Effect of accommodative adaptation on static and dynamic accommodation in emmetropia and late-onset myopia.

PURPOSE: Prolonged near work is considered to be an environmental factor leading to the development of late-onset myopia. Accommodation may be the specific mechanism underlying the association between near work and late-onset myopia. To determine whether late-onset myopes have abnormal accommodation, we compared accommodative static responses and dynamic facilities before and after a near task in two groups of subjects, emmetropes and late-onset myopes. METHODS: In experiment 1, the accommodative stimulus/response function with monocular viewing and the dark focus (the accommodative response in the dark) were objectively measured with a Canon R-1 infrared optometer before (preadaptation) and after (postadaptation) a 20-min near task. In experiment 2, monocular accommodative facility (AF) and dark focus were measured before and after the near task. Facility was measured as the subjective time needed to clear an accommodative target (20/40 letters) at 40 cm through +/-2.00 D lenses. The time between when the subject flipped the lenses from viewing through the +2.00 D to the -2.00 D lenses was recorded by a computer. RESULTS: In both experiments, inward shifts of the dark focus were observed after the near task. In experiment 1, after the near task, static accommodative responses also showed a small but statistically significant inward shift. Neither postadaptation effect differed between refractive groups. The only difference between groups was that late-onset myopes had a lower slope of the accommodative stimulus/response function, both pre- and postadaptation. In experiment 2, both refractive groups showed the same results. After the near task, the duration for accommodation from near to far (relaxation) increased but the duration for accommodation from far to near (stimulation) did not change. CONCLUSIONS: Late-onset myopes have shallower accommodative stimulus/response functions. As suggested in a previous study, this may be due to their reduced sensitivity to defocus. In both emmetropes and late-onset myopes, the near task causes an increase in static accommodative responses. Although our results show it to be a small increase, it is consistent with predictions of Hung and Semmlow's model of accommodation. In both emmetropes and late-onset myopes, the near task also increases the duration for relaxing accommodation, but not for stimulating accommodation. This suggests there are two subsystems which may adapt to prolonged accommodation differently.     

Evaluation of a new criterion of binocularity

The purpose of this study was to assess a new criterion for binocular comfort analogous to the classical Sheard's criterion. Instead of equating the fusional demand with the monocular phoria as is done when Sheard's criterion is applied, the new criterion uses a calculated binocular fusional demand. The binocular demand was derived using a clinical measurement of the convergence accommodation per convergence (CA/C) ratio. Sheard's criterion was also evaluated. Other commonly used indicators of binocularity (heterophoria, vergences, accommodative amplitude, facility and response, fixation disparity, and the associated phoria) were measured. One hundred subjects (52 males, 48 females; mean age 26 years) were classified as either symptomatic or asymptomatic by an interviewing clinician. The examining clinician was intentionally masked as to the classification of the subjects. We hypothesized that the new criterion would best discriminate between the two groups of patients inasmuch as it is based on currently accepted dual-interaction models of accommodation and vergence. Our analysis confirmed that the CA/C ratio corresponded closely to those published previously (mean = 0.06 D/delta). Significant differences (p less than 0.05) were determined between the symptomatic and asymptomatic groups for gender, near phoria through a +2.00 D add, accommodative amplitude, positive vergences at near, and both the classical Sheard's and the new criterion. The new criterion was the best discriminator between the groups, identifying 72% correctly, an improvement of 6% over the classical Sheard's. However, various stepwise discriminant analysis procedures consistently failed to demonstrate that the calculated binocular fusional demand or the new criterion was superior to the near phoria or the classical Sheard's value. These results suggest potential clinical utility for new procedures based on recently described models of accommodation and vergence, but further development appears necessary.     

Effect of near-vision addition lenses on the accuracy of the accommodative response.

BACKGROUND: Addition lenses (adds) are frequently used to increase the accuracy of the near-vision focusing response, and may also play a role in the prevention or retardation of refractive error development. However, following the introduction of such a lens, if the accommodative response is reduced by an amount equal to the magnitude of the near add, then the resulting accommodative error (and degree of retinal defocus) would remain unchanged. METHODS: This study measured the accommodative response in 28 subjects while they viewed a near target binocularly, either through their distance refractive correction alone or this correction combined with a +0.75 D, +1.50 D, +2.00 D, or +2.50 D near add. RESULTS: The mean findings demonstrated a small (0.03 D) lead of accommodation to the near target through the distance correction, and monotonically increasing leads of accommodation with larger adds. Further, the additional lens power required to reduce the accommodative error to zero correlated significantly with the initial accommodative error. CONCLUSIONS: Near addition lenses may actually increase the degree of retinai defocus for individuals who manifest small accommodative errors.     

