Neural Contrast Sensitivity Function Research Articles

Correlation between Contrast Sensitivity and Modulation Transfer Functions.

Previous studies found no correlation between visual acuity and optical quality in a population of young subjects with good vision. Using sinusoidal gratings, we systematically investigate the correlation between contrast sensitivity and optical quality as a function of spatial frequency. This study describes the correlation between the contrast sensitivity function (CSF) and the modulation transfer function (MTF) in a sample of young and informed subjects. Our results are compared with prior studies on the correlation between visual acuity and metrics of image quality. We also compare our results with previous studies that compare the CSF, the MTF, and the neural contrast sensitivity function (NCSF). The CSF of 28 informed subjects is measured in photopic conditions. The polychromatic MTF is computed from the measurements of monochromatic aberrations. The (CSF, MTF) correlation is estimated as the Pearson correlation coefficient, at each spatial frequency. The NCSF of each subject is estimated as the ratio of CSF to MTF. We obtain high correlation coefficients (0.8) in the range of spatial frequencies of 3 to 6 cycles per degree, which also corresponds to high NCSF. Correlation decreases with increasing spatial frequency in the range of 6 to 18 cycles per degree (down to 0.0 at 18 cycles per degree). In that range, optical and neural contrast sensitivities are both approximately reduced by factor 4. In our sample of young subjects with good vision, the CSF with sinusoidal gratings better differentiates eyes of good optical quality at intermediate spatial frequencies (3 to 6 cycles per degree) than at higher spatial frequencies (12 to 18 cycles per degree). At the highest tested spatial frequency of sinusoidal gratings (18 cycles per degree), there is no significant correlation between optical quality and contrast sensitivity.

Orientation-specific long-term neural adaptation of the visual system in keratoconus

Eyes with the corneal ectasia keratoconus have performed better than expected (e.g. visual acuity) given their elevated levels of higher-order aberrations that cause rotationally asymmetric retinal blur. Adapted neural processing has been suggested as an explanation but has not been measured across multiple meridional orientations. Using a custom Maxwellian-view laser interferometer to bypass ocular optics, sinusoidal grating neural contrast sensitivity was measured in six eyes (three subjects) with keratoconus and four typical eyes (two subjects) at six spatial frequencies and eight orientations using a two-interval forced-choice paradigm. Total measurement duration was 24 to 28 hours per subject. Neural contrast sensitivity functions of typical eyes agreed with literature and generally showed the oblique effect on a linear-scale and rotational symmetry on a log-scale (rotational symmetry was quantified as the ratio of the minor and major radii of an ellipse fit to all orientations within each spatial frequency; typical eye mean 0.93, median 0.93; where a circle = 1). Mean sensitivities of eyes with keratoconus were 20% to 60% lower (at lower and higher spatial frequencies respectively) than typical eyes. Orientation-specific neural contrast sensitivity functions in keratoconus showed substantial rotational asymmetry (ellipse radii ratio: mean 0.84; median 0.86) and large meridional reductions. The visual image quality metric VSX was used with a permutation test to combine the asymmetric optical aberrations of the eyes with keratoconus and their measured asymmetric neural functions, which illustrated how the neural sensitivities generally mitigated the detrimental effects of the optics.

Visual Strehl Performance of IOL Designs with Extended Depth of Focus

The use of monofocal, bifocal, or multifocal intraocular lenses (IOLs) is a common option to restore the refractive power of the eye in aphakic patients after cataract surgery. In this article, we study the predicted performance of two new designs of IOL, both with extended depth of focus: the quartic axicon and the light sword optical element (LSOE). These elements provide continuous focal segments spanning the range of dioptric power required for presbyopia compensation. The performance analysis is based on the visual Strehl ratio (SR) computed in the spatial frequency domain, a neuro-optical quality metric that takes into account the effects of both the optical transfer function and the neural contrast sensitivity function. Furthermore, the classical SR and compound modulation transfer function were calculated. Some conventional transmittances of commercially available IOLs are also analyzed. The LSOE design has a more homogeneous behavior than other available solutions, providing a more uniform image quality over a significant fraction of the required addition range. The angular average of the visual SR computed in the spatial frequency domain and compound modulation transfer function indicate that both designs of extended depth of focus elements provide better optical quality on the whole addition range, except at the end points, than the discrete focus designs. The LSOE performed better than the quartic axicon in terms of uniformity of image quality within the same range.

