A population study on changes in wave aberrations with accommodation

Effects of long-term neural adaptation to habitual sspherical aberration on through-focus visual acuity in adults

We investigated how long-term visual experience with habitual spherical aberration (SA) influences subjective depth of focus (DoF). Nine healthy cycloplegic eyes with habitual SAs of different signs and magnitudes were enrolled. An adaptive optics (AO) visual simulator was used to measure through-focus high-contrast visual acuity after correcting all monochromatic aberrations and imposing + 0.5 μm and - 0.5 μm SAs for a 6-mm pupil. The positive (n = 6) and negative (n = 3) habitual SA groups ranged from 0.17 to 0.8 μm and from - 1.2 to - 0.12 μm for a 6-mm pupil, respectively. Although all optical conditions were identical, and the subjective DoFs were expected to be the same for all participants, the DoFs of individuals differed between the positive and negative habitual SA groups. For the positive habitual SA group, the mean DoF with positive AO-induced SA (2.14 D) was larger than that with negative AO-induced SA (1.88 D); for the negative habitual SA group, a smaller DoF was measured with positive AO-induced SA (1.94 D) than that with negative AO-induced SA (2.14 D). Subjective DoF tended to be larger when the induced SA in terms of sign and magnitude was closer to the participant's habitual SA. Our findings suggest that neural adaptation to habitual SA compensated for optical blur at multiple object distances, perceptually expanding DoF. As a result, the outcomes of optical treatments for presbyopia may differ due to the neural compensation mechanism influenced by an individual's visual experience with their habitual optics.

Spherical Aberration Changes in Patients With Early Presbyopia Wearing Aspheric Multifocal Soft Contact Lenses in South Korea

OBJECTIVES

The aim of this study was to evaluate the impact of wearing center-near (CN) and center-distance (CD) multifocal contact lenses (MFCLs) on spherical aberrations and visual acuity in patients with early presbyopia.

METHODS

Fifty participants with early presbyopia wore CN-MFCLs and CD-MFCLs for 1 week. The average corrected refractive power was -2.65±1.67 D. Spherical aberration was measured using an auto-refractor after 1 week of lens use.

RESULTS

No significant difference in overall visual acuity was observed when using either lens. Participants favored CD-MFCLs for distance vision and CN-MFCLs for near vision. This study highlighted variations in aberration and satisfaction based on age, refractive errors, and individual responses. Patients with positive spherical aberrations tended to benefit from CN-MFCLs, which improved both distance and near vision, although additional correction was required for clear distance vision. Patients with early presbyopia generally preferred CN-MFCLs when positive aberration was prevalent, whereas those with negative aberration reported greater satisfaction with distance vision when wearing CD-MFCLs.

CONCLUSIONS

This study confirmed that wearing MFCLs leads to changes in spherical aberration and visual acuity in patients with early presbyopia, particularly when positive aberration prevails. Future research should investigate these effects across different stages of presbyopia.

Accommodating version of a schematic eye for emmetropia and myopia

AIM

To develop an accommodating, wide-angle, schematic eye for emmetropia and myopia in which spectacle refraction and accommodation level are input parameters.

METHOD

The schematic eye is based on an earlier unaccommodated refraction-dependent eye for myopia developed by Atchison in 2006. This has a parabolic gradient index lens and parameters derived from biometric and optical measurements on young adults. Several parameters are linearly dependent upon spectacle refraction (anterior radius of curvature of the cornea, axial length and vertex radii of curvature and conic asphericities of a biconic retina). The new accommodated schematic eye incorporates accommodation-dependent changes in several lens-related parameters. These changes are based on literature values for anterior chamber depth, lens thickness, vitreous chamber depth, lens surface radii of curvature and lens front surface asphericity. A parabolic variation of refractive index with relative distance from the lens centre is retained, with the same edge and centre refractive indices as the earlier model, but the distribution has been manipulated to maintain focus near the retina for the emmetropic case at 0 and 4 D accommodation. The asphericity of the lens back surface is changed so that spherical aberration and peripheral refraction approximately match typical literature trends. The model is used to compare spherical aberration and peripheral refraction in eyes with up to 4 D of myopia and 4 D of accommodation.

RESULTS

The levels of spherical aberration in the unaccommodated schematic eyes are similar to literature values for young adults, but the changes in spherical aberration with accommodation are approximately two-thirds of that found in an experimental study. As intended, peripheral refractions in the accommodated schematic eyes are similar to those of their unaccommodated counterparts.

CONCLUSION

The wide-angle model extends the range of schematic eyes to include both refraction and accommodation as variable input parameters. It may be useful in predicting aspects of retinal image quality.

Statistical Model of Ocular Wavefronts With Accommodation

Purpose

The purpose of this study was to determine the minimum number of orthonormal basis functions, applying Principal Component Analysis (PCA), to represent the most wavefront aberrations at different accommodation stages. The study also aims to generate synthetic wavefront data using these functions.

Methods

Monocular wavefront data from 191 subjects (26.15 ± 5.56 years old) were measured with a Hartmann-Shack aberrometer, simulating accommodation from 0 diopters (D) to 5 D in 1 D steps. The wavefronts for each accommodative demand were rescaled for different pupil sizes: 4.66, 4.76, 4.40, 4.09, 4.07, and 3.68 mm. PCA was applied to 150 wavefront parameters (25 Zernike coefficients × 6 accommodation levels) to obtain eigenvectors for dimensional reduction. A total of 49 eigenvectors were modeled as a sum of 2 multivariate Gaussians, from which 1000 synthetic data sets were generated.

Results

The first 49 eigenvectors preserved 99.97% of the original data variability. No significant differences were observed between the mean values and standard deviation of the generated and original 49 eigenvectors (two one-sided test [TOST], P > 0.05/49) and (F-test, P > 0.05/49), both with Bonferroni correction. The mean values of the generated parameters (1000) were statistically equal to those of the original data (TOST, P > 0.05/150). The variability of the generated data was similar to the original data for the most important Zernike coefficients (F-test, P > 0.05/150).

Conclusions

PCA significantly reduces the dimensionality of wavefront aberration data across 6 accommodative demands, reducing the variable space by over 66%. The synthetic data generated by the proposed wavefront model for accommodation closely resemble the original clinical data.

The Influence of Accommodative Demand on Ocular Aberrations: A Study of Zernike Coefficients Repeatability and Variability

PURPOSE

To evaluate the repeatability of the Zernike coefficients in healthy eyes when monocular accommodation was stimulated at different vergences demands.

METHODS

A total of 36 right eyes from healthy volunteers were prospectively and consecutively recruited for this study. Wavefront aberrometry was conducted to objectively characterize the ocular optical quality during accommodation, from the individual's far point to a 5 D accommodation demand in steps of 0.5 D. The repeatability of Zernike coefficients up to the fourth order was assessed by calculating the within-eye repeatability (Sw), the coefficient of repeatability (CR), the coefficient of variation (CV), and the intraclass correlation coefficient (ICC) as an indicator of measurement reliability.

RESULTS

Correlation among repeated measurements showed high reliability (ICC > 0.513) for all parameters measured except some fourth-order Zernike coefficients, C(4, -4) (ICC < 0.766), C(4, -2) (ICC < 0.875), C(4, 2) (ICC < 0.778) and C(4, 4) (ICC < 0.811). Greater repeatability and less variability were obtained for high-order Zernike coefficients (CR < 0.154), although an increase in CR in the coefficients analyzed was observed with increasing accommodative demand. No clear trend was evident in CV; however, it was observed that the low-order Zernike coefficients exhibit lower CV (CV < 1.93) compared to the high-order Zernike coefficients (CV > 0).

CONCLUSIONS

The reliability of Zernike coefficients up to the fourth order in healthy young individuals demonstrated a strong consistency in measuring terms up to the fourth order, with more variability observed for high-order terms. The Zernike coefficients up to the third order exhibited the highest level of repeatability.

