Characteristics of dynamic accommodation responses: comparison between the dominant and non-dominant eyes

BCLA CLEAR presbyopia: Mechanism and optics

With over a billion adults worldwide currently affected, presbyopia remains a ubiquitous, global problem. Despite over a century of study, the precise mechanism of ocular accommodation and presbyopia progression remains a topic of debate. Accordingly, this narrative review outlines the lenticular and extralenticular components of accommodation together with the impact of age on the accommodative apparatus, neural control of accommodation, models of accommodation, the impact of presbyopia on retinal image quality, and both historic and contemporary theories of presbyopia.

Ocular dominance in cataract surgery: research status and progress

Ocular dominance (OD), a commonly used concept in clinical practice, plays an important role in optometry and refractive surgery. With the development of refractive cataract surgery, the refractive function of the intraocular lens determines the achievement of the postoperative full range of vision based on the retinal defocus blur suppression and binocular monovision principle. Therefore, OD plays an important role in cataract surgery. OD is related to the visual formation of the cerebral cortex, and its plasticity suggests that visual experience can influence the visual system. Cataract surgery changes the visual experience and transforms the dominant eye, which confirms the plasticity of the visual system. Based on the concept and mechanism of OD, this review summarizes the application of OD in cataract surgery.

Digital Pupillometry and Centroid Shift Changes in Dominant and Nondominant Eyes

PURPOSE

To investigate the differences between dominant and nondominant eyes in a predominantly young patient population by analyzing the angle kappa, pupil size, and center position in dominant and nondominant eyes.

METHODS

A total of 126 young college students (252 eyes) with myopia who underwent femtosecond laser-combined LASIK were randomly selected. Ocular dominance was determined using the hole-in-card test. The WaveLight Allegro Topolyzer (WaveLight Laser Technologies AG, Erlangen, Germany) was used to measure the pupil size and center position. The offset between the pupil center and the coaxially sighted corneal light reflex (P-Dist) of the patients was recorded by the x- and y-axis eyeball tracking adjustment program of the WaveLight Eagle Vision EX500 excimer laser system (Wavelight GmbH). The patient's vision (uncorrected distance visual acuity [UDVA], best-corrected visual acuity (BCVA), and refractive power (spherical equivalent, SE) were observed preoperatively, 1 week, 4 weeks, and 12 weeks postoperatively, and a quality of vision (QoV) questionnaire was completed.

RESULTS

Ocular dominance occurred predominantly in the right eye [right vs. left: (178) 70.63% vs. (74) 29.37%; p < 0.001]. The P-Dist was 0.202 ± 0.095 mm in the dominant eye and 0.215 ± 0.103 mm in the nondominant eye (p = 0.021). The horizontal pupil shift was - 0.07 ± 0.14 mm in dominant eyes and 0.01 ± 0.13 mm in nondominant eyes (p = 0.001) (the temporal displacement of the dominant eye under mesopic conditions). The SE was negatively correlated with the P-Dist (r = - 0.223, p = 0.012 for the dominant eye and r = - 0.199, p = 0.025 for the nondominant eye). At 12 weeks postoperatively, the safety index (postoperative BDVA/preoperative BDVA) of the dominant and nondominant eyes was 1.20 (1.00, 1.22) and 1.20 (1.00, 1.20), respectively, and the efficacy index (postoperative UDVA/preoperative BDVA) was 1.00 (1.00, 1.20) and 1.00 (1.00, 1.20), respectively; the proportion of residual SE within ± 0.50 D was 98 and 100%, respectively.

CONCLUSIONS

This study found that ocular dominance occurred predominantly in the right eye. The pupil size change was larger in the dominant eye. The angle kappa of the dominant eye was smaller than that of the nondominant eye and the pupil center of the dominant eye was slightly shifted to the temporal side under mesopic conditions. The correction of myopia in the dominant and nondominant eyes exhibits good safety, efficacy, and predictability in the short term after surgery, and has good subjective visual quality performance after correction. We suggest adjusting the angle kappa percentage in the dominant eye to be lower than that of the nondominant eye in individualized corneal refractive surgery in order to find the ablation center closest to the visual axis.

