Accommodation steps, target spatial frequency and refractive error

A reduced sensitivity to retinal image blur has been reported in myopes. Diminished blur detection reduces the error signal to the retinotopic (blur-induced) accommodation system and results in impaired accommodation responses under retinotopic conditions. This study was conducted to investigate retinotopic accommodation responses in emmetropia and myopia under dynamic conditions. Static accommodation responses to a blur-only target with vergences of 0 to 4.5 D were measured with an optometer. Microfluctuations of accommodation were recorded with the subject viewing the target at a vergence of 4 D, and dynamic step responses were measured for step stimuli from 2.5 to 3.5 D and 2.0 to 4.0 D, with the optometer in dynamic recording mode. Measurements were obtained from a group of 32 visually normal emmetropes (EMMs) and subjects with progressing myopia. Stimulus-response curves were not significantly different between the refractive groups. Subjects with late-onset myopia (LOMs) demonstrated significantly larger accommodation microfluctuations compared with emmetropes and subjects with early-onset myopia (EOMs). Fourier analysis revealed that the increase in the magnitude of the fluctuations was mediated by the low-frequency components. Accommodation step responses revealed longer reaction times in LOMs. Further analysis showed that LOMs responded to accommodation step stimuli only between 43% and 64% of the time. In contrast, the other groups showed a response rate of almost 100%. The experiments demonstrate a reduction in retinotopic processing in LOMs, which results in an increased variability in their dynamic accommodation response to stationary near targets and reduced performance for dynamic step tasks. The results demonstrate a reduced blur appreciation under dynamic conditions in these refractive groups that may lead to periods of retinal image blur of varying magnitude during near work.

Face perception in adults depends on skilled processing of interattribute distances ('configural' processing), which is disrupted for faces presented in inverted orientation (face inversion effect or FIE). Children are not proficient in configural processing, and this might relate to an underlying immaturity to use facial information in low spatial frequency (SF) ranges, which capture the coarse information needed for configural processing. We hypothesized that during adolescence a shift from use of high to low SF information takes place. Therefore, we studied the influence of SF content on neural face processing in groups of children (9-10years), adolescents (14-15years) and young adults (21-29years) by measuring event-related potentials (ERPs) to upright and inverted faces which varied in SF content. Results revealed that children show a neural FIE in early processing stages (i.e. P1; generated in early visual areas), suggesting a superficial, global facial analysis. In contrast, ERPs of adults revealed an FIE at later processing stages (i.e. N170; generated in face-selective, higher visual areas). Interestingly, adolescents showed FIEs in both processing stages, suggesting a hybrid developmental stage. Furthermore, adolescents and adults showed FIEs for stimuli containing low SF information, whereas such effects were driven by both low and high SF information in children. These results indicate that face processing has a protracted maturational course into adolescence, and is dependent on changes in SF processing. During adolescence, sensitivity to configural cues is developed, which aids the fast and holistic processing that is so special for faces.

To investigate the relationship between pupil diameter and refractive error and how refractive correction, target luminance, and accommodation modulate this relationship. Sixty emmetropic, myopic, and hyperopic subjects (age range, 18 to 35 years) viewed an illuminated target (luminance: 10, 100, 200, 400, 1000, 2000, and 4100 cd/m) within a Badal optical system, at 0 diopters (D) and -3 D vergence, with and without refractive correction. Refractive error was corrected using daily disposable contact lenses. Pupil diameter and accommodation were recorded continuously using a commercially available photorefractor. No significant difference in pupil diameter was found between the refractive groups at 0 D or -3 D target vergence, in the corrected or uncorrected conditions. As expected, pupil diameter decreased with increasing luminance. Target vergence had no significant influence on pupil diameter. In the corrected condition, at 0 D target vergence, the accommodation response was similar in all refractive groups. At -3 D target vergence, the emmetropic and myopic groups accommodated significantly more than the hyperopic group at all luminance levels. There was no correlation between accommodation response and pupil diameter or refractive error in any refractive group. In the uncorrected condition, the accommodation response was significantly greater in the hyperopic group than in the myopic group at all luminance levels, particularly for near viewing. In the hyperopic group, the accommodation response was significantly correlated with refractive error but not pupil diameter. In the myopic group, accommodation response level was not correlated with refractive error or pupil diameter. Refractive error has no influence on pupil diameter, irrespective of refractive correction or accommodative demand. This suggests that the pupil is controlled by the pupillary light reflex and is not driven by retinal blur.