Fatigue reduces tonic accommodation

Ocular accommodation adopts a mean baseline response level of approximately 1.0 D in the absence of blur feedback (open-loop state). This baseline or tonic accommodation (TA) can be elevated following a sustained monocular accommodative response to a dioptric stimulus (lens adaptation) that exceeds the baseline open-loop level of TA. The accommodative response to the lens persists in the open-loop state (accommodative hysteresis), and eventually decays to a stable end-point. Interestingly, if the baseline TA is high, the monocularly adapted accommodative state can decay to an end-point that is below the initial pre-adapted baseline level of the TA (counter-adaptive response) (McBrien, N.A. and Millodot, M., (1988). Differences in adaptation of TA with refractive state. Invest. Ophthalmol. Vis. Sci., 29, 460-469). We have investigated the possible contribution of accommodation fatigue to the counter-adaptive change in baseline TA following sustained accommodation. Two fatigue procedures were used while viewing a target at 66 or 33 cm. In a monocular condition, accommodation was stimulated for 3 min with lens values alternating from -1.5 to +1.5 D at a rate of 0.25 Hz. In the binocular condition, convergence was stimulated with alternating prism values from 9 prism diopters (PD) base-out to 9 PD base-in. Both monocular and binocular tasks resulted in a significant reduction of TA. These results suggest that previously reported reductions of baseline TA following sustained monocular accommodation or binocular convergence could have resulted from fatigue of the accommodative system. Accommodative fatigue could be responsible for the lower values of TA observed in counter-adaptive responses to sustained accommodative or convergence effort.     

Relationship of accommodative response and nearpoint phoria in a sample of myopic children.

Esophoria has been associated with onset and progression of myopia in children. The induction of myopia by optical defocus shown by animal models suggests that a high lag of accommodation during near work may contribute to myopia in children. This paper examines the relationship of nearpoint phoria and accommodative response in a sample of children with myopia. Accommodative response was measured under binocular conditions with the Canon Autoref R-1 autorefractor with a 40 cm viewing distance. Phorias were measured with the von Graefe method using a 40 cm test distance. In the statistical analysis exophoria was scored as a negative number and esophoria was scored as a positive number. The coefficient of correlation of accommodative response with phoria was -0.32 (n = 73; p<0.01), thus showing an association of a more positive (more convergent) near phoria with lower accommodative response. The correlation coefficient increased to -0.39 when an exponential function was used. When only esophores were considered, the correlation coefficient was -0.59 (n = 44; p<0.001). Lower accommodative response (higher lag of accommodation) was associated with greater esophoria.     

Binocular adaptation to near addition lenses in emmetropic adults

Near addition lenses are prescribed to pre-presbyopic individuals for treatment of binocular motor problems such as convergence excess and to control the progression of myopia. To date, no investigation has looked at the complete sequence of binocular motor responses during a period of near work with +2D lenses. This investigation evaluated changes to accommodation and vergence responses when young adults sustained fixation at 33 cm with +2D addition lenses. In addition, the effect of the accommodative vergence cross-link (AV/A) on the magnitude and the completeness of binocular adaptation to these lenses were evaluated. The results showed that +2D lenses initiate an increase in exophoria and convergence driven accommodation. The degree of the initial induced phoria was dependant upon the magnitude of the AV/A ratio. Vergence adaptation occurred after 3 min of near fixation and reduced the exophoria and convergence driven accommodation. The magnitude of vergence adaptation was dependant upon the size of the induced phoria and hence the AV/A ratio. The completeness of adaptation was seen to vary inversely with induced exophoria and thus the AV/A ratio.     