Comparative study of refractive and visual quality after wavefront-optimized FS-LASIK for angle kappa adjustment in dominant and nondominant eyes

PURPOSE

To investigate the differences between dominant and nondominant eyes in femtosecond laser-assisted laser in situ keratomileusis (FS-LASIK) with 50% angle kappa compensation on diopter and visual quality.

SETTING

University hospital.

DESIGN

Retrospective clinical study.

METHODS

109 patients (218 eyes, 100%) with myopia who underwent FS-LASIK were randomly selected. The preoperative pupil size, center position, and offset between the coaxially sighted corneal light reflex ( P-Dist ) of the patients was recorded. In preoperative and postoperative 6 months, an iTrace wavefront aberrometer was used to measure the corneal, internal optics, and total aberrations.

RESULTS

The 6 months postoperatively for corneal coma of the dominant eyes were 0.141 ± 0.055 μm and the nondominant eyes were 0.157 ± 0.033 μm, which was significantly greater than the dominant eyes ( P = .028). The postoperative corneal coma aberration changes were positively correlated with preoperative P-Dist , the dominant eyes ( r = 0.221, P = .023), and the nondominant eyes ( r = 0.251, P = .009).

CONCLUSIONS

Adjusting the angle kappa percentage in the nondominant eyes to be higher than that of the dominant eyes in individualized corneal refractive surgery may help find the ablation center closest to the visual axis.

Effects of anthocyanin, astaxanthin, and lutein on eye functions: a randomized, double-blind, placebo-controlled study

We examined the effects of a test food containing anthocyanin, astaxanthin, and lutein on the eye function in healthy Japanese adults with eye fatigue after operating visual display terminals. Forty-four subjects were randomly but equally assigned to the active or placebo group. Two active or placebo capsules were taken once daily for 6 weeks. Accommodative function, tear film break-up time, visual acuity, the value of Schirmer's test, macular pigment optical density level, muscle hardness, and a questionnaire were evaluated before and after a 6-week intervention. Each group included 20 subjects in the efficacy analysis. The active group showed a significant improvement in the percentage of pupillary response of an average of both eyes and dominant eye pre- and post-visual display terminal operation at 6 weeks compared with the placebo group. Moreover, the active group showed a significant improvement in the scores of "A sensation of trouble in focusing the eyes" and "Difficulty in seeing objects in one's hand and nearby, or fine print" compared with the placebo group between before and after ingestion. Therefore, 6-weeks consumption of the test food inhibited a decrease in the accommodative function caused by visual display terminal operation (UMIN000036989).

Electrophysiological and Psychophysical Studies of Meridional Anisotropies in Children With and Without Astigmatism

Purpose

We investigated the pattern of meridional anisotropies, if any, for pattern onset-offset visual evoked potential (POVEPs) responses and psychophysical grating acuity (GA) in children with normal letter visual acuity (20/20 or better).

Methods

A total of 29 children (aged 3-9 years), nine of whom were astigmatic (AS), were recruited. Orientation-specific monocular POVEPs were recorded in response to sinewave grating stimuli oriented along the subjects' principal AS meridians. Horizontal and vertical gratings were designated Meridians 1 and 2, respectively, for nonastigmatic patients (Non-AS). Binocular POVEPs in response to the same stimuli, but oriented at 45°, 90°, 135°, and 180°, were recorded. Psychophysical GAs were assessed monocularly and binocularly along the same meridians using the same stimuli by a 2-alternative-forced-choice staircase technique. The C3 amplitudes and peak latencies of the POVEP and GAs were compared across meridians using linear mixed models (monocular) and ANOVA (binocular).

Results

There were significant meridional anisotropies in monocular C3 amplitudes regardless of astigmatism status (P = 0.001): Meridian 2 (mean ± SE Non-AS, 30.13 ± 2.07 μV; AS, 26.53 ± 2.98 μV) was significantly higher than Meridian 1 (Non-AS, 26.14 ± 1.87 μV; AS, 21.68 ± 2.73 μV; P = 0.019), but no meridional anisotropies were found for GA or C3 latency. Binocular C3 amplitude in response to horizontally oriented stimuli (180°, 29.71 ± 3.06 μV) was significantly lower than the oblique (45°, 36.62 ± 3 .05 μV; P = 0.03 and 135°, 35.95 ± 2.92 μV; P = 0.04) and vertical (90°, 37.82 ± 3.65 μV; P = 0.02) meridians, and binocular C3 latency was significantly shorter in response to vertical than oblique gratings (P ≤ 0.001).

