Vergence adaptation in subjects with convergence excess

The main purpose of this study was to evaluate the vergence adaptive ability in subjects diagnosed with convergence excess (CE) phoria (ie, subjects with an esophoric shift from distance to near but without an intermittent tropia at near). Vergence adaptation was measured at far and near with both base-in and base-out prisms using a "flashed" Maddox rod technique in 20 control subjects and 16 subjects with CE. In addition, accommodative adaptation and the stimulus AC/A and CA/C cross-links were measured. The AC/A and CA/C ratios were found to be high and low, respectively, and accommodative adaptation was found to be reduced in CE subjects as compared with the controls (P<0.005), all as predicted by the present theory. However, vergence adaptive ability was found to be reduced in the CE subjects at both distance and near and in response to both base-in and base-out prisms (P=0.002). This finding is not in accordance with and is difficult to reconcile with the present theory of CE.     

Convergence Insufficiency Neuro-Mechanism Adult Population Study: Phoria Adaptation Results

PurposeThe purpose of this study was to compare changes in phoria adaptation between young adult binocularly normal controls (BNCs) and participants with symptomatic convergence insufficiency (CI), who were randomized to either office-based vergence accommodative therapy (OBVAT) or office-based placebo therapy (OBPT).MethodsIn the double-masked randomized clinical trial, 50 BNC and 50 CI participants were randomized to the following therapeutic interventions: OBVAT or OBPT with home reinforcement for 12 one-hour office sessions. A 6∆ base-out and 6∆ base-in phoria adaptation experiment at near (40 cm) was conducted using the flashed Maddox rod technique at baseline and at outcome. Measurements included the rate and the magnitude of phoria adaptation.ResultsAt baseline, BNC and CI participants had significantly different rates and magnitudes of base-in and base-out phoria adaptation (P < 0.001). When comparing the outcome to baseline measurements, significant main effect differences in longitudinal measurements were observed for the magnitude and the rate of phoria adaptation for both base-out and base-in experiments (P < 0.05). For the magnitude and rate of phoria adaptation, post hoc analyses using paired t-tests revealed that the CI group administered the OBVAT intervention exhibited a significant increase in the magnitude and rate of phoria adaptation compared to baseline for both base-in and base-out phoria adaptation (P < 0.01) but not for those administered OBPT.ConclusionsPhoria adaptation is significantly different at baseline between those with normal binocular vision and symptomatic CI participants. OBVAT significantly improves the rate and magnitude of both base-out and base-in phoria adaptation at near compared to OBPT. Results have clinical implications for new therapeutic interventions.     

Binocular and Accommodative Characteristics in a Normal Population

Purpose: To study binocular and accommodative characteristics and their associations with age and gender in an Iranian young adult population.

Methods: In this cross-sectional study, multistage cluster sampling was done from the students of Mashhad University of Medical Sciences. All participants had visual acuity, refraction, and cover tests followed by measurements of the near point of convergence (NPC), amplitude of accommodation (AA), monocular and binocular accommodative facility (MAF and BAF) using ±2.00 diopter (D) flipper lenses, and negative and positive relative accommodation (NRA and PRA). Near and distance fusional vergence reserves were measured using prism bar, and near associated phoria was assessed using the Mallett unit.

Results: The mean age of the participants was 22.5±4.4 years (range: 18-35 years). The binocular and accommodative characteristics and their means in the studied sample included: mean distance dissociated phoria: 1.15 exophoria±2.04 prism diopters (PD), near dissociated phoria: 5.02 exophoria±4.74 PD, near associated phoria: 0.55 base-in±1.02, gradient accommodative convergence/accommodation (AC/A) ratio: 4.66±1.59, NPC: 5.27±3.60 cm, MAF: 11.33±5.58 cpm, BAF: 8.84±4.47 cpm, NRA: 2.08±0.33 D, PRA:-2.92±0.76 D, and AA: 11.14±2.6 D. In the multiple regression model including age and gender, near exophoria was significantly higher in men and levels of near base-out-break and near base-out-recovery were higher in females. Distance exophoria, distance base-in-break, distance base-in-recovery, and NPC increased with age and near base-out-break, PRA, BAF, MAF, and AA significantly decreased with age.

