Fourier tools for the evaluation of refractive multifocal designs.

This paper presents innovative tools and methodologies for the theoretical assessment of optical properties in refractive multifocal designs. Utilizing lens segmentation techniques and classical Fourier optics, these tools can be of help evaluating multifocal contact lenses, intraocular lenses, small aperture designs, and corneal inlays. As an example of their utility, this study presents the through-focus Visual Strehl ratios in the frequency domain of 12 multifocal contact lenses from four companies, derived from the sagittal power profiles obtained with a NIMO equipment (LAMBDA-X) for three base prescriptions (- 6.00 D, - 3.00 D, and + 1.00 D). The contact lenses are also assessed alongside higher-order aberrations obtained from 65 eyes, measured using a Wavefront Sciences Complete Ophthalmic Analysis System (AMO). Diameter variations, corresponding to individual pupil sizes (2.45-6.27 mm), were considered in the evaluation. These novel tools enable the theoretical evaluation of multifocal solutions without the need for prototypes. In the case examples presented, they differentiate between lenses tailored for different presbyopic age groups, offer guidance on optimizing hyperfocal distance in contact lens design, and underscore the relevance of the effective aperture effect. Notably, this paper introduces the pioneering conversion of sagittal powers of multifocal solutions into an equivalent wavefront and optical quality metric, with potential applications in myopia control assessments. The author hopes that readers recognize and utilize these tools to advance the field of refractive multifocality.

Changes in Optical Quality Induced by Tilt and Decentration of a Trifocal IOL and a Novel Extended Depth of Focus IOL in Eyes With Corneal Myopic Ablations.

PURPOSE: To assess the effect of decentration and tilt combined with prior myopic ablations on the optical performance of a trifocal intraocular lens (IOL) and a novel IOL with an extended depth of focus (EDOF) design. METHODS: The XACT Mono-EDOF ME4 (Santen Pharmaceutical Co Ltd) and the trifocal FineVision (PhysIOL) IOLs were analyzed with and without simulated previous myopic ablations. The optical quality of the IOLs was evaluated with the PMTF optical bench (LAMBDA-X). The through-focus modulation transfer function (MTF) curves were recorded. Measurements were done for three situations: centered, 0.4 mm decentered, and 4 degrees tilted. RESULTS: The trifocal IOL showed three peaks of vision and the EDOF IOL showed a far distance peak with intermediate addition. When decentration or tilt were induced, the trifocal IOL showed negligible changes but the EDOF IOL showed a -0.50 diopters (D) shift of the overall curve. With simulated myopic ablation, the trifocal IOL showed a -0.50 D shift of the curve. When tilt or decentration were also induced, the better optical results were found at -1.00 D. With myopic ablations, the EDOF IOL showed a -0.50 D shift of the optical quality and when decentration or tilt were then induced, negative shifts over -1.00 D were found. CONCLUSIONS: The trifocal IOL was less affected by mis-alignments. When myopic ablations were induced, both lenses decreased their optical quality and the effects of misalignments were higher. In patients who have undergone corneal myopic ablation procedures, proper alignment of the implanted IOL and obtaining effective emmetropia becomes even more critical. [J Refract Surg. 2021;37(8):532-537.].

Optical tolerance to rotation of trifocal toric intraocular lenses as a function of the cylinder power.

BACKGROUND: The aim was to assess the impact of 5- and 10-degree rotations in the optical quality of a trifocal toric intraocular lens with different amounts of cylinder. METHODS: Two Physiol Toric intraocular lenses with 1.5 and 3.0 D of cylinder were analysed in three different positions: centred, 5 and 10 degrees rotated. The optical quality of the intraocular lenses was evaluated with the PMTF optical bench through specific perpendicular targets. The analysis was performed by the through-focus modulation transfer function curves and the modulation transfer function corresponding to distance vision (0 D of vergence). RESULTS: For a centred situation, the through-focus modulation transfer function curves of both intraocular lenses showed the classical three peaks corresponding to the powers of the two principal meridians of the intraocular lenses. When 5 and 10 degrees of rotation were induced, the three peaks were attenuated in both cases. The case with the intraocular lens with 3.0 D of cylinder and 10 degrees of rotation showed the worst optical quality and a significant loss of trifocality. The modulation transfer function values obtained for distance vision also showed the worst optical quality for the intraocular lens with 3.0 D of cylinder and 10 degrees of rotation. CONCLUSION: Rotations over 5 degrees decreased the optical quality of trifocal toric intraocular lenses, being this reduction moderate from 5 to 10 degrees for low levels of cylinder (≤1.5 D). For mid-high levels of cylinder (≥3.0 D), rotations over 5 degrees cause a significant loss of optical quality at all object distances.

