The effect of multifocal contact lenses on the dynamic accommodation step response.

PURPOSE: To measure the dynamic accommodation response (AR) to step stimuli with and without multifocal contact lenses (MFCLs), in emmetropes and myopes. METHODS: Twenty-two adult subjects viewed alternating distance (0.25D) and near (3D) Maltese crosses placed in free space, through two contact lens types: single vision (SVCL) or centre-distance multifocal (MFCL; +2.50D add). The AR level was measured along with near to far (N-F) and far to near (F-N) step response characteristics: percentage of correct responses, magnitude, latency, peak velocity and duration of step response. RESULTS: There was no difference between N-F and F-N responses, or between refractive groups in any aspect of the accommodation step response dynamics. The percentage of correct responses was unaffected by contact lens type. Through MFCLs, subjects demonstrated smaller magnitude, longer latency, shorter duration and slower peak velocity steps than through SVCLs. When viewing the near target, the AR through MFCLs was significantly lower than through SVCLs. When viewing the distance target with the MFCL, the focal points from rays travelling through the distance and near zones were approximately 0.004D behind and 2.50D in front of the retina, respectively. When viewing the near target, the respective values were approximately 1.89D behind and 0.61D in front of the retina. CONCLUSION: The defocus error required for accommodation control appears not to be solely derived from the distance zone of the MFCL. This results in reduced performance in response to abruptly changing vergence stimuli; however, these errors were small and unlikely to impact everyday visual tasks. There was a decrease in ocular accommodation during near tasks, which has previously been correlated with a reduced myopic treatment response through these lenses. With MFCLs, the estimated dioptric myopic defocus was the largest when viewing a distant stimulus, supporting the hypothesis that the outdoors provides a beneficial visual environment to reduce myopia progression.

IMI - Clinical Management Guidelines Report.

Best practice clinical guidelines for myopia control involve an understanding of the epidemiology of myopia, risk factors, visual environment interventions, and optical and pharmacologic treatments, as well as skills to translate the risks and benefits of a given myopia control treatment into lay language for both the patient and their parent or caregiver. This report details evidence-based best practice management of the pre-, stable, and the progressing myope, including risk factor identification, examination, selection of treatment strategies, and guidelines for ongoing management. Practitioner considerations such as informed consent, prescribing off-label treatment, and guides for patient and parent communication are detailed. The future research directions of myopia interventions and treatments are discussed, along with the provision of clinical references, resources, and recommendations for continuing professional education in this growing area of clinical practice.

Is Pupil Diameter Influenced by Refractive Error?

PURPOSE: To investigate the relationship between pupil diameter and refractive error and how refractive correction, target luminance, and accommodation modulate this relationship. METHODS: 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. RESULTS: 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. CONCLUSIONS: 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.

Quantifying interactions between accommodation and vergence in a binocularly normal population.

Stimulation of the accommodation system results in a response in the vergence system via accommodative vergence cross-link interactions, and stimulation of the vergence system results in an accommodation response via vergence accommodation cross-link interactions. Cross-link interactions are necessary in order to ensure simultaneous responses in the accommodation and vergence systems. The crosslink interactions are represented most comprehensively by the response AC/A (accommodative vergence) and CA/C (vergence accommodation) ratios, although the stimulus AC/A ratio is measured clinically, and the stimulus CA/C ratio is seldom measured in clinical practice. The present study aims to quantify both stimulus and response AC/A and CA/C ratios in a binocularly normal population, and determine the relationship between them. 25 Subjects (mean ± SD age 21.0 ± 1.9 years) were recruited from the university population. A significant linear relationship was found between the stimulus and response ratios, for both AC/A (r² = 0.96, p < 0.001) and CA/C ratios (r² = 0.40, p < 0.05). Good agreement was found between the stimulus and response AC/A ratios (95% CI -0.06 to 0.24 MA/D). Stimulus and response CA/C ratios are linearly related. Stimulus CA/C ratios were higher than response ratios at low values, and lower than response ratios at high values (95% CI -0.46 to 0.42 D/MA). Agreement between stimulus and response CA/C ratios is poorer than that found for AC/A ratios due to increased variability in vergence responses when viewing the Gaussian blurred target. This study has shown that more work is needed to refine the methodology of CA/C ratio measurement.

Leptonic decay of the ϒ(1S) meson at third order in QCD.

We present the complete next-to-next-to-next-to-leading order short-distance and bound-state QCD correction to the leptonic decay rate Γ(ϒ(1S)→ℓ+ℓ-) of the lowest-lying spin-1 bottomonium state. The perturbative QCD prediction is compared to the measurement Γ(ϒ(1S)→e+e-)=1.340(18) keV.

The effect of ocular rigidity upon the characteristics of saccadic eye movements.

