Accommodation Stimulus Response Curves Research Articles

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.

Extrinsic and Intrinsic Factors Regulating Juvenile Refractive Development and Eye Growth.

PurposePeripheral refraction and accommodation are intrinsic factors that were once hypothesized to trigger myopia but are now controversial. Previously, home nearwork environment (i.e., extrinsic factor) was reported to be associated with myopia progression. In this study, we aimed to evaluate the potential interaction between extrinsic and intrinsic factors with juvenile refractive development.MethodsNearwork environmental parameters were measured for 50 children (aged 9.3 ± 1.2 years), including net amount and dispersion of defocus. Refraction was measured at near distances and in central field (±30° horizontal) at 3m. The relative peripheral refraction (RPRE) was obtained and presented in a vectoral approach. The linear regression coefficient was extracted (mAcc) from the accommodative stimulus–response curve. RPRE was quadratically regressed against field eccentricity, and the first coefficients (aM, aJ0, aP90, and aP180) were extracted. Relationships between RPRE, baseline accommodation, and 1-year myopia progression (∆M), controlled for the nearwork environment, were evaluated.ResultsCoefficients of RPRE were independent of ∆M. However, additional nearwork environmental parameters significantly improved the variance in ∆M explained by aM and aP180 (P < 0.03). The relationship between intrinsic factor and ∆M was stronger when the extrinsic risk was low (P ≤ 0.01), whereas the relationship was abolished when extrinsic risk was high. For mAcc, it also significantly improved the variance in ∆M explained by nearwork environmental parameters.ConclusionsThe interaction between extrinsic (environment) and intrinsic (RPRE and accommodation) factors is speculated to contribute to juvenile myopia progression. Our findings may also explain the inconsistencies of such intrinsic factors in the literature.

Accommodation is unrelated to myopia progression in Chinese myopic children

This study shows accommodative accuracy and distance accommodation facility in myopic children do not play a role in myopia progression. In 144 subjects, the monocular distance accommodative facility (DAF) and continuous accommodative stimulus–response curves (ASRCs) were measured at the enrolment. Retrospective and prospective refraction with regard to the enrolment visit were obtained from the outpatient database system based on noncycloplegic subjective spherical equivalent refraction (SER). The rate of myopic progression at enrolment was the first derivative of the Gompertz function, which was fitted with each subject's longitudinal refractive error data, including at least four records of SER with an interval of more than 6 months between each visit. A mixed linear model for multilevel repeated-measures data was used to explore the associations between the rate of myopia progression and accommodative parameters. The mean rate of myopia progression at enrolment was -0.61 ± 0.31 D/y with a mean age of 12.27 ± 1.61 years. By adjusting for age and SER, it was shown that the myopic progression rate was not associated with the accommodative lag (F = 0.269, P = 0.604), accommodative lag area (F = 0.086, P = 0.354), slope of ASRC (F = 0.711, P = 0.399), and DAF (F = 0.619, P = 0.432).

Accommodative stimulus-response curves to low-pass filtered natural images.

To assess how the monocular steady-state accommodative stimulus-response curve is modified when viewing low-pass filtered natural images. Eighteen adult subjects participated in the study. The accommodative stimulus-response curve was objectively assessed by means of a Hartmann-Shack wavefront sensor. Measurements were taken at different accommodative demands. Target images were low-pass filtered versions of a natural image that were obtained applying different digital spatial filters that limited the spatial frequency content of the natural image. Cutoff spatial frequencies were set at 30, 21, and 15 cycles per degree (cy/deg). Mean data obtained for each target were fitted to linear models. For the low-pass filtered natural image with a cutoff spatial frequency at 30 cy/deg, the slope for the averaged stimulus-response curve was 0.614, while the slopes obtained for the other two low-pass filtered images corresponding to cutoff frequencies at 21 and 15 cy/deg were 0.613 and 0.619, respectively (p < 0.01). The determination coefficient was R2 ≥ 0.988 for all targets. An ANCOVA analysis revealed that these slopes were not significantly different from each other (p = 0.82). Additionally, accommodative error indexes were obtained to measure both the discrepancy between the regression lines and the ideal lines and the degree of correlation between the stimulus and the response. Our study reveals that the low and middle spatial frequencies (< 15 cy/deg) are the most important to guide to the needed levels the accommodative response to natural images.

