Method to Quickly Map Multifocal Pupillary Response Fields (mPRF) Using Frequency Tagging.

We present a method for mapping multifocal Pupillary Response Fields in a short amount of time using a visual stimulus covering 40° of the visual angle divided into nine contiguous sectors simultaneously modulated in luminance at specific, incommensurate, temporal frequencies. We test this multifocal Pupillary Frequency Tagging (mPFT) approach with young healthy participants (N = 36) and show that the spectral power of the sustained pupillary response elicited by 45 s of fixation of this multipartite stimulus reflects the relative contribution of each sector/frequency to the overall pupillary response. We further analyze the phase lag for each temporal frequency as well as several global features related to pupil state. Test/retest performed on a subset of participants indicates good repeatability. We also investigate the existence of structural (RNFL)/functional (mPFT) relationships. We then summarize the results of clinical studies conducted with mPFT on patients with neuropathies and retinopathies and show that the features derived from pupillary signal analyses, the distribution of spectral power in particular, are homologous to disease characteristics and allow for sorting patients from healthy participants with excellent sensitivity and specificity. This method thus appears as a convenient, objective, and fast tool for assessing the integrity of retino-pupillary circuits as well as idiosyncrasies and permits to objectively assess and follow-up retinopathies or neuropathies in a short amount of time.

Accommodative response and visual fatigue following a non-congruent visual task in non-asthenopic and asthenopic individuals.

PURPOSE: Asthenopia is related to near vision activities or visual tasks that dissociate accommodation from vergence. Since the results of previous studies using objective measures to diagnose asthenopia are inconsistent, this study compared optometric tests and objective metrics of accommodation in non-asthenopic and asthenopic young adults before and after a visual fatigue task. METHODS: The accommodative response was recorded objectively for 6 min at a 3.33 D accommodative demand using an autorefractor, before and after a 5-min non-congruent visual task. Accommodation was disassociated from vergence with a ±2.00 D accommodative flipper while reading at the same distance. Optometric tests and subjective evaluations of asthenopia were performed before and after the task. Twenty-six non-presbyopic adults (23.15 ± 2.56 years) were included and identified as asthenopic (n = 14) or non-asthenopic (n = 12) based on their score on the Computer Vision Syndrome Questionnaire. RESULTS: A mixed ANOVA found no significant difference between the groups for objective (accommodative response) or subjective metrics (feeling of fatigue, optometric tests), although all participants reported greater visual fatigue after the task. A significant effect of time (before and after the non-congruent task) was identified for the overall sample for mean accommodative lag (+0.10 D, p = 0.01), subjective visual fatigue (+1.18, p < 0.01), negative relative accommodation (-0.20 D, p = 0.02) and near negative fusional reserve (blur: +2.46Δ, p < 0.01; break: +1.89Δ, p < 0.01; recovery: +3.34Δ, p = 0.02). CONCLUSIONS: The task-induced asthenopia, measured both objectively and subjectively, was accompanied by a change in accommodative lag, greater visual fatigue and a decrease in negative relative accommodation. Conversely, near negative fusional reserves seem to adapt to the task. No significant differences were found between the two groups with respect to accommodative metrics (objective) or subjective and optometric tests.

Does visual acuity predict visual preference in progressive addition lenses?