Wide-field optical eye models for emmetropic and myopic eyes

Ocular wavefront aberrations are used to describe retinal image formation in the study and modeling of foveal and peripheral visual functions and visual development. However, classical eye models generate aberration structures that generally do not resemble those of actual eyes, and simplifications such as rotationally symmetric and coaxial surfaces limit the usefulness of many modern eye models. Drawing on wide-field ocular wavefront aberrations measured previously by five laboratories, 28 emmetropic (-0.50 to +0.50 D) and 20 myopic (-1.50 to -4.50 D) individual optical eye models were reverse-engineered by optical design ray-tracing software. This involved an error function that manipulated 27 anatomical parameters, such as curvatures, asphericities, thicknesses, tilts, and translations-constrained within anatomical limits-to drive the output aberrations of each model to agree with the input (measured) aberrations. From those resultant anatomical parameters, three representative eye models were also defined: an ideal emmetropic eye with minimal aberrations (0.00 D), as well as a typical emmetropic eye (-0.02 D) and myopic eye (-2.75 D). The cohorts and individual models are presented and evaluated in terms of output aberrations and established population expectations, such as Seidel aberration theory and ocular chromatic aberrations. Presented applications of the models include the effect of dual focus contact lenses on peripheral optical quality, the comparison of ophthalmic correction modalities, and the projection of object space across the retina during accommodation.

Outcomes of Corneal Compound Hyperopic Astigmatism With Presbyopia by Zeiss PRESBYOND Laser Blended Vision LASIK Using Default Custom Refractive Software Master Target Refractions for Reduced Anisometropia

PURPOSE

To evaluate the effectiveness, safety, and stability of a modified PRESBYOND Laser Blended Vision protocol (Carl Zeiss Meditec AG) for correcting hyperopic astigmatism and presbyopia, using Custom Refractive Software Master (CRSM) targeting over a 6-month period.

METHODS

A total of 636 eyes of 318 patients with a mean age of 51.05 ± 4.71 years (range: 40 to 60 years) met the inclusion and exclusion criteria. All patients completed a 6-month follow-up. CRSM software was used to generate ablation profiles for the MEL90 excimer laser (Carl Zeiss Meditec AG). The target refraction was emmetropic for the dominant eyes and between -0.75 and -1.12 diopters (D) for the near eyes.

RESULTS

Visual and refractive results were studied separately by the dominant and non-dominant eyes. The mean attempt to correct for spherical equivalent refraction was +2.17 ± 1.16 D (range: -1.00 to +5.37 D). The mean attempted cylinder was -0.60 ± 0.75 D (range: -4.00 to 0.00 D). All eyes monocularly achieved uncorrected distance visual acuity (UDVA) of 20/25 or better after refractive treatment and 88% achieved 20/20. Binocularly all eyes achieved UDVA of 20/25 or better and 96.54% achieved 20/20. Ninety-eight percent of the patients maintained their corrected distance visual acuity before surgery and UDVA 6 months after surgery.

CONCLUSIONS

This hyperopic micro-anisometropia protocol with PRESBYOND Laser Blended Vision was an effective, safe, and well-tolerated refractive treatment. It was an effective procedure with excellent results for UDVA and uncorrected near visual acuity and demonstrates that binocular summation exists. [ J Refract Surg. 2024;40(7):e480-e489.].

Wavefront Changes during a Sustained Reading Task in Presbyopic Eyes

The objective of this study was to assess the effect of sustained reading on the temporal changes in the wavefront error in the presbyopic eye. The wavefront aberration of the eyes was measured using an IRX3 Shack-Hartmann aberrometer before and after (immediately, 5 min, and 10 min after) a reading task. Temporal changes in C20, C40, and C3-1 coefficient values of the eyes were plotted, showing a predominant number of V-shaped patterns (for C40 and C3-1) and inverse V-shaped patterns (for C20) among the study group, and the percentages (between 27 and 73%) were reported. The median of the total RMS of aberrations and the RMS of HOA (higher-order aberrations), which included comatic (3rd order) and spherical-like aberrations (4th and 6th order), increased immediately after finishing the near-vision reading task and then decreased. The median of RMS of comatic aberrations had a similar pattern of variations, while the median of RMS of spherical-like aberrations displayed an opposite pattern. Simulating the aberration changes due to lens decentration caused by relaxed zonules during 4 D accommodation in an eye model demonstrated that the expected range of changes for the vertical coma and spherical aberrations are in the order of 0.001 and 0.01 μm, respectively, which could justify why the observed changes were not statistically significant. The observed dynamic changes in HOA might be linked to the biomechanical characteristics and alterations in the displacement of the crystalline lens following prolonged near-vision tasks in presbyopic people. Although some predominant patterns under some conditions were shown, they exhibit considerable inter-subject and inter-ocular variability. This might be due to slight misalignments while fixating on the internal extended object in the aberrometer.

Accommodation response and spherical aberration during 1-Year of orthokeratology lens wear and after discontinuation

BACKGROUND

To assess accommodation and spherical aberration changes during one year of orthokeratology lens wear and one month after lens cessation.

METHODS

A prospective, randomized, longitudinal study was conducted on forty-seven young healthy subjects at the Optometry Clinic of the Complutense University of Madrid (Spain). Non-cycloplegic refraction, high and low uncorrected visual acuity, high and low best corrected visual acuity, accommodative lag, horizontal near phoria, corneal topography, and high-order aberrations were performed at baseline, 1-day, 1-week, 1-, 6- and 12-months of lens wear and after one month of wash out period. p < 0.05 was considered as statistically significant.

RESULTS

Spherical equivalent refraction (SE) was -3.23 ± 1.57D at baseline and -0.36 ± 0.64D after 12-months of lens wear, while accommodative lag changed from 0.53 ± 0.39D to 0.15 ± 0.29D after one year of lens wear. No significant differences were found when comparing SE at baseline and after one month of lens cessation (p > 0.05). A high correlation was found between the accommodative lag at baseline and after 12 M of lens wear. 22 out of 25 subjects with exophoria at baseline showed a significant reduction in the deviation at 12-months (p < 0.05). Total spherical aberration increased during all visits due to the lens wear (p < 0.05) although internal spherical aberration showed a significant decrease for 1-week, 1-month and 12-month visits (p < 0,05).

CONCLUSION

Orthokeratology lenses may change the accommodative response of the patient as a reduction on accommodative lag on exophoric patients and an overall increase on the internal spherical aberrations was found during treatment but return to nearly baseline values when cessation.

Risk Factors for Corneal Monochromatic Aberrations and Implications for Multifocal and Extended Depth-of-Focus Intraocular Lens Implantation

PURPOSE

To discuss factors influencing corneal aberrations that might influence the optical quality after intraocular lens (IOL) implantation.

METHODS

PubMed and Scopus were the main resources used to search the medical literature. An extensive search was performed to identify relevant articles concerning factors influencing the level of corneal aberrations as of August 27, 2023. The following keywords were used in various combinations: corneal, aberrations, defocus, astigmatism, spherical aberration, coma, trefoil, quadrafoil, intraocular lens, and IOL.

RESULTS

Conclusive evidence is lacking regarding the correlation between age and changes in corneal aberrations. Patients with astigmatism have greater corneal higher-order aberrations than those with minimal astigmatism, particularly concerning trefoil and coma. Increased levels of corneal higher-order aberrations are noted following contact lens wear, in patients with dry eye disease, and with pterygium. Increased higher-order aberrations have been reported following corneal refractive surgery and for 3 months following trabeculectomy; regarding intraocular lens surgery, the results remain controversial.

CONCLUSIONS

Several factors influence the level of corneal higher-order aberrations. Multifocal and extended depth-of-focus IOLs can share similarities in their optical properties, and the main difference arises in their design and performance with respect to spherical aberration. Preoperative evaluation is critical for proper IOL choice, particularly in corneas with risk of high levels of aberrations. [J Refract Surg. 2024;40(6):e420-e434.].

Theoretical impact of chromatic aberration correction on visual acuity

It has been known for more than 220 years that the image quality of the human eye is significantly degraded by chromatic aberrations. Recently, it was shown experimentally that correcting chromatic aberrations results in a 0.2- to 0.8-line improvement in visual acuity. Here we ask, is this expected? We developed tools that enable simulations of the optical impact of physiologically relevant amounts of chromatic aberration in real human eyes and combined these with tools that compute the visual acuity of an ideal observer. This allows us to characterize the theoretical impact of chromatic aberration correction on visual acuity. Results indicate a substantive improvement of 0.4- to 2-lines in ideal observer visual acuity with chromatic aberration correction. Ideal observer thresholds benefit significantly more from correction of longitudinal than correction of transverse chromatic aberration. Finally, improvements in ideal observer visual acuity are greater for subjects with less monochromatic aberration, such that subjects with better baseline optical quality benefit most from correction of chromatic aberrations.

