by 55%, 51%, and 52%, whereas CSF improved by 37% 48% in and 43% in MFIOL, MIOL, and phakic eyes, respectively (P < .0001 for each). NEI Visual Function Questionnaire analyses showed improved visual well-being. Patients with vision degrading myodesopsia who elected vitrectomy had greater vitreous echodensity and worse CSF than controls, but no other differences in age, sex, or myopia. MFIOL eyes had worse CSF than MIOL and phakic eyes, very possibly due to combined effects of the MFIOL and vitreous opacification. Limited vitrectomy reduced vitreous echodensity and improved CSF in all eyes. All patients with CSF-degrading vitreous opacities benefited from limited vitrectomy, including those with MFIOL. As MFIOL eyes had 37% improvement in CSF, patients with MFIOL and vision degrading myodesopsia merit consideration of vitrectomy.

Impact of posterior vitreous detachment on contrast sensitivity in patients with multifocal intraocular lens.

To investigate posterior vitreous detachment (PVD) and pars plana vitrectomy (PPV) effects on contrast sensitivity function (CSF) in patients with a multifocal intraocular lens (MfIOL). This single-center prospective case-control study analyzed 27 patients with 43 consecutive eyes. Twenty patients with 36 consecutive eyes received MfIOL implantation with either ZLB00 or ZMB00. CSF was measured as the area under the log contrast sensitivity function (AULCSF) in the presence and absence of PVD (PVD+ group and PVD- group, respectively). Seven eyes associated with a symptomatic PVD and severe visual dissatisfaction after MfIOL implantation underwent PPV (symptomatic PVD+ group). CSF was measured prior to and after PPV. The mean AULCSF was significantly lower in the PVD+ group (1.5 ± 0.1) versus the PVD- group (1.7 ± 0.1, p < 0.0001). Major complaints in the symptomatic PVD+ group included floaters (n = 2) and blurry vision (n = 5). The preoperative AULCSF (1.4 ± 0.1) was significantly lower in the symptomatic PVD+ group versus the PVD- group (p < 0.0001) and PVD+ group (p = 0.02). The preoperative AULCSF in the symptomatic PVD+ group was significantly improved after PPV (1.4 vs. 1.7, respectively, p = 0.002). PVD significantly decreased CSF in patients with MfIOL. Patients with symptomatic PVD exhibited the greatest decrease in CSF, which was significantly improved after PPV. Measurement of CSF and careful assessment of PVD may be useful in determining the appropriateness of surgical intervention for improving visual performance and satisfaction in MfIOL patients with symptomatic PVD.

Cost-Effectiveness of Limited Vitrectomy for Vision-Degrading Myodesopsia

Patients afflicted with clinically significant vitreous floaters suffer from vision-degrading myodesopsia, characterized by impairment in contrast sensitivity function (CSF) and decreased quality of life. This study determined the cost-effectiveness of limited vitrectomy for this condition. Retrospective, interventional case series and third-party insurer cost-utility analysis. Sixty-seven patients suffering from unilateral vitreous floaters (20 non-myopic patients with posterior vitreous detachment [PVD]; 17 myopic patients [>-2 diopters] without PVD; 30 myopic patients with PVD) completed the National Eye Institute Visual Function Questionnaire (VFQ-39) and were tested with best-corrected visual acuity (BCVA) and CSF measurements before and after limited vitrectomy. A reference case cost-utility analysis was performed. The mean VFQ-39 increased 19% (P < 0.00001) after surgery, with general vision improving 27% for the entire group and 37% for non-myopic PVD (P < 0.00001 for each). VFQ-39 correlations with time tradeoff utilities indicated a 14.4% improvement in quality of life. Mean BCVA improved 13.5% postoperatively (P < 0.00001) and CSF improved 53% (P < 0.00001). The incremental patient value gain conferred by limited vitrectomy was 2.38 quality-adjusted life-years (QALYs), and the average cost-utility ratio in 2018U.S. real dollars was $1,574/QALY. Limited vitrectomy for vision-degrading myodesopsia is clinically effective, in that it improves BCVA, CSF, and patient well-being. It is also highly cost-effective ($1,574/QALY), with an average cost-utility ratio vs. no therapy that is superior to cataract surgery ($2,262/QALY), amblyopia therapy ($2,710/QALY), and retinal detachment repair ($45,304/QALY). Myopic patients without PVD had the lowest cost-utility ratio of all ($1,338/QALY).