PURPOSE: We aimed to determine if visual acuity (VA) could differentiate the quality of vision with two ophthalmic lenses with unwanted astigmatism. METHODS: Twenty presbyopic subjects (48 to 62 years old; VA better than 0.0 logMAR) graded the magnitude of their preference between two progressive addition lenses (plano addition 2.00D) and their visual acuities were measured with both lenses at various eccentricities from -12 to +12 mm from the near vision point every 3 mm in controlled conditions. RESULTS: The Lens with the least peripheral astigmatism was preferred by 75% of the subjects. VA measured at the near vision point was statistically worse (p<0.01) with this lens whereas the contrary was observed in the periphery (± 12 and -9 mm of eccentricity). The Friedman test shows that the eccentricity (p<0.001) has a significant effect on visual acuity. However, the lens did not show any significant effect (p=0.76). The choice of the favorite lens was predicted for only 35% when considering central VA (up to 6mm) and 80% of the subjects when considering peripheral VA (9 to 12mm). However, the magnitude of the difference could be predicted by peripheral VA in only 60% of the subjects. CONCLUSION: High contrast Visual acuity was clearly able to differentiate the 2 lens designs tested in our experiment. However, even under the controlled conditions of this study, it was not possible to predict the quality of vision, as measured by a subjective appreciation, through progressive addition lenses at various eccentricities from the near vision with an addition of 2.0D.

Adaptive optics visual simulators: a review of recent optical designs and applications [Invited].

In their pioneering work demonstrating measurement and full correction of the eye's optical aberrations, Liang, Williams and Miller, [JOSA A14, 2884 (1997)10.1364/JOSAA.14.002884] showed improvement in visual performance using adaptive optics (AO). Since then, AO visual simulators have been developed to explore the spatial limits to human vision and as platforms to test non-invasively optical corrections for presbyopia, myopia, or corneal irregularities. These applications have allowed new psychophysics bypassing the optics of the eye, ranging from studying the impact of the interactions of monochromatic and chromatic aberrations on vision to neural adaptation. Other applications address new paradigms of lens designs and corrections of ocular errors. The current paper describes a series of AO visual simulators developed in laboratories around the world, key applications, and current trends and challenges. As the field moves into its second quarter century, new available technologies and a solid reception by the clinical community promise a vigorous and expanding use of AO simulation in years to come.

CENTRAL SEROUS CHORIORETINOPATHY: High-Resolution Imaging of Asymptomatic Fellow Eyes Using Adaptive Optics Scanning Laser Ophthalmoscopy.

PURPOSE: To investigate cone density in the asymptomatic fellow eye of patients with unilateral central serous chorioretinopathy (CSCR). METHODS: Seventeen asymptomatic fellow eyes of patients with unilateral CSCR and 17 eyes of aged-matched and gender-matched healthy controls underwent adaptive optics ophthalmoscopy. Cone density and spacing were assessed at the fovea. Clinical and multimodal imaging findings were also recorded. RESULTS: In the CSCR group, the patient mean age was 48.9 ± 9.8 years. The mean (±SD) subfoveal choroidal thickness was 417.8 ± 125.2 µm. The foveal external limiting membrane and ellipsoid zone were intact in all patients. Adaptive optics fundus imaging showed a significant decrease in cone density at 2° of eccentricity nasal and temporal to the fovea in asymptomatic fellow eyes of patients with unilateral CSCR compared with controls (P = 0.001 and P = 0.027, respectively). No statistically significant difference in cone density was found at 4° of eccentricity nasal and temporal to the fovea between both groups. CONCLUSION: Asymptomatic fellow eyes of patients with unilateral CSCR showed a reduced density of foveal cones in the absence of a decreased visual acuity and photoreceptor line disruption on optical coherence tomography. These results suggest that the photoreceptors could be damaged independently of the occurrence of a serous retinal detachment.

Subjective Evaluation of Defocus and Astigmatism Combinations Using Image Simulation in Presbyopes.