Optical Performance of a Trifocal IOL and a Novel Extended Depth of Focus IOL Combined With Different Corneal Profiles.

PURPOSE: To assess the effect of prior myopic ablations on the optical performance of a trifocal diffractive intraocular lens (IOL) and a novel extended depth of focus (EDOF) diffractive design. METHODS: The novel XACT Mono-EDOF ME4 diffractive IOL (Santen Pharmaceutical) and the trifocal diffractive FineVision IOL (PhysIOL) were analyzed standing alone and combined with a simulated myopic corneal ablation. The optical quality of the IOLs in both situations was evaluated with the PMTF optical bench (LAMBDA-X). The through-focus modulation transfer function (MTF) curves and the MTF at three different focal points (+0.50, 0.00, and -0.50 diopters [D]) were recorded. RESULTS: The through-focus MTF curves showed three differentiated peaks for the trifocal IOL and two overlapped peaks for the EDOF IOL. The presence of simulated myopic corneal ablations induces a -0.50 D shift on the overall through-focus curves and softens the multifocal properties of both lenses by decreasing the variations through focus of the MTF. For the analysis of the lenses standing alone, the highest MTF values were obtained for an object vergence of 0.00 D. For a simulated myopic corneal ablation, both IOLs showed better optical quality results at -0.50 D. CONCLUSIONS: The trifocal IOL provides better optical quality at far and near distances when analyzed alone. The EDOF IOL optical properties are more stable when a myopic ablation is introduced. Preoperative calculations of both lenses should consider that prior myopic corneal ablations induce a -0.50 D shift on their far peak quality. [J Refract Surg. 2020;36(7):435-441.].

Evaluation of Two Strategies for Alleviating the Impact on the Circadian Cycle of Smartphone Screens.

SIGNIFICANCE: Electronic display devices used before bed may negatively affect sleep quality through the effects of short-wavelength (blue) light on melatonin production and the circadian cycle. We quantified the efficacy of night-mode functions and blue-light-reducing lenses in ameliorating this problem. PURPOSE: The purpose of this study was to compare the radiation produced by smartphones that reaches the eye when using night-mode functions or blue-light-reducing spectacle lenses. METHODS: Radiant flux of 64 smartphones was measured with an integrating sphere. The retinal illuminance was calculated from the radiant flux of the smartphones. For the night-mode functions, the spectra produced by the smartphones were measured. The transmittance of four blue-light-reducing spectacle lenses, which filter light with either antireflective coatings or tints, was measured using a spectrometer. To determine the impact of blue-light-reducing spectacles, the radiant flux of the smartphone was weighted by the transmission spectrum of these glasses. Visual and nonvisual (circadian) parameters were calculated to compute the melatonin suppression values (MSVs) through a logistic fitting of previously published data. The MSV was used as the figure of merit to evaluate the performance of blue-light spectacles and smartphone night-mode functions. RESULTS: Night-mode functions in smartphones reduced MSVs by up to 93%. The warmest mode produced the least suppression. Blue-light-reducing spectacles reduced melatonin suppression by 33%, the coated lenses being more efficient than tinted lenses. CONCLUSIONS: All smartphones in this study emit radiant power in the short-wavelength region of the visible spectrum. Such smartphones may impair the regulation of circadian cycles at nighttime. The activation of night-mode functions was more efficient than the commercially available blue-light-reducing spectacle lenses in reducing the amount of short-wavelength light (up to 2.25 times). These results can be extrapolated to most electronic devices because they share the same type of white radiant sources with smartphones.

Comparing habitual and i. Scription refractions.