Effects of persistent viewing of 3 D TV on human visual function

目的:研究持续观看3D电视对视功能的影响,以及探索不同视功能参数之间的关系.方法:本研究录入19位受试者,每位受试者观看90分钟的2 D电视或90分钟的3 D电视,两部电视观看间隔时间为一周,顺序随机.每次观看电视前及观看后15 min内都做相关视功能检查,检查包括以下四种视功能参数:调节功能(调节反应、调节微波动、调节灵敏度、正相对调节、负相对调节、AC/A),融像性聚散功能(远距负融像性聚散功能、远距正融像性聚散功能、近距负融像性聚散功能、近距正融像性聚散功能),隐斜量(远距隐斜量、近距隐斜量),立体视.结果:无论是与观看前的基础值比较,还是与观看2D电视后的数据比较,观看3D电视后近距离调节反应增加,汇聚减少,远距隐斜量向外隐斜改变(P<0.05).结论:持续观看3D电视会对人们的视功能有一定影响,主要是打破了调节和聚散系统的平衡.厂家和公众应该引起重视,将调节功能、融像性聚散功能、隐斜量等参数作为评估3D电视安全性的指标.     

The effect of positive-lens addition and base-in prism on accommodation accuracy and near horizontal phoria in Chinese myopic children.

The effect of positive-lens addition (0, +0.75, +1.50, +2.25, +3.00 D each eye) and base-in prism power (0, 1.5, 3 Delta each eye) on both near focusing errors and latent horizontal deviations was evaluated in 29 Chinese myopic children (age: 10.3 +/- 1.9 years, refractive error: -2.73 +/- 1.31 D). Accommodation response and phoria were measured by the Shin-Nippon auto-refractor (right eye) and Howell-Dwyer near phoria card at 33 cm with each of the 15 lens/prism combinations in random order. The initial accommodative error was -0.96 +/- 0.67 D (lag) and near phoria was -0.8 +/- 5.0 Delta (exophoria). The positive-lens addition decreased the accommodative lag but increased the exophoria as the power increased (e.g. up to -9.1 +/- 4.1 Delta with +3 D). A 6-Delta base-in prism totally controlled the exophoria induced by a +1.50 D addition (-0.3 +/- 4.3 Delta), but the accommodative lag was still considerable (-0.69 +/- 0.54 D). In the graphical analysis of the data, a lens addition of +2.25 D combined with a 6-Delta base-in prism minimized both the lag and lens-induced exophoria to -0.33 D and -2.4 Delta respectively (regression analysis). This lens and prism combination decreased the lens-induced exophoria by 4.5 Delta compared with that measured with +2.25 D alone (-2.4 Delta vs -6.9 Delta). The results suggest that incorporating near base-in prism when prescribing bifocal lenses for young progressing myopes with exophoria could reduce the positive lens-induced oculomotor imbalance.     

近视青少年配戴角膜塑形镜前后调节参数变化

目的：:观察近视青少年配戴角膜塑形镜前后调节参数及隐斜度的变化,探讨角膜塑形镜延缓近视进展的机制及近视发病病因。方法：:回顾性研究。收集2011年1月至2019年3月在中国医科大学附属第一医院眼科门诊进行角膜塑形镜配戴前后调节参数资料完整的患者51例（102眼）,比较角膜塑形镜配戴前、配戴后1、12个月或以上的正负相对...     

Accommodative and vergence difficulties interfering with image clarity through a binocular indirect ophthalmoscope.

PURPOSE: This study sought to identify accommodative and vergence deficiencies that could explain why some students have difficulty seeing clearly when using a binocular indirect ophthalmoscope (BIO) containing its standard +2.00 D lenses. METHODS: A survey was distributed to Illinois College of Optometry 3rd- and 4th-year students. Based on the information supplied by the survey, students were divided into two groups: those who are unable ("BIO plano") and those who are able ("BIO plus") to obtain a clear image with the +2.00 D lenses in their BIO's. Forty-seven subjects participated: 22 in the BIO plano group and 25 in BIO plus group. Two of the authors, masked to subject group, measured all subjects' accommodative amplitudes and facilities, monocular estimation method (MEM) retinoscopy, negative relative accommodation and positive relative accommodation (NRA/PRA), distance and near vergence ranges, distance and near phorias, Worth 4-dot test, and near point of convergence (five times). RESULTS: The Mann-Whitney U analysis of numerical data for the two groups showed a statistically significant difference for accommodative facility in the right eye (p = 0.004). The difference between the two groups approached significance for accommodative facility with both eyes (p = 0.02), facility in the left eye (p = 0.03), distance base-out blur (p = 0.02), near base-out break (p = 0.02), and near base-out recovery (p = 0.04). For all findings in which the difference between the two groups was significant or approached significance, the BIO plus group had higher median values. When subjects were classified by difficulty with the plus side of the flippers during accommodative facility testing, there was a statistically significant difference with both eyes (Fisher exact test, p = 0.003) and with the right eye (p = 0.008) between the BIO plus and BIO plano groups. When subjects were classified by the presence or absence of an accommodative or binocular vision syndrome, categorical data analysis showed the difference between the two groups approached significance, with more BIO plano subjects having syndromes (p = 0.03). CONCLUSION: No one test absolutely defined who would have difficulty with the +2.00 D lenses in the BIO. There are several skills required; less developed plus acceptance and convergence may cause difficulties.     