SIGNIFICANCE: Image simulation is a useful and efficient tool to explore the impact of defocus and astigmatism combinations on visual acuity and image quality score when accommodation is taken into account. PURPOSE: The goal of this experiment was to determine if a simulation is able to predict visual acuity and image quality score (IQS) with defocus and astigmatism combinations in presbyopes. METHODS: We measured visual acuity and IQS in five defocus and astigmatism combinations in either real or simulated conditions. In real conditions, the subjects viewed a stimulus through an ophthalmic lens or a deformable mirror. In simulated conditions, subjects viewed images of the same stimulus with simulated blur. The amounts of defocus and astigmatism combinations of a progressive addition lens in near vision were generated through a static correction of the subject's aberrations. We simulated three levels of accommodation: subject could not accommodate (FOC0), subject could accommodate to the less hyperopic focal point (FOC1), or subject could accommodate to the circle of least confusion (FOC2). RESULTS: Visual acuity or IQS did not differ between mirror and progressive addition lens conditions. Visual acuity measured in real blur conditions differed significantly from that in FOC0 simulated blur condition but were similar to that in FOC1 and FOC2 simulated blur conditions. Image quality score obtained in real conditions were between scores measured with the FOC0 and FOC1 simulated conditions, suggesting that the subjects were able to produce a low level of accommodation. CONCLUSIONS: Accommodation may play a role when comparing optical and simulated defocus and astigmatism combinations. Presbyopic subjects are able to produce a low level of accommodation that may counterbalance a part of the deleterious effect of the astigmatism on image quality. Simulation remains a useful tool if the correct accommodation state is taken into account.

Effect of Simulated and Real Spherical and Astigmatism Defocus on Visual Acuity and Image Quality Score.

SIGNIFICANCE: Image simulation is a useful and efficient tool to explore the impact of spherical and astigmatic blur on visual acuity (VA) and image gradation. It could help to design new optical corrections more efficiently and rapidly. PURPOSE: The purpose of this study was to compare the effects of simulated (convolution by an artificial eye) and real spherical and astigmatic defocus on VA and image gradation. METHODS: Experiments were performed under highly controlled conditions: dynamic correction of the subjects' aberrations at 1 Hz and application of an artificial pupil. In experiment 1, Landolt C VA was measured in various conditions of spherical and astigmatism defocus. The amounts of spherical or positive astigmatic defocus oriented at 45° that gives a Landolt C VA of 0.0, 0.2, and 0.5 logMAR were measured in experiment 2. In experiment 3, the subjects scored the quality of the perceived image (three high-contrast 0.4 logMAR letters) with a five-item continuous grading scale. RESULTS: Simulated blur was always more detrimental than optical blur. We measured a difference of 0.08 ± 0.03 and 0.11 ± 0.05 logMAR between both conditions, respectively, in presence of spherical and astigmatism defocus. An average ± standard deviation difference of 0.16 ± 0.06 D (i.e., spherical defocus) and 0.24 ± 0.15 D (i.e., astigmatism defocus) was observed between simulated and real optics blur to provide a given VA. The differences of image quality score between both conditions were, respectively, 15.13 ± 9.63 and 13.33 ± 4.83 for spherical and astigmatism defocus. Most of the differences were statistically significant. CONCLUSIONS: We observed a difference of about 20 and 35% between simulated and real optics blur, respectively, in presence of spherical and astigmatism blur. However, the difference between both methods remains equal to or below the clinically significant difference.

Distribution of mid-peripheral cones in emmetropic and myopic subjects using adaptive optics flood illumination camera.