The study on neural contrast sensitivity function at temporal frequencies

The neural contrast sensitivity function (NCSF) of human eye at temporal frequencies is acquired with a new method in this paper. Firstly the human eye's contrast sensitivity function (CSF) at temporal frequencies is measured by means of travelling-wave stimuli, and the modulation transfer function (MTF) of the eye's optics is obtained by constructing the eye model of the subject. Then the NCSF at temporal frequencies is calculated with the two functions. It is shown that the overall value of the NCSF decreases as the temporal frequency increases. As the temporal frequency increases from 0 cycles per second (c/s) to 1 c/s, 16 c/s and 30 c/s, the NCSF curve changes from the band-pass shape to the low-pass, and then to almost monotonic variation. The attenuation factor of the NCSF, which represents the sensitivity of visual neural system to the temporal frequency, varies little as spatial frequency increases, while that of the CSF declines dramatically in the region of high spatial frequencies. Because it is the NCSF, rather than the CSF, that reflects the characteristics of visual neural system, the investigation of the NCSF at temporal frequency is more essentially.

Luminance Effects on Neural Mechanism at Photopic Level

In order to obtain the influence of the luminance at photopic level on the neural mechanism, a neural contrast sensitivity function (NCSF) measurement system is established. The contrast sensitivity function (CSF) of the visual system and the modulation transfer function (MTF) of the eye's optical system are first measured with correspondent instruments respectively. Then the NCSF is calculated as the ratio of CSF to MTF. Four individual eyes are involved in the cases of green light and white light. With increasing luminance, the tendency of the variation of the CSFs is similar to that of the NCSFs, while the gain is larger than that of the NCSFs, especially in the region of higher spatial frequency. It is the NCSF, rather than CSF, that reflects tie luminance sensitivity in the retina-brain neural system, because the influence of the eye's optical system is excluded.

Neural contrast sensitivity calculated from measured total contrast sensitivity and modulation transfer function

To test the feasibility of calculating neural contrast sensitivity function (neural CSF) from conventionally measured total contrast sensitivity function (total CSF) and measured modulation transfer function (MTF). Neural CSF considers the retina and the brain, whereas total CSF considers the optical eye media, the retina and the brain together. We studied three groups comprising nine eyes each: one group with normal ocular optics but retinal alterations (mild diabetic retinopathy), one with altered ocular optics and normal retina (keratoconus), and a normal control group. Total CSF in the keratoconus and retinopathy groups was significantly lower compared to the control group. Modulation transfer function for keratoconus was lower, and in the retinopathy group was similar to that of the control group. Calculated neural CSF in the diabetes mellitus group was lower than in the control group whereas in the keratoconus group it was similar to that of the control group, with overestimations for some keratoconus cases. It is possible to calculate a meaningful neural CSF from measured total CSF and MTF data. The neural CSF represents a CSF adjusted for optical aberrations. This would allow comparison of the neural component of visual function in eyes with different optical aberrations.

