Accommodative Stimulus Research Articles

High-Order Aberrations: A Key Factor in Accommodative Dysfunctions

This study investigated the relationship between high-order aberrations (HOAs) and accommodative dysfunctions by analyzing their changes with accommodation. Understanding this relationship is important for understanding the mechanisms underlying these conditions. Sixty-three subjects were divided into five groups: control, infacility of accommodation (INFA), excess of accommodation (EA), insufficiency of accommodation (INSA), and symptomatic without dysfunction (SWD). Variations in root-mean-square (RMS) of the 3rd, 4th, 5th, and 6th orders and HOAs, and fluctuations of RMS HOAs, were measured using a Shack–Hartmann aberrometer at different accommodative stimuli and during residual accommodation after their removal, in the following order: 0.00 D, 1.00 D, 0.00 D, 2.45 D, 0.00 D, 4.73 D and 0.00 D. The SWD group showed a significant increase in RMS HOAs during accommodation and residual accommodation. In contrast, the EA group showed an improvement in the ocular optical quality at higher stimuli. Different patterns of changes in the 3rd, 4th, 5th, and 6th orders were observed across all groups, and fluctuations of RMS HOAs increased significantly in the SWD group during accommodation and residual accommodation. These distinct patterns of aberration changes in different accommodative dysfunctions suggest a potential link between their underlying mechanisms, providing insights that may aid their earlier diagnosis and improved management.

Exploring the relationship between accommodation and intraocular pressure: a systematic literature review and meta-analysis.

To investigate the relationship between accommodation and intraocular pressure (IOP). Systematic literature search and meta-analysis following PRISMA guidelines was conducted on studies analyzing the relationship between accommodation and intraocular pressure. After removal of duplicates, title and abstract screening, full-text analysis was performed to select relevant articles and meta-analysis was then conducted as well. Of the 1357 records identified, 17 met the selection criteria and were included. Overall, all studies showed that accommodation can influence IOP levels and meta-analysis indicated a significant IOP reduction of 1.10 mmHg (95%CI, -1.77; -0.42) following accommodative stimulus in healthy individuals, albeit with high heterogeneity among studies. Differences in IOP changes between emmetropic and progressing myopic individuals were not significant. Controversial results were obtained in patients with glaucoma with significantly lower IOP fluctuations being noted in eyes with previous trabeculectomy; however, the clinical heterogeneity of enrolled patients among studies made it not possible to combine results. Type of accommodative task, extraocular muscle contraction, head and body position all could potentially play a role in the measured IOP changes with, interestingly, near reading on a smartphone suggesting IOP increase. Accommodation has an impact on IOP measurements and, overall, determines IOP decrease in healthy individuals. While such variations might not hold clinical significance for individuals in good health, their impact in patients with glaucoma should be considered. Further studies focused on specific components of such relationship are required to elucidate their individual impact and to define their potential role as non-pharmacological strategies to reduce IOP levels in selected patient categories.

Changes in pupil size, ocular wavefront aberrations, and accommodation in healthcare workers using FFP3 masks.

To evaluate changes in pupil size, ocular wavefront aberrations (WA), and accommodation in healthcare workers after 4-h usage of Filtering Facepiece class 3 (FFP3) masks. This prospective study included 22 healthy healthcare workers. Pupil size, ocular WA, and accommodation changes before and after FFP3 mask usage were evaluated using a Hartmann Schack aberrometer. Accommodative responses to stimulus ranging from 0 to 5 diopters (D) in increments of 0.5 D were assessed. Ocular high-order aberrations (HOAs) were recorded at baseline and at every accommodative stimulus. Oxygen saturation (SpO2) was measured by pulse oximetry before and after the mask usage. The mean age was 36.6 ± 8.5 years. The SpO2 significantly decreased from 98.95 to 97.95% after usage of the FFP3 mask (p < 0.001). The mean pupil size did not significantly differ before (6.22 ± 0.75 mm) and after (6.38 ± 0.83 mm) the 4-h mask usage (p = 0.093). The mean total RMS of the total HOAs was 0.36 ± 0.17 before and 0.39 ± 0.15 after the mask usage (p = 0.071). Post-mask accommodation showed a significant decrease at the 2 D (p = 0.041), 2.5D (p = 0.022), and 3 D (p = 0.025) stimuli. The present study shows that after 4 h-usage of FFP3 mask, both SpO2 and accommodative response to increasing stimuli might be significantly decreased.