Comparison of three monocular methods for measuring accommodative stimulus–response curves

PurposeThe aim was to evaluate the repeatability of dynamic measurement of the accommodative stimulus–response curve () at three different dioptric speeds using a modified instrument and its agreement with two other methods.MethodsTwenty‐nine adults (23.5 ± 2.0-years) were enrolled in the study. ASRC was measured monocularly using three methods: dynamic and static measurement using a motorised Badal system mounted on an open‐field auto‐refractor (WAM‐5500, Grand Seiko Co., Ltd, Japan) and the minus lens technique. Dynamic measurements were conducted at three dioptric stimulus speeds to simulate continuous stimuli for ASRC (0.25, 0.40 and 0.55 D/s), with three repetitions for each speed. All three types of ASRCs were fitted with third‐degree polynomial equations. The slope and objective accommodative amplitude of the ASRC were analysed.ResultsThe repeatability of objective accommodative amplitude worsened as the speed of the stimuli increased. The repeatability of the slope was best at a speed of 0.40 D/s and worst at 0.55 D/s. The measurement method significantly influenced the objective accommodative amplitude values and slope (both, p < 0.001). The minus lens technique yielded the highest amplitude of accommodation (6.21 ± 0.84 D) and steepest slope (1.11 ± 0.14), followed by the static Badal method (5.60 ± 0.83 D and 0.89 ± 0.09 D). The objective accommodative amplitude decreased with increasing speed during dynamic measurements. There was no difference between the slopes at 0.25 D and 0.40 D/s (p > 0.05) and the slope was lowest at 0.55 D/s.Conclusion values are method‐dependent and the significant differences between three methods used to determine the based on slope and accommodative amplitude indicate that these methods are non‐interchangeable. Using dynamic measurements, accommodative behaviour varies with the speed of dioptric‐change of the stimulus. A speed of 0.40 D/s appears to be the best compromise in terms of time, results and repeatability for dynamic measurement.

Accommodative Stimulus-Response Curve with Emoji Symbols.

Purpose To evaluate the static measurement of the accommodative stimulus-response curve with emoji symbols. Methods The accommodative stimulus-response curve was measured in 18 subjects using a Hartmann-Shack sensor to obtain the objective accommodative response from the Zernike defocus term. Measurements were acquired at different accommodative demands, from 0 to 3 D with a step of 0.5 D. Detailed and nondetailed emoji targets were used with two different sizes, corresponding to the two most common visual angles used in smartphones. Results A regression analysis was performed to fit the mean results obtained for each target. The determination coefficient was R2 ≥ 0.988 for all targets. For the detailed targets, the slopes for the averaged stimulus-response curve were 0.65 and 0.66 for the bigger and smaller sizes, respectively. For the nondetailed targets, the slopes were 0.60 and 0.58 for the bigger and smaller sizes, respectively. p values for these slopes were statistically significant for the two types of targets (p < 0.01). Conclusions Our results reveal that the replacement of a word or several words by detailed or nondetailed emoji symbols seems not to provoke a different accommodative response in normal subjects and under standard viewing conditions in the use of smartphones.