PURPOSE: We measured in vivo cone photoreceptors up to 24° of eccentricity along the horizontal meridian of healthy human retina. We also investigated the impact on cone densities of axial eye length elongation occurring with myopia. METHODS: Using a flood illumination device coupled with an adaptive optics system, rtx1™, ( www.imagine-eyes.com), 55 right healthy retinas were imaged along the horizontal (i.e. nasal and temporal) meridian over a 48° field (i.e. from 3° to 24° each 3°). Then, cones were manually detected within 80 × 80 pixel regions of interest. Cone density and packing geometry (i.e. number of neighbours) were calculated (AOdetect software™). Subjects were divided into three groups: a group of 36 emmetropic (i.e. refractive error from -0.25D to +0.50D) subjects; a group of 10 low myopic subjects (i.e. refractive error from -0.50D to -2.50D); and a group of nine high myopic subjects (i.e. >-2.50D). RESULTS: Cone density decreased with eccentricity in both semi-meridians. The decrease in cone photoreceptors occurred mainly in the first 9°. The difference of cone density between the nasal and temporal semi-meridian increased with eccentricity from 0.6% at 3° to 26% at 24°. Average cone density of emmetropes (850 cones deg-2 or 11 087 cones mm-2 ), low myopes (830 cones deg-2 or 9731 cones mm-2 ), and high myopes (912 cones deg-2 or 9744 cones mm-2 ), suggested that the retinas of the high myopic subjects were more stretched than the low myopic subjects retinas and even more stretched than that of the emmetropes. The axial eyeball elongation (square of the ratio of the axial eye length of 9%) seems to explain the cone density (11%) difference between emmetropes and low myopes. However, while the eyeball elongation between low and high myopes is still important (i.e. 11%), cone density difference between both populations was negligible (i.e. 3%). The ratio of cone density varied from -17% to 22% as a function of eccentricity involving that the retinal stretching is not uniform along the horizontal meridian. CONCLUSION: The difference of cone density (i.e. cone mm-2 ) between groups supports the hypothesis that the retina is stretched with the eyeball elongation. However, this elongation does not seem to be uniform along the horizontal meridian favouring the hypothesis of a local elongation of the retina.

Distribution of cone density, spacing and arrangement in adult healthy retinas with adaptive optics flood illumination.

The aim of this article is to analyse cone density, spacing and arrangement using an adaptive optics flood illumination retina camera (rtx1™) on a healthy population. Cone density, cone spacing and packing arrangements were measured on the right retinas of 109 subjects at 2°, 3°, 4°, 5° and 6° of eccentricity along 4 meridians. The effects of eccentricity, meridian, axial length, spherical equivalent, gender and age were evaluated. Cone density decreased on average from 28 884 ± 3 692 cones/mm2, at 2° of eccentricity, to 15 843 ± 1 598 cones/mm2 at 6°. A strong inter-individual variation, especially at 2°, was observed. No important difference of cone density was observed between the nasal and temporal meridians or between the superior and inferior meridians. However, the horizontal and vertical meridians differed by around 14% (T-test, p<0.0001). Cone density, expressed in units of area, decreased as a function of axial length (r2 = 0.60), but remained constant (r2 = 0.05) when cone density is expressed in terms of visual angle supporting the hypothesis that the retina is stretched during the elongation of the eyeball. Gender did not modify the cone distribution. Cone density was slightly modified by age but only at 2°. The older group showed a smaller density (7%). Cone spacing increased from 6,49 ± 0,42 µm to 8,72 ± 0,45 µm respectively between 2° and 6° of eccentricity. The mosaic of the retina is mainly triangularly arranged (i.e. cells with 5 to 7 neighbors) from 2° to 6°. Around half of the cells had 6 neighbors.

Visual resolution and cone spacing in the nasal and inferior retina.

PURPOSE: To determine the retinal eccentricity at which cones are no longer an observable substitute for ganglion cells on nasal and inferior parafoveal visual acuity. METHOD: Visual acuities were measured on 12 healthy volunteers, under dynamic adaptive optic aberrations correction (crx1™) in white light, from 0° to 6°, every two degrees, along the nasal and inferior retinal meridians. Cone spacing was measured on images of the retina acquired using an adaptive optic flood illumination retina camera (rtx1™) at the same eccentricity, except at 0°. RESULTS: Cone spacing increased by around 0.13 min of arc per degree of eccentricity and a difference of 7% between both meridians was observed (higher cone spacing in the inferior retinal meridian). Visual resolution was higher in the nasal retinal meridian (difference of around 28% or 0.15 logMAR at 6°). Cone spacing can predict minimum angle of resolution (MAR) at 2° in both semi retinal meridians. In the inferior retinal meridian, MAR measurements are fairly well predicted by Watson's 50% mathematical model based on the midget retinal ganglion cell density. Along the nasal retinal meridian, the measured MAR lies between Watson's 50% and 100% models. CONCLUSIONS: At 2° of eccentricity, cone density accurately predicts visual resolution in both the nasal and inferior retina, supporting the idea that only 50% of the foveal midget retinal ganglion cells determine VA. The 50% model can also predict VA in the inferior retinal meridian at 4° and 6° of eccentricity. However, the 50% model underestimated visual acuity in the nasal retinal meridian at 4° and 6° of eccentricity consistent with the partially overlapping ON and OFF midget retinal ganglion cell receptive fields.