Conclusions

Meridional anisotropy was observed in children with normal vision. The findings suggest that horizontal gratings result in a small, but significantly lower POVEP amplitude than for vertical and oblique gratings.

Validation of Novel Metrics from the Accommodative Dynamic Profile

Objective and subjective methods of assessing time taken for accommodative change (ToAC) include accommodative dynamics (AD) and accommodative facility (AF). This study investigates the validity of novel metrics derived from the AD-profile and explores their relationship with AF. AD were assessed using a modified open-field autorefractor in 43 healthy adults. Non-linear regression curves were fitted to the data to derive: latency-of-accommodation (nLoA) and -disaccomodation (nLoD), Time-for-accommodation (ToA) and -disaccommodation (ToD), and objective-ToAC (oToAC). Latencies were also calculated through visual inspection of the AD data as in previous studies (pLoA and pLoD). AF was used to assess subjective-ToAC. Statistical analysis explored the relationships between the AD-metrics and AF. Subjects were assessed on three visits to examine intra- and inter-observer repeatability. nLoA and nLoD were greater than pLoA (p = 0.001) and pLoD (p = 0.004) respectively. nLoA and nLoD also demonstrated greater intra- and inter-observer repeatability than pLoA and pLoD. AF demonstrated a moderate, inverse correlation with ToA (p = 0.02), ToD (p = 0.007), and oToAC (p = 0.007). ToD was the single best accommodative predictor of AF (p = 0.011). The novel method for deriving latency was more repeatable, but not interchangeable with the techniques used in previous studies. ToD was the most repeatable metric with the greatest association with AF.

Importance of Accommodation and Eye Dominance for Measuring Objective Refractions

PURPOSE

To explore factors affecting the difference between objective refractive data measured under monocular closed-field viewing and binocular open-field viewing.

DESIGN

Prospective observational case series.

METHODS

setting: Institutional.

STUDY POPULATION

Twenty-nine healthy volunteers (58 eyes; mean age, 38.4 ± 10.0 years; range, 25-60 years).

OBSERVATION PROCEDURES

Objective monocular refractions (MR) measured with the Nidek Auto Ref/Keratometer ARK-730A; objective binocular refractions (BR) and objective accommodative amplitude (AA) measured with the Grand Seiko Auto Ref/Keratometer WAM-5500; ocular dominance measured using the hole-in-the-card test; presence and magnitude of far/near (30 cm) phoria evaluated by the cover test and alternating cover test using a prism bar.

MAIN OUTCOME MEASURE

The difference between objective refractive data measured under monocular closed-field viewing and binocular open-field viewing.

RESULTS

The spherical equivalent (SE) of the BR was significantly (P < .001) more hyperopic by 0.51 ± 0.33 diopter (D) than the MR. The difference (BR minus MR) tended to decline with increasing age and decreasing AA (r = -0.231, P = .08; r = 0.223, P = .092, respectively). The correlation between age and difference in SE was significant in dominant eyes (r = -0.372, P = .047) but not in nondominant eyes (r = -0.102, P = .60). In nondominant eyes, the amount of near phoria was correlated significantly (r = 0.403, P = .03) with the difference in SE. The correlation was strong (r = 0.598, P = .01) in 17 subjects with more than 3 D of AA.

CONCLUSIONS

Binocular assessment of refraction is important for precise refractive therapy.

The short-term accommodation response to aniso-accommodative stimuli in isometropia

PURPOSE

There have been only a limited number of studies examining the accommodative response that occurs when the two eyes are provided with disparate accommodative stimuli, and the results from these studies to date have been equivocal. In this study, we therefore aimed to examine the capacity of the visual system to aniso-accommodate by objectively measuring the interocular difference in the accommodation response between fellow dominant and non-dominant eyes under controlled monocular and binocular viewing conditions during short-term exposure to aniso-accommodative stimuli.