Contrast sensitivity reveals an oculomotor strategy for temporally encoding space

The contrast sensitivity function (CSF), how sensitivity varies with the frequency of the stimulus, is a fundamental assessment of visual performance. The CSF is generally assumed to be determined by low-level sensory processes. However, the spatial sensitivities of neurons in the early visual pathways, as measured in experiments with immobilized eyes, diverge from psychophysical CSF measurements in primates. Under natural viewing conditions, as in typical psychophysical measurements, humans continually move their eyes even when looking at a fixed point. Here, we show that the resulting transformation of the spatial scene into temporal modulations on the retina constitutes a processing stage that reconciles human CSF and the response characteristics of retinal ganglion cells under a broad range of conditions. Our findings suggest a fundamental integration between perception and action: eye movements work synergistically with the spatio-temporal sensitivities of retinal neurons to encode spatial information.

Efficient Characterization and Classification of Contrast Sensitivity Functions in Aging

The contrast sensitivity function (CSF), delineating contrast sensitivity over a wide range of spatial frequencies, provides a comprehensive characterization of spatial vision and a sensitive test for many physiological and pathological processes. A precise CSF measurement tool for the aging population is of great theoretical and practical importance. In the current study, we tested whether the assumptions of the newly developed quick CSF method were valid and whether it can rapidly, reliably, and effectively evaluate CSFs in the aging population. The quick CSF method combines Bayesian adaptive inference with an information gain strategy to directly estimate four parameters that define the observer’s CSF. Eighteen young and twenty-five old observers participated in the evaluation of the quick CSF method. All observers were screened for ophthalmological and mental diseases. Our results showed that the CSFs derived from the quick CSF method well matched with those from the traditional Ψ method, with excellent test-retest reliability. More importantly, the quick CSF method can accurately detect the difference of CSFs between the young and old groups. Aging significantly degrades contrast sensitivity. The quick CSF method demonstrates great potentials for both laboratory research and clinical applications in the aging population.

Bayesian Inference of Two-Dimensional Contrast Sensitivity Function from Data Obtained with Classical One-Dimensional Algorithms Is Efficient.

The contrast sensitivity function that spans the two dimensions of contrast and spatial frequency is crucial in predicting functional vision both in research and clinical applications. In this study, the use of Bayesian inference was proposed to determine the parameters of the two-dimensional contrast sensitivity function. Two-dimensional Bayesian inference was extensively simulated in comparison to classical one-dimensional measures. Its performance on two-dimensional data gathered with different sampling algorithms was also investigated. The results showed that the two-dimensional Bayesian inference method significantly improved the accuracy and precision of the contrast sensitivity function, as compared to the more common one-dimensional estimates. In addition, applying two-dimensional Bayesian estimation to the final data set showed similar levels of reliability and efficiency across widely disparate and established sampling methods (from classical one-dimensional sampling, such as Ψ or staircase, to more novel multi-dimensional sampling methods, such as quick contrast sensitivity function and Fisher information gain). Furthermore, the improvements observed following the application of Bayesian inference were maintained even when the prior poorly matched the subject's contrast sensitivity function. Simulation results were confirmed in a psychophysical experiment. The results indicated that two-dimensional Bayesian inference of contrast sensitivity function data provides similar estimates across a wide range of sampling methods. The present study likely has implications for the measurement of contrast sensitivity function in various settings (including research and clinical settings) and would facilitate the comparison of existing data from previous studies.

Influência do Cronotipo e do Horário da Medida na Sensibilidade ao Contraste Visual

Este estudo teve como objetivo avaliar a curva de sensibilidade ao contraste para estimulos de grades senoidais verticais de frequencias espaciais de 0,2; 0,6; 1; 3,1; 6,1; 8,8; 13,2 e 15,6 ciclos por grau de ângulo visual; em um ritmo de 24 horas de adultos saudaveis de diferentes cronotipos. Participaram desta pesquisa 18 voluntarios do sexo masculino com idade de 19 a 31 anos (M=23,8; DP=3,29). Os participantes foram divididos em grupos de acordo com o cronotipo: Matutino (n=5), Intermediario (n=9) e Moderadamente vespertino (n=4). Utilizaram-se como instrumentos medidas neuropsicologicas e o software Metropsis para avaliar a Funcao de Sensibilidade ao Contraste (FSC). As medidas da FSC foram realizadas com o metodo psicofisico da escolha forcada entre duas alternativas espaciais. Os resultados apresentaram alteracoes nas dimensoes relacionadas ao processamento cognitivo e na FSC de sujeitos Matutinos [F (14; 76303) = 38,92; p<0,05], Intermediarios [F(14; 505) = 2,79; p<0,05] e Moderadamente vespertinos [F(14; 279) = 2,75; p<0,05] de acordo com os horarios de medida. Concluiu-se que a sensibilidade ao contraste e um aspecto importante para o estudo da percepcao visual circadiana, sugerindo que os mecanismos sensorios que processam o contraste visual estao diretamente relacionados a hora e o padrao do cronotipo.