Simulation of commercial vs theoretically optimised contact lenses for presbyopia.

PURPOSE: To compare theoretically optimised bifocal contact lens optical designs to commercially available optical designs for presbyopia. METHODS: Retinal images were simulated, using a numerical eye model, from -6 (i.e., near vision) to +2 D for each 0.25 D. Ten optical profiles were simulated. Four of them corresponded to commercial contact lenses (i.e., Acuvue Oasys for Presbyopia®, Air Optix Aqua Multifocal®, Purevision Multifocal® and Distance Biofinity Multifocal®). We also included six optimised profiles: (1) a combination of primary and secondary spherical aberration, (2) bifocal profiles with 2, 5 and 8 concentric zones, and (3) a combination of spherical aberrations with the 5 and 8 zones profiles. Twenty subjects scored the quality of vision of calculated images (i.e., three high-contrast 0.40 logMAR letters) for each design and vergence with a five-item continuous grading scale. They viewed these images through their best sphero-cylindrical correction and a 3-mm pupil to limit the impact of their aberrations. To quantify the ability of a bifocal optic to maintain a certain level of quality of vision, we calculated two criteria: (1) the area under the through-focus quality of vision curve higher than 2 (i.e., limit between poor and fair quality of vision) normalised by the same area calculated on the naked eye's curve, and (2) the width of the curve at a level of 2 (i.e., depth-of-focus). RESULTS: Commercial contact lens profiles did not give an image quality and depth-of-focus as good as the theoretically optimised optical profiles. Based on these two criteria, the best bifocal profiles were those with 5 and 8 concentric zones. Important inter-individual variations were observed for all profiles. We also observed that some subjects did not obtain any benefit with all the designs whereas others seemed to be satisfied whatever the optical profiles. CONCLUSION: Our previously optimised designs with 5 and 8 zones gave the best benefit and depth-of-focus. As their image quality is better than commercially available designs, it would be interesting to prototype these designs and to test them in a clinical setting.

Vision science and adaptive optics, the state of the field.

Adaptive optics is a relatively new field, yet it is spreading rapidly and allows new questions to be asked about how the visual system is organized. The editors of this feature issue have posed a series of question to scientists involved in using adaptive optics in vision science. The questions are focused on three main areas. In the first we investigate the use of adaptive optics for psychophysical measurements of visual system function and for improving the optics of the eye. In the second, we look at the applications and impact of adaptive optics on retinal imaging and its promise for basic and applied research. In the third, we explore how adaptive optics is being used to improve our understanding of the neurophysiology of the visual system.

Effect of age, decentration, aberrations and pupil size on subjective image quality with concentric bifocal optics.