Purpose: We investigated the correlation between changes in pupil size with accommodation stimuli and accommodation response after refractive correction by using soft contact lenses in myopes. Methods: Participants were young myopes (N=50, 100 eyes; 23.15 ±1.70 years; age range, 20~28 years) and refractive errors were corrected by using soft contact lenses. Pupil sizes were measured with a pupillometer at the modes of scotopic, low and high mesopic condition (light off, 0.3 and 3 lx) at 3.5 m and 25 cm in the 100 lx illuminance condition. Accommodation amplitude was measured with the push-up test, and the accommodation response was measured by using an open field autorefractometer. The changes of pupil size with the accommodation stimulus were analyzed by paired t-test and the correlation between the amount of changes in pupil size with the accommodation stimulus and accommodation amplitude and accommodation response were analyzed by Pearson correlation and the significance level was p<0.05. Results: Pupil size was significantly increased by accommodation stimulus in uncorrected refractive error in myopia (p<0.05), and significantly decreased after refractive correction with soft contact lenses (p<0.05). After refractive correction, the larger the miosis caused by accommodation stimulus, the smaller the binocular and monocular accommodation responses (p<0.05). However, the percentage of participants shown no difference in pupil size in the lighting condition were 35~37%, and shown mydriasis was 7~11% and the accommodation response of the group not shown miosis was significantly larger than that of the miosis group (p<0.05). Conclusions: The pupil size in myopes corrected with contact lenses decreased by accommodation stimulus, and the accommodation response was decreased. However, in the participants not shown miosis, accommodation response was more than that of miosis group. This study will be cornerstones to understanding of the asthenopia during near works in the contact lens wearers and the visual function of the multifocal contact lens wearers.

Orbital frontal cortex (OFC) is known to play a role in object recognition by generating "first-pass" hypotheses about the identity of naturalistic images based on low spatial frequency (SF) information. These hypotheses are evaluated by more detailed (and slower) ventral visual pathway processes. While it has been suggested on theoretical grounds, it remains unknown whether OFC also receives postrecognition feedback about stimulus identity. We used a novel paradigm in the context of functional magnetic resonance imaging that permits the first few hundred milliseconds of object recognition to be spread out over 120 s. OFC shows a robust response to low and relatively high SFs, whereas ventral stream regions display unimodal response distributions shifted toward high SFs. These findings in OFC were modulated by hemisphere, with right OFC differentially responding to low SFs and left OFC differentially responding to high SFs. Psychophysical experiments confirmed that the same ranges of SFs preferred by ventral stream regions are critical for determining the accuracy and speed of object recognition. Our findings indicate that OFC accesses global form (low SF information, right OFC) and object identity (high SF information, left OFC), and suggest that OFC receives feedback about the accuracy of its initial hypothesis regarding stimulus identity.

Purpose. Recent work has shown that differences exist in the accommodation response characteristics of myopes and emmetropes, although the exact nature of the differences has yet to be ascertained. This may in part be due to the classification of the refractive error employed in many studies. Previously it has been suggested that inaccuracies in the accommodation response occur predominantly during the progression of myopia. To test this hypothesis we measure nearwork induced transient myopia (NITM) in progressing myopes (PMs), stable myopes (SMs) and emmetropes (EMMs). Methods. A total of 41 young (18–27 years) subjects participated in the study (13 PMs, 14 SMs, 14 EMMs). Following a 10 minute near task (4D) the change in accommodation response back to distance viewing was measured over a two minute time period. Results. Grouped mean data revealed a significant nearwork after-effect in PMs in comparison to SMs and EMMs after 10 seconds (p < 0.01) and 30 seconds (p < 0.01) post-task. Significantly longer time constants were also found in the PMs group. Conclusions. Our results suggest that NITM is manifest during the progressive phase of myopia development.