Conclusion: Studied indices in this study significantly differ from available guidelines and these differences must be considered when making diagnostic or therapeutic decisions. Certain indices can be affected by age and gender.     

Changes in accommodative and vergence responses when viewing through near addition lenses.

It has been proposed that near addition lenses reduce the lag of accommodation and may slow myopia progression. In this study, we investigated the differences in accommodative response and near phoria in subjects with and without near addition lenses. Fourteen subjects (7 emmetropic and 7 myopic) participated in the study. Monocular and binocular accommodative responses to a target at 40 cm were measured with and without +2.00 diopter (D) lenses using a Canon R-1 optometer (Canon Europe N.V., Amsterdam, The Netherlands). Near dissociated phoria was measured using 3 testing methods: Maddox rod, cover test, and Von Graefe technique. The differences in accommodative response and near phoria between the 2 viewing conditions with and without the near addition lens were significant (P < 0.0001). No significant differences were revealed in accommodative response and near phoria between refractive error groups. The average accommodative responses of all subjects were 2.03 +/- 0.06 (SE) D (without +2.00 D lens) and 0.60 +/- 0.07 D (with +2.00 D lens) under monocular viewing conditions and 2.11 +/- 0.06 D (without +2.00 D lenses) and 0.77 +/- 0.07 D (with +2.00 D lenses) under binocular viewing conditions. The average near phorias of all subjects were -2.08 +/- 0.69 prism diopters (PD, without +2.00 D lenses) and -7.90 +/- 0.68 PD (with +2.00 D lenses). We discuss the effect of near addition lenses on the defocus of the retinal image, accommodative response, and near phoria. In addition, we propose that the observed difference between binocular and monocular accommodation, when viewing through near addition lenses, is caused by an increased vergence accommodation.     

The symptomatic patient with normal phorias at distance and near: what tests detect a binocular vision problem?

PURPOSE: Patients often manifest symptoms that appear to be related to binocular distress. Many of these patients have normal heterophoria at distance and near, making the etiology of such symptoms perplexing. We performed a visual examination of patients having normal heterophoria at distance and near in order to investigate which visual analysis tests differentiate symptomatic from asymptomatic patients. METHODS: Eighty subjects (30 symptomatic, 50 asymptomatic) with ages between 18 to 35 years of either sex and any race were pooled based on vision-symptom level determined by a 9-question standardized visual-symptoms questionnaire scored using a 100-point scale (asymptomatic: score > or = 85; symptomatic: score < or = 75). Inclusion/exclusion criteria included vision correctable to 6/6 (20/20) Snellen acuity or better in each eye, normal phorias, no latent cyclovertical heterophoria, and normal ocular health. RESULTS: Of the 30 symptomatic patients, 18 had reduced vergence facility response using 3 pd base-in/12 pd base-out loose prism at distance (n = 10; t-score = 2.41, p < 0.02, d = 76) and near (n = 15; t-score = 3.32, p < 0.01, df = 78) with a significant difference beyond the 0.02 level. No other test including measurement of accommodation, showed a significant between-group difference. However, three patients with normal vergence facility (distance and near) showed a reduced binocular accommodative facility response (+/-2.00 D at 40 cm). CONCLUSION: Given a patent with asthenopia, normal phorias, and visual acuity, a differential diagnosis may be made based primarily on using vergence facility and accommodative facility testing. From a clinical standpoint, the results expedite diagnosis of binocular vision abnormalities and direct treatment.     