Optical quality and intraocular scattering in a healthy young population

Background: We objectively assessed the optical quality and intraocular scattering by means of parameters provided by a clinical double‐pass system in healthy young subjects and thereby we obtained new reference data for clinical diagnosis. We calculated normal values of neural contrast sensitivity function (nCSF) from the measured modulation transfer function (MTF) and the contrast sensitivity function (CSF).Methods: Eligible subjects were healthy adults aged from 18 to 30-years with a logMAR visual acuity (VA) of 0.0 or better and normal values of CSF. Optical quality measurements for a 4.0-mm pupil were performed using the Optical Quality Analysis System (OQAS) based on the double‐pass technique. The following parameters were analysed: the modulation transfer function cutoff frequency (MTFcutoff), the Strehl2D ratio, the OQAS values (OV) at 100, 20 and nine per cent contrasts and the objective scatter index (OSI).Results: A total of 178 volunteers responded to the call, of whom 181 eyes were finally part of the study taking into account the criteria for inclusion. The values for the optical quality parameters were: 44.54 ± 7.14-cpd (MTFcutoff), 0.27 ± 0.06 (Strehl2D ratio), 1.48 ± 0.24 (OV100%), 1.58 ± 0.32 (OV20%), 1.64 ± 0.39 (OV9%), and 0.38 ± 0.19 (OSI). The nCSF calculated was 1.76 ± 0.21 (3-cpd), 2.13 ± 0.23 (6-cpd), 2.01 ± 0.28 (12-cpd) and 1.86 ± 0.33 (18-cpd).Conclusion: The normal values provided can be a useful tool for discriminating healthy eyes from early abnormal ones in which the optical quality or sensory function is impaired.

Study on NCSFs of individual color mechanisms of human vision based on wave-front aberrations

Neural contrast sensitivity functions (NCSFs) of isolated color mechanisms are obtained based on the measurements of wave-front aberrations and isoluminant color contrast sensitivity functions (CSFs). Our study indicates that the mean NCSF and CSF of the red mechanism are higher than those of the green mechanism, respectively, while those of the blue mechanism are the lowest. However, the relative heights of the peak of NCSF and CSF between red and green mechanisms vary in subjects. There are some individuals whose peak values of NCSF and/or CSF of green mechanism are higher than that of the red mechanism. On the other hand, we find that the NCSFs and CSFs of isolated color mechanisms all exhibit the similar characteristics and variation tendency. With the statistical average, the NCSFs of the red, green and blue mechanisms are higher than the corresponding CSFs in the whole spatial frequency. The peaks of the NCSFs of isolated color mechanisms, comparing with the corresponding CSFs curves, shift toward higher spatial frequencies, especially for that of blue mechanism which has a largest shift of 3.9 c/deg.

Neural contrast sensitivity calculated from measured total contrast sensitivity and modulation transfer function

Abstract Purpose To test the feasibility of calculating neural contrast sensitivity function (neural CSF) from conventionally measured total contrast sensitivity function (total CSF) and measured modulation transfer function (MTF). Neural CSF considers the retina and the brain, whereas total CSF considers the optical eye media, the retina and the brain together. Methods Three groups with 9 eyes each, one group with normal ocular optics but with retinal alterations (mild diabetic retinopathy), another with altered ocular optics and normal retina (keratoconus) and a normal control group were studied. Results Total CSF in the keratoconus and retinopathy group was significantly lower as compared with the control group. MTF for keratoconus was lower and in the retinopathy group was similar to the control group. Calculated neural CSF in the diabetes mellitus group was lower than in the control group whereas in the keratoconus group it was similar to the control group, with overestimations for some keratoconus cases. Conclusion It is possible to calculate a meaningful neural CSF from measured total CSF and MTF data. The neural CSF represents a CSF adjusted for optical aberrations. This would allow comparing the neural component of visual function in eyes with different optical aberrations.