Alterations in Lens Free Water Distribution Are Associated with Shape Deformation in Accommodation

To investigate whether a redistribution of water within the crystalline lens is associated with the shape deformation that occurs during accommodation. Observational, cross sectional study. Eleven young adults without presbyopia (aged 18-39 years) and 9 middle-aged adults with presbyopia (aged 40-55 years). Magnetic resonance imaging (MRI) scans of the lens were acquired on a 3 Tesla clinical MRI scanner, without and with the presentation of a 3 Diopter accommodative stimulus. The MRIs were postprocessed using established methods to extract the geometric dimensions and spatial maps of water distribution of the lens. Accommodative changes in the full 3-dimensional description of lens shape, the lens total-water distribution profile, and the lens free-water distribution profile. Viewing of an accommodative stimulus by young subjects elicited an elastic shape deformation of the lens consistent with accommodation that was associated with an elevated, smoother free-water distribution, primarily in the anterior region of the lens. In contrast, viewing of an accommodative stimulus by presbyopic subjects produced an atypical shape deformation of the lens that was instead associated with a lowered free-water distribution, primarily in the anterior region of the lens. No discernible changes to the lens total-water distribution were observed in response to the accommodative stimulus in either subject cohort. The present study suggests that protein-mediated alterations in the free-water distribution of the anterior region of the lens influence the shape deformation in accommodation, presenting pharmacological modulation of free-water distribution as an attractive novel approach for treating presbyopia. The authors have no proprietary or commercial interest in any materials discussed in this article.

Topical Review: Methodological Variables in Clinical and Laboratory Measurements of Fixation Disparity.

Fixation disparity is a small vergence error that does not disrupt fusion. Fixation disparity measures correlate with binocular symptoms. This article covers methodological differences between clinical fixation disparity measurement devices, findings when objective and subjective fixation disparities are compared, and the potential impact of binocular capture on fixation disparity measurements. Fixation disparity is a small vergence error that occurs in nonstrabismic individuals and does not disrupt fusion. This article reviews clinical fixation disparity variables and their clinical diagnostic value. Clinical devices that are used to measure these variables are described, as are studies in which the output from these devices has been compared. Methodological differences between the devices such as the location of the fusional stimulus, the rate at which judgments of dichoptic alignment are made, and the strength of the accommodative stimulus are all considered. In addition, the article covers theories of the neural origins of fixation disparity and control system models incorporating fixation disparity. Studies in which objective fixation disparities (oculomotor portion of fixation disparity assessed with an eye tracker) and subjective fixation disparities (sensory portion of fixation disparity assessed psychophysically with dichoptic Nonius lines) have been compared are also examined, and consideration is given to why some investigators find differences in these measures, whereas other investigators do not. The conclusion thus far is that there are likely complex interactions between vergence adaptation, accommodation, and the location of the fusional stimulus that lead to differences in objective and subjective fixation disparity measures. Finally, capture of the visual direction of monocular stimuli by adjacent fusional stimuli and the implications for fixation disparity measures are considered.

System for Objective Assessment of the Accommodation Response During Subjective Refraction.

To evaluate a system based on a Hartmann-Shack wavefront sensor attached to a phoropter that allows the user to obtain real-time information about the refractive state of the eye and the accommodation response (AR). The objective refractions (ME) and ARs of 73 subjects (50 women, 23 men; ages, 19-69 years) were assessed with the system developed while placing in the phoropter the subjective refraction (MS) plus a set of trial lenses with differences in spherical equivalent power (ΔM) between ±2 diopters (D). The objective estimations (ME) showed a good correlation with the subjective values (MS) (r = 0.989; P < 0.001). The means of the ARs presented a region where the accommodation remained stable (ΔM from +2 D to about 0 D), followed by another in which the response increased progressively (ΔM from about 0 to -2 D) with the magnitude of the accommodation stimulus. The analysis of variance within subjects applied to ARs introducing age and MS as covariates showed an increasing effect size of age from medium to large between ΔM of -0.5 and -2 D. In contrast, MS had a medium effect size (between ΔM of +2 and 0 D). The implemented system permitted an objective estimation of the refraction of the eye and its AR. Because it is coupled to a phoropter, the system can be used to retrieve the AR during subjective refraction procedures. The developed system can be used as a supporting tool during subjective refraction to provide certainty about the true state of accommodation.

Spherical Aberration and Accommodative Insufficiency: Is There a Link?