A longitudinal study of vergence adaptation in incipient presbyopia

BACKGROUND: To investigate vergence adaptation during the incipient phase of presbyopia, when the amplitude of accommodation approaches the level where the first reading addition is required. The study aimed to assess the ability of the vergence system to counteract changes in the component contributions to the overall vergence response with the decline in the amplitude of accommodation in presbyopia, although previous reports on the nature of changes in accommodative, tonic and proximal vergence are equivocal. METHODS: Using a 'flashed' Maddox rod technique, an assessment of vergence adaptation to 6delta base-out and 6delta base-in prism was made for 28 subjects (aged 35-45 years at the commencement of the study). The measurements were taken four times over a 2-year period. RESULTS: Using a repeated measures analysis of variance, the results show that with the decline in amplitude of accommodation, there is a statistically significant reduction in the magnitude of vergence adaptation to both base-out (p < 0.05) and base-in prism (p < 0.01). CONCLUSIONS: This study shows that with ageing, there is a decrease in the ability of the slow vergence mechanism to overcome a change in fusional vergence demand and would suggest that either the fast component of fusional vergence must cope with any change in fusional vergence demand or that the sum of the accommodative, tonic and proximal vergence responses are virtually stable with age.     

Vergence adaptation in clinical vergence testing

BackgroundThe purposes of this investigation were to determine whether vergence adaptation occurs after vergence range testing and vergence facility testing and to determine whether vergence adaptation correlates with the results of these tests.MethodsThirty subjects participated in 3 testing sessions on different days. During each session 1 of the following was tested: base-out prism bar vergences, vergence facility (12 base-out/3 base-in binocular prism flippers for 1 minute), and 5 minutes viewing with 6 prism diopters of base-out prism. Before and after each test, the near phoria was measured using the modified Thorington method.ResultsThere was no correlation between the amplitude of the vergence ranges and the amplitude of vergence facility. Significant vergence adaptation as indicated by an esophoric shift of approximately 3 prism diopters occurred in all testing sessions. The amplitude of vergence adaptation did not correlate with either the amplitude of the blur vergence range or vergence facility. There was a significant correlation between the amplitude of vergence adaptation and the amplitude of the break vergence range.ConclusionsThe lack of correlation between the blur vergence range and the vergence facility is not likely because of vergence adaptation. The lack of correlation between the break vergence range and the vergence facility may be in part caused by vergence adaptation.     

Contact lenses vs spectacles in myopes: is there any difference in accommodative and binocular function?

Background  

Theoretically, the accommodative and vergence demands are different between single-vision contact lenses and spectacle lenses. The aim of the present study was to determine whether these differences exist when these two correction methods are used in clinical practice. For this, different visual parameters that characterize the accommodative (accommodation amplitude, accommodative facility, and accommodative response) and binocular function (near and distance horizontal and vertical dissociated phorias, near and vertical associated phorias, near and distance negative and positive fusional vergence, vergence facility, near point of convergence, negative and positive relative accommodation, stimulus AC:A ratio and stereoacuity) were evaluated in a student population when their myopia was corrected with either spectacles or soft contact lenses (SCL).     

不同程度近视青少年儿童双眼视功能的差异

目的通过比较不同程度近视儿童双眼协动参数的差异性及其与近视程度相关性,进一步探索近视发展的原理。方法横断面研究。研究对象包括128例7～14岁近视青少年儿童,根据等效球镜度分为低度近视组（-0.50～-3.00 D）、中度近视组（-3.25～-6.00 D）和高度近视组（>-6.00 D）。双眼协动参数测量包括远距及近距水平聚散力,远距及近距水平隐斜,梯度性调节性集合与调节的比率（AC/A比率）。采用单因素方差分析和卡方检验对3组数据进行分析。结果在融像性聚散范围中,远距散开力的破裂点、近距散开力的恢复点、远距集合力的恢复点、近距集合力的模糊点及破裂点随近视程度加深而减小（F=3.271、3.579、4.931、6.507、4.887,P<0.05）,其余参数的差异无明显统计学意义（P>0.05）;在隐斜视类型的构成比中,远距及近距隐斜类型构成比例的差异在3组中无明显统计学意义（P>0.05）,总体上近距内隐斜构成比例高于远距内隐斜（χ²=6.609,P<0.05）;梯度性AC/A随近视程度的增加而增加（F=3.625,P<0.05）,其中高度近视组明显高于低度近视组（P<0.05）。结论随着青少年儿童近视程度的增加,融像性聚散范围减少,梯度性AC/A比率增高。近视儿童表现出的近距内隐斜可能与近视发展相关。     

Variation and correlation of standard clinical phoropter tests of phorias, vergence ranges, and relative accommodation in a sample of school-age children.