Aim: To find out the correlation of choroidal thickness (CHT) with refractive error (RE) &amp; axial length (AL) in North-Indian population of age group of 18-35 years having myopia or emmetropia using A-scan and Oct imaging. Objective is to check for a relationship of CHT with AL &amp; RE in myopic – emmetropic individuals with help of A-scan and Oct imaging. Methods this study is an observation- analysis based cross sectional study which involved 200 eyes of individuals presented at outpatient department of Eye care solution consisting 50 beings with ≥4 D Myopia &amp; 50 other Emmetropic presenting for ailments other than refractive error taken as Control group. The criteria for selection of subjects were done on basis of selective age 18-35 years, degree of refractive error and clear ocular media. However, subjects with history of any intraocular pathology, surgery, inflammation or any associated systemic disorder such or vascular diseases were excluded another thing where in person with OCT scan less signal strength, motion artifact &amp; focal signal loss were too excluded. A written-informed consent was taken from all subjects prior to enrolment. Results: This study investigated the structural characteristics of the eye across three groups of myopic individuals and a control group. Myopia Group I (with myopia ranging from -3.00 D to -4.75 D) showed an average axial length of 24.78 mm, macular thickness of 100.08 µm, and choroidal thickness of 309.54 µm. Myopia Group II (with myopia between -5.00 D and -6.75 D) exhibited a greater axial length of 25.83 mm, a macular thickness of 112.34 µm, and a choroidal thickness of 289.47 µm. Myopia Group III (with myopia of -7.00 D and above) had the longest axial length at 26.10 mm, a macular thickness of 110.38 µm, and the thinnest choroidal thickness at 255.38 µm. In comparison, the control group, consisting of emmetropic individuals, had an average axial length of 23.26 mm, macular thickness of 322.24 µm, and a significantly thicker choroid (242.23 µm) across both Sattler’s and Haller’s layers. These findings highlight the progressive structural changes—particularly axial elongation and choroidal thinning—associated with increasing myopia severity. Conclusion: The results of this study reveal a definite link between the degree of myopia and anatomical variations in the eye. Axial length increases in tandem with myopia, and the choroid significantly thins, especially in the deeper layers (Sattler's and Haller's). According to these results, axial elongation and choroidal thinning are progressive features of myopia, with alterations becoming more noticeable as refractive error increases. Gaining knowledge of these structural changes may help direct future treatment approaches and offer significant understanding into the pathophysiology of myopia

A frequent configuration in computational fluid mechanics combines an explicit time advancing scheme for accuracy purposes and a computational grid with a very small portion of much smaller elements than in the remaining mesh. Examples of such situations are the traveling of a discontinuity followed by a moving mesh, and the large eddy simulation of high Reynolds number flows around bluff bodies where together very thin boundary layers and vortices of much more important size need to be captured. For such configurations, explicit time advancing schemes with global time stepping are very costly. In order to overcome this problem, the multirate time stepping approach represents an interesting improvement. The objective of such schemes, which allow to use different time steps in the computational domain, is to avoid penalizing the computational cost of the time advancement of unsteady solutions which can become large due to the use of small global time steps imposed by the smallest elements such as those constituting the boundary layers. In the present work, a new multirate scheme based on control volume agglomeration is proposed for the solution of the compressible Navier-Stokes equations possibly equipped with turbulence models. The method relies on a prediction step where large time steps are performed with an evaluation of the fluxes on macro-cells for the smaller elements for stability purpose, and on a correction step in which small time steps are employed only for the smaller elements. The efficiency of the proposed method is evaluated on several benchmarks flows: the problem of a moving contact discontinuity (inviscid flow), the computation with hybrid turbulence model of flows around bluff bodies like a tandem cylinders at Reynolds number $1.66 × 10 5$ , a circular cylinder at Reynolds number $8.4 × 10 6$ , and a flow around a space probe model at Reynolds number $1 × 10 6$ .

Figure correction of thin x-ray telescope mirrors may be critical for future missions that require high angular resolution and large collecting areas. One promising method of providing figure correction is to use stress generated via ion implantation. Since stress-based figure correction strategies cannot correct high spatial frequency errors, it is critical to obtain glass with only low spatial frequency error. One method is thermal gas bearing slumping, where glass is softened while floating on thin films of gas. This method avoids introducing mid- or high- spatial frequency errors by eliminating contact between the glass and mandrel. Together, these two methods form a promising approach to fabricating mirrors for a high angular resolution, large-area x-ray observatory. In this paper we report on progress in understanding gas bearing slumping, and advancing the technology to curved geometry. We also report on continued progress on advancing the ion implantation technology toward correcting flight-sized mirror substrates.