An evaluation of the lag of accommodation using photorefraction

OBJECTIVE: The lag of accommodation which occurs in most human subjects during reading has been proposed to explain the association between reading and myopia. However, the measured lags are variable among different published studies and current knowledge on its magnitude rests largely on measurements with the Canon R-1 autorefractor. Therefore, we have measured it with another technique, eccentric infrared photorefraction (the PowerRefractor), and studied how it can be modified. METHODS: Particular care was taken to ensure correct calibration of the instrument. Ten young adult subjects were refracted both in the fixation axis of the right eye and from the midline between both eyes, while they read text both monocularly and binocularly at 1.5, 2, 3, 4 and 5 D distance ("group 1"). A second group of 10 subjects ("group 2"), measured from the midline between both eyes, was studied to analyze the effects of binocular vs monocular vision, addition of +1 or +2 D lenses, and of letter size. Spherical equivalents (SE) were analyzed in all cases. RESULTS: The lag of accommodation was variable among subjects (standard deviations among groups and viewing distances ranging from 0.18 to 1.07 D) but was significant when the measurements were done in the fixation axis (0.35 D at 3 D target distance to 0.60 D at 5 D with binocular vision; p<0.01 or better all cases). Refracting from the midline between both eyes tended to underestimate the lag of accommodation although this was significant only at 5 D (ANOVA: p<0.0001, post hoc t-test: p<0.05). There was a small improvement in accommodation precision with binocular compared to monocular viewing but significance was reached only for the 5 D reading target (group 1--lags for a 3/4/5 D target: 0.35 vs 0.41 D/0.48 vs 0.47 D/0.60 vs 0.66 D, ANOVA: p<0.0001, post hoc t-test: p<0.05; group 2--0.29 vs 0.12 D, 0.33 vs 0.16 D, 0.23 vs -0.31 D, ANOVA: p<0.0001, post hoc t-test: p<0.05). Adjusting the letter height for constant angular subtense (0.2 deg) induced scarcely more accommodation than keeping letter size constantly at 3.5 mm (ANOVA: p<0.0001, post hoc t-test: n.s.). Positive trial lenses reduced the lag of accommodation under monocular viewing conditions and even reversed it with binocular vision. CONCLUSIONS: After consideration of possible sources of measurement error, the lag of accommodation measured with photorefraction at 3 D (0.41 D SE monocular and 0.35 D SE binocular) was in the range of published values from the Canon R-1 autorefractor. With the measured lag, simulations of the retinal images for a diffraction limited eye suggest surprisingly poor letter contrast on the retina.     

The effect of mental effort on open- and closed-loop accommodation

The accommodative response to stimuli in normal visual environments is determined by a complex and subtle integration of optical and non-optical factors. Mental effort associated with the visual task can modify significantly the steady-state accommodative level, but, owing to the diversity of experimental designs, there is no clear consensus on the mechanisms involved. Changes in the accommodation response of ten emmetropic subjects (mean (+/- SD) age = 20.4 +/- 4.5 years) under open- and closed-loop conditions were investigated for three levels of mental activity. (1) A passive task whereby subjects simply read letters to themselves. (2) A stimulus-dependent task (SDT) whereby subjects are instructed to respond only when the letter 'e' appears in one of a series of presentations. (3) A stimulus-independent task (SIT) whereby subjects count backwards in sevens to themselves while viewing the target. An objective infra-red (IR) optometer was used in its static mode of operation to make monocular measurements of accommodation under monocular viewing conditions. Open-loop conditions were achieved by placing a pinhole (0.5 mm diameter), drilled into an IR filter, 12 mm in front of the eye. Under closed-loop conditions the mean accommodation response for passive viewing of the near target was +3.08 D. A significant (F = 5.45 d.f. 9,18 P less than 0.005) accommodative shift induced by mental effort in the mean response of +0.17 D occurred for the SDT. The SIT induced a mean shift of -0.05 D which was not significantly different to the passive viewing response.(ABSTRACT TRUNCATED AT 250 WORDS)     