Accommodation response to Chinese and Latin characters in Chinese‐illiterate young adults

BackgroundDifferences in accommodation when reading Chinese, as compared to Latin, characters have been suggested to have a role in the higher prevalence of myopia in some Asian countries. Yeo and colleagues (Optom Vis Sci 2013; 90: 156‐163) found that, in Chinese‐literate children, accommodation was marginally more accurate (by less than 0.05 D), when reading Chinese text. This was attributed to the additional cognitive demand associated with interpreting the more complex Chinese symbols. The present study compared responses to single Chinese and Latin characters, while controlling for cognitive demand.MethodsThe monocular accommodative response was measured in Chinese‐illiterate adults (10 emmetropes, mean spherical equivalent: ‐0.07 ± 0.42 D, age: 29.9 ± 4.2 years; 11 myopes, mean spherical equivalent: ‐4.28 ± 2.84 D, age: 31.7 ± 4.6 years) with an open‐field autorefractor. Four Chinese and three Latin characters (approximately 1.15 degrees subtense) were individually presented on a display screen one metre away from the subject, while their vergence was varied over the range zero to 5.00 D using spectacle trial lenses. The slope and the accommodative error index (AEI) were calculated from the accommodative stimulus/response curves (ASRC).ResultsNo statistically significant differences were found between refractive groups or among characters within the same refractive group in ARSC slopes (Latin: 0.87 ± 0.14 for myopes versus 0.81 ± 0.12 for emmetropes; Chinese: 0.84 ± 0.12 for myopes versus 0.85 ± 0.12 for emmetropes). No significant differences were found between characters in accommodative error index either (Latin, 0.78 ± 0.42 D for myopes versus 1.15 ± 0.72 D for emmetropes; Chinese, 0.74 ± 0.37 D for myopes versus 1.17 ± 0.83 D for emmetropes). However, accommodative error indices and accommodative errors were significantly higher for emmetropes.ConclusionUnder controlled cognitive demand, Chinese and Latin characters elicited similar responses in both individual refractive groups. This study fails to support the hypothesis that development of myopia in some Asian populations is associated with larger lags of accommodation when reading or viewing Chinese characters.

Differences in the accommodation stimulus response curves of adult myopes and emmetropes: a summary and update

To provide a summary of the classic paper "Differences in the accommodation stimulus response curves of adult myopes and emmetropes" published in Ophthalmic and Physiological Optics in 1998 and to provide an update on the topic of accommodation errors in myopia. The accommodation responses of 33 participants (10 emmetropes, 11 early onset myopes and 12 late onset myopes) aged 18-31 years were measured using the Canon Autoref R-1 free space autorefractor using three methods to vary the accommodation demand: decreasing distance (4 m to 0.25 cm), negative lenses (0 to -4 D at 4 m) and positive lenses (+4 to 0 D at 0.25 m). We observed that the greatest accommodation errors occurred for the negative lens method whereas minimal errors were observed using positive lenses. Adult progressing myopes had greater lags of accommodation than stable myopes at higher demands induced by negative lenses. Progressing myopes had shallower response gradients than the emmetropes and stable myopes; however the reduced gradient was much less than that observed in children using similar methods. This paper has been often cited as evidence that accommodation responses at near may be primarily reduced in adults with progressing myopia and not in stable myopes and/or that challenging accommodation stimuli (negative lenses with monocular viewing) are required to generate larger accommodation errors. As an analogy, animals reared with hyperopic errors develop axial elongation and myopia. Retinal defocus signals are presumably passed to the retinal pigment epithelium and choroid and then ultimately the sclera to modify eye length. A number of lens treatments that act to slow myopia progression may partially work through reducing accommodation errors.

Accommodative Responses Under Different Stimulus Conditions

The method and the sequence of accommodative stimuli are two factors affecting the steady-state accommodative response. This study investigated the possible effects of these two factors on the accommodative stimulus response curves (ASRCs) and compared three indexes to evaluate ASRC in the different stimulus conditions. In this study, we investigated the difference in the accommodative stimulus response curves under six stimulus conditions. The ASRCs of 10 emmetropes were measured when the accommodative stimulus (AS) was induced using three methods: negative lenses, positive lenses, and a Badal stimulator; and the stimulus was presented using two sequences: ascending and descending sequences. Three indexes, accommodative error area (AEA), accommodative error index (AEI), and the slope of ASRC, were used for comparison. The accommodative error was larger when accommodative stimulus was presented in the ascending sequence than in the descending sequence (p < 0.05) in the Badal stimulator method whenever AEI, AEA, or the slope of ASRC was used. The ASRCs elicited with positive lenses were more accurate than that elicited with negative lenses or the Badal stimulator when AEA and AEI were used. However, when the slope of the ASRC was used, the result was not significant. The results suggest that the accommodative response in the steady state may be affected by the method used for inducing AS and the sequence of AS presented. The AEA is suggested to be used in the evaluation of the accuracy of the ASRC in future studies.