Optical and aberrometric evaluation of a new enhanced monofocal intraocular lens with isofocal optic design

PURPOSE

To evaluate the optical and aberrometric outcomes of an enhanced monofocal intraocular lens (ISOPure) compared with those of a standard monofocal lens (MicroPure) having the same platform and material.

METHODS

A prospective, comparative and randomised clinical study. A total of 28 eyes of 28 patients were randomly assigned to either group. Monocular visual acuity (VA) was measured at distance and intermediate under photopic and mesopic conditions. Aberrometry was analysed for 3.0-, 4.0-, 4.5- and 5.0 mm pupils. The contrast sensitivity defocus curve was measured for 3.0- and 4.5-mm pupils, while the modulation transfer function (MTF) and Strehl ratio (SR) were assessed with a double-pass system. All measurements were performed monocularly 3 months after surgery.

RESULTS

No significant differences were found for distance VA. Under photopic conditions, intermediate VA was better with the ISOPure lens, while no significant differences were found between the lenses under mesopic conditions. Internal and total aberrations were higher for the ISOPure lens. No significant differences were found for corneal aberrations. Additionally, both the contrast sensitivity defocus curve and optical quality showed similar behaviour for each lens, with the MTF cut-off frequency exceeding 30 c/deg in both cases.

CONCLUSION

The isofocal ISOPure lens enhanced intermediate VA without affecting distance VA under photopic conditions. Moreover, there were no significant differences in visual quality between the ISOPure and MicroPure lenses, despite the former exhibiting higher internal and total aberrations than the monofocal model.

Comparatively analysing the postoperative optical performance of different intraocular lenses: a prospective observational study

BACKGROUND

Postoperative performance, including best corrected distance visual acuity (BCDVA) and optical metrics (from the OQAS and iTrace devices), was compared among 4 different intraocular lenses (IOLs).

METHODS

This prospective observational study included 104 eyes from 104 subjects who underwent cataract surgery combined with implantation of 4 different IOLs: monofocal (Mon) IOLs, segmental refractive (SegRef) IOLs, diffractive (Dif) IOLs and extended depth of focus (EDoF) IOLs. Postoperative BCDVA and optical metrics were collected at the 6th month. The OQAS optical metrics included the objective scattering index (OSI), Strehl ratio (SR), modulation transfer function (MTF) cut-off frequency, and predicted visual acuity (PVA); the iTrace optical metrics included blur/double vision, glare/halo, starburst, mixed focus, night myopia, and night hyperopia.

RESULTS

There was no significant difference in BCDVA among the 4 groups (P = 0.059; power = 70.3%). Differences were observed in all OQAS optical metrics among the groups (all P < 0.001). Overall, Mon IOLs and EDoF IOLs exhibited better performance than Dif IOLs and SegRef IOLs. Starburst was the only iTrace optical metric that differed among the groups (P < 0.001): SegRef IOLs caused more starbursts than Mon IOLs (P = 0.001), Dif IOLs (P = 0.006) and EDoF IOLs (P < 0.001). Spearman rank correlation analysis was used to determine the relationships among the iTrace optical metrics, OQAS optical metrics and BCDVA: starburst was negatively correlated with BCDVA, PVA at contrasts of 100% and 20%, OSI, and MTF cut-off frequency (all P ≤ 0.001); mixed focus was positively correlated with BCDVA, PVA at contrasts of 100% and 20%, OSI, and MTF cut-off frequency (all P ≤ 0.001).

CONCLUSIONS

Postoperative BCDVA and optical metrics varied among the different IOLs, which should be taken into account in the selection and management of IOLs for cataract patients.

TRIAL REGISTRATION

This study was approved by the First Affiliated Hospital of Guangzhou Medical University Ethical Review Board (No. 50 2022).

Effects of Neural Adaptation to Habitual Spherical Aberration on Depth of Focus

We investigated how long-term visual experience with habitual spherical aberration (SA) influences subjective depth of focus (DoF). Nine healthy cycloplegic eyes with habitual SAs of different signs and magnitudes were enrolled. An adaptive optics (AO) visual simulator was used to measure through-focus high-contrast visual acuity after correcting all monochromatic aberrations and imposing +0.5 μm and -0.5 μm SAs for a 6-mm pupil. The positive (n=6) and negative (n=3) SA groups ranged from 0.17 to 0.8 μm and from -1.2 to -0.12 μm for a 6-mm pupil, respectively. For the positive habitual SA group, the median DoF with positive AO-induced SA (2.18D) was larger than that with negative AO-induced SA (1.91D); for the negative habitual SA group, a smaller DoF was measured with positive AO-induced SA (1.81D) than that with negative AO-induced SA (2.09D). The difference in the DoF of individual participants between the induced positive and negative SA groups showed a quadratic relationship with the habitual SA. Subjective DoF tended to be larger when the induced SA in terms of the sign and magnitude was closer to the participant's habitual SA, suggesting the importance of considering the habitual SA when applying the extended DoF method using optical or surgical procedures.

Stability of the retinal image under normal viewing conditions and the implications for neural adaptation

Previous studies have demonstrated that the visual system adapts to the specific aberration pattern of an individual's eye. Alterations to this pattern can lead to reduced visual performance, even when the Root Mean Square (RMS) of the wavefront error remains constant. However, it is well-established that ocular aberrations are dynamic and can change with factors such as pupil size and accommodation. This raises an intriguing question: can the neural system adapt to continuously changing aberration patterns? To address this question, we measured the ocular aberrations in four subjects under various natural viewing conditions, which included changes in accommodative state and pupil size. We subsequently computed the associated Point Spread Functions (PSFs). For each subject, we examined the stability in the orientation of the PSFs and analyzed the cross-correlation between different PSFs. These findings were then compared to the characteristics of a distribution featuring PSF shapes akin to random variations. Our results indicate that the changes observed in the PSFs are not substantial enough to produce a PSF shape distribution resembling random variations. This lends support to the notion that neural adaptation is indeed a viable mechanism even in response to continuously changing aberration patterns.

Boosting 2-photon vision with adaptive optics

The 2-photon effect in vision occurs when two photons of the same wavelength are absorbed by cone photopigment in the retina and create a visual sensation matching the appearance of light close to half their wavelength. This effect is especially salient for infrared light, where humans are mostly insensitive to 1-photon isomerizations and thus any perception is dominated by 2-photon isomerizations. This phenomenon can be made more readily visible using short-pulsed lasers, which increase the likelihood of 2-photon excitation by making photon arrivals at the retina more concentrated in time. Adaptive optics provides another avenue for enhancing the 2-photon effect by focusing light more tightly at the retina, thereby increasing the spatial concentration of incident photons. This article makes three contributions. First, we demonstrate through color-matching experiments that an adaptive optics correction can provide a 25-fold increase in the luminance of the 2-photon effect-a boost equivalent to reducing pulse width by 96%. Second, we provide image-based evidence that the 2-photon effect occurs at the photoreceptor level. Third, we use our results to compute the specifications for a system that could utilize 2-photon vision and adaptive optics to image and stimulate the retina using a single infrared wavelength and reach luminance levels comparable to conventional displays.

Spherical Aberration of Astigmatic Corneas in a Cataract Population

PURPOSE

To study the distribution of spherical aberration (SA) in astigmatic corneas in a cataract population and the relationship between magnitude of corneal astigmatism and fourth-order corneal SA.

METHODS

Data routinely collected using a Scheimpflug camera (Pentacam; Oculus Optikgeräte GmbH) were retrospectively analyzed. Patients with a minimum age of 60 years were included. Total corneal SA (from anterior and posterior corneal surface) was obtained for a 6-mm cor-neal area aligned with the pupil center. Exclusion criteria were insufficient measurement quality, total deviation index (Belin/Ambrósio Deviation) greater than 1.60, and corneal thickness at the thinnest point of less than 490 μm. One eye per patient was chosen randomly. Eyes were divided into low (≤ 1.00 diopters [D]), moderate (> 1.00 to ≤ 2.00 D), and high (> 2.00 D) astigmatism groups according to the Scheimpflug measurements.