METHODS

The accommodative response of each eye of 16 young isometropic adults (mean age 22 ± 2 years) with normal binocular vision was measured using an open-field autorefractor during a range of testing conditions; monocularly (accommodative demands ranging from 1.97 to 2.90 D) and binocularly while altering the accommodation demand for each eye (aniso-accommodative stimuli ranging from 0.08 to 0.53 D) [Corrected].

RESULTS

Under monocular viewing conditions, the dominant and non-dominant eyes displayed a highly symmetric accommodative response; mean interocular difference in spherical equivalent 0.01 ± 0.06 D (relative) and 0.22 ± 0.06 D (absolute) (p > 0.05). During binocular viewing, the dominant eye displayed a greater accommodative response (0.11 ± 0.34 D relative and 0.24 ± 0.26 D absolute) irrespective of whether the demand of the dominant or non-dominant eye was altered (p = 0.01). Astigmatic power vectors J0 and J45 did not vary between eyes or with increasing accommodation demands under monocular or binocular viewing conditions (p > 0.05).

CONCLUSION

The dominant and non-dominant eyes of young isometropic individuals display a similar consensual lag of accommodation under both monocular and binocular viewing conditions, with the dominant eye showing a small but significantly greater (by 0.12-0.25 D) accommodative response. Evidence of short-term aniso-accommodation in response to asymmetric accommodation demands was not observed.

The Effects of Visual Field Conditions on Electromyography of the Lower Extremities during Reaching Tasks in Healthy Adults

[Purpose] The purpose of this study was to identify the effects of visual field condition on electromyography of the lower extremities during arm reaching in healthy adults, and to compare differences in electromyography of the lower extremities between young and old adults according to visual fields condition. [Subjects and Methods] Twenty-nine young persons in their 20s and 19 elderly persons in their 60s, a total of 48 persons, participated in this study. Prior to participation in the study, each subject signed an informed consent form to comply with ethics guidelines dictated by the ethics committee for research at Silla University, Korea. We collected the muscle activation data for both of tibialis anterior and gastrocnemius muscle during reaching by subjects using electromyography. Data analysis with SPSS for Window Version 20.0 was performed using repeated one-way analysis of variance according to visual fields and age. [Results] There were no significantly differences between subjects in their 20s and 60s to visual field conditions except for left tibialis anterior muscle activation during left-side reaching. Left tibialis anterior muscle activation in subjects in their 60s was higher than in subjects in their 20s during left-side reaching. [Conclusion] We determined that tibialis anterior muscle activation in subjects in their 60s was higher than in subjects in their 20s. We suggest that visual field conditions are the important factor for physical therapy interventions to improve balance and priority of intervention .

The effect of 0.5% tropicamide/0.5% phenylephrine mixed eye drop in Chinese adults with myopia and its inter-eye difference in refractive outcomes

OBJECTIVE

To evaluate the effect of 0.5% tropicamide/0.5% phenylephrine mixed eye drop and make the inter-eye comparison of refractive outcomes in Chinese adults with myopia.

METHODS

Refractive measurements were performed without cycloplegia and repeated 30 minutes later with 0.5% tropicamide/0.5% phenylephrine mixed eye drop (Mydrin-P*) on 341 myopic adults. Vector analysis was used to analyze the data. Changes of spherical equivalent (M) and astigmatism for both J0 and J45 components between these two refractions were calculated as Error_M, Error_J0 and Error_J45. Inter-eye correlations were studied. The inter-eye difference after cycloplegics were described as Diff M, Diff J0 and Diff J45. The effect of anisometropia, age and the higher order aberrations (HOAs) on inter-eye differences toward the cycloplegic agent were analyzed.

RESULTS

Difference was found only for the Error_J45 component between the two eyes (p=0.0040). Pearson correlation coefficients between the two eyes for Error_M, Error_J0, and Error_J45 were 0.3140 (p<0.0001), 0.1464 (p=0.0068), and 0.0099 (p=0.8558), respectively. The inter-eye differences (Diff) in response to cycloplegic agent increased with the amount of anisometropia. The oldest group had the highest Diff M values. However, HOAs were found not to be related to the inter-eye differences.