Contrast Sensitivity Function after Correcting Residual Wavefront Aberrations during RGP Lens Wear

To investigate the effect on the contrast sensitivity function (CSF) of correcting the residual wavefront aberrations in myopic and keratoconic subjects wearing rigid gas permeable (RGP) contact lenses. Seventeen eyes of 16 myopic subjects and 20 eyes of 19 keratoconic subjects were included in this study. All eyes were habitually corrected with RGP lenses. The residual aberrations of the RGP lens-wearing eyes were compensated by an adaptive optics (AO) system. The contrast sensitivities were measured through a 4-mm artificial pupil at spatial frequencies of 2, 4, 8, 16, and 32 cycles per degree (cpd) during RGP lens wear for the myopic and keratoconic groups, respectively. The CSF measurements were repeated with and without AO correction. Comparisons of contrast sensitivity at all spatial frequencies with and without AO correction were performed respectively for the myopic and keratoconic groups during RGP lens wear. In the myopic RGP lens-wearing group, the differences in contrast sensitivity at each spatial frequency, with and without AO correction, were not significant (all p values > 0.05). In the keratoconic RGP lens-wearing group, the contrast sensitivities at all spatial frequencies with AO correction were higher than those without AO correction, but differences only at the low (2 cpd) and intermediate (4, 8, and 16 cpd) spatial frequencies were significant (p = 0.039, 0.005, 0.001, and 0.007). The residual aberrations significantly reduced the contrast sensitivities at low and intermediate spatial frequencies for keratoconic RGP lens-wearing eyes but did not have any effect on the CSF for the myopic RGP lens-wearing eyes. Developing techniques that could more completely correct the wavefront aberrations may improve visual performance in keratoconus.

The influence of the chromatic contrast change of digital prints on the measured contrast sensitivity function

The colour appearance of a stimulus is not independent of its spatial and temporal characteristics. The prints in the graphic arts are both colorimetrically and spatially variable surfaces due to the use of halftoning with different inks. The spatial and temporal characteristics of the human visual system are typically explored through the measurement of contrast sensitivity functions. Contrast sensitivity functions (CSFs) in vision science are analogous to modulation transfer functions (MTFs) in imaging science. The contrast sensitivity function (CSF) is essential for the detail perception and it is one of the main compo­nents of visual models and metrics. CSF is a well researched but never the less, CSF has not been widely researched in terms of application in hardcopy prints made by digital printing systems, but mainly on colour displays. The aim of this paper was to determine if there is any similarity between two types of reducing contrast: (1) type C1 where two opponent colours get mixed; and (2) type C2 where the colour saturation is reduced. A group of 15 subjects evalu­ated a printed test form containing frequency and contrast variable elements using magnifying glass. The results showed that the eye is similarly sensitive to both types of the contrast change. The plots of reducing saturation (C2) showed a similar shape like C1 but had slightly lower sensitivity, especially in the red-green contrast. This can be useful for color difference metrics cut-offs and for designers in determining which details and contrasts do not have to be used as they cannot be seen by the final observer.

Spatial-frequency cutoff requirements for pattern recognition in central and peripheral vision

It is well known that object recognition requires spatial frequencies exceeding some critical cutoff value. People with central scotomas who rely on peripheral vision have substantial difficulty with reading and face recognition. Deficiencies of pattern recognition in peripheral vision, might result in higher cutoff requirements, and may contribute to the functional problems of people with central-field loss. Here we asked about differences in spatial-cutoff requirements in central and peripheral vision for letter and face recognition. The stimuli were the 26 letters of the English alphabet and 26 celebrity faces. Each image was blurred using a low-pass filter in the spatial frequency domain. Critical cutoffs (defined as the minimum low-pass filter cutoff yielding 80% accuracy) were obtained by measuring recognition accuracy as a function of cutoff frequency (in cycles per object). Our data showed that critical cutoffs increased from central to peripheral vision by 20% for letter recognition and by 50% for face recognition. We asked whether these differences could be accounted for by central/peripheral differences in the contrast sensitivity function (CSF). We addressed this question by implementing an ideal-observer model which incorporates empirical CSF measurements and tested the model on letter and face recognition. The success of the model indicates that central/peripheral differences in the cutoff requirements for letter and face recognition can be accounted for by the information content of the stimulus limited by the shape of the human CSF, combined with a source of internal noise and followed by an optimal decision rule.