Given the relationship between spherical aberrations and accommodation, the study of these aberrations can be helpful to understand accommodative response in subjects with accommodative dysfunctions. The purpose of this study was to evaluate on-axis and off-axis changes of primary and secondary spherical aberrations, Z(4,0) and Z(6,0), with accommodation in subjects with accommodative insufficiency (AI). Ten subjects with AI and eleven without any accommodative dysfunction (control) participated in this study. On-axis defocus Z(2,0), Z(4,0), and Z(6,0) were obtained in both groups with a Hartmann–Shack aberrometer for the unaccommodated state and with 1.00 D, 2.44 D, 3.83 D, and 4.73 D of accommodative stimuli. Z(4,0) and Z(6,0) were also measured on 11.5° and 23° temporal, nasal, superior, and inferior retinal areas for unaccommodated state and for 2.44 D of accommodative stimulus. In the control group, Z(4,0) became more negative with accommodation and Z(6,0) became more positive, as was expected according to previous studies. This tendency was not observed in the group of subjects with AI group for Z(4,0) or for Z(6,0). No differences on off-axis Z(4,0) and Z(6,0) were observed between the groups. The changes of spherical aberrations with accommodation seem different in subjects with AI compared to those without any accommodative dysfunction. Those with AI do not present a decrease in Z(4,0) and an increase in Z(6,0) with accommodation as occurs in eyes without this type of dysfunction. Understanding how the optics of the eye changes with accommodation can be helpful to understand the origin of accommodative dysfunctions.

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

To present FIAT, a novel optical instrument and analysis package that is designed to elicit and optically record accommodation in human eyes. 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. 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. FIAT is an effective instrument for making accurate, objective measures of accommodation in phakic and pseudophakic eyes. We present a device that can play an important role in the development and testing of accommodating intraocular lenses.

Central and peripheral choroidal thickness and eye length changes during accommodation.

Eye length increases during accommodation, both on-axis and in the periphery. The aim of this study was to determine whether the peripheral choroid thins with accommodation and to determine the relationship with eye length changes measured at the same location. Subjects included 53 young adults in good ocular and general health, with 19 emmetropes and 34 myopes. Measurements from the right eye were made for 0 D and 6 D accommodation stimuli for ±30° horizontal visual field/retinal locations in 10° steps. Valid eye length and choroidal thickness measurements were obtained for 37 and 47 participants, respectively, and both measures were taken for 31 participants. 2.5% phenylephrine was instilled to dilate the pupils. Participants turned their eyes, without head movement, to fixate targets and to make the target 'as clear as possible' during measurements. Correction was made for the influence of lens thickness changing at different peripheral angles. Choroidal thickness was measured with a spectral-domain-Optical Coherence Tomographer. For peripheral images, the internal cross target on the capture screen was moved from the centre to 17.25° nasal/temporal positions. In accordance with previous literature, eye length increased with accommodation. The greatest change (mean ± SD) of 41 ± 17 μm occurred at the centre, with a mean change across the locations of 33 μm. There were no significant differences between emmetropes and myopes. Choroidal thickness decreased with accommodation, with changes being about two-thirds of those occurring for eye length. The greatest change of -30 ± 1μm occurred at the centre, with a mean change of -21 μm. Greater choroidal thinning occurred for myopes than for emmetropes (23 ± 11 vs. 17 ± 8μm, p=0.02). With accommodation, eye length increased and the choroid thinned, at both central and peripheral positions. Choroidal thinning accounted for approximately 60% of the eye length increase across the horizontal ±30°.

Wavefront sensing for objective assessment of vision therapy efficacy: Preliminary results

The aim of this study was to use wavefront sensing to objectively evaluate the effects of vision therapy in subjects with insufficiency (AI) and infacility of accommodation (AINF). Aberrometry was performed with a Shack-Hartmann wavefront aberrometer for different accommodative stimuli in one subject with AI and one with AINF before and after treatment with vision therapy (VT). A control subject received a placebo treatment. Real-time accommodative response, accommodation and disaccommodation reaction time, accommodative microfluctuations and root mean square of higher order aberrations were compared before and after VT/placebo. VT was effective and wavefront sensing can be used to detect AI and AINF and evaluate these subjects during VT.