CONCLUSIONS

Accommodation was still relaxed by tropicamide/phenylephrine eye drops in myopic adults. The changes of refraction due to cycloplegia were not well correlated between the two eyes in myopic patients. Anisometropia and ocular dominance might be an important factor for the inter-eye difference.

The horizontal dark oculomotor rest position

BACKGROUND

This study sought to investigate whether eye dominance and age are related to the stimulus-free oculomotor resting state described via the dark disconjugate position (near or far), the dark conjugate position (left to right), and the near dissociated phoria.

METHODS

Nineteen non-presbyopes and 25 presbyopes with normal binocular vision participated in two identical sessions. The left-eye and the right-eye positions were recorded using a video-based infrared eye tracker while the subjects were in total darkness. Dark disconjugate responses and dark conjugate responses were calculated by computing the difference and the average of the left-eye and the right-eye response, respectively. The right-eye decaying to the phoria level was recorded for 15 s.

RESULTS

A one-way ANOVA assessed statistical differences in dark conjugate and dark disconjugate positions, comparing 1) the right-eye and the left-eye sensory and/or motor dominant groups and 2) the non-presbyope and presbyope groups. The test-retests of the dark disconjugate position, the dark conjugate position and the near dissociated heterophoria were high between sessions (r > 0.85; p < 0.00001). For non-presbyopes the right-eye (left-eye) motor and sensory dominant subjects showed a rightward (leftward) dark conjugate position (p < 0.01). The dark disconjugate position was receded in presbyopes compared to non-presbyopes (p < 0.0001).

CONCLUSION

The data support that the left-eye, or the right-eye, motor and sensory dominance predicts the direction of the dark conjugate position. Future studies could investigate the underlying neural substrates that may, in part, contribute to the resting state of the oculomotor system in a stimulus-free environment. Knowledge of the brain-behavior governing visual-field preference has implications for understanding the natural aging process of the visual system.

Effect of laser in situ keratomileusis on accommodation

The accommodative function before and after laser in situ keratomileusis (LASIK) was observed, and the effect of LASIk on accommodation was investigated. In a prospective clinical trial, 48 myopic patients (96 eyes) subject to bilateral LASIK in Refractive Surgery Center, Tongji Hospital, Tongji Medical College, Huazhong University of Science and Technology (China) from March 2006 to June 2006 were selected and studied. Refractions, accommodative range, amplitude of accommodative response and high frequency component (HFC) of accommodative microfluctuations were measured with NEDIK-730A before and one week and 30 days after operation. Dominant and non-dominant eyes were determined by hole-in-card method. It was found that all of the operative eyes showed an uncorrected visual acuity of 0.8 or better one week postoperatively, and 1.0 or better 30 days postoperatively. Compared with those preoperatively, accommodative range and HFC had no significant difference at first week and 30th day after operation in both dominant eyes and non-dominant eyes (P>0.05), but there was a significant difference in the amplitude of accommodative response/accommodative stimulus ratio (A/S) after operation (P<0.01), and no significant difference was found in accommodation between one week and 30 days postoperation. No ocular dominance's change was noted. There was no significant difference in accommodative function between dominant eyes and non-dominant eyes. It was suggested that LASIK produced no significant effect on accommodation.

A longitudinal study on the relationship between myopia development and near accommodation lag in myopic children

PURPOSE

To investigate the possible relationship between myopia progression and near accommodative lag.

METHODS

A 1-year longitudinal study was carried out to measure the accommodative response and myopia progression in 62 children with mild and progressing myopia at two visits: they were 10.81 +/- 1.60 years old with refractive error -1.70 +/- 0.76 D on entry. Repeated measurements included refractive error, ocular biometry and accommodative response at 33 cm. The refractive error was determined by autorefraction after cycloplegia; ocular biometry by A-scan ultrasonography; and accommodative response by an open-field autorefractor. Results were based on the right eye and analysed by paired t-test and Pearson's correlation coefficient.