PURPOSE: We investigated the impact of lens centration, wearer aberrations, pupil size and age on the optics of two bifocal contact lenses using image simulation. METHOD: Fourteen conditions (i.e. two optical profiles with two and eight concentric zones; two conditions of centration: centred and 0.77 mm decentred; and three conditions of aberrations: 0, 0.15 and 0.35 µm RMS; three pupil sizes: 3, 4.5 and 6 mm) were tested on two populations (i.e. 20-40 and 40-60 years old) using a numerical simulation method. For each condition, images were calculated for proximities ranging from -4D to + 2D with steps of 0.25D. Subjects graded the quality of each simulated image (i.e. a target 'HEV' of 0.4 logMAR) on a continuous scale from 0 to 5. To limit the effect of the observer's own aberrations, subjects viewed the displayed images through a 3-mm pupil and their optimal correction. RESULTS: Both populations reported similar image quality (i.e. average absolute difference of 0.23) except for sharp and low contrast images, which obtained slightly higher grades with younger subjects, probably due to a better contrast sensitivity in this population. Typical decentration had no effect on bifocal contact lenses wearers' vision, as the ratio between areas dedicated to near and distance vision did not change. Aberrations (i.e. mainly 0.24 µm of spherical aberration on a 4.5-mm pupil) reduced the addition of the two radial zones bifocal optics and introduced a hyperopic shift (i.e. 0.50D) of the through-focus image quality for the eight radial zone bifocal lens. The combination of typical aberrations with typical decentration created the same effect as typical aberrations alone, meaning that aberration impact was stronger than decentration impact. The two radial zone bifocal lens was dependent on the pupil whereas the eight radial zone lens was not. CONCLUSIONS: When fitting new bifocal optics, the aberrations of the patients, as well as their pupil diameter, are the main subject dependent parameters influencing quality of vision. Typical contact lens decentration and lower cortical treatment efficiency of retinal images of older subjects had relatively little impact.

Effect of Number of Zones on Subjective Vision in Concentric Bifocal Optics.

PURPOSE: To evaluate the influence of the number of concentric zones of a center-near bifocal optics on the subjective quality of vision. METHODS: Twenty-two subjects scored with a five-item continuous grading scale the quality of vision of calculated images (i.e., three high-contrast 20/50 letters) viewed through their best sphero-cylindrical correction and a 3-mm pupil to limit the impact of their aberrations. Through-focus images were calculated from -4 to +2 diopters (D), each 0.25 D, in the presence of center-near bifocal optics (Add 2.5 D) varying by their number of concentric zones (from 2 to 20). RESULTS: To compare the results obtained with these profiles, we calculated the area under the (through-focus) curve (AUC) higher than 2 out of 5 (i.e., limit between a poor and a fair image quality, considered as the limit of acceptability). This value was normalized by the naked eye condition and divided into distance, intermediate, and near AUC. The results showed large interindividual variations. Distance AUC remained quite similar whatever the profile, near AUC decreased with the number of concentric zones, and intermediate AUC rose with the number of concentric zones. With 10 and 20 concentric zones, diffraction phenomenon induced constructive interferences at intermediate proximities and destructive interferences at distance and near proximities. CONCLUSIONS: To balance distance, intermediate, and near quality of vision, a number of zones between 8 and 10 should be chosen. If the subject does not need intermediate quality of vision, then a profile with two to five zones should be favored.

Which ratio of areas improves vision quality in simultaneous focus optics?

PURPOSE: To evaluate the impact of the center optical zone diameter (COZD) of center-near bifocal optics on the through-focus subjective quality of vision. METHODS: Subjective image quality was assessed by 14 young, normally sighted subjects. Computed images of three high-contrast 20/50 letters were generated, across a range of object vergences from +2 diopters (D) to -4 D in 0.25-D steps. The center near optical zone addition power was +2.50 D, and the diameter of this center zone was varied in 10% steps to cover from 0% (single vision distance) to 90% of the 4.5-mm pupil diameter. Subjects rated image clarity of these computed images on a 0 to 5 scale, through a 3-mm pupil to limit the effect of their own aberrations. RESULTS: To quantify the efficiency of bifocal optics, we calculated the area under the through-focus subjective quality of vision curve. A criterion higher than 2 was judged to be an acceptable level of quality of vision, normalized by the naked eye condition. The average benefit of the optical profiles is highly subject dependent (i.e., from 0.8 to 1.9), potentially explaining why some subjects are not satisfied with simultaneous vision multifocal corrections. Averaged across subjects, the best benefit (i.e., 1.42) was obtained with a COZD covering 40% of the pupil area, whereas the 20, 30, and 50% profiles provide slightly lower benefit (i.e., ∼1.35). A COZD covering 20% of the pupil area equalized distance and near quality of vision. CONCLUSIONS: Quality of vision with bifocal optics is highly subject dependent. Peripheral rays do not seem to play an important role in the through-focus quality of vision, as the central pupil area is more heavily weighted in determining subjective image quality.