This paper presents a study of standard clinical phoropter tests of dissociated phorias, fusional vergence ranges, and relative accommodation ranges in 244 school-age (7.9 to 15.9 years of age) children. The tests studied included von Graefe phorias and base-in and base-out fusional vergence ranges at both distance and near, as well as negative relative accommodation (NRA) and positive relative accommodation (PRA) tests. Coefficients of correlation among the various tests are presented. Means and correlations were similar to those previously reported for adult populations. Distributions of distance lateral phorias and some distance fusional vergence parameters were leptokurtic.     

配戴多焦点硬性角膜接触镜对近视患者双眼视功能的影响

目的：探讨多焦点设计的硬性角膜接触镜对近视患者双眼视功能的影响。

方法：自身前后对照研究。于2020-07/08在川北医学院招募近视学生15人作为试验者,试验者首先配戴框架眼镜行双眼视功能检查,然后分别配戴单焦点与多焦点硬性角膜接触镜(间隔1wk),每种镜片配戴2wk后行双眼视功能检查。采用单因素方差分析比较多焦点硬性角膜接触镜(MFRGP)、单焦点硬性角膜接触镜(SVRGP)和框架眼镜双眼视功能的差异。

结果：三种镜片立体视、远距水平隐斜、远距正融像性聚散、远距负融像性聚散、近距正融像性聚散、聚散灵活度、集合近点、调节幅度、调节灵活度、负相对调节比较均无差异(P>0.05)。与框架眼镜相比,配戴MFRGP近距水平隐斜、近距负融像性聚散、调节滞后、正相对调节增大,AC/A降低(P=0.023、0.048、0.001、0.013、0.046); 与SVRGP相比,MFRGP近距水平隐斜、调节滞后、正相对调节增大,AC/A降低(P=0.014、<0.001、0.001、0.009)。

结论：配戴MFRGP会引起近距水平隐斜、调节滞后、正相对调节增大和AC/A降低,这些变化可能对配戴者近距离用眼产生一定影响,在临床应用中要考虑这些预期的变化,以便正确评估和管理患者。     

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...     

Resting positions of vergence and their relation to asthenopic complaints

Dark vergence is a resting position of vergence, measured in a dark visual field to eliminate fusional, accommodative, and proximal stimuli. Dark vergence differs among subjects: the average subject converges to a viewing distance of about 1 m, while the inter-individual range is from infinity to about 40 cm. This paper reviews previous ergonomic studies on dark vergence in relation to asthenopic complaints that occur when working at near computer screens: subjects with distant dark vergence exert more convergence and experience stronger asthenopic complaints than subjects with near dark vergence. The dissociated phoria, a common clinical measure of resting vergence, is only weakly correlated with asthenopic complaints, probably because of accommodative influences that cause the difference between dark vergence and dissociated phoria.     

Contribution of accommodation and disparity-vergence to transient nearwork-induced myopic shifts

Many investigations have attempted to demonstrate a relationship between sustained near-vision and the aetiology of environmentally-induced myopia, but it remains unclear whether myopic development relates to the actions of either accommodation or vergence. The present study investigated the effect of varying the disparity-vergence demand during a near-vision task while maintaining the accommodative stimulus constant. We required 20 young subjects to perform a near task (viewing distance = 20 cm) for 20 min through base-in, zero power and base-out prisms. The magnitude of the prisms for each individual corresponded to one-third their near vergence range. Pre- and post-task measurements of refractive state were determined objectively using an infrared optometer, with post-task readings being recorded over the initial 50 s following task completion. The results indicated no significant difference between the transient far-point shift for the three disparity-vergence conditions. However, combining data across conditions, a significant, mean shift in the myopic direction of 0.14 D was observed during the 10-20 s period immediately following task completion which dissipated within 20-50 s post-task. These findings suggest that the transient post-task myopic shift was not related to the output of disparity-vergence.     