Avaliação da sensibilidade ao contraste em pacientes com migrânea

O objetivo foi medir a Função de Sensibilidade ao Contraste (FSC) de pacientes com migrânea e de voluntários saudáveis sem a patologia. Participaram dos testes 12 voluntários do sexo feminino, seis com migrânea e seis sem migrânea na faixa etária de 20 a 37 anos. As medidas de FSC foram realizadas utilizando estímulos visuais estáticos de grades senoidais angulares com frequências espaciais de 2, 3, 4, 24 e 64 ciclos/360º Foi utilizado o método psicofísico da escolha forçada entre duas alternativas temporais, condições de luminância fotópica (luminância média da tela de 41 cd/m²) e visão binocular com pupila natural. Os resultados demonstram que a percepção visual de contraste dos voluntários com migrânea foi menor nas frequências de 2, 3, 4 e 64 ciclos/360º. Esses achados preliminares sugerem alterações na FSC relacionadas a essa patologia.

Measurements of retinal aerial image modulation (AIM) for white light based on wave-front aberration of human eye

The aerial image modulation (AIM) curve of retina under the condition of white light is obtained based on the wave-front aberration of human eye. According to the relationship between the wavelength and defocus, we modify the monochromatic wave-front aberration data to calculate the modulation transfer function (MTF) of human eye in the white-light illumination. Combined with the measurement of contrast sensitivity function (CSF) for complete eye and visual acuity (VA) under the same luminance condition, we deduce the AIM curve in natural light. We find that AIM varies slightly at lower and intermediate spatial frequencies among different eyes; at higher frequencies AIM is the predominant factor for VA when the wave-front aberration is not significant. In addition, retinal AIM is expressed in terms of neural contrast sensitivity function (NCSF) which is the clinical valuable for ophthalmologists. Considering the real illumination circumstance, it is of practical significance to obtain the AIM curve and NCSF curve under white-light condition.

LASIK and the contrast sensitivity function

We read with interest the work of Quesnel et al.1 They describe the clinical effects of laser in situ keratomileusis (LASIK) on the cornea and visual performance by the contrast sensitivity function (CSF). We agree with their comment that CSF measurement is necessary to assess visual function. For several years, our research group has evaluated the visual performance of refractive surgery patients by the CSF assessment.2–8 Quesnel et al. report that previous studies of CSF measurement were done under photopic conditions only. This is not true because our group has studied the effect of phototherapeutic keratectomy,3 LASIK,4,6,7 and other refractive surgeries8 on CSF under mesopic conditions. (Our study was cited in their references.) Quesnel et al. suggest that the reduction in CSF after LASIK cannot be attributed to optical defocus because they measured CSF with and without the best optical correction, yielding to similar results. They showed a postoperative spherical equivalent ranging from +0.75 to −0.75 diopter at 1 month (no data available for longer times). In our opinion, it is impossible to discount the negative effect of optical defocus on CSF measurement with these values. Lower levels of defocus than those reported by the authors significantly modify the CSF. Perhaps, in addition to defocus, microstriae such as they suggest would affect their results and a combination of defocus and mircrostriae plays a role in CSF reduction. More information about microstriae in their patients should be noted in the paper. Another point to discuss is that the authors failed to mention the pupil diameter of the patients under photopic and mesopic conditions, which affect the CSF, and the luminance of the room where CSF was measured (not lux values, which refer to illuminance, but cd/m2, nits, or apostilb units, which refer to luminance). Thus, no comparison with previous studies, especially those performed under mesopic conditions,4 could be done. Finally, we believe that CSF measurement is an excellent technique to report changes in visual performance in patients having laser refractive surgery, but caution will need to be taken in CSF measurement and the conclusions derived from this. Robert Montés-Micó OD, MPhil, PhD Jorge L. Alió MD, PhD Alicante, Spain

Changes in corneal asphericity after laser in situ keratomileusis

Purpose To analyze the origin of the changes in corneal asphericity (p-factor) after laser in situ keratomileusis (LASIK) and the effect of postsurgery asphericity on contrast-sensitivity function (CSF) under photopic conditions. Setting Department of Optics, University of Granada, Granada, Spain. Methods The p-factor and CSF (best corrected before surgery and 1, 3, and 6 months after surgery) were measured in 24 eyes. Results An increase in the p-factor after LASIK was noted; there was an 87.2% change in the asphericity using the paraxial formula of Munnerlyn and coauthors. Other factors such as decentration, type of laser, optical role of the flap, wound healing, biomechanical effects, technical procedures, and reflection losses of the laser on the cornea could account for the greater than expected increase (12.8%) in the p-factor. The CSF measurements deteriorated after LASIK; the change was significant ( P<.05) in patients with myopia worse than −4.0 diopters at frequencies of 9.2, 12, 15, and 20 cycles per degree. Conclusion The increase in corneal asphericity after surgery, greater with a higher degree of myopia, and the deterioration in CSF with high myopia justify new ablation algorithms and further study of the variables that could modify the ablation unpredictably.

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.

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.