Objective Characteristics of Accommodation in Present-Day Schoolchildren with Different Levels of Myopia

Purpose: We study the state of the accommodative function in present-day schoolchildren using the method of computer accomodography. Patients and methods: 74 children (10–16 years old), 54 of them with different degrees of myopia and 20 children (control group) with emmetropia were tested on the computer accomodography devise Righton Speedy-K ver. MF-1. The strength of the accommodative response accorded to the presented accommodative stimulus was determined by calculating the accommodative coefficient response (CAO) and the contraction’s nature of the ciliary body fibers by determining the microfluctuation coefficient (KMF).

Effect of accommodation on coma at central and peripheral retina

Coma is one of the most common ocular higher order aberrations and highly affects the quality of image. It is assumed that corneal aberrations are balanced by internal (lenticular) aberrations so that retinal image quality may not have great impact. However, during accommodation, the shape, position, and curvature of the crystalline lens changes which might disrupt this balance between internal and corneal aberration. This study aimed to investigate the effect of accommodation on primary coma ( and ) and secondary coma ( and ) in relaxed and accommodated eyes. Zernike coefficients were measured in 53 subjects with Hartmann-Shack aberrometer both at the central and peripheral retina up to 30° off-axis in horizontal and vertical meridians. The process was repeated with 2.50 D accommodation stimulus and comas were compared with and without accommodation. Root-mean-square of total coma was also assessed. With accommodation, vertical comas changed to more negative value and horizontal comas changed to more positive values in most of the off-axis positions. In contrast, the secondary vertical comas became less negative and secondary horizontal comas became more negative with accommodation in most of the off-axis fixations. Thus, the results showed that accommodation affects coma which depends up on position of the fixation.

Assessment of central and peripheral accommodative lag by aberrometry

Accommodation lag is important factor for normal vision. Higher lag of accommodation may cause various ocular symptoms particularly during near tasks. In this study, the lag of accommodation was assessed in the peripheral retina and it was compared with the central accommodative lag with aberrometer. In this cross-sectional study, fifty-three young subjects with normal visual acuity and without any active ocular disease or past ocular surgery were included. Aberrations in the central and peripheral field of view up to 30° off axis from the centre in horizontal and vertical meridian in 10° steps were measured with Hartmann-Shack aberrometer with stimulation of accommodation by -2.50D lens. Accommodative stimulus and accommodative response were calculated with defocus and hence accommodative lag was obtained. Accommodative lag in the centre and periphery was compared. Repeated measure of ANOVA showed that there were significant differences in lag of accommodation in various eccentricities (F(8.912, 454.514) = 2.372, p = 0.013). Pairwise test showed that lag in the centre was similar with lag on other peripheral field of view (p > 0.05). However, accommodative lag at 10° nasal field was significantly lower than the lag at 20° temporal, 20° nasal, 30° temporaland 30° nasal (p < 0.05). Similarly, lag at 10° superior fixation was lower than lag at 20° temporal, 20° nasal, 30° temporal and 30° nasal fixations (p < 0.05). We found higher lag of accommodation in horizontal off-axis fixations in comparison to that of vertical off-axis fixations (p < 0.05). Lag of accommodation was positive correlated with vertical coma and primary spherical aberrations but negative correlated with secondary spherical aberrations (p < 0.05). Thus, Hartmann-Shack aberrometer was successfully used to assess accommodative lag in the peripheral field of view up to 60° visual field. Peripheral lag of accommodation depends up on eccentricity. Lag was found higher in horizontal off-axis fixation than at vertical fixations. Coma and spherical aberration had association with lag.

Establishment of Personalized Finite Element Model of Crystalline Lens Based on Sweep-Source Optical Coherence Tomography

The virtual lens model has important value in ophthalmic research, clinical diagnosis, and treatment. However, the establishment of personalized lens models and the verification of accommodation accuracy have not been paid much attention. We proposed a personalized lens model establishment and the accommodation accuracy evaluation method based on sweep-source optical coherence tomography (SS-OCT). Firstly, SS-OCT is used to obtain a single lens image in the maximum accommodation state. After refraction correction, boundary detection, and curve fitting, the central curvature radius, thickness, and lens nucleus contour of the anterior and posterior surfaces of the lens were obtained. Secondly, a personalized finite element model improved from Burd’s model was established using these individual parameters, and the adaptation process of the lens model was simulated by pulling the suspensory ligament. Finally, the shape and refractive power changes of the real human lens under different accommodation stimuli were collected and compared with the accommodation process of the finite element model. The results show that the accommodation process of the finite element model is highly consistent with that of the real lens. From the un-accommodation state to the maximum-accommodation state, the difference rate of all geometric and refractive parameters between the two is less than 5%. Thus, the personalized lens finite element model obtained by the calibration and correction of the existing model can accurately simulate the regulation process of a specific human lens. This work helps to provide a valuable theoretical basis and research ideas for the study of clinical diagnosis and treatment of related diseases.