Age‐related changes in accommodation measured with a double‐pass system

To measure the accommodative response in a wide age range population using the retinal image quality assessments provided by a double-pass system. The accommodative response was measured using a custom-built double-pass setup in 84 patients from 15 to 55years of age. Patients were classified in four groups (A: 15-25year old; B: 26-35; C: 36-45; D: 46-55). Accommodation was stimulated from 0 to 5 dioptres (D) with the push up method using an open field fixation test. The total accommodative response in the stimulated range, the accommodative stimulus-response curve, the slope and the progression of optical quality with accommodation were measured. The total accommodation obtained in groups A and B was high, with a mean value of 4D or higher, whereas values in older individuals were significantly lower. The accommodative stimulus-response curve and the slope were also high with a sudden decrease in patients over 35years of age. The optical quality of the eye during accommodation did not change significantly. Participants aged 15-35years showed a good accommodative response. Thereafter, a significant decrease of the response in the total accommodation, stimulus response curve and slope was observed. The younger groups showed a larger accommodative response than previously published.

The effects of spherical aberration on static accommodative responses in emmetropes and myopes

To compare the effects of spherical aberration (SA) on accommodative responses between emmetropes (EMs), stable myopes (SMs), and progressing myopes (PMs). The accommodative responses (AR) induced by negative lenses from 0 to -5 D in 1 D steps were measured with a Complete Ophthalmic Analysis System (COAS) for 10 emmetropes (EMs), 13 stable myopes (SMs), and 9 progressing myopes (PMs). Three types of AR were calculated from wavefront aberration data based on ocular foci within a paraxial area, natural pupil area, and a 3.5 mm-diameter annular pupil area. The accommodative stimulus response curves (ASRCs) were compared between the three groups and between the three AR conditions. The difference in the slope of ASRC was significant between the three AR conditions (p < 0.0001) but it was not significant between the three refractive groups. In each group, the slope of ASRC for the accommodative response measured within the paraxial area of the pupil (paraxial AR) was significantly steeper than that measured for the natural pupil (total AR) and also for that estimated for the 3.5 mm-diameter annular pupil (p < 0.01). The difference in the y-intercept of ASRC between the three AR conditions was also significant (p = 0.02) but not between the three refractive groups. The y-intercept of ASRC for paraxial AR was more positive than that for total AR in SMs (p < 0.01) and in PMs (p < 0.05); the y-intercept of ASRC for the 3.5 mm peripheral AR was more positive than that for total AR in SMs (p < 0.05). The spherical aberration of the eye has a significant effect on the slope of ASRC and is less in PMs than in EMs and SMs.

Visual field does not affect steady-state accommodative response and near-work induced transient myopia

To investigate whether or not peripheral retinal defocus contributes to the refractive development of myopia by influencing the overall accommodative function. The steady-state accommodative stimulus response curve (ASRC) and the near-work induced transient myopia (NITM) after a near visual task were compared between different visual field conditions in emmetropes (EMMs), stable myopes (SMs) and progressing myopes (PMs). Results showed that visual field had no effect on the ASRC and NITM but PMs exhibited greater NITM than EMMs and SMs. The results of this study suggest that peripheral defocus does not influence the overall accommodative system so its probable contribution to myopia development is not via the accommodative system.