BACKGROUND: Many patients voice concerns regarding poor night vision, even when they see 20/20 or better in the exam room. During mesopic and scotopic conditions the pupil size increases, increasing the effects on visual performance of uncorrected (residual) refractive errors. The i.Scription refraction method claims to optimize traditional refractions for mesopic and scotopic conditions, by using the information that the Zeiss i.Profilerplus gathers of ocular aberrations (low and high order). The aim of this study was to investigate any differences between habitual and i.Scription refractions and their relationship to night vision complaints. METHODS: Habitual, subjective, and i.Scription refractions were obtained from both eyes of eighteen subjects. Low and high order aberrations of the subjects were recorded with the Zeiss i.Profilerplus. The root mean square (RMS) metric was calculated for small (3 mm) and maximum pupil sizes. Subjects rated their difficulty with driving at night on a scale of 1-10. RESULTS: There was a statistically significant difference between the habitual and i.Scription refractions on both the sphere and cylinder values [(t = 3.12, p < 0.01), (t = 5.39, p < 0.01)]. The same was found when comparing the subjective and i.Scription refractions [(t = 2.31, p = 0.03), (t = 2.54, p = 0.02)]. There were no significant differences found when comparing the sphere and cylinder values between the habitual and subjective refractions or on any combination of spherical equivalent refraction. The maximum pupil size of the subject population on this study, measured with the i.Profilerplus, was 4.8 ± 1.04 mm. Ten out of the eighteen subjects had discomfort at night with an average magnitude of 4 ± 2.7. Ratings of difficulty with night vision correlated with the change in spherical equivalent correction between the habitual and i.Scription refractions (p = 0.01). A sub-analysis of myopic subjects (n = 15) showed an increase in the significance of this relationship (p = 0.002). CONCLUSIONS: The i.Scription method improves night vision by correcting the sphere and cylinder more precisely. There was a correlation between the amount of change in the cylinder value between habitual and i.Scription prescriptions and the magnitude of the reported visual discomfort at night.

Optimal orientation for angularly segmented multifocal corrections.

PURPOSE: Evaluate the importance of orientation of multifocal lens designs with angular increments of addition. METHODS: Optical properties of one monofocal and three multifocal designs were analysed with the visual Strehl ratio (VSOTF) metric through-focus (-1 to 5 D). Designs were tested in combination with the higher-order aberrations (HOAs) of 782 subjects (1564 eyes). Simulations included one monofocal, one bifocal (eight orientations), one trifocal (four orientations), and a 4-foci design (four orientations). Monocular and binocular performances of all designs were assessed by computing the area under the through-focus VSOTF plots, the through-focus range of acceptable optical performance, and, for binocular combinations, optical disparity between left and right eyes. RESULTS: Under monocular conditions, bifocal designs generated larger areas under the through focus VSOTF than trifocal designs and 4-foci designs. Specifically, bifocal designs divided vertically were optimal for 48% of eyes. Trifocal designs and 4-foci designs offered longer intervals of acceptable through-focus vision. Coma and spherical aberration values were correlated with the optimal orientation of multifocal corrections. The best binocular combination was achieved with a monofocal and a trifocal lens. The orientation of a multifocal design with angular areas affected the final optical properties of the combination (lens plus eye). CONCLUSIONS: The optical aberration distributions for our population of physiologically normal eyes demonstrated improved performance for some lens design orientations (i.e., left-right segments for 2-zone bifocals). Taking into account the HOAs of healthy patients, with special attention to coma and spherical aberration, will increase the optical quality of angularly divided multifocal solutions.

Perceived image quality with simulated segmented bifocal corrections.

Bifocal contact or intraocular lenses use the principle of simultaneous vision to correct for presbyopia. A modified two-channel simultaneous vision simulator provided with an amplitude transmission spatial light modulator was used to optically simulate 14 segmented bifocal patterns (+ 3 diopters addition) with different far/near pupillary distributions of equal energy. Five subjects with paralyzed accommodation evaluated image quality and subjective preference through the segmented bifocal corrections. There are strong and systematic perceptual differences across the patterns, subjects and observation distances: 48% of the conditions evaluated were significantly preferred or rejected. Optical simulations (in terms of through-focus Strehl ratio from Hartmann-Shack aberrometry) accurately predicted the pattern producing the highest perceived quality in 4 out of 5 patients, both for far and near vision. These perceptual differences found arise primarily from optical grounds, but have an important neural component.

Erratum: Perceived image quality with simulated segmented bifocal corrections: publisher's note.

[This corrects the article on p. 4388 in vol. 7.].

Optical properties of monovision corrections using multifocal designs for near vision.