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.     

青少年儿童近视性屈光参差双眼眼动参数的临床研究

目的：观察儿童和青少年近视性屈光参差患者双眼眼动参数,初步探讨儿童和青少年近视性屈光参差对眼动参数的影响。

方法：病例对照研究。选取2014-09/2016-05于重庆医科大学附属大学城医院就诊的7～14岁儿童及青少年82例,其中正视者(对照组)47例,近视性屈光参差者(试验组)35例,检测所有入选者的屈光度、5m和40cm隐斜、梯度性和计算性AC/A比值及调节功能\〖40cm的调节反应(FCC)、正负相对调节(NRA/PRA)、调节力(AMP)和调节灵敏度(AF)\〗。

结果：两组受检者5m和40cm隐斜度数、40cm FCC、PRA及AC/A比值差异均有统计学意义(P<0.05); AF、NRA、AMP与正常值最小值的差值差异均无统计学意义(P>0.05)。

结论：近视性屈光参差对儿童和青少年5m和40cm隐斜、40cm FCC、PRA及AC/A比值有显著影响。     

Short exposure to telestereoscope affects the oculomotor system

Under natural viewing conditions, the accommodation and vergence systems adjust the focus and the binocular alignment of the eyes in response to changes in viewing distance. The two responses are linked via cross‐coupling and proceed almost simultaneously. Some optical devices, such as virtual reality or helmet mounted displays, create an oculomotor conflict by modifying demands on both vergence and accommodation. Previous studies extensively investigated the effect of such a conflict on the cross‐coupling between vergence and accommodation, but little is known about the plasticity of the whole oculomotor system. In the present study, an oculomotor conflict was induced by a telestereoscope which magnified the standard inter‐pupillary separation threefold and thus increased the convergence demand while accommodation remained almost unchanged. The effect of a 10 min exposure was assessed via a series of optometric parameters selected on the basis of existing oculomotor models. Associated with subject’s visual complaints, most of the oculomotor parameters tested were modified: there was (1) deterioration of stereoscopic threshold; (2) increase in AC/A ratio; (3) increase in near and far phorias; and (4) shift of the zone of clear and single binocular vision towards convergence. These results showed a change in gain of accommodative vergence and a shift of vergence reserves towards convergence in response to telestereoscopic viewing. The subject’s binocular behaviour tended towards esophoria with convergence excess as confirmed by Sheard’s and Percival’s criteria. Such changes in oculomotor parameters support adaptive behaviour linked with telestereoscopic viewing.     

Accommodative vergence is driven by the phasic component of the accommodative controller

Conflicting opinions exist as to whether the phasic (reflex) component alone or both the phasic and tonic (adaptive) components of the accommodation and vergence systems drive accommodative vergence and vergence accommodation crosslinks. In this study the dissociated phoria to a 2 D target was measured before and after accommodative adaptation to discriminate the two possibilities. Results showed a significant difference in the dark-focus of accommodation pre- and post- near-vision task, indicating that accommodative adaptation had occurred. No significant change occurred in dark-vergence or in the accommodative response to the 2 D target. However, a significant decrease was found in the dissociated phoria presumably because of decreased phasic accommodation and its stimulation of accommodative vergence after the adaptation. This result is consistent with a model in which the accommodative vergence crosslink is driven by phasic accommodation only.     

Fixation disparity and accommodation for stimuli closer and more distant than oculomotor tonic positions

Both the vergence and the accommodative system have individual tonic positions (also referred to as dark vergence and dark focus, respectively) where the static response may be expected to be most accurate. This was confirmed by measuring fixation disparity with nonius lines and accommodation with an autorefractometer for foveal stimuli at viewing distances of 460, 100, 60, 40, and 30 cm. Multiple regression analysis was used at each viewing distance to predict fixation disparity from dark vergence, dark focus, accommodative gain and accommodative convergence: these accommodative measures had little effect on the inter-individual variability of near fixation disparity nor on the linear slope of fixation disparity as a function viewing distance.