Objective Accommodative Amplitude and Dynamics with the 1CU Accommodative Intraocular Lens

To compare the objective accommodative amplitude and dynamics of eyes implanted with the one-compartment-unit (1CU; HumanOptics AG, Erlangen, Germany) accommodative intraocular lenses (IOLs) with that measured subjectively. Twenty eyes with a 1CU accommodative IOL implanted were refracted and distance and near acuity measured with a logMAR (logarithm of the minimum angle of resolution) chart. The objective accommodative stimulus-response curve for static targets between 0.17 and 4.00 D accommodative demand was measured with the SRW-5000 (Shin-Nippon Commerce Inc., Tokyo, Japan) and PowerRefractor (PlusOptiX, Nürnberg, Germany) autorefractors. Continuous objective recording of dynamic accommodation was measured with the SRW-5000, with the subject viewing a target moving from 0 to 2.50 D at 0.3 Hz through a Badal lens system. Wavefront aberrometry measures (Zywave; Bausch & Lomb, Rochester, NY) were made through undilated pupils. Subjective amplitude of accommodation was measured with the RAF (Royal Air Force accommodation and vergence measurement) rule. Four months after implantation best-corrected acuity was -0.01 +/- 0.16 logMAR at distance and 0.60 +/- 0.09 logMAR at near. Objectively, the static amplitude of accommodation was 0.72 +/- 0.38 D. The average dynamic amplitude of accommodation was 0.71 +/- 0.47 D, with a lag behind the target of 0.50 +/- 0.48 seconds. Aberrometry showed a decrease in power of the lens-eye combination from the center to the periphery in all subjects (on average, -0.38 +/- 0.28 D/mm). Subjective amplitude of accommodation was 2.24 +/- 0.42 D. Two years after 1CU implantation, refractive error and distance visual acuity remained relatively stable, but near visual acuity, and the subjective and objective amplitudes of accommodation decreased. The objective accommodating effects of the 1CU lens appear to be limited, although patients are able to track a moving target. Subjective and objective accommodation was reduced at the 2-year follow-up. The greater subjective amplitude of accommodation is likely to result from the eye's depth of focus of and the aspheric nature of the IOL.

The Effect of Monocular and Binocular Viewing on the Accommodation Response to Real Targets in Emmetropia and Myopia

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. 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. 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. 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.

Accommodation responses in late‐onset myopia are improved by spatiotopic stimulation

Purpose: Inaccurate accommodation responses to retinotopic stimuli have been shown in late‐onset myopia (LOM). The aim of this experiment was to determine whether spatiotopic (perceived proximity) and binocular stimulation would improve the quality of accommodation responses in LOM subjects.Methods: Ten emmetropic subjects (mean age 22.3 ± 2.3 years) and 10 LOM subjects (mean age 21.8 ± 1.5 years) participated. A specially modified Canon R‐1 infrared optometer was used to measure accommodation responses. Three conditions were presented: (1) Monocular blur‐only stimulus, (2) Monocular free‐space stimulus, and (3) Binocular free‐space stimulus. Each condition was presented on a separate day to avoid fatigue effects.Results: Accommodation stimulus–response curves in the LOM group showed improved accuracy with the spatiotopic stimulus. Microfluctuations were significantly (p &lt; 0.01) smaller in magnitude in the LOM group with the spatiotopic stimulus, because of reductions in the low frequency components of the fluctuations. A significant (p &lt; 0.01) increase in the percentage of correct step accommodation responses for the spatiotopic stimulus was found in the LOM group. However, step response times in the LOM group with the spatiotopic stimulus were not significantly different than those found with the retinotopic stimulus, and were significantly (p &lt; 0.01) longer than those found in the emmetropic group.Conclusions: (1) Spatiotopic stimulation produces significant improvements in static accommodative accuracy in LOM subjects compared with retinotopic stimulation. (2) The quality of dynamic accommodation responses in LOM subjects was found to improve significantly with spatiotopic stimulation. (3) LOM subjects appear to rely upon proximity driven stimuli to improve accommodative response accuracy.