PURPOSE: To evaluate how multiple-zone multifocal designs maximize optical performance of modified monovision corrections. SETTING: Midwestern University, Chicago College of Optometry, Downers Grove, Illinois, USA. DESIGN: Experimental study. METHODS: Optical performance under monovision conditions combining monofocal, bifocal, trifocal, and designs with spherical aberration was evaluated using computer simulations of the visual Strehl ratio based on the optical transfer function in relation to the optical quality provided by design (limiting performance at best focus), through-focus performance of design (evaluating real multifocal usability), and difference between images on each eye (limiting tolerance for monovision corrections). RESULTS: Monovision corrections with bifocal or trifocal patterns for near vision offered higher optical performance (larger area under values of the visual Strehl ratio and larger range of acceptable vision through-focus) than an aspheric design. A bifocal design with 1.5 diopters (D) of addition and centered through-focus between 2.0 D and 3.5 D had the best range above threshold (3.98 D) for a monofocal design (centered at 0 D, distance vision) combined with a bifocal design. The largest optical disparity was achieved with 2 monofocal designs (1 centered at 0 D, 1 centered at 4.0 D). CONCLUSIONS: Bifocal and trifocal combinations produced higher optical quality (5%) and through-focus performance (35%) than spherical aberration designs. For any given amount of tolerable optical disparity in presbyopia, a combination of monofocal and bifocal/trifocal designs offered better optical performance than a spherical aberration design. Bifocal and trifocal designs can be implemented in laser in situ keratomileusis equipment to improve conventional monovision and will soon be available in new multifocal contact and intraocular lenses. FINANCIAL DISCLOSURE: The author has no financial or proprietary interest in any material or method mentioned.

Automatic counting of microglial cell activation and its applications.

Glaucoma is a multifactorial optic neuropathy characterized by the damage and death of the retinal ganglion cells. This disease results in vision loss and blindness. Any vision loss resulting from the disease cannot be restored and nowadays there is no available cure for glaucoma; however an early detection and treatment, could offer neuronal protection and avoid later serious damages to the visual function. A full understanding of the etiology of the disease will still require the contribution of many scientific efforts. Glial activation has been observed in glaucoma, being microglial proliferation a hallmark in this neurodegenerative disease. A typical project studying these cellular changes involved in glaucoma often needs thousands of images - from several animals - covering different layers and regions of the retina. The gold standard to evaluate them is the manual count. This method requires a large amount of time from specialized personnel. It is a tedious process and prone to human error. We present here a new method to count microglial cells by using a computer algorithm. It counts in one hour the same number of images that a researcher counts in four weeks, with no loss of reliability.

Automatic Counting of Microglial Cells in Healthy and Glaucomatous Mouse Retinas.

Proliferation of microglial cells has been considered a sign of glial activation and a hallmark of ongoing neurodegenerative diseases. Microglia activation is analyzed in animal models of different eye diseases. Numerous retinal samples are required for each of these studies to obtain relevant data of statistical significance. Because manual quantification of microglial cells is time consuming, the aim of this study was develop an algorithm for automatic identification of retinal microglia. Two groups of adult male Swiss mice were used: age-matched controls (naïve, n = 6) and mice subjected to unilateral laser-induced ocular hypertension (lasered; n = 9). In the latter group, both hypertensive eyes and contralateral untreated retinas were analyzed. Retinal whole mounts were immunostained with anti Iba-1 for detecting microglial cell populations. A new algorithm was developed in MATLAB for microglial quantification; it enabled the quantification of microglial cells in the inner and outer plexiform layers and evaluates the area of the retina occupied by Iba-1+ microglia in the nerve fiber-ganglion cell layer. The automatic method was applied to a set of 6,000 images. To validate the algorithm, mouse retinas were evaluated both manually and computationally; the program correctly assessed the number of cells (Pearson correlation R = 0.94 and R = 0.98 for the inner and outer plexiform layers respectively). Statistically significant differences in glial cell number were found between naïve, lasered eyes and contralateral eyes (P<0.05, naïve versus contralateral eyes; P<0.001, naïve versus lasered eyes and contralateral versus lasered eyes). The algorithm developed is a reliable and fast tool that can evaluate the number of microglial cells in naïve mouse retinas and in retinas exhibiting proliferation. The implementation of this new automatic method can enable faster quantification of microglial cells in retinal pathologies.

Multiple zone multifocal phase designs.

New multifocal phase designs aiming at expanding depth of focus in the presbyopic eye are presented. The designs consist of multiple radial or angular zones of different powers or of combined low- and high-order aberrations. Multifocal performance was evaluated in terms of the dioptric range for which the optical quality is above an appropriate threshold, as well as in terms of the area under the through-focus optical quality curves. For varying optical power designs optimal through-focus performance was found for a maximum of three to four zones. Furthermore adding more zones decreased the optical performance of the solution. Angular zone designs provided better multifocal performance (1.95 times on average) than radial zone designs with identical number of zones and the same power range. The optimal design (angular design with three zones) surpassed by 33% the multifocal performance of a bifocal angular zone design and by 32% a standard multifocal phase plate with induced spherical aberration only. By using combinations of low- and high-order aberrations the through-focus range can be extended further by another 0.5 D beyond that of the best design of varying optical power. These designs can be implemented in adaptive optics systems for testing their visual performance in subjects and converted into multifocal contact lenses, intraocular lenses, or presbyopic corneal laser ablation profiles.