RESULTS

A total of 528 eyes were included in this analysis. Low astigmatism was found in 129 patients, moderate astigmatism in 265 patients, and high astigmatism in 134 patients. Mean astigmatism was 0.68 ± 0.24, 1.45 ± 0.28, and 2.91 ± 0.95 D in the low, moderate, and high astigmatism groups, respectively. Mean corneal SA in patients with moderate and high astigmatism was higher than in the low astigmatism group. The difference reached the significance level for the comparison of low and high astigmatism groups (P = .023). The fourth-order SA increased gradually with the magnitude of astigmatism with a slope of 0.015.

CONCLUSIONS

SA was significantly larger in the cataract population with high corneal astigmatism. The increase of positive sign SA with the magnitude of astigmatism suggests that patients with moderate to high astigmatism may benefit more from intraocular lenses with negative sign SA correction. [J Refract Surg. 2023;39(8):532-538.].

Higher order aberrations and retinal image quality during short-term accommodation in myopic and non-myopic children

INTRODUCTION

Despite the known associations between near work and myopia, and retinal image quality and eye growth, accommodation-induced changes in higher order aberrations (HOA's) and retinal image quality in children with different refractive errors are poorly understood.

METHODS

Ocular HOA's were measured using a Hartmann-Shack wavefront sensor (COAS-HD, Wavefront Sciences) in 18 myopic and 18 age- and sex-matched non-myopic children during short-term accommodation tasks (four demands of 0, 3, 6 and 9 D) presented using a Badal optometer. Eighth order Zernike polynomials were fitted across a 2.3 mm pupil diameter to determine refractive power vectors (M, J₁₈₀ and J₄₅ ) and the accommodation error, and a 4 mm pupil was used for HOA analyses. Retinal image quality was examined using the visual Strehl ratio based on the optical transfer function (VSOTF) for third to eighth radial orders only.

RESULTS

Most refractive error group differences were observed for the 6 and 9 D demands. Myopic children underwent greater changes in with-the-rule astigmatism (J₁₈₀ ), higher order and third order RMS values, primary vertical ( C 3 - 1 $$ {C}_3^{-1} $$ ) and horizontal coma ( C 3 1 $$ {C}_3^1 $$ ), and several other individual Zernike coefficients compared with non-myopic children (all refractive error group by demand interaction p-values of ≤0.02). Non-myopic children exhibited a greater negative shift in primary ( C 4 0 $$ {C}_4^0 $$ ) and positive shift in secondary spherical aberration ( C 6 0 $$ {C}_6^0 $$ ) (both refractive error group by demand interaction p-values of ≤0.002). The VSOTF degraded for the 6 and 9 D demands in both groups, but the myopic children underwent a greater mean (SE) reduction from 0 D of -0.274 (0.048) for the 9 D demand, compared with -0.131 (0.052) for the non-myopic children (p = 0.001).

CONCLUSION

These results may have implications for the association between near work, accommodation and myopia development, particularly related to the use of short working distances during near tasks.

Clinical validation of a novel smartphone application for measuring best corrected visual acuity

PURPOSE

Personal mobile devices such as smartphones are proving their usefulness in ever more applications in tele-eyecare. An inconvenience and potential source of error in these past approaches stemmed from the requirement for the subjects to situate their devices at a distance. The present study aims to clinically validate best corrected visual acuity (BCVA) measures carried out by a novel smartphone application "vision.app" (VisionApp Solutions S.L.) using comparative statistics against clinical measurements.

MATERIALS AND METHODS

BCVA was measured in both eyes of 40 subjects using vision.app which displayed a black Landolt-C optotype with crowding on a white background, and utilized a 4 forced-choice procedure for the subjects to find (by means of swiping in either of four directions) the smallest optotype size they could resolve. Results were compared to BCVA measurements taken using a standard Snellen chart placed at 20 feet (6 m).

RESULTS

The t-test revealed no significant differences between the app- and clinically-measured VA (p = 0.478 (OD) and 0.608 (OS)), with a mean difference between clinical and app measurements of less than one line of the eye chart (-0.009 logMAR (OD) and -0.005 logMAR (OS)). A limit of agreement for a 95% confidence interval of ± 0.08 logMAR for OD and OS was found.

CONCLUSIONS

The results show the potential use of a smartphone to measure BCVA at a handheld distance. The newly validated study results can hold major future advancements in tele-eyecare and provide eye care professionals with a reliable and accessible method to measure BCVA.

Central and Peripheral Ocular High-Order Aberrations and Their Relationship with Accommodation and Refractive Error: A Review

High-order aberrations (HOAs) are optical defects that degrade the image quality. They change with factors such as pupil diameter, age, and accommodation. The changes in optical aberrations during accommodation are mainly due to lens shape and position changes. Primary spherical aberration (Z(4.0)) is closely related to accommodation and some studies suggested that it plays an important role in the control of accommodation. Furthermore, central and peripheral HOAs vary with refractive error and seem to influence eye growth and the onset and progression of myopia. The variations of central and peripheral HOAs during accommodation also appear to be different depending on the refractive error. Central and peripheral high-order aberrations are closely related to accommodation and influence the accuracy of the accommodative response and the progression of refractive errors, especially myopia.

Impact of temporal fluctuations in optical defocus on visual acuity: Empirical results and modeling outcomes

Optical defocus in human eyes is seldom steady during naturalistic steady-state viewing. It fluctuates by 0.3 to 0.5 diopters (D) from accommodative microfluctuations and by 1.5 to 2.5 D in dysfunctions such as spasm of near reflex, both with ≤2 Hz low-pass frequency spectra. This study observed losses in monocular visual acuity of cyclopleged adults who encountered varying amplitude (0.25-2.0 D) and temporal frequency (0.25-2.0 Hz) combinations of sinusoidal defoci induced using an electrically tunable lens. Visual acuity, recorded for 300-ms flashes of Sloan optotype presentation using the method of constant stimuli, deteriorated with defocus amplitude at a rate steeper for lower than higher temporal frequencies. A template matching model of acuity, incorporating optical and neural low-pass filters, neural noise, and a cross-correlated decision operator, showed the best match with empirical data when acuity was governed by the minimum defocus available during optotype display. This criterion minimized acuity loss for higher temporal frequencies due to the increased probability of zero-defocus encounters within the presentation duration. Other decision criteria such as defocus averaging across the entire or parts of the presentation duration yielded less satisfactory results. These results imply that vision loss in humans encountering broadband time-varying defocus is dictated by the dominant low frequencies, with higher frequencies largely compensated using the least defocus decision strategy.

Emmetropization and nonmyopic eye growth

Most eyes start with a hypermetropic refractive error at birth, but the growth rates of the ocular components, guided by visual cues, will slow in such a way that this refractive error decreases during the first 2 years of life. Once reaching its target, the eye enters a period of stable refractive error as it continues to grow by balancing the loss in corneal and lens power with the axial elongation. Although these basic ideas were first proposed over a century ago by Straub, the exact details on the controlling mechanism and the growth process remained elusive. Thanks to the observations collected in the last 40 years in both animals and humans, we are now beginning to get an understanding how environmental and behavioral factors stabilize or disrupt ocular growth. We survey these efforts to present what is currently known regarding the regulation of ocular growth rates.

The visual benefits of correcting longitudinal and transverse chromatic aberration

We describe a system-the Binocular Varichrome and Accommodation Measurement System-that can be used to measure and correct the eye's longitudinal and transverse chromatic aberration (LCA and TCA) and to perform vision tests with custom corrections. We used the system to investigate how LCA and TCA affect visual performance. Specifically, we studied the effects of LCA and TCA on visual acuity, contrast sensitivity, and chromostereopsis. LCA exhibited inter subject variability but followed expected trends compared with previous reports. TCA at the fovea was variable between individuals but with a tendency for the shift at shorter wavelengths to be more temporalward in the visual field in each eye. We found that TCA was generally greater when LCA was corrected. For visual acuity, we found that a measurable benefit was realized only with both LCA and TCA correction unless the TCA was low. For contrast sensitivity, we found that the best sensitivity to a 10-cycle/degree polychromatic grating was attained when LCA and TCA were corrected. Finally, we found that the primary cause of chromostereopsis is the TCA of the eyes.

FIAT: A Device for Objective, Optical Measures of Accommodation in Phakic and Pseudophakic Eyes

Purpose

To present FIAT, a novel optical instrument and analysis package that is designed to elicit and optically record accommodation in human eyes.