Characteristics and New Measurement Method of NCSFs of Individual Color Mechanisms of Human Vision

We propose a new method for determining neural contrast sensitivity functions (NCSFs) of isolated color mechanisms based on the measurements of wave-front aberrations and isoluminant color contrast sensitivity functions (CSFs). Compared with the traditional method, this technique avoids the coherent noise and speckle noise, which are brought by the interference of laser beams, and has great flexibility for the measurements of NCSF of different color mechanisms. Our experiments indicate that the mean NCSF and CSF of the red mechanism are higher than those of the green mechanism, respectively, while those of the blue mechanism are the lowest. However the relative heights of the peak of NCSF and CSF between red and green mechanisms vary in subjects. There are some individuals whose peak values of NCSF and/or CSF of green mechanism are higher than that of the red mechanism. The NCSFs and CSFs of isolated color mechanisms all exhibit the similar characteristics and variation tendency. With the statistical average, the NCSFs of the red, green and blue mechanisms are higher than the corresponding CSFs in the whole spatial frequency. Compared with the corresponding CSFs curves, the peaks of the NCSFs of isolated color mechanisms shift toward higher spatial frequencies, especially for that of blue mechanism which has a largest shift of 3.9c/deg.

利用视标和波前数据的NCSF测量

A system for measurement to obtain Neural Contrast Sensitivity Function(NCSF) is constructed,according to the relationship between Modulation Transfer Function(MTF)calculated from wave-front date and Contrast Sensitivity Function(CSF) with a wide range of spatial frequencies.Compared with previous measurement method,the coherent noise and speckle noise can be avoided using the proposed method which are brought in by the interference of laser beams,and white-light NCSF can also be provieded.The green-light and white-light NCSF are acquired with this technique for different eyes.It is shown that NCSF,which is independent of the optical system of eye,for green-light is higher than that for white-light under the condition of the same luminance.The maximum value of CSF appears at 8 c/deg of the green-light and white-light,while the maximum value of NCSF of the green-light and white-light appears at a higher spatial frequency of 12 c/deg.

神经对比敏感度的亮度变化机制研究

神经对比敏感度的亮度变化机制研究

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.

Estimating visual quality from wavefront aberration measurements.

Root mean square (RMS) wavefront error may not be the best metric for predicting a patient's visual function; other metrics should be considered. We describe the most important metrics of optical quality, which are being investigated to predict vision quality and visual performance. Optical quality can be described in two different ways. Pupil plane metrics describe variability of the wavefront error at the pupillary plane (eg, RMS wavefront error). Image plane metrics describe the retinal image and do so for either a point source of light (eg, point-spread function [PSF]) or sinusoidal gratings (optical transfer function [OTF]). Visual quality metrics, however, must also consider neural processing and subjective perception. Since vision is more sensitive to rays coming from the center of the pupil, "pupil fraction" appears to be a better predictor of visual acuity (r2 = 0.50) than RMS error (r2 = 0.13). However, image plane metrics, such as the visual Strehl ratio (r2 = 0.62) and the volume between the optical transfer function and neural contrast sensitivity function (r2 = 0.80) appear to be even better. Visual perception is highly subjective and involves many aspects of image quality. A single metric to describe all aspects of image quality may be unrealistic. Nevertheless, improved visual quality metrics need further investigation and will likely involve preferential weighing of light passing through the central area of the pupil and/or incorporating neural factors into image quality computation.

Influence of the type of illumination on the measurement of the modulation transfer function in the living human eye: A theoretical study

Applications such as refractive surgery demand an objective appraisal of the retinal image quality. The modulation transfer function (MTF) provides that information when measured directly. Moreover, the MTF obtained using a simple and objective method such as that described in this paper allows the neural contrast sensitivity function (CSF) to be obtained from the global CSF and the MTF. When calculating the MTF it must be borne in mind whether the applicable theory is coherent or incoherent. In the literature, the developed theory presents some approximations and incongruities. Also, it is interesting to note that the method of recording the MTF (short or long time of integration, sum of images, etc.) and the source used (laser or others) can essentially change the nature of the problem. This theory is not directly applicable to any experiment. This work comprises a thorough theoretical study of the possible cases according to the experimental method and therefore as a function of the coherence degree. Two different solutions are found: the MTF calculated as the square root of the Fourier Transform (FT) of the recorded intensity for any light source or the MTF calculated as the FT square root of the image.