Astigmatism impact on visual performance: meridional and adaptational effects.

PURPOSE: Astigmatic subjects are adapted to their astigmatism and perceptually recalibrate upon its correction. However, the extent to which prior adaptation to astigmatism affects visual performance, whether this effect is axis dependent, and the time scale of potential changes in visual performance after astigmatism correction are not known. Moreover, the effect of possible positive interactions of aberrations (astigmatism and coma) might be altered after recalibration to correction of astigmatism. METHODS: Visual acuity (VA) was measured in 25 subjects (astigmats and non-astigmats, corrected and uncorrected) under induction of astigmatism and combinations of astigmatism and coma while controlling subject aberrations. Astigmatism (1.00 diopter) was induced at three different orientations, the natural axis, the perpendicular orientation, and 45 degrees for astigmats and at 0, 90, and 45 degrees for non-astigmats. Experiments were also performed, adding coma (0.41 µm at a relative angle of 45 degrees) to the same mentioned astigmatism. Fourteen different conditions were measured using an 8-Alternative Forced Choice procedure with Tumbling E letters and a QUEST algorithm. Longitudinal measurements were performed up to 6 months. Uncorrected astigmats were provided with proper astigmatic correction after the first session. RESULTS: In non-astigmats, inducing astigmatism at 90 degrees, produced a statistically lower reduction in VA than at 0 or 45 degrees, whereas in astigmats, the lower decrease in VA occurred for astigmatism induced at the natural axis. Six months of astigmatic correction did not reduce the insensitivity to astigmatic induction along the natural axis. Differences after orientation of astigmatism were also found when adding coma to astigmatism. CONCLUSIONS: The impact of astigmatism on VA is greatly dependent on the orientation of the induced astigmatism, even in non-astigmats. Previous experience to astigmatism plays a significant role on VA, with a strong bias toward the natural axis. In contrast to perceived isotropy, the correction of astigmatism does not shift the bias in VA from the natural axis of astigmatism.

Experimental simulation of simultaneous vision.

PURPOSE: To present and validate a prototype of an optical instrument that allows experimental simulation of pure bifocal vision. To evaluate the influence of different power additions on image contrast and visual acuity. METHODS: The instrument provides the eye with two superimposed images, aligned and with the same magnification, but with different defocus states. Subjects looking through the instrument are able to experience pure simultaneous vision, with adjustable refractive correction and addition power. The instrument is used to investigate the impact of the amount of addition of an ideal bifocal simultaneous vision correction, both on image contrast and on visual performance. the instrument is validated through computer simulations of the letter contrast and by equivalent optical experiments with an artificial eye (camera). Visual acuity (VA) was measured in four subjects (AGE: 34.3 ± 3.4 years; spherical error: -2.1 ± 2.7 diopters [D]) for low and high contrast letters and different amounts of addition. RESULTS: The largest degradation in contrast and visual acuity (∼25%) occurred for additions around ±2 D, while additions of ±4 D produced lower degradation (14%). Low additions (1-2 D) result in lower VA than high additions (3-4 D). CONCLUSIONS: A simultaneous vision instrument is an excellent tool to simulate bifocal vision and to gain understanding of multifocal solutions for presbyopia. Simultaneous vision induces a pattern of visual performance degradation, which is well predicted by the degradation found in image quality. Neural effects, claimed to be crucial in the patients' tolerance of simultaneous vision, can be therefore compared with pure optical effects.

Perceptual adaptation to the correction of natural astigmatism.