Seeing the future: Predictive control in neural models of ocular accommodation.

Ocular accommodation is the process of adjusting the eye's crystalline lens so as to bring the retinal image into sharp focus. The major stimulus to accommodation is therefore retinal defocus, and in essence, the job of accommodative control is to send a signal to the ciliary muscle which will minimize the magnitude of defocus. In this article, we first provide a tutorial introduction to control theory to aid vision scientists without this background. We then present a unified model of accommodative control that explains properties of the accommodative response for a wide range of accommodative stimuli. Following previous work, we conclude that most aspects of accommodation are well explained by dual integral control, with a “fast” or “phasic” integrator enabling response to rapid changes in demand, which hands over control to a “slow” or “tonic” integrator which maintains the response to steady demand. Control is complicated by the sensorimotor latencies within the system, which delay both information about defocus and the accommodation changes made in response, and by the sluggish response of the motor plant. These can be overcome by incorporating a Smith predictor, whereby the system predicts the delayed sensory consequences of its own motor actions. For the first time, we show that critically-damped dual integral control with a Smith predictor accounts for adaptation effects as well as for the gain and phase for sinusoidal oscillations in demand. In addition, we propose a novel proportional-control signal to account for the power spectrum of accommodative microfluctuations during steady fixation, which may be important in hunting for optimal focus, and for the nonlinear resonance observed for low-amplitude, high-frequency input. Complete Matlab/Simulink code implementing the model is provided at https://doi.org/10.25405/data.ncl.14945550.

Near work symptoms and measures of accommodation in children

ABSTRACT Clinical relevance Some children experience significant symptoms while doing near work, and accommodative deficits can be a contributory factor. However, studies investigating near work symptoms in children are sparse. Background To investigate the association between clinical and objective measures of accommodation and near point symptoms. Methods Twelve asymptomatic and 14 symptomatic children (mean age = 11.1 and 11.8 years, respectively) based on their Convergence Insufficiency Symptom Survey scores participated in the study. The clinical measures of accommodation were monocular amplitude of accommodation, monocular accommodative facility, and monocular estimation method. Objective measurements of the accommodative stimulus response function were recorded with a WAM-5500 autorefractor for two consecutive minutes at five viewing distances (0.33, 2, 3, 4, and 5 Dioptres [D]). Accommodative findings were compared between the groups using the Mann–Whitney U-tests. Spearman’s rank correlation coefficient was used to assess the association between symptoms and clinical and objective measures of accommodation. Results The mean CISS scores were 32.8 and 7.3 for the symptomatic and asymptomatic groups, respectively (p = <0.001). The symptomatic group showed a reduced accommodative functions compared to the asymptomatic group (p = 0.002 for accommodative facility, p = 0.04 for accommodative amplitude, p = 0.029 and 0.01 for objective measures of accommodation at 4D and 5D viewing distance, respectively). Clinical tests of accommodative amplitude and facility (correlation coefficient = −0.407 and −0.54, respectively) showed the highest correlation with the CISS scores, compared to the objective measures of accommodation. Conclusion Clinical tests of accommodation showed a greater association with symptoms than objective measures of accommodation in children aged 8–16 years. In children presenting with visual discomfort symptoms, measurement of accommodative amplitude and facility should be considered.

Accommodation lags are higher in myopia than in emmetropia: Measurement methods and metrics matter.