PURPOSE: To determine whether variation in ocular rigidity (a quantity that describes the elastic properties of the globe) affects the characteristics of horizontal saccadic eye movements. METHODS: Thirty-three young, visually healthy subjects participated with informed consent in the study. Axial length was measured using the IOLMaster ocular biometer. Ocular rigidity coefficients were determined using Schiotz tonometry. Horizontal saccades were stimulated randomly to 40° in 10° steps. Eye movements were recorded continuously at a sampling rate of 60 Hz using the Viewpoint video-eyetracker. RESULTS: Peak velocity increased significantly with increasing ocular rigidity (F [2,263] = 30.635, P < 0.001). Time to peak velocity (F [2,263] = 27.723, P < 0.001) and total response time (F [2,263] = 21.133, P < 0.001) decreased significantly with increasing ocular rigidity. Ocular rigidity was significantly positively correlated with peak velocity (R(2) = 0.67, P < 0.001), and significantly negatively correlated with time to peak velocity (R(2) = 0.64, P < 0.001), and total response time (R(2) = 0.62, P < 0.001). CONCLUSIONS: The known relationship of ocular rigidity with myopia can be extended to shorter hyperopic eyes, which are found to have higher ocular rigidity. The dynamic characteristics of saccadic eye movements are found to vary systematically with ocular rigidity. These findings suggest that the structural characteristics of the eye are an important factor in determining dynamic characteristics of eye movements.

Spatial frequency selectivity of visual suppression during convergence eye movements.

Visual suppression of low-spatial frequency information during eye movements is believed to contribute to a stable perception of our visual environment. While visual perception has been studied extensively during saccades, vergence has been somewhat neglected. Here, we show that convergence eye movements reduce contrast sensitivity to low spatial frequency information around the onset of the eye movements, but do not affect sensitivity to higher spatial frequencies. This suggests that visual suppression elicited by convergence eye movements may have the same temporal and spatial characteristics as saccadic suppression.

Image jitter enhances visual performance when spatial resolution is impaired.

PURPOSE: Visibility of low-spatial frequency stimuli improves when their contrast is modulated at 5 to 10 Hz compared with stationary stimuli. Therefore, temporal modulations of visual objects could enhance the performance of low vision patients who primarily perceive images of low-spatial frequency content. We investigated the effect of retinal-image jitter on word recognition speed and facial emotion recognition in subjects with central visual impairment. METHODS: Word recognition speed and accuracy of facial emotion discrimination were measured in volunteers with AMD under stationary and jittering conditions. Computer-driven and optoelectronic approaches were used to induce retinal-image jitter with duration of 100 or 166 ms and amplitude within the range of 0.5 to 2.6° visual angle. Word recognition speed was also measured for participants with simulated (Bangerter filters) visual impairment. RESULTS: Text jittering markedly enhanced word recognition speed for people with severe visual loss (101 ± 25%), while for those with moderate visual impairment, this effect was weaker (19 ± 9%). The ability of low vision patients to discriminate the facial emotions of jittering images improved by a factor of 2. A prototype of optoelectronic jitter goggles produced similar improvement in facial emotion discrimination. Word recognition speed in participants with simulated visual impairment was enhanced for interjitter intervals over 100 ms and reduced for shorter intervals. CONCLUSIONS: Results suggest that retinal-image jitter with optimal frequency and amplitude is an effective strategy for enhancing visual information processing in the absence of spatial detail. These findings will enable the development of novel tools to improve the quality of life of low vision patients.

Accommodation steps, target spatial frequency and refractive error.

PURPOSE: Errors in the accommodation response of myopes have been reported in many studies although questions remain about the exact differences in accommodation steps when compared with emmetropic individuals. METHODS: The characteristics of the accommodation step response to large (4/1D) and small (3/2D) steps in targets with low (0.5 cpd), mid (4 cpd) and high (16 cpd) spatial frequency (SF) information was measured in myopes (MYOs) and emmetropes (EMMs). RESULTS: In terms of step size, the larger steps showed a greater response in the 4 cpd condition than the 0.5 and 16 cpd conditions and an improved percentage correct response in the 4 cpd compared to the 16 cpd steps. In small step conditions target SF had less effect upon the magnitude of the response. In terms of refractive group differences, MYOs had a lower proportion of correct accommodation responses compared to EMMs during the small steps only, however, when correct steps were performed there were no differences in the characteristics of both large and small step responses between MYOs and EMMs. CONCLUSIONS: These findings suggest that MYOs have some difficulty interpreting small changes in defocus to initiate or possibly fine tune a small accommodation response, however, when a correct accommodation step response is made, the MYOs accommodation plant responds in a similar manner to EMMs.

Investigating the mechanisms that may underlie the reduction in contrast sensitivity during dynamic accommodation.