Methods

FIAT employs a Shack-Hartmann wavefront sensor and a retro-illumination pupil camera that records from a single eye at video rates. It is effective at eliciting accommodation by offering the subject a full-field binocular view of an alternating distant target and a near-eye display. FIAT analysis software computes wave aberrations for each video frame over full- or subpupil sizes and computes accommodative dynamics and accommodative range.

Results

The system is validated by showing accurate refraction measurements in model eyes and human eyes with trial lenses. Robust accommodative responses are shown for young eyes, and a lack of accommodative response is shown for a known presbyopes. Accommodative stimulus-response curves from five phakic subjects over a range of ages show expected results. Results from two individuals with monofocal intraocular lenses are shown.

Conclusions

FIAT is an effective instrument for making accurate, objective measures of accommodation in phakic and pseudophakic eyes.

Translational Relevance

We present a device that can play an important role in the development and testing of accommodating intraocular lenses.

Latest Development in Extended Depth-of-Focus Intraocular Lenses: An Update

In recent years, there has been an overwhelming influx of different types of intraocular lenses (IOLs) as treatment for presbyopia. The extended depth-of-focus (EDOF) technology creates a single elongated focal point to enhance depth of focus, in contrast to the multiple foci of multifocal (MF) lenses. In this way, the EDOF lenses aim to reduce photic phenomena, glare, and halos, which have been reported in MF IOLs. A potential disadvantage of this is a blur due to decreased retinal image quality when the amount of the aberrations is increased excessively. Multifocality and EDOF characteristics are not exclusive of each other. Frequently, EDOF IOLs are combined with MF optical designs, a bifocal IOL may exhibit EDOF characteristics, likewise an aspheric monofocal IOL or a diffractive or refractive trifocal IOL. Thus, EDOF lenses are commonly subjected to confusion. A wide range of different types of EDOF lenses are available on the market to surgeons. In this practical update, we aim to clarify what is a true EDOF lens, classify the different types of the EDOF lenses based on their optical principle and review their recently reported outcomes. Comprehensive patient examination and selection, combined with knowledge of the most updated options and adequate patient counseling, can avoid dissatisfaction and yield the desired outcomes.

Optical modelling of an accommodative light field display system and prediction of human eye responses

The spatio-angular resolution of a light field (LF) display is a crucial factor for delivering adequate spatial image quality and eliciting an accommodation response. Previous studies have modelled retinal image formation with an LF display and evaluated whether accommodation would be evoked correctly. The models were mostly based on ray-tracing and a schematic eye model, which pose computational complexity and inaccurately represent the human eye population's behaviour. We propose an efficient wave-optics-based framework to model the human eye and a general LF display. With the model, we simulated the retinal point spread function (PSF) of a point rendered by an LF display at various depths to characterise the retinal image quality. Additionally, accommodation responses to the rendered point were estimated by computing the visual Strehl ratio based on the optical transfer function (VSOTF) from the PSFs. We assumed an ideal LF display that had an infinite spatial resolution and was free from optical aberrations in the simulation. We tested points rendered at 0-4 dioptres of depths having angular resolutions of up to 4x4 viewpoints within a pupil. The simulation predicted small and constant accommodation errors, which contradict the findings of previous studies. An evaluation of the optical resolution on the retina suggested a trade-off between the maximum achievable resolution and the depth range of a rendered point where in-focus resolution is kept high. The proposed framework can be used to evaluate the upper bound of the optical performance of an LF display for realistically aberrated eyes, which may help to find an optimal spatio-angular resolution required to render a high quality 3D scene.

Impact of Degraded Optics on Monocular and Binocular Vision: Lessons from Recent Advances in Highly-Aberrated Eyes

PURPOSE

Optical imperfections of the eye, characterized by higher-order wavefront aberrations, are exaggerated in corneal disease (e.g., keratoconus) and iatrogeny (e.g., keratorefractive surgery for myopia correction, keratoplasty for optical clarity restoration). This article reviews the recent advances on this topic for a comprehensive understanding of how optical degradations in disease models impact retinal image quality and monocular and binocular visual performance.

METHODS

Published literature over the last decade on retinal image quality and/or monocular and binocular visual functions with corneal irregularity was reviewed based on their relevance to the current topic, study population and strength of study design. The literature was summarized into four themes: 1) wavefront errors and retinal image quality of highly aberrated eyes, 2) monocular and binocular vision loss consequent to degraded optics and visual strategies to optimize performance, 3) impact of optical correction modalities on visual performance and 4) implications for clinical management of patients.

RESULTS

Across the 46 articles reviewed, the results clearly indicated that an increase in higher-order aberrations across these conditions had a significant negative impact on the patient's retinal image quality, and monocular and binocular visual functions. Interocular differences in retinal image quality deteriorated visual performance more than an overall worsening of image quality bilaterally. Minimizing optical degradation using rigid contact lenses and adaptive optics technology significantly improves retinal image quality and monocular and binocular vision, but performance remains sub-optimal relative to age-similar healthy controls.

CONCLUSION

Corneal disease and iatrogeny are useful models to understand the impact of optical degradation on retinal image quality and visual performance. Clinical management will greatly benefit from equalizing retinal image quality of both eyes of these patients. Future studies that deepen our understanding of the structure-function relation in these conditions are desirable for advancing vision science in this area and for developing novel clinical management strategies.

Effect of Accommodation on Peripheral Higher Order Aberrations

Knowledge of the effect of accommodation on image quality of peripheral retina is crucial for better understanding of the visual system, but only a few studies have been carried out in this area. This study was designed to evaluate the effect of accommodation on higher order aberrations from third to sixth Zernike polynomials in central and peripheral retina up to 23° off-axis. We used a Hartmann–Shack aberrometer to measure Zernike coefficients with both accommodated and non-accommodated eyes of 15 healthy subjects. Each Zernike coefficient, total higher order aberrations, spherical aberrations and astigmatism were compared between accommodated and non-accommodated status. Additionally, aberrations in the central retina were compared with the peripheral retina. Accommodation induced significant changes in the Zernike coefficients of vertical pentafoil C5−5 and secondary vertical tetrafoil C6−4 in central retina, secondary vertical astigmatism C4−2 on 23° of temporal retina, secondary vertical tetrafoil C6−4 and tertiary vertical astigmatism C6−2 on 10° of nasal retina, secondary vertical trefoil C5−3 and secondary vertical tetrafoil C6−4 on 23° of nasal retina, and horizontal tetrafoil C44, and secondary horizontal tetrafoil C64 on 23° of inferior retina (p < 0.05). Total higher order aberration was lower in each retinal area examined with accommodation, but it was statistically significant only on 23° temporal retina and 11.5° and 23° of superior retina (p < 0.05). Spherical aberration decreased with accommodation on 23° temporal retina (p = 0.036). Astigmatism was similar in non-accommodated and accommodated eyes. Overall, accommodation affected higher order aberration (HOA) asymmetrically in different peripheral retinal areas.

Simultaneous measurements of foveal and peripheral aberrations with accommodation in myopic and emmetropic eyes

The difference in peripheral retinal image quality between myopic and emmetropic eyes plays a major role in the design of the optical myopia interventions. Knowing this difference under accommodation can help to understand the limitations of the currently available optical solutions for myopia control. A newly developed dual-angle open-field sensor was used to assess the simultaneous foveal and peripheral ( 20 ∘ nasal visual field) wavefront aberrations for five target vergences from -0.31 D to -4.0 D in six myopic and five emmetropic participants. With accommodation, the myopic eyes showed myopic shifts, and the emmetropic eyes showed no change in RPR. Furthermore, RPR calculated from simultaneous measurements showed lower intra-subject variability compared to the RPR calculated from peripheral measurements and target vergence. Other aberrations, as well as modulation transfer functions for natural pupils, were similar between the groups and the accommodation levels, foveally and peripherally. Results from viewing the same nearby target with and without spectacles by myopic participants suggest that the accommodative response is not the leading factor controlling the amplitude of accommodation microfluctuations.

Near Vision Tasks and Optical Quality of the Eye

Purpose

To study the effect of near-vision reading task on optical quality of the eye when performed on a computer monitor and on printed paper, and to identify which of the two results in greater changes.

Methods

Two groups of subjects performed a 30-min reading task in two different conditions: on a computer monitor and on printed paper. Ocular, corneal, and internal wavefront aberrations (Zernike coefficients up to 6 th order), root-mean-square of low- and high-order aberrations, spherical equivalent, vectoral components of ocular astigmatism (J45 and J0), and the compensation factor between internal and corneal aberrations were measured before and after the tasks. Their changes were analyzed in each group and between groups.