<i>Purpose: </i>To determine the frequency of refractive errors in squinting eyes of children from 4 to 16 years presenting at tertiary care hospital. <i>Study Design:</i> A descriptive cross-sectional prospective study was done. <i>Place and Duration: </i>The study was conducted in Paedriatic Ophthalmology, Hayatabad Medical Complex, Peshawar. The duration of the study was 15^th Sep to 15^th Oct, 2021. <i>Materials and Methods: </i>Sample size was 146 keeping 41.45% proportion of refractive errors in children with squinting eyes, 95% confidence interval and 8% margin of error under WHO sample size calculations. Non-probability consecutive sampling was done. <i>Result: </i>Mean age was 8.57±2.66 years. Male were 89 (61.0%) and female were 57 (39.0%). Refractive error was present in 56 (38.4%), including 9 myopic, 32 hyperrmetropic, and 15 astigmatic children, and was absent in 90 (61.6%) patients. 57 positive parent refractive error patients, 21 (36.8%) showed refractive errors. However, In 89 patients without parent refractive errors, 35 (39.3%) showed refractive errors, p value 0.763. Early use of electric equipment against the refractive error showed that of total 56 patients with early use of electric equipment, 24 (42.9%) showed refractive errors. In 90 patient without the early use of electric equipment, 32 (35.6%) showed refractive errors There was no association of gender, age, parent refractive errors or early usage of electric equipment with the refractive errors. <i>Conclusion: </i>Prevalence of refractive errors is high in patient with strabismus. There is no association of age, gender, parent refractive errors or early usage of electric equipment in the occurrence of refractive errors. Further studies are recommended for confirmation of these.

Purpose: This study was conducted to evaluate the accommodative response in young participants with visual impairment in comparison with visually normal participants. Methods: Fifteen participants with confirmed visual impairment and 30 visually normal participants aged 12–15 years were recruited. Accommodative response was measured using autorefractor (Grand Seiko WV500) at distances of accommodative demand of 33, 25, and 20 cm. The targets were one-line-above participant threshold acuity. The participants’ accommodative responses were compared between both groups after calibration for refractive errors and the vertex distance of the glasses. Visual acuity and refractive status were also assessed. Results: The age was not significantly different between both participant groups. The visual acuity of visually impaired patients was 6/30 to 6/240, and that of visually normal participants was 6/7.5 or better. Ten of the visually impaired patients and 29 of visually normal participants were myopic. In total, 61–73% of visually impaired patients showed an accommodative lead. Five subtypes of accommodative response were observed. In general, the accommodative inaccuracy increased with increasing accommodative demand. However, the visually normal participants largely exhibited an accommodative lag. A mild-to-moderate relationship was observed between visual acuity and accommodative response (r = 0.3–0.5, p < 0.05). Conclusion: Accommodative response in young visually impaired patients can be variable and on an individual basis. Low vision specialists should anticipate accommodative response outside the normal range. Therefore, we shall consider evaluating each patient’s accommodative response before prescribing any near addition lenses. Accommodation inaccuracy is often more complex than predicted due to increased depth of focus caused by reduced visual acuity.

Purpose: The aim of this study was to evaluate the distribution of wavefront aberrations in Indian children with refractive errors and to determine the correlation between the degree of refractive error and aberration. Materials and Methods: A prospective study was conducted on 216 eyes of 108 consecutive children attending the outpatient clinic. Based on refractive error, the children were allocated to five groups: “Emmetropic,” “hyperopic,” “simple astigmatism,” “compound astigmatism,” and “myopic” group. Lower order aberrations (LOAs) and higher order aberrations (HOAs) were analyzed within and between the groups. Results: Mean age of the children was 10.9 years. Of the total 216 eyes, 40 eyes had emmetropia, 52 had simple astigmatism, 54 had compound astigmatism, 43 had myopia, and 27 had hyperopia. In all the groups, increase in spherical equivalent was associated with increase in LOAs of defocus and astigmatism and the root mean square (RMS) of total HOAs. In comparison with the “emmetropic” group, all other groups showed a significant increase in LOAs (P < 0.001) and RMS of total HOAs (P < 0.001), with the “compound astigmatism” group showing higher values. Spherical aberrations were found to be associated with simple astigmatism, compound astigmatism (P = 0.008), and myopia (P = 0.041). Statistical analysis was done using analysis of variance applying Bonferroni correction factor and Pearson's correlation coefficient. Conclusions: Ametropic eyes are associated with HOAs. Indian children were found to have higher values of aberrations when compared to other races. Practitioners may need to factor this while treating children for refractive errors.