RESULTS

Myopia progression in the year was -0.72 +/- 0.37 D (p < 0.001) with a range from -0.06 to -1.96 D. The change of axial length and vitreous depth were 0.41 +/- 0.25 mm (p < 0.001) and 0.36 +/- 0.24 mm (p < 0.001), respectively. The near lag was 0.76 +/- 0.29 D on entry and 0.72 +/- 0.38 D 1 year later (p = 0.79). No statistically significant correlations were found between near lag vs myopia progression and the change of ocular biometry as a whole (p > 0.10 for all). There was no significant difference in myopia progression between myopic children with greater than, compared to less than the mean amount of near lag (p = 0.36).

CONCLUSIONS

This study demonstrates no statistically significant relationship between myopia progression and near accommodation lag in children with mild and progressing myopia. There is no evidence that near lag provides a stimulus to progression in this stage of myopia.

Quantitative measurement of ocular dominance using binocular rivalry induced by retinometers

PURPOSE

To develop a new method using binocular rivalry and retinometers to quantitatively examine ocular dominance and to investigate the magnitude of ocular dominance in cataract patients preoperatively and postoperatively.

SETTING

Eye Clinic, Kitasato University School of Medicine Hospital, Sagamihara, Kanagawa, Japan.

METHODS

The duration of exclusive visibility of the dominant and nondominant eye target in binocular rivalry were measured in 60 healthy volunteers (study 1) and preoperatively and postoperatively in 10 cataract patients (study 2). Rivalry targets were presented directly to the retina of each eye using 2 retinometers. Subjects reported the exclusive visibility of 1 eye target, and the total duration of exclusive visibility for each eye in dominant and nondominant eye trials was evaluated.

RESULTS

In study 1, the magnitude of ocular dominance was quantitatively assessed with 4 grades based on differences in total duration of exclusive visibility between dominant and nondominant eyes. In study 2, magnitude of ocular dominance could be evaluated in all cataract patients regardless of refractive and cataract conditions. Magnitude of ocular dominance displayed significant correlations between preoperative and postoperative conditions (simple regression, P<.001).

CONCLUSIONS

Ocular dominance can be quantitatively evaluated using this new method based on binocular rivalry and retinometers, particularly in cataract patients. Magnitude of ocular dominance may indicate preoperatively whether a patient with cataracts will have sufficient ocular dominance to adjust to monovision correction.

Ocular dominancy in conjugate eye movements at reading distance

We recorded conjugate eye movements to elucidate whether ocular dominancy was present at reading distance in 21 normal volunteers with the right-handedness by using a video-oculographic (VOG) measurement. This included the velocity of smooth pursuits, and the latency and velocity of saccades. We defined the dominant eye for each subject by means of the near-far alignment test and 20 subjects showed the right dominant eyes. Although the ocular dominancy was not found in the velocity of smooth pursuit and vertical saccades, the velocity of horizontal saccades in the dominant eyes was faster than that in the non-dominant eyes. These results suggest that the dominant eye is functionally activated prior to non-dominant eye in horizontal saccades at reading distance, which thus indicates the functional dominancy of the dominant eye in conjugate eye movements.

Accommodation dynamics as a function of age

Experiments are described in which the dynamic accommodation response to a stimulus whose vergence was varying sinusoidally with time between 1.33 and 2.38 D was measured as a function of frequency for 19 subjects, with ages distributed between 18 and 49 years. Response to abrupt stimulus change between the same levels was also measured. The results showed that at any age, for the sinusoidal stimuli, gain fell with frequency and phase lag increased: at fixed frequency, gain fell with age and phase lag increased. Neither reaction nor response times for step stimuli changed with age. Analysis of the sinusoidal data suggests the possible existence of a cut-off frequency of about 2 Hz, which varies little with age and above which the system cannot respond. The phase data is compatible with the existence of a frequency-independent time delay, which increases with age from about 0.17 s at 20 years to 0.48 s at 40 years. The results are discussed in terms of current knowledge of the factors contributing to the development of presbyopia.

The binocular accommodative response in uncorrected ametropia

PURPOSE

To measure the changes in astigmatism and in the degree of anisometropia when ametropes respond to accommodative stimulation.

METHODS

The accommodative responses of ametropes were binocularly measured with an improved photorefractometer (PR-1100), which objectively measured binocular refraction in all meridians simultaneously, when a visual fixation target was shown in natural space at 5 and 0.5 m.