Results

Statistically significant changes in wavefront aberrations and in root mean square of low- and high-order aberrations were observed in both groups which was significantly greater when the task was performed on printed paper. Partial loss of compensation mechanism and variation in spherical equivalent in a negative direction occurred after both reading tasks; however, it was statistically significant only with printed paper reading task. The vectoral components of ocular astigmatism did not show statistically significant changes in either groups.

Conclusion

Near-vision reading tasks can change the optical quality of the eye, especially when the task is performed on printed paper.

[Optical aberrations of the eyes with various degrees of myopia]

Purpose - to comparatively analyze the wavefront aberrations and biometric parameters of the eyes with various degrees of myopia.

MATERIAL AND METHODS

The study included 134 eyes of 67 patients with mild, moderate and high myopia aged 7-28 (mean age 19.3±1.5 years). The following biometric parameters were examined: anterior chamber depth (ACD), lens thickness (LT), axial length (AL), as well as corneal and total aberrations. The parameters were studied on the Galilei G6 system (Ziemer Ophthalmic Systems AG, Switzerland) and the OPD-Scan III aberrometer (Nidek, Japan). Spherical aberration (SA) was estimated as the sum of Z4+Z8+Z12.

RESULTS

As the refraction increased, the root mean square higher-order aberrations (RMS HOA) also increased significantly: from 0.24±0.02 μm in mild myopia to 0.45±0.03 μm in high myopia, and in eyes with AL of ≥27.0 mm - to 0.57±0.02 μm (p=0.01). An increase in vertical tilt, vertical coma and vertical trefoil were also observed. Total SA was positive and increased in eyes with moderate myopia compared to those with low myopia (from 0.02±0.01 μm to 0.06±0.02 μm, p=0.02), which coincided with changes in the internal optics of the eye: an increase in ACD and a decrease in LT. At the same time, no differences in corneal aberrations were observed among patients with low and moderate myopia. A significant decrease of SA occurred in high myopia (from 0.06 μm in low myopia to 0.015±0.02 μm in high myopia). The average value of SA was 0.005±0.01 μm in eyes with AL of ≥27.0 mm and appeared to be negative in 40% of cases. The average value of corneal SA was negative (-0.002±0.01μm) in eyes with AL of ≥27.0 mm. This group had predominantly patients with congenital myopia.

CONCLUSION

An increase of total positive SA in patients with moderate myopia compared to those with low myopia is associated with changes in the internal optics of the eye (ACD, LT). Significant increase of higher-order aberrations and decrease of SA with the transition to negative values was observed in patients with high axial myopia.

Objective changes in astigmatism during accommodation

PURPOSE

Previous studies have shown small but clinically significant changes in the power and axis of astigmatism when the eye accommodates. Monocular objective measurements of the eye during accommodation, when the object approaches the eye without convergence, also reveal small astigmatic changes. Moreover, it is known that the eye exhibits ocular cyclotorsion at different gaze angles. Since accommodation and convergence normally occur simultaneously, we studied the change in the magnitude and axis of astigmatism during accommodation for different convergence angles.

METHODS

The left eye of 15 subjects between 20 and 49 years old (mean 28.5 ± 9.7 years) having ≤1.5 D astigmatism was evaluated. Measurements were made using a Shack-Hartmann aberrometer for an accommodation range of +0.50 D to -10 D in 0.50 D steps, and for four monocular convergence demands: 0°, 5°, 10° and 15°. Statistical analysis used power vectors to quantify the change in cylinder power and axis for each accommodation and convergence demand with age.

RESULTS

Jackson cross-cylinder component J₄₅ did not change during accommodation for all vergences tested. However, J₀ changed by an average of -0.02 D per dioptre of accommodation (D/Dacc) for convergence demands of 0°, 5° and 10° and -0.03 D/Dacc for the 15° demand. This corresponds to an average cylinder power change of -0.05 D/Dacc for convergences of 0°, 5° and 10° and -0.08 D/Dacc for 15° of convergence. The cylinder axis always changed towards 90° (against-the-rule), and age did not play a significant role.

CONCLUSIONS

Except for accommodation demands >4 D, we did not find a clinically significant change in astigmatism for convergence angles up to 15º. The small changes in cylinder power and axis may be due to shifts in the position of the crystalline lens during accommodation.

Retinal Responses to Simulated Optical Blur Using a Novel Dead Leaves ERG Stimulus

Purpose

The purpose of this study was to evaluate retinal responses to different types and magnitudes of simulated optical blur presented at specific retinal eccentricities using naturalistic images.

Methods

Electroretinograms (ERGs) were recorded from 27 adults using 30-degree dead leaves naturalistic images, digitally blurred with one of three types of optical blur (defocus, astigmatism, and spherical aberrations), and one of three magnitudes (0.1, 0.3, or 0.5 µm) of blur. Digitally computed blur was applied to the entire image, or on an area outside the central 6 degrees or 12 degrees of retinal eccentricity.

Results

ERGs were significantly affected by blur type, magnitude, and retinal eccentricity. ERGs were differentially affected by defocus and spherical aberrations; however, astigmatism had no effect on the ERGs. When blur was applied only beyond the central 12 degrees eccentricity, the ERGs were unaffected. However, when blur was applied outside the central 6 degrees, the ERG responses were significantly reduced and were no different from the ERGs recorded with entirely blurred images.

Conclusions

Blur type, magnitude, and location all affect the retinal responses. Our data indicate that the retinal area between 6 and 12 degrees eccentricity has the largest effect on the retinal responses to blur. In addition, certain optical blur types appear to have a more detrimental effect on the ERGs than others. These results cannot be solely explained by changes to image contrast and spatial frequency content, suggesting that retinal neurons might be sensitive to spatial cues in order to differentiate between different blur types.

Higher order aberrations and retinal image quality during short-term accommodation in children

Changes in higher order aberrations (HOA's) and retinal image quality during accommodation have not previously been examined in children. This study measured ocular HOA's in ninety non-myopic, school-aged children during short-term accommodation tasks at 0, 3, 6, and 9 D demands presented via a Badal optometer mounted to a Hartmann-Shack wavefront aberrometer (COAS-HD, Wavefront Sciences). Eighty-four participants who exhibited active accommodation were included in the analyses. An eighth order Zernike polynomial was fit across a 2.3 mm, 4 mm, and natural pupil diameter to evaluate changes in refractive power vectors (M, J₁₈₀, and J₄₅), accommodation errors (lags and leads), HOA root mean square (RMS) variables, individual Zernike coefficients, and the visual Strehl ratio based on the optical transfer function (VSOTF). All HOA RMS variables changed significantly with accommodation, with the greatest change observed for the 9 D demand. Of the individual Zernike coefficients, primary (C₄⁰) and secondary spherical aberration (C₆⁰) exhibited the greatest magnitude of change, becoming negative and positive with increasing accommodation, respectively. The VSOTF changed significantly with greater accommodation for both the 4 mm and natural pupil size, becoming significantly worse for the 9 D demand. HOA's increase and retinal image quality decreases significantly during higher levels of accommodation in children, similar to adults. These findings provide a greater understanding of the optical properties of children's eyes and insights into possible mechanisms for the association between accommodation, near work, and refractive error development.

Lags and leads of accommodation in humans: Fact or fiction?

The focusing response of the human eye — accommodation — exhibits errors known as lags and leads. Lags occur when the stimulus is near and the eye appears to focus farther than the stimulus. Leads occur with far stimuli where the eye appears to focus nearer than the stimulus. We used objective and subjective measures simultaneously to determine where the eye is best focused. The objective measures were made with a wavefront sensor and an autorefractor, both of which analyze light reflected from the retina. These measures exhibited typical accommodative errors, mostly lags. The subjective measure was visual acuity, which of course depends not only on the eye's optics but also on photoreception and neural processing of the retinal image. The subjective measure revealed much smaller errors. Acuity was maximized at or very close to the distance of the accommodative stimulus. Thus, accommodation is accurate in terms of maximizing visual performance.