Head and eye movements, together with ocular accommodation enable us to explore our visual environment. The stability of this environment is maintained during saccadic and vergence eye movements due to reduced contrast sensitivity to low spatial frequency information. Our recent work has revealed a new type of selective reduction of contrast sensitivity to high spatial frequency patterns during the fast phase of dynamic accommodation responses compared with steady-state accommodation. Here were report data which show a strong correlation between the effects of reduced contrast sensitivity during dynamic accommodation and velocity of accommodation responses, elicited by ramp changes in accommodative demand. The results were accounted for by a contrast gain control model of a cortical mechanism for contrast detection during dynamic ocular accommodation. Sensitivity, however, was not altered during attempted accommodation responses in the absence of crystalline-lens changes due to cycloplegia. These findings suggest that contrast sensitivity reduction during dynamic accommodation may be a consequence of cortical inhibition driven by proprioceptive-like signals originating within the ciliary muscle, rather than by corollary discharge signals elicited simultaneously with the motor command to the ciliary muscle.

The relationship between object spatial profile and accommodation microfluctuations in emmetropes and myopes.

The accommodation microfluctuations are thought to be used by the accommodation controller to obtain information about the direction and magnitude of the required response by monitoring changes in the contrast gradient of this image. The contrast gradient can be altered by presenting different spatial frequency (SF) targets to the eye. Twelve myopes (MYOs) and 12 emmetropes (EMMs) viewed sine and square wave targets of SF 0.5, 1, 2, 4, 8, 16 cpd in a Badal optical system. Accommodation responses were recorded continuously using the Shin-Nippon SRW-5000 autorefractor. There is no change in magnitude of the accommodation microfluctuations as the SF of square waves is altered. While viewing sine wave targets, the microfluctuations are smallest for mid (2, 4 cpd) SFs and increase for low (0.5 cpd) and high (16 cpd) SFs. MYOs show a significantly larger increase in the microfluctuations for the 16 cpd target compared to the EMMs. MYOs have significantly larger microfluctuations than the EMMs throughout. The microfluctuations seem to be monitoring the contrast gradient of the cortical image, which is likely to be used by the accommodation control system during error detection. The results indicate that MYO subjects may have a shallower contrast gradient and the potential reasons and implications of this are discussed.

The effect of modulating ocular depth of focus upon accommodation microfluctuations in myopic and emmetropic subjects.

The magnitude of accommodation microfluctuations increases in emmetropic subjects viewing low luminance targets or viewing a target through small artificial pupils. Larger microfluctuations reported in myopia may result from an abnormally large depth of focus (DoF). The effect of modulating the size of the DoF has not been investigated in myopic subjects and may help to explain the cause of the increased DoF. Accommodation microfluctuations were recorded under two experimental conditions. Firstly, 12 emmetropes (EMMs), and 24 myopes (MYOs) viewed a Maltese Cross target with luminance levels of 0.002, 0.2, 6 and 600cd/m(2) and in darkness, and second, 14 EMMs and 16 MYOs viewed a Maltese Cross target through pupil diameters of 0.5, 1, 2, 3, 4 and 5mm presented in Maxwellian view. The magnitude of the accommodation microfluctuations increased significantly with a target luminance of 0.002cd/m(2) (p<.03) and pinhole diameters of <2mm (p<.05). For all other luminance levels and pupil diameters the magnitude was constant. For both conditions, MYOs had significantly larger microfluctuations than EMMs (p<.01). Considerable inter-subject variability was observed in the degree to which the magnitude of the microfluctuations increased, for both the 0.002cd/m(2) luminance and 0.5mm pupils, however, this was not correlated with refractive error. The increase in the magnitude of the microfluctuations while viewing a low luminance target (0.002cd/m(2)) may be due to a shallower contrast gradient in the cortical image, with a consequent increase in DoF. The microfluctuations also increase when viewing through small pupils (<2mm), which increases the DoF without altering the contrast gradient. The larger microfluctuations found in the MYOs consolidates the theory that MYOs have a larger DoF than EMMs and therefore have a higher threshold for retinal image blur.

Technical note: effect of contact lenses on measurement of the accommodation microfluctuations.