The purpose of this study was to measure near heterophoria in young children to determine the impact of early growth and development on the alignment of the eyes. Fifty young children (≥2 and <7 years of age; range of spherical equivalent refractive error -1.25 diopters [D] to +3.75 D) and 13 adults participated. Their eye position and accommodation responses, in the absence of optical correction, were measured using simultaneous Purkinje image tracking and photorefraction technology (MCS PowerRefractor, PR). The resulting heterophorias, and both accommodative convergence/accommodation (AC/A) and convergence accommodation/convergence (CA/C) ratios were then computed as a function of age, refractive error, and an alternating cover test. The mean heterophoria after approximately 60 seconds of dissociation at a 33-cm viewing distance was 5.0 prism diopters (pd) of exophoria (SD ± 3.7) in the children (78% of children > 2 pd exophoric) and 5.6 pd of exophoria (SD ± 4.7) in adults (69% of adults > 2pd exophoric; a nonsignificant difference), with no effect of age between 2 and 6 years. In these children, heterophoria was not significantly correlated with AC/A (r = 0.25), CA/C (r = 0.12), or refractive error (r = 0.21). The mean difference between heterophoria measurements from the PR and the clinical cover test was -2.4 pd (SD = ±3.4), with an exophoric bias in the PR measurements. Despite developmental maturation of interpupillary distance, refractive error, and AC/A, in a typical sample of young children the predominant dissociated position is one of exophoria.

To quantify changes in ocular dimensions associated with age, refractive error, and accommodative response, in vivo, in 30- to 50-year-old human subjects. The right eyes of 91 adults were examined using ultrasonography, phakometry, keratometry, pachymetry, interferometry, anterior segment optical coherence tomography, and high-resolution magnetic resonance imaging. Accommodation was measured subjectively with a push-up test and objectively using open-field autorefraction. Regression analyses were used to assess differences in ocular parameters with age, refractive error, and accommodation. With age, crystalline lens thickness increased (0.03 mm/yr), anterior lens curvature steepened (0.11 mm/yr), anterior chamber depth decreased (0.02 mm/yr), and lens equivalent refractive index decreased (0.001/yr) (all p < 0.01). With increasing myopia, there were significant increases in axial length (0.37 mm/D), vitreous chamber depth (0.34 mm/D), vitreous chamber height (0.09 mm/D), and ciliary muscle ring diameter (0.10 mm/D) (all p < 0.05). Increasing myopia was also associated with steepening of both the cornea (0.16 mm/D) and anterior lens surface (0.011 mm/D) (both p < 0.04). With accommodation, the ciliary muscle ring diameter decreased (0.08 mm/D) and the muscle thinned posteriorly (0.008 mm/D), allowing the lens to shorten equatorially (0.07 mm/D) and thicken axially (0.06 mm/D) (all p < 0.03). Refractive error is significantly correlated with not only the axial dimensions but also the anterior equatorial dimension of the adult eye. Further testing and development of accommodating intraocular lenses should account for differences in patients' preoperative refractive error.

Near work, accommodative inaccuracy and ambient lighting conditions have all been implicated in the development of myopia. However, differences in accommodative responses with age and refractive error under different visual conditions remain unclear. This study explores differences in accommodative ability and refractive error with exposure to differing ambient illumination and visual demands in Malay schoolchildren and adults. Sixty young adults (21-25years) and 60 schoolchildren (8-12years) were recruited. Accommodative lag and accommodative fluctuations at far (6m) and near (25cm) were measured using the Grand Seiko WAM-5500 open-field autorefractor. The effects of mesopic room illumination on accommodation were also investigated. Repeated-measures ANOVA indicated that accommodative lag at far and near differed significantly between schoolchildren and young adults [F(1.219, 35.354) = 11.857, p < 0.05]. Post hoc tests using the Bonferroni correction showed that at near, there was a greater lag in schoolchildren (0.486 ± 0.181 D) than young adults (0.259 ± 0.209 D, p < 0.05). Repeated-measures ANOVA also revealed that accommodative lag at near demands differed statistically between the non-myopic and myopic groups in young adults and schoolchildren [F(3.107, 31.431) = 12.187, p < 0.05]. Post hoc tests with Bonferroni correction showed that accommodative lag at near was significantly greater in myopic schoolchildren (0.655 ± 0.198 D) than in non-myopic schoolchildren (0.202 ± 0.141 D, p < 0.05) and myopic young adults (0.316 ± 0.172 D, p < 0.05), but no significant difference was found between myopic young adults (0.316 ± 0.172 D) and non-myopic young adults (0.242 ± 0.126 D, p > 0.05). Accommodative lag and fluctuations were greater under mesopic room conditions for all ages [all p < 0.05]. Greater accommodative lag was found in myopes than in emmetropes, in schoolchildren than in adults, and under mesopic conditions than under photopic conditions. Accommodative fluctuations were greatest in myopes and in mesopic conditions. These results suggest that differences exist in the amount of blur experienced by myopes and non-myopes at different ages and under different lighting conditions.