Cycloplegic Effects on the Cylindrical Components of the Refraction

It is important to predict which astigmatic patients require separate refraction for near vision. This study compared cylindrical components changes by cyclopentolate 1% for the low and high amount of astigmatism. The right eyes of 1014 healthy individuals (307 males and 707 females) with cylindrical refractive power more than -0.5 diopter on autorefractometer were selected. Both male and female patients in the age range of 17-45 years were refracted before and after cycloplegia, using 1% cyclopentolate. All volunteers were classified into 2 subgroups including the lower astigmatism group (-2.25 to -0.50) and the higher astigmatic group (-2.50 to over). Alpines' method was used to compare the effect of cycloplegic drop on cylindrical power. The mean age in the lower astigmatism group (29.58; 95% CI: 29.18 to 29.99 years) was not significantly different from the higher astigmatic group (29.85; 95% CI: 29.07 to 30.62) and there were no significant differences in gender between these two groups (P=0.54). Differences between wet and dry refraction in J0 (-0.03; 95% CI:-0.06 to -0.008) and J45 (-0.03; 95% CI:-0.06 to -0.01) were significant only in the higher astigmatic group. Axis changes by the cycloplegic drop in the lower astigmatism group were 3.51 (CI: 3.22 to 3.81) and axis changes by the cycloplegic drop in the higher astigmatism group were 2.21 (CI: 1.73 to 2.49). In patients with a lower amount of astigmatism (-2.25 to -0.50), additional near subjective refraction could be done for precise determination of axis and in patients with a higher amount of astigmatism (-2.50 to over), near subjective refraction might be done for precise determination of power.

Contrast Rivalry Paradigm Reveals Suppression of Monocular Input in Keratoconus

Purpose

Keratoconus results in image quality loss in one or both eyes due to increased corneal distortion. This study quantified the depth of monocular suppression in keratoconus due to this image quality loss using a binocular contrast rivalry paradigm.

Methods

Contrast rivalry was induced in 50 keratoconic cases (11–31 years) and 12 age-matched controls by dichoptically viewing orthogonal Gabor patches of 5 cycles per degree (cpd) and 1.5 cpd spatial frequency for 120 seconds with their best-corrected spectacles and rigid gas permeable (RGP) contact lenses. The dwell time on each eye's percept was determined at baseline (100% contrast bilaterally) and at varying contrast levels (80–2.5%) in the stronger eye of keratoconus or dominant eye of controls. The contrast reduction needed in the stronger eye to balance dwell times on both eyes was considered a measure of suppression depth.

Results

At baseline with 5 cpd stimuli and spectacle correction, the rivalry switches were less frequent and biased toward the stronger eye of cases, all relative to controls (P < 0.001). The contrast balance point of cases (20.51% [10.7–61%]) was lower than the controls (99.80% [98.6–100%]; P < 0.001) and strongly associated with the overall and interocular difference in disease severity (r = 0.83, P < 0.001). The suppression depth reduced for 1.5 cpd (70.8% [21.7–94%]), relative to 5 cpd stimulus (P < 0.001) and with contact lenses (80.1% [49.5–91.7%]), relative to spectacles (P < 0.001).

Conclusions

The eye with lesser disease severity dominates binocular viewing in keratoconus. The suppression depth of the poorer eye depends on the extent of bilateral disease severity, optical correction modality, and the target spatial frequency.

Optical Aberrations of Guinea Pig Eyes

Purpose

The guinea pig is widely used in studies of refractive error development and myopia which often involve experimental optical manipulations. The study described here investigated the optical quality of the guinea pig eye, for which there are limited data, despite its fundamental importance to understanding visually guided eye growth.

Methods

The ocular aberrations of eight adolescent New Zealand pigmented guinea pigs (6–11 weeks old) were measured after cycloplegia using a custom-built Shack–Hartmann aberrometer and fit with a Zernike polynomial function to the 10th order (65 terms). The optical quality of their eyes was assessed in terms of individual Zernike coefficients, and data were further analyzed to derive root-mean-square (RMS) wavefront errors, modulation transfer functions (MTFs), point spread functions (PSFs), Strehl ratios, and depth of focus. A 4-mm pupil was used in all computations. The derived data are compared with equivalent data from normal young adult human eyes.

Results

The guinea pigs exhibited low hyperopia and a small amount of positive spherical aberration, with other aberration terms decreasing with increasing order. Their average depth of focus, estimated from through-focus modulation, was 3.75 diopters. The RMS wavefront error of the guinea pig eye was found to be larger than that of the human eye for the same pupil size, reflecting a higher degree of aberrations, although the PSF (area) on the retina was smaller and sharper due to its shorter focal length. The radial average best-focus MTF derived for the guinea pig eye showed good performance at very low spatial frequencies, with a steeper decline with increasing frequency than for the human eye, dropping below 0.3 at 9 cpd. When converted to linear units (cycles/mm), the guinea pig eye had a higher spatial frequency cutoff and a slight contrast advantage for low spatial frequencies compared to the human eye.

Conclusions

The optical quality of the guinea pig eye is far superior to their reported behavioral visual acuity. This implies a neuroanatomical limit to their vision, which contrasts with the close match of optical and neural limits to spatial resolution in human eyes. The significance for eye growth regulation of the relative optical advantages exhibited by guinea pig eyes, when optical quality is expressed in linear rather than angular retinal units, warrants further consideration.

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.

Changes in accommodative function following small-incision lenticule extraction for high myopia

PURPOSE

To examine whether the amplitude of accommodation, the accommodative response, and the accommodative facility is affected and correlated with changes in higher-order aberrations for patients with high myopia surgically treated with small-incision lenticule extraction (SMILE).

METHODS

35 highly myopic eyes (myopic spherical equivalent of at least 6 diopters) of 35 patients treated with SMILE were included. Assessments were made before and 3 months after surgery. Donders push-up-method was used to measure the amplitude of accommodation. The accommodative response was assessed using an open-field autorefractor"Grand Seiko WAM-5500" (Grand Seiko Co. Ltd., Hiroshima, Japan) in combination with a Badal optometer and stimuli of accommodation at 0.0, 0.5, 1.25, 2.0, 3.0, and 4.0 D, respectively. Accommodative facility was measured at 40 cm with ±2,00D flipper lenses. All measurements of accommodation were performed monocularly with the refractive error corrected with soft contact lenses.

RESULTS

The amplitude of accommodation did not change statistically significantly (mean difference -0.24 D (SD 0.98), 95% CI of mean difference -0.58 D to 0.11 D, paired-sample t(34) = -1.39; P = 0.17). The accommodative responses at 0.0, 0.5, 1.25, 2.0, 3.0, and 4.0 D did not statistically significantly change either (F(6,29) = 1.15; P = .36). Finally, the accommodative facility was also unchanged with a mean difference of 1.11 cycles per minute (SD 5.11, 95% CI of mean difference -0.64 to 2.87, paired-sample t(34) = 1.29; P = 0.21). No clinically significant associations between changes in accommodation and higher-order aberrations were found.

CONCLUSIONS

SMILE does not alter the amplitude of accommodation, the accommodative response, nor the accommodative facility for highly myopic patients, and the surgically induced corneal higher-order aberrations do not affect the accommodative function.

Simultaneous Measurement of Objective and Subjective Accommodation in Response to Step Stimulation

Purpose

This study aimed to evaluate differences in objective and subjective accommodation dynamically and simultaneously.

Methods

Thirty-four pre-presbyopic healthy volunteers (mean age ± SD, 41.0 ± 3.2 years) participated in this study. Initially, the reaction time for detecting a change in the target was measured at near. Dynamic accommodation was then monocularly recorded using an open-view Shack-Hartmann aberrometer and compared with the amplitude and velocity of subjective accommodation.

Results

The objective amplitude of accommodation (0.97 ± 0.32 diopter [D]) was significantly greater than the subjective amplitude of accommodation (0.62 ± 0.43 D; P < 0.001). The accommodative velocity was significantly faster for the "before the accommodation" response time (0.47 ± 0.38 D/s) than the "after the accommodation" response time (0.21 ± 0.22 D/s; P = 0.007).

Conclusions

The human eye under the monocular condition quickly adjusts to the focal plane to clearly archive the nearby object, and the focal plane thereafter is slowly and accurately adjusted to the visual target after visual recognition.

Static and Dynamic Factors Associated With Extended Depth of Focus in Monofocal Intraocular Lenses

PURPOSE

To analyze factors affecting depth of focus (DOF) and near vision functionality in eyes implanted with aspheric monofocal intraocular lenses (IOLs).