BACKGROUND: The visual system adjusts to changes in the environment, as well as to changes within the observer, adapting continuously to maintain a match between visual coding and visual environment. We evaluated whether the perception of oriented blur is biased by the native astigmatism, and studied the time course of the after-effects following spectacle correction of astigmatism in habitually non-corrected astigmats. METHODS AND FINDINGS: We tested potential shifts of the perceptual judgments of blur orientation in 21 subjects. The psychophysical test consisted on a single interval orientation identification task in order to measure the perceived isotropic point (astigmatism level for which the image did not appear oriented to the subject) from images artificially blurred with constant blur strength (B=1.5 D), while modifying the orientation of the blur according to the axis of natural astigmatism of the subjects. Measurements were performed after neutral (gray field) adaptation on naked eyes under full correction of low and high order aberrations. Longitudinal measurements (up to 6 months) were performed in three groups of subjects: non-astigmats and corrected and uncorrected astigmats. Uncorrected astigmats were provided with proper astigmatic correction immediately after the first session. Non-astigmats did not show significant bias in their perceived neutral point, while in astigmatic subjects the perceived neutral point was significantly biased, typically towards their axis of natural astigmatism. Previously uncorrected astigmats shifted significantly their perceived neutral point towards more isotropic images shortly (2 hours) after astigmatic correction wear, and, once stabilized, remained constant after 6 months. The shift of the perceived neutral point after correction of astigmatism was highly correlated with the amount of natural astigmatism. CONCLUSIONS: Non-corrected astigmats appear to be naturally adapted to their astigmatism, and astigmatic correction significantly changes their perception of their neutral point, even after a brief period of adaptation.

Dependence of subjective image focus on the magnitude and pattern of high order aberrations.

The image formed by the eye's optics is inherently blurred by aberrations specific to the individual's eyes. We examined to what extent judgments of perceived focus depend on the total magnitude as opposed to the specific pattern of blur introduced by the eye's high order aberrations (HOA). An Adaptive Optics system was used to simultaneously correct each subject's wave aberrations and display natural images blurred by simulated aberrations. To isolate the effects of blur magnitude, images were blurred by pure symmetric defocus, and subjects judged the level of the defocus that subjectively appeared best focused (i.e., neither too blurred nor too sharp). These settings were strongly correlated with the native blur magnitude. To isolate the effect of the HOA pattern, retinal image blur was instead maintained at a constant blur (Strehl Ratio) equal to each subject's natural blur, and subjects judged the best-focused image from pairs of images blurred by different patterns of HOA, one selected from 100 patterns, the other blurred by a reference pattern which included the subject's natural HOA, rotated HOA, or nine other HOA patterns. The percentage of images judged as best focused was not systematically higher when filtered with the subject's own HOA pattern. However, all subjects preferred their own HOA to the rotated version significantly more often (57% versus 45% on average across subjects). The representation of subjective image focus thus appears to be driven primarily by the overall amount of blur and only weakly by HOA blur orientation.

Vision is adapted to the natural level of blur present in the retinal image.

BACKGROUND: The image formed by the eye's optics is inherently blurred by aberrations specific to an individual's eyes. We examined how visual coding is adapted to the optical quality of the eye. METHODS AND FINDINGS: We assessed the relationship between perceived blur and the retinal image blur resulting from high order aberrations in an individual's optics. Observers judged perceptual blur in a psychophysical two-alternative forced choice paradigm, on stimuli viewed through perfectly corrected optics (using a deformable mirror to compensate for the individual's aberrations). Realistic blur of different amounts and forms was computer simulated using real aberrations from a population. The blur levels perceived as best focused were close to the levels predicted by an individual's high order aberrations over a wide range of blur magnitudes, and were systematically biased when observers were instead adapted to the blur reproduced from a different observer's eye. CONCLUSIONS: Our results provide strong evidence that spatial vision is calibrated for the specific blur levels present in each individual's retinal image and that this adaptation at least partly reflects how spatial sensitivity is normalized in the neural coding of blur.

Contrast sensitivity benefit of adaptive optics correction of ocular aberrations.

While correcting the aberrations of the eye produces large increases in retinal image contrast, the corresponding improvement factors in the contrast sensitivity function have been little explored and results are controversial. We measured the CSF of 4 subjects with and without correcting monochromatic aberrations. Monochromatic CSF measurements were performed at four orientations (0, 45, 90, and 135 deg) and at six spatial frequencies (2-30 c/deg). In two subjects, the CSF was also measured in polychromatic light. The MTF increased on average by 8 times and meridional changes in improvement were associated to individual meridional changes in the natural MTF. CSF increased on average by 1.35 times (only for the mid- and high spatial frequencies) and was lower (0.93 times) for polychromatic light. Under natural aberrations, the horizontal and vertical CSFs tended to be higher than the oblique CSFs, but the meridional differences in the CSF were partially reduced when the aberrations were corrected. The consistently lower benefit in the CSF than in the MTF of correcting aberrations suggests a significant role for the neural transfer function in the limit of contrast perception. Polychromatic aberrations play an additional role in degrading contrast, particularly in the absence of monochromatic high-order aberrations.