动态检影法下近视患者反应性与刺激性AC/A

目的通过测量调节滞后量和眼位,研究在不同调节刺激下,患者反应性AC/A和刺激性AC/A的相关性。方法横断面研究。选择在校大学生29例,在全矫基础上,利用棱镜分离法测量被检者[平均年龄（23.3±3.8）岁,除近视外,无其他眼部及全身疾病]在5 m和40 cm处的隐斜量。在全矫度数的基础上添加+1.00、+1.50、-1.00、-2.00 D球镜,重新检查被检者在40 cm处的隐斜视,应用MEM动态检影法测量患者的调节滞后量。采用秩和检验对数据进行统计分析。结果在不同的调节刺激下,患者的调节滞后量、梯度法反应性AC/A及梯度法刺激性AC/A的差异均有统计学意义（x²=116.85、8.992、17.319,P<0.05）。基于梯度法得到的反应性AC/A与刺激性AC/A均呈正相关（+1.00 D：r=0.542,P<0.01;-1.00 D：r=0.789,P<0.01;-2.00 D：r=0.812,P<0.01）。基于计算法得到的反应性AC/A与刺激性AC/A也呈正相关（r=0.859,P<0.01）。结论附加负球镜时,调节滞后量更大。计算法求的反应性AC/A与刺激性AC/A的相关性最好。     

Diagnostic signs of accommodative insufficiency.

PURPOSE: To determine which are the most sensitive tests, together with accommodative amplitude, to classify accommodative insufficiency (Al), we analyzed the relation between monocular estimated method (MEM) dynamic retinoscopy, monocular and binocular accommodative facility (MAF, BAF), and positive relative accommodation (PRA) with or without the presence of reduced amplitude of accommodation. METHODS: We studied 328 symptomatic patients who presented consecutively to an optometric clinic. From this sample, we selected the 41 patients who presented amplitude of accommodation at least 2 D below the minimum age-appropriate amplitude according to Hofstetter's formula: 15 - 0.25 x age. We also selected data from 40 consecutive subjects (control group) with no general binocular disorders and normal accommodative amplitudes. We studied the specificity and sensitivity of the four signs related with the accommodative insufficiency: high MEM dynamic retinoscopy, failing MAF and BAF with minus lenses of +/- 2 D flipper lenses, and low PRA. RESULTS: Using the standard deviation as the cutoff, the specificity values were MEM = 0.88, MAF = 1, BAF = 0.93, and PRA = 1. When using the mean value as the cutoff, the specificity diminished, fundamentally for MEM. The sensitivity for the 41 patients using standard deviation as the cutoff was MEM = 0.44, MAF = 0.34, BAF = 0.27, and PRA = 0.27, and when using the mean value as the cutoff the four, sensitivity values increased. CONCLUSIONS: According to the sensitivity results, with both cutoffs used, failing the +/- 2 D MAF test seems to be the sign that is most associated with the accommodative insufficiency.     

Clinical testing of accommodative facility: part II. Development of an amplitude-scaled test.

BACKGROUND: Standard accommodative facility testing, using +/- 2.00 D lenses @ 40 cm, stresses a much different proportion of the available accommodation for a 10-year-old patient with a binocular accommodative amplitude of 12 D and a 35-year-old patient with a binocular amplitude of 5 D. This may explain why research using adult subjects has failed to associate reduced accommodative facility with symptoms. METHODS: For 19 adult subjects with normal age-related amplitudes of accommodation, accommodative facility was measured with the standard test (+/- 2.00 D @ 40 cm) and 36 experimental combinations of test distance demand and lens power range, based on percentages of each individual's amplitude. In a masked study. these results were compared to symptom scores, quantified by a 9-item quality of vision questionnaire. RESULTS: The strongest relation of facility with symptoms was for the 75% distance demand/30% power range (p = 0.0216), with six other combinations also significant. The standard test combination did not significantly differentiate symptomatic from asymptomatic subjects (p = 0.1 515). The combination of the 45% distance demand/30% power range was significantly related to symptom score (p = 0.0315; r = -0.47603). CONCLUSION: Amplitude scaled facility testing provides the same percentage test distance and range of amplitude stimulated for all patients. The 45%/30% test combination differentiates symptomatic from asymptomatic subjects better than the standard test (+/- 2.00 D @ 40 cm) and is the one we suggest for future clinical investigation. Care should be taken when testing symptomatic patients over a long period of time, as they may compensate by relying on a predictor operator during the highly repetitive accommodative facility test, thus achieving a more-rapid response.     