METHODS

This prospective study included 111 eyes of 74 patients that underwent phacoemulsification with monofocal IOL implantation. Ninety-one normal eyes were randomized to receive aberration-free (n = 30) or negative-spherical aberration (SA) IOLs (n = 61). Twenty post-hyperopic femto-LASIK eyes received aberration-free IOLs. Corneal higher-order aberrations (SA, coma, trefoil, and corneal asphericity) for a 6 mm pupil were measured by Scheimpflug tomography. Ray-tracing metrics (visual Strehl optical transfer function [VSOTF], effective range of focus [EROF], sphere shift [SS], EROF-SS), pupil size measurements at far and near, and ocular and corneal SA were obtained using ray-tracing aberrometry. Distance-corrected near visual acuity (DCNVA) and subjective defocus curves up to ±4.0 diopters were evaluated.

RESULTS

Multivariable logistic regression found corneal profile and IOL type to be determinants of extended DOF with monofocal IOLs. The aberration-free IOL group showed significantly better DCNVA and higher total SA than the negative-SA group. Post-hyperopic LASIK eyes showed significantly better DCNVA; higher negative SA, coma, and Q value (P < .05), and smaller pupil size (P = .05) than normal eyes implanted with aberration-free IOLs.

CONCLUSION

Corneal profile and type of IOL implanted were the most important factors influencing near vision functionality with aspheric monofocal IOLs. Higher positive SA in the aberration-free group potentially led to better DCNVA than the negative-SA group in normal eyes. Hyperprolate corneas had better DOF curves and DCNVA than normal corneas. NOTE: Publication of this article is sponsored by the American Ophthalmological Society.

Objective optical quality and visual outcomes after the PresbyMAX monocular ablation profile

AIM

To assess objective visual quality after presbyopia correction using the PresbyMAX monocular mode.

METHODS

This prospective, nonrandomized study included 28 eyes from 18 patients (mean age 50.4±5.6y) who underwent presbyopia correction with the PresbyMAX monocular mode. Monocular and binocular visual acuities were evaluated preoperatively, 1d, 1wk, 1, 3mo, and 1y after surgery. Optical quality was analyzed by Hartmann-Shack wavefront aberration supported cornea ablation. Modulation transfer function (MTF) cutoff frequency, Strehl ratio, and objective scattering index (OSI) were analyzed using an optical quality analysis system.

RESULTS

One year after surgery, 100% and 94.4% of patients achieved binocular uncorrected distance and near visual acuity of 20/25, respectively. At the last visit Spherical aberration and total higher aberration were higher than the corresponding preoperative levels (P<0.001); however, no significant difference was found in MTF, OSI, or Strehl ratio. Transient decreases in OSI and MTF mainly occurred in the nondominant eyes. There was no significant difference in optical quality between the dominant and nondominant eyes, except for spherical aberration and horizontal coma (P<0.05).

CONCLUSION

The PresbyMAX monocular mode is safe and effective for presbyopia correction. It has little effect on optical quality, though short-term degraded optical quality occurred mainly in the bi-aspheric ablated eyes.

Retinal Image Formation and Sampling in a Three-Dimensional World

In this review, I develop an empirically based model of optical image formation by the human eye, followed by neural sampling by retinal ganglion cells, to demonstrate the perceptual effects of blur, aliasing, and distortion of visual space in the brain. The optical model takes account of ocular aberrations and their variation across the visual field, in addition to variations of defocus due to variation of target vergence in three-dimensional scenes. Neural sampling by retinal ganglion cells with receptive field size and spacing that increases with eccentricity is used to visualize the neural image carried by the optic nerve to the brain. Anatomical parameters are derived from psychophysical studies of sampling-limited visual resolution of sinusoidal interference fringes. Retinotopic projection of the neural image onto brainstem nuclei reveals features of the neural image in a perceptually uniform brain space where location and size of visual objects may be measured by counting neurons.

Extended Depth-of-Field Intraocular Lenses: An Update

Extended depth-of-focus (EDOF) is a new intraocular lens (IOL) technology in the treatment of presbyopia. In contrast to multifocal (MF) IOLs, EDOF lenses create a single elongated focal point, rather than several foci, to enhance depth of focus. In this way, EDOF IOLs aim to reduce photic phenomena, glare, and halos, which have been reported in MF IOLs. A potential disadvantage is a decrease of retinal image quality if the amount of the aberrations is excessively increased. Frequently, EDOF IOLs are combined with MF optical designs; for this reason, EDOF IOLs are commonly a subject of confusion with optical multifocality concepts. The aim of this article is to clarify what an EDOF IOL is and to discuss the recently reported outcomes with these IOLs. We propose naming lenses that have combined optical designs as "hybrid IOLs."

Customized models of ocular aberrations across the visual field during accommodation

We aimed to create individual eye models that accurately reproduce the empirical measurements of wave-front aberrations across the visual field at different accommodative states, thus providing a mechanistic explanation for the changes in the eye's aberration structure due to accommodation. Structural parameters of a generic eye model were optimized using optical design software to account for published measurements of wave-front aberrations measured for 19 individuals at 37 test locations over the central 30°-diameter visual field at eight levels of accommodative demand. Biometric data for individual eyes were used as starting values and normative data were used to constrain optimizations to anatomically reasonable values. Customizations of the accommodating eye model accurately accounted for ocular aberrations over the central 30° of visual field with an averaged root mean square fitting error typically below 0.2 μm at any given field location. Optimized structural parameters of the eye models were anatomically reasonable and changed in the expected way when accommodating. Accuracy for representing spherical aberration was significantly improved by relaxing anatomical constraints on the anterior surface of the lens to compensate for not including gradient-index media. Use of the model to compute pan-retinal image quality revealed large penalties of accommodative lag for activating photoreceptor responses to the retinal image.

A computational analysis of retinal image quality in eyes with keratoconus

Higher-order aberrations (HOA’s) are exaggerated in eyes with keratoconus but little is known about their impact on the retinal image quality (IQ) of these eyes. This computational study determined changes in IQ [peak IQ, best focus and depth of focus (DOF)] of 12 subjects with manifest keratoconus in both eyes (KCE cohort), 9 subjects with very asymmetric ectasia (VAE cohort) with and without their Rigid Gas Permeable contact lenses (RGP CL’s) and 20 age-matched controls, using a HOA-based through-focus analysis performed on the logNS IQ metric over 5 mm pupil diameter following cycloplegia. All IQ parameters were significantly worse in the KCE cohort with their native HOA’s, relative to controls and in the ectatic eye of the VAE cohort, relative to the fellow non-ectatic eye (p ≤ 0.008 for all). Reduction in HOA’s of these eyes with RGP CL’s resulted in a significant improvement in all IQ parameters but they all remained significantly poorer than controls (p ≤ 0.02 for all). The inter-subject variability of best focus and the DOF range were inversely related to peak IQ in these eyes (r = 0.85; p < 0.001). These results provide the optical basis for two clinical observations on keratoconus: (1) optical performance of keratoconic eyes are significantly better with RGP CL’s than with spectacles or unaided conditions and (2) the endpoint of subjective refraction is elusive in keratoconic eyes, relative to healthy controls or to the non-ectatic eye in bilaterally asymmetric ectasia.

Higher order aberrations, refractive error development and myopia control: a review

Evidence from animal and human studies suggests that ocular growth is influenced by visual experience. Reduced retinal image quality and imposed optical defocus result in predictable changes in axial eye growth. Higher order aberrations are optical imperfections of the eye that alter retinal image quality despite optimal correction of spherical defocus and astigmatism. Since higher order aberrations reduce retinal image quality and produce variations in optical vergence across the entrance pupil of the eye, they may provide optical signals that contribute to the regulation and modulation of eye growth and refractive error development. The magnitude and type of higher order aberrations vary with age, refractive error, and during near work and accommodation. Furthermore, distinctive changes in higher order aberrations occur with various myopia control treatments, including atropine, near addition spectacle lenses, orthokeratology and soft multifocal and dual-focus contact lenses. Several plausible mechanisms have been proposed by which higher order aberrations may influence axial eye growth, the development of refractive error, and the treatment effect of myopia control interventions. Future studies of higher order aberrations, particularly during childhood, accommodation, and treatment with myopia control interventions are required to further our understanding of their potential role in refractive error development and eye growth.