RESULTS

(1) Changes of astigmatism and anisometropia occur during binocular accommodation. (2) Changes of astigmatism mainly result from lag of accommodation in the horizontal meridian. (3) Changes of anisometropia result from the effort to focus. (4) The interaction of both eyes is suggested as the cause of the changes of astigmatism and anisometropia with accommodation. (5) In the majority of strong anisometropes (nonoverlapping group in this paper), the magnitude of anisometropia decreases (approaching isometropia) with accommodation.

CONCLUSION

Changes in astigmatism and anisometropia can occur during accommodation, and these interactions of both eyes with accommodation may contribute to the development and maintenance of binocular function.

Dynamics of the accommodation response to abrupt changes in target vergence as a function of age

The dynamic accommodation responses to small, abrupt changes in an accommodation stimulus were studied in two experiments. In the first, responses of 19 subjects with ages distributed between 18 and 49 years were measured for step stimuli of +/- 1.05 D. In the second, responses to small step stimuli (+/- 0.75, +/- 1.75 D) were recorded for a group of six 'young' (mean age 22, range 16-26 years) and six 'old' (mean age 42, range 36-48 years) subjects. In both experiments, the low target vergences always lay within the accommodation range of all subjects. Whether the data were analysed in terms of simple reaction and response times, or in terms of the frequency response, no marked systematic changes with age were found in the dynamics of the response in either of the experiments. It is concluded that, for small stimuli within the amplitude of accommodation, the response dynamics over the adult age range studied remain remarkably constant, even though the amplitude progressively reduces with age as complete presbyopia is approached.

Subjective measurement of the near point of accommodation in pre/early literates

PURPOSE

This study was undertaken to develop a tool and acquire data on subjective accommodation measurements in young children. Previously, subjective measurements of accommodation in children has been assessed with tools requiring literacy or reliable reporting of a blur point with the standard lower age limit of eight years. It was our belief that younger children could yield reliable subjective accommodation measurements given an age appropriate tool.

METHOD

We devised a tool (modified tape measure using preliterate symbols) which was compared to our gold standard tool (RAF rule). These tools were compared in a literate group of subjects (N = 34) to assess agreement between the two devises. The modified tape measure was also tested on a pre/early literate group of subjects (N = 51) to assess their ability to respond consistently and to acquire data on subjective accommodation values for children ages three to seven.

RESULTS

Literate group-Agreement between the two devises was good with concordance correlation coefficient values of 84 for the right eye and .87 for the left eyes. Greater than .87% of responses for both devices differed by two centimeters or less. Based on the nature of these types of subjective accommodation tests, agreement of within two centimeters indicates good clinical reliability. Pre/ Early Literate group-For the purposes of statistical analysis, the three year olds were not included due to low numbers (N = 5). The four/five year olds (N = 29) and six/seven year olds (N = 17) formed two subgroups for statistical analysis. T test results indicated no significant difference in accommodation amplitudes between a 4-5 year old and 6-7 year subgroups. Evaluation of the best two out of three responses in this group indicated good reliability for most subjects. As a group the mean subjective accommodation amplitude was 9.1 centimeters with a standard deviation of 2.3 centimeters.

CONCLUSION

The new tool appears to be safe, effective, acceptable to young children, and comparable to our current tool used for older age groups.

On the linearity of accommodation dynamics

Available experimental data on the gain and phase lags in the closed-loop accommodation responses to stimuli whose dioptric vergence changes sinusoidally with time are examined. It is shown that both phase lags and gain change almost linearly with the temporal frequency of the stimulus. This implies that the phase lags correspond to a frequency-independent time delay and that, if the system is linear, the impulse response should take a symmetrical (sin x/x)(2) form, with a corresponding standard form of step response. Comparison of this derived step response with the quasi-exponential results found experimentally underlines the limitations of attempting to generalize dynamic accommodation performance from responses obtained with predictable sinusoidally-changing stimuli and the application of a linear model. Consideration of the frequency response which would lead to an exponential step response supports the argument that, although the gain results obtained with sinusoidal stimuli are reasonably representative of those applying with other forms of stimulus, the predictable nature of sinusoidally-changing stimuli makes the derived phase lags inapplicable to non-predictable step or other stimuli. Other limitations in linear models of the response are discussed.