PurposeTo determine whether accommodative errors in emmetropes and myopes are systematically different, and the effect of using different instruments and metrics.MethodsSeventy‐six adults aged 18–27 years comprising 24 emmetropes (spherical equivalent refraction of the dominant eye +0.04 ± 0.03 D) and 52 myopes (−2.73 ± 0.22 D) were included. Accommodation responses were measured with a Grand Seiko WAM‐5500 and a Hartmann–Shack Complete Ophthalmic Analysis System aberrometer, using pupil plane (Zernike and Seidel refraction) and retinal image plane (neural sharpness—NS; and visual Strehl ratio for modulation transfer function—VSMTF) metrics at 40, 33 and 25 cm. Accommodation stimuli were presented to the corrected dominant eye, and responses, referenced to the corneal plane, were determined in the fellow eye. Linear mixed‐effects models were used to determine influence of the refractive group, the measurement method, accommodation stimulus, age, race, parental myopia, gender and binocular measures of heterophoria, accommodative convergence/accommodation and convergence accommodation/convergence ratios.ResultsLags of accommodation were affected significantly by the measurement method (p < 0.001), the refractive group (p = 0.003), near heterophoria (p = 0.002) and accommodative stimulus (p < 0.05), with significant interactions between some of these variables. Overall, emmetropes had smaller lags of accommodation than myopes with respective means ± standard errors of 0.31 ± 0.08 D and 0.61 ± 0.06 D (p = 0.003). Lags were largest for the Grand Seiko and Zernike defocus, intermediate for NS and VSMTF, and least for Seidel defocus.ConclusionsThe mean lag of accommodation in emmetropes is approximately equal to the previously reported depth of focus. Myopes had larger (double) lags than emmetropes. Differences between methods and instruments could be as great as 0.50 D, and this must be considered when comparing studies and outcomes. Accommodative lag increased with the accommodation stimulus, but only for methods using a fixed small pupil diameter.

Objective characteristics of accommodation in present-day schoolchildren with progressive myopia

Purpose: to study the accommodative function in contemporary schoolchildren using the method of computer accommodography.Material and methods. 74 children aged 10–16 (54 with different degrees of myopia and the control group of 20 emmetropic children) were tested on a Righton Speedy-K ver. MF-1 computer accommodograph to determine the accommodative response to accommodation stimulus (by calculating the coefficient of the accommodative response, CAR) and the contraction of ciliary muscle fibers (by determining the microfluctuation coefficient, CMF).Results. In groups of patients with emmetropia and weak myopia, CAR and CMF were found to exceed the normal values. The low myopia group demonstrated especially pronounced changes. In moderate and high myopia, the CAO is significantly lower than in low myopia or emmetropia, while the CMF also exceeds normal values.Conclusion. The spastic component of accommodation is of great importance in the pathogenesis of progressive myopia of present-day schoolchildren, which is expressed in the strengthening of the accommodation response with regard to the accommodation stimulus and pathological frequency increase of accommodative microfluctuations.

Axial Elongation During Short-Term Accommodation in Myopic and Nonmyopic Children.

PurposeAxial length increases during accommodation in adults and children; however, refractive error group differences are conflicting and have not been explored in pediatric populations. This study aimed to evaluate differences in accommodation-induced axial elongation between myopic and nonmyopic children.MethodsA range of ocular biometric measurements were captured during brief accommodation tasks (0, 3, 6, and 9 D) using a Badal optometer mounted to a noncontact optical biometer (Zeiss IOLMaster 700). Reliable measurements were captured for 15 myopic and 15 age- and sex-matched nonmyopic children. The average central corneal thickness (CCT), anterior chamber depth (ACD), crystalline lens thickness (LT), anterior segment length (ASL), vitreous chamber depth (VCD), and axial length (AL) were determined for each accommodation stimulus. Raw measurements of AL and VCD were corrected for the estimated error associated with LT increases during accommodation.ResultsAll biometric parameters, except CCT, changed significantly during accommodation (all P < 0.001). Myopic children exhibited significantly greater accommodation-induced axial elongation than nonmyopic children (P = 0.002) at the 3, 6, and 9 D accommodation stimuli, with a mean difference of 7, 10, and 16 µm, respectively (all pairwise comparisons, P ≤ 0.03). The changes in all other biometric parameters were not different between the refractive error groups (P ≥ 0.23).ConclusionsAccommodation-induced axial elongation was greater in myopic than nonmyopic children. This finding could support a potential mechanism linking near work, axial elongation, and myopia development in children or may reflect greater susceptibility to accommodation-induced axial elongation in children with established myopia.

Compact Models of Presbyopia Accommodative Errors for Wearable Adaptive-Optics Vision Correction Devices

Subjective accommodation refractive error models are essential for implementing adaptive vision correction devices that utilize varifocal optics. This article describes compact empirical models of subjective accommodative refractive errors in subjects with advanced presbyopia. The models are based on measurements of subjective refractive errors from fifteen presbyopes over the age of 45 using commercially available focus-tunable eyeglasses under three different illumination conditions over a 3.08D accommodation stimulus range. The resulting average residual root-mean-squared (RMS) error values for the best fitting 8-parameter model was 0.25D compared to an average RMS error of 0.4D for the conventional DDF and HHG models. The RMS error for the best-fitting model is below the average refractive error of the human eye.