Differences in the accommodation stimulus response curves of adult myopes and emmetropes

SummaryWhile the accommodation system has been implicated in myopia development, the nature of this relationship remains obscure. This study investigated the differences in accommodation stimulus response curves between adult myopes and emmetropes. Myopic subjects were classified according to age of onset and stability of their myopia. Accommodation stimulus response curves were measured using three different methods: (i) real targets presented at viewing distances of 4 m to 0.25 m, (ii) a target at 4 m viewed through negative lenses of increasing power, and (iii) a target at 0.25 m viewed through positive lenses of decreasing power. A Canon Autoref R‐1 measured the accommodation responses at 5 levels of demand (increasing from 0 D to 4 D in 1 D steps). We found significant differences between the three methods used to stimulate an accommodation response in all subject groups, for example, accommodation lags at high accommodative demands were greatest for the negative lens series and least for the positive lens series. In addition, while differences between early‐onset myopes, late‐onset myopes and emmetropes were not observed, we did observe differences when myopic subjects were reclassified according to whether their myopia was progressing or stable. A reduced accommodation response to negative lens‐induced accommodative demand was found in progressing myopes but not in stable myopes. These results provide further evidence for the link between myopia progression and inaccurate accommodation. The data also suggest that adult myopes with stable refractive errors show accommodation responses similar to that of emmetropes.

Differences in the accommodation stimulus response curves of adult myopes and emmetropes

While the accommodation system has been implicated in myopia development, the nature of this relationship remains obscure. This study investigated the differences in accommodation stimulus response curves between adult myopes and emmetropes. Myopic subjects were classified according to age of onset and stability of their myopia. Accommodation stimulus response curves were measured using three different methods: (i) real targets presented at viewing distances of 4 m to 0.25 m, (ii) a target at 4 m viewed through negative lenses of increasing power, and (iii) a target at 0.25 m viewed through positive lenses of decreasing power. A Canon Autoref R-1 measured the accommodation responses at 5 levels of demand (increasing from 0 D to 4 D in 1 D steps). We found significant differences between the three methods used to stimulate an accommodation response in all subject groups, for example, accommodation lags at high accommodative demands were greatest for the negative lens series and least for the positive lens series. In addition, while differences between early-onset myopes, late-onset myopes and emmetropes were not observed, we did observe differences when myopic subjects were reclassified according to whether their myopia was progressing or stable. A reduced accommodation response to negative lens-induced accommodative demand was found in progressing myopes but not in stable myopes. These results provide further evidence for the link between myopia progression and inaccurate accommodation. The data also suggest that adult myopes with stable refractive errors show accommodation responses similar to that of emmetropes.

Accommodation responses to flickering stimuli

It has been suggested that accommodation to visual display unit (VDU) symbols or to stimuli lit by fluorescent tubes or similar temporally modulated light sources may be less accurate due to flicker. Furthermore, if the microfluctuations of accommodation play a part in the control of steady-state accommodation, the effects of stimulus flicker might affect the quality of this control. Experiments are described in which monocular accommodation stimulus—response curves for sinusoidal grating stimuli (1.0, 5.3 and 8.9c/deg) were measured under the following conditions of temporal modulation: (1) square-wave on-off modulation to give spatial modulation varying between 0 and 37%; (2) sinusoidal modulation to give spatial modulation varying between 0 and 37%; (3) sinusoidal modulation to give spatial modulation varying between 16 and 32%; and (4) on-off modulation with varying mark/space ratio. Temporal modulation frequencies were between 0.5 and 7.8 Hz and above the critical fusion frequency (CFF) i.e. ⩾ 40 Hz. In general, the results suggest that while lower-frequency flicker may adversely affect the accuracy and stability of the accommodation response, the latter are very little affected by flicker at frequencies ≥ 40Hz. Thus flicker from fluorescent lamps or VDUs is unlikely to cause systematic accommodation difficulties. The possible relevance of the results to theories which ascribe a role for the higher-frequency (> 0.5 Hz) accommodative microfluctuations in the control of the response is considered.