Subjective through-focus quality of vision with various versions of modified monovision.

BACKGROUND/AIMS: To evaluate and compare the effect of various modified monovision on binocular through-focus quality of vision. METHODS: Simulated images were computed using a numerical eye model, with a 4.7 mm pupil diameter, for various target vergences and with various combinations of spherical (SA4) and secondary spherical (SA6) aberrations. Binocular vision was provided using a video projector synchronised with active glasses. Three subjects evaluated monocular and binocular through-focus images by scoring the displayed image with a five-item continuous grading scale. Performance was evaluated in terms of depth-of-focus and area under the through-focus subjective quality of vision curves (AUC). RESULTS: On average, viewing through a combination of 0.4 µm of SA4 and -0.2 µm of SA6 with one eye and through a combination of -0.4 µm of SA4 and 0.2 µm of SA6 with the other eye, improved depth-of-focus and AUC, respectively, by 193% and 71% compared with naked eyes. Binocular summation occurred when both eyes viewed comparable image quality, whereas the level of binocular inhibition increased with the interocular difference of image quality. CONCLUSIONS: Binocular performance could be optimised by choosing different multifocal profiles for each eye and by adding a defocus term between eyes.

Depth-of-field of the accommodating eye.

PURPOSE: To obtain experimental values of the depth-of-field (DOFi) of the human eye for different accommodative states. METHODS: First, the monochromatic ocular wavefront of seven eyes from young subjects (mean [±SD] age, 29.7 [±7.7] years) was measured at eight different accommodative demands (ADs) (from -1 to 6 diopters [D] in steps of 1 D). Then, in a second part, accommodation was paralyzed and an adaptive optics system was used to correct the aberrations of the paralyzed eye and to simulate, with the aid of an artificial pupil, the wavefront of the accommodated eye. The simulation was performed for each AD measured in the first part of the experiment. A Badal system was used to modify the stimulus vergence so as to obtain three repeated measurements of the subjective DOFi, based on the criterion of an objectionable blur. RESULTS: When increasing AD from 0 to 6 D, the mean intersubject pupil diameter and DOFi changed from 5.70 to 4.62 mm and from 0.85 ± 0.26 D to 1.07 ± 0.19 D, respectively. All subjects presented a similar DOFi for all AD (intrasubject SD never exceeded 0.23 D). Paraxial accommodation response showed a lag that increased with the AD. For the lowest (0 D) and the highest (6 D) values of AD, the refractive state of the eye was close to the nearest and furthermost ends of the DOFi, respectively. CONCLUSIONS: The visual system takes advantage of the DOFi to change the refractive state less than necessary to form the paraxial image at the retina when it comes to focusing a near target (5 to 6 D of AD). This indicates that the main purpose of accommodation is not to maximize retinal image quality but to form one that is good enough.

Optical aberrations in patients with recurrent herpes simplex keratitis and apparently normal vision.