AIM: Dynamic measurement of accommodation in subjects with myopia usually involves recording through soft contact lenses (CLs) to correct the refractive error. Conversely, dynamic accommodation measurement in emmetropic control subjects is generally undertaken without any corrective lenses. The aim of this experiment was to determine whether CL correction affects the measurement of accommodation microfluctuations using infrared refractometry, and whether this needs to be considered in studies which attempt to compare accommodation responses between the two groups. METHODS: Ten young emmetropic subjects viewed a high contrast Maltese cross target monocularly using the right eye at a target vergence of 0 D. The subjects viewed the target under two conditions: with CL condition and without CL condition, where the subjects viewed the target with the eye only. Accommodation responses of the right eye were recorded continuously for 2 min at a sampling rate of 52 Hz using the Shin-Nippon SRW-5000 autorefractor. RESULTS: No significant difference (two-tailed paired t-test, t(9) = -1.499, p = 0.168) was found in mean accommodation response between the with CL (mean +/- S.D. = -0.02 +/- 0.24 D) and without CL conditions (mean +/- S.D. = +0.01 +/- 0.25 D). No significant (two-tailed paired t-test, t(9) = 0.151, p = 0.883) difference in the magnitude of the accommodation microfluctuations was found between the with CL (mean +/- S.D. = 0.162 +/- 0.04 D) and without CL condition (mean +/- S.D. = 0.169 +/- 0.04 D). Power spectrum analysis revealed no differences in the characteristics of the microfluctuations waveform between the two conditions. A control experiment carried out on a subgroup of five subjects using a negative (-3 D) CL demonstrated that there was no significant effect of the dioptric power of the CL on the magnitude of the accommodation microfluctuations (anova: F(3,15) = 0.254, p = 0.782). CONCLUSION: Thin soft CLs do not affect the magnitude or frequency characteristics of accommodation microfluctuations when measured using the Shin-Nippon SRW-5000.

Refractive group differences in accommodation microfluctuations with changing accommodation stimulus.

PURPOSE: Microfluctuations of accommodation are known to increase in magnitude with increasing accommodation stimulus. Reduced sensitivity to blur in myopic subjects could also lead to increases in the magnitude of the microfluctuations. The aim of this study is to examine the effect of variations in accommodation stimulus upon the microfluctuations in different refractive groups. METHODS: Thirty-six subjects were divided into three groups depending upon their refractive error and age of onset of their myopia; 12 emmetropes (EMMs), 12 early onset myopes (EOMs) and 12 late-onset myopes (LOMs). Steady-state accommodation responses were recorded continuously for 2 min using the Shin-Nippon SRW-5000 autorefractor at a sampling rate of 52 Hz while viewing targets at accommodation stimuli levels of 0, 1, 2, 3 and 4 D in a Badal (+5 D) optical system. RESULTS: The EMMs and EOMs showed systematic increases in the root mean square (r.m.s.) value of the microfluctuations with increasing accommodation stimulus. In contrast, no systematic variation with accommodation stimulus was found for the LOMs. Power spectrum analysis demonstrated that increases in the size of the microfluctuations were mediated by increases in the power of the low frequency components of the accommodation response. CONCLUSIONS: The magnitude of the microfluctuations in the EMMs and EOMs may be influenced primarily by accommodation response-induced zonular relaxation effects or to changes in the physical properties of the accommodation plant with increasing accommodation response. The LOMs may have an increased baseline neural blur threshold, which appears to modulate the magnitude of the accommodative microfluctuations for low accommodation levels. At higher accommodation demands, the changes in the physical properties of the accommodation plant or the zonular relaxation effects appear to exceed the blur threshold, and the known association between microfluctuations and accommodation stimulus level is restored.

The effect of monocular and binocular viewing on the accommodation response to real targets in emmetropia and myopia.

PURPOSE: Decreased blur-sensitivity found in myopia has been linked with reduced accommodation responses and myopigenesis. Although the mechanism for myopia progression remains unclear, it is commonly known that myopic patients rarely report near visual symptoms and are generally very sensitive to small changes in their distance prescription. This experiment investigated the effect of monocular and binocular viewing on static and dynamic accommodation in emmetropes and myopes for real targets to monitor whether inaccuracies in the myopic accommodation response are maintained when a full set of visual cues, including size and disparity, is available. METHODS: Monocular and binocular steady-state accommodation responses were measured with a Canon R1 autorefractor for target vergences ranging from 0-5 D in emmetropes (EMM), late-onset myopes (LOM), and early-onset myopes (EOM). Dynamic closed-loop accommodation responses for a stationary target at 0.25 m and step stimuli of two different magnitudes were recorded for both monocular and binocular viewing. RESULTS: All refractive groups showed similar accommodation stimulus response curves consistent with previously published data. Viewing a stationary near target monocularly, LOMs demonstrated slightly larger accommodation microfluctuations compared with EMMs and EOMs; however, this difference was absent under binocular viewing conditions. Dynamic accommodation step responses revealed significantly (p < 0.05) longer response times for the myopic subject groups for a number of step stimuli. No significant difference in either reaction time or the number of correct responses for a given number of step-vergence changes was found between the myopic groups and EMMs. CONCLUSION: When viewing real targets with size and disparity cues available, no significant differences in the accuracy of static and dynamic accommodation responses were found among EMM, EOM, and LOM. The results suggest that corrected myopes do not experience dioptric blur levels that are substantially different from emmetropes when they view free space targets.

Retinotopic accommodation responses in myopia.

PURPOSE: 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. METHODS: 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. RESULTS: 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%. CONCLUSIONS: 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.