Influence of fogging lenses and cycloplegia on open-field automatic refraction

PURPOSE: To compare refractive values measured with and without cycloplegia, or with fogging lenses, using an open-field auto-refractor. METHODS: One hundred and forty-two young adults were enrolled from a university population; 96 were female (67.6%) and 46 were male (32.4%), the age range was 18-26 years (mean 22.3 +/- 3.7 years). The refraction measurement was obtained for the right eye of each subject with the Grand Seiko Auto Ref/Keratometer WAM-5500 (GS) under three conditions, always in this sequence: (1) without cycloplegia (GS), (2) without cycloplegia but using a + 2.00 D fogging lens (GS_2D) and (3) with cycloplegia (GS_cycl). RESULTS: When the average values of spherical equivalent were compared, both accommodation control strategies were almost equally successful: GS, M = -0.85 +/- 2.21 D; GC_2D, M = -0.53 +/- 2.10 D and GS_cycl, M = -0.57 +/- 2.24 D (Kruskal-Wallis test, p < 0.001). When the results were analysed separately for different refractive groups, emmetropes and hyperopes show statistically significant differences while myopes did not. When both accommodation strategies were compared there was a trend for more myopic subjects to display more negative values under cycloplegia, while low myopes, emmetropes and hyperopes tend to display more negative values with the +2.00 D fogging lenses, suggesting this was less effective for accommodation control. CONCLUSIONS: Over-refraction through +2.00 D fogging lenses is useful to achieve additional relaxation of the accommodative response in a similar way to cycloplegia when open-field autorefraction is performed in young adults.     

间歇性外斜视的调节灵活度和调节反应

目的：比较间歇性外斜视和正常眼位人群之间,间歇性外斜视注视眼和非注视眼之间的调节灵活度和调节反应。方法：病例对照研究。选取2016年10月至2017年1月在温州医科大学附属眼视光医院门诊就诊的35例间歇性外斜视患者作为间歇性外斜视组,另选取24例正位眼或外隐斜斜视度≤6 △ 的门诊患者作为对照组。采用±2.00 D的反转拍和开放视野式自动验光仪分别测量受试者在单眼和双眼注视近距视标时的调节灵活度和调节反应。采用t检验对数据进行分析。结果：间歇性外斜视组的双眼调节灵活度为（8.8±4.1）cpm,显著低于对照组[（10.9±3.1）cpm],两者差异有统计学意义（t=-2.165,P=0.035）。间歇性外斜视组的非注视眼调节灵活度显著低于注视眼（t=4.657,P<0.001）。双眼注视40 cm处视标时,间歇性外斜视组的注视眼调节反应高于对照组的主导眼（t=-2.163,P=0.035）。双眼注视状态下,间歇性外斜视组注视眼的调节反应为（1.89±0.30）D,高于其在单眼注视状态下的调节反应[ （1.64±0.34）D],两者差异有统计学意义（t=3.801,P=0.001）。结论：间歇性外斜视患者的双眼调节灵活度低于对照人群,其注视眼和非注视眼的调节灵活度和调节反应均不一致,且双眼注视时调节反应高于单眼注视状态。     

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.     

Clinical factors in proximal vergence

Using forced vergence fixation disparity curves, proximal vergence was analyzed in two asymptomatic patient samples; 20 young adults (average age 25.2 +/- 4.71 years) and 20 presbyopes (average age 61.6 +/- 7.8 years). Total proximal vergence was significantly larger when measured under binocular (closed loop) conditions than monocular (open loop) conditions for pre-presbyopes (binocular 10.51 delta +/- 4.7 vs. 6.4 delta +/- 3.84 monocular) and presbyopes (binocular 11.59 delta +/- 3.13 vs. 4.71 delta +/- 2.15 monocular). Associated proximal vergence was shown to predict associated phoria magnitude in presbyopes and in pre-presbyopes when vergence adaptation and convergence accommodation (CA/C) interactions with accommodative convergence (AC/A) are included. A vergence/accommodation model is presented which includes influences of proximal vergence. Clinical implications of the findings relating to diagnosis and therapy are discussed.