AIMS: To analyse high-order aberrations (HOA), modulation transfer function (MTF) and Strehl ratio in patients with a history of herpes simplex keratitis (HSK) and apparently normal vision. METHODS: Fifteen patients with a history of recurrent unilateral HSK and normal Snellen visual acuity (0 logMAR) were enrolled. Eyes with HSK (HSK group) were statistically compared with normal fellow eyes (Control group). HOA, MTF and Strehl ratio were measured using the OPD-SCAN II (Nidek Co, Gamagori, Japan) aberrometer. Measures were performed at least 3 months after the last episode of herpes. Statistical significance was indicated by p<0.05. RESULTS: Despite apparently normal vision in both eyes (as assessed by routine visual acuity charts), significantly higher total HOA, trefoil and tetrafoil were present in the HSK group compared with the Control group. The MTF and strehl ratio were lower in the HSK group compared with the Control group. In the HSK group, eyes with corneal opacities tended to present with greater optical aberrations than eyes with a clear cornea. CONCLUSIONS: Using patients as their own controls, the outcomes of this study indicate that eyes with recurrent HSK with no apparent decrease in visual acuity (0 logMAR) have significantly greater optical aberrations than eyes with no past history of herpetic disease. This outcome may explain some visual complaints of HSK patients, such as a decrease in contrast quality or reduced colour perception, compared with the unaffected contralateral eye despite apparently normal vision in both eyes.

Measurement and prediction of subjective gradations of images in presence of monochromatic aberrations.

The three objectives of this study were (i) to explore the effect of various levels of aberrations on subjective vision by scoring images, (ii) to compare subjective scores obtained with real optics and simulated images and (iii) to test the ability of image quality metrics to predict these scores. In a first experiment, 14 subjects evaluated the quality of images degraded by 0.05, 0.1, 0.2, 0.4 and 0.8µm of defocus, astigmatism, trefoil, coma, spherical aberration (SA4) and secondary spherical aberration (SA6) by putting a mark on a 5-items continuous grading scale. The desired aberration was introduced either by a deformable mirror or by displaying a simulated image. In the second experiment, 5 of the previous subjects evaluated the quality of through-focus images in presence of SA4, SA6 and combinations of SA4 and SA6. Both experiments were performed with an artificial pupil of 6mm diameter. The addition of increasing amounts of aberrations reduced the subjective grading of the targets, with SA6, SA4 and defocus being the most degrading aberrations. The correlation between the results obtained with the AO device and with simulated images gave a r(2) of 0.95. Combinations of 0.4µm of SA4 and 0.2µm of SA6 of opposite signs induced a bimodal through-focus image score curve. We were able to anticipate the subjective gradation of subject's vision thanks to image quality metrics (r(2)=0.92). Image quality score shows similar results as that obtained by objective image quality metrics, which provides a useful tool for optical designers and practitioners.

Effect of coma and spherical aberration on depth-of-focus measured using adaptive optics and computationally blurred images.

PURPOSE: To compare the effect of primary spherical aberration and vertical coma on depth of focus measured with 2 methods. SETTING: Laboratoire Aimé Cotton, Centre National de la Recherche Scientifique, and Université Paris-Sud, Orsay, France. DESIGN: Evaluation of technology. METHODS: The subjective depth of focus, defined as the interval of vision for which the target was still perceived acceptable, was evaluated using 2 methods. In the first method, the subject changed the defocus term by reshaping the mirror, which also corrected the subject's aberrations and induced a certain value of coma or primary spherical aberration. In the second procedure, the subject changed the displayed images, which were calculated for various defocuses and with the desired aberration using a numerical eye model. Depth of focus was measured using a 0.18 diopter (D) step in 4 nonpresbyopic subjects corrected for the entire eye aberrations with a 6.0 mm and 3.0 mm pupil and with the addition of 0.3 µm and 0.6 µm of positive primary spherical aberration or vertical coma. RESULTS: There was good concordance between the depth of focus measured with both methods (differences within 1/3 D, r(2) = 0.88). Image-quality metrics failed to predict the subjective depth of focus (r(2) < 0.41). CONCLUSION: These data confirm that defocus in the retinal image can be generated by optical or computational methods and that both can be used to assess the effect of higher-order aberrations on depth of focus. FINANCIAL DISCLOSURE: No author has a financial or proprietary interest in any material or method mentioned.