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).     

Vergence and accommodation responses in the control of intermittent exotropia

Purpose

Individuals with different types of intermittent exotropia (IXT) may use neurally coupled accommodation and vergence responses differently from those without exotropia to achieve eye alignment. This study examined the relationship between simultaneously recorded accommodation and vergence responses in children and young adults with a range of types of IXT while aligned and deviated.

Methods

Responses of 29 participants with IXT (4–31 years) and 24 age-matched controls were recorded using simultaneous eye-tracking and eccentric photorefraction while they watched a movie in binocular or monocular viewing at varying viewing distances. Gradient response AC/A ratios and fusional vergence ranges were also assessed. Eight participants had divergence or pseudo-divergence excess type IXT, 5 had convergence insufficiency and 16 had basic IXT.

Results

Control and IXT participants accommodated similarly both in monocular and binocular-aligned conditions to visual targets at 80 and 33 cm. When deviated in binocular viewing, most participants with IXT exhibited changes in accommodation <0.5D relative to alignment. Gradient response AC/A ratios were similar for control [0.56 MA/D (IQR: 0.51 MA/D)] and IXT participants [0.42 MA/D (0.54 MA/D); p  = 0.60]. IXT participants showed larger vergence to accommodation ratios with changes from distance to near fixation [1.19 MA/D (1.45 MA/D)] than control participants [0.78 MA/D (0.60 MA/D); p = 0.02], especially among IXT participants with divergence or pseudo-divergence excess. Participants with IXT exhibited typical fusional divergence ranges beyond their dissociated position [8.86 Δ (7.10 Δ)] and typical fusional convergence ranges from alignment [18 Δ (15.75 Δ)].

Conclusions

This study suggests that control of IXT is typically neither driven by accommodative convergence alone nor associated with over-accommodation secondary to fusional convergence efforts. These simultaneous measurements confirmed that proximal vergence contributed significantly to IXT control, particularly for divergence or pseudo-divergence excess type IXT. For IXT participants in this study, achieving eye alignment did not conflict with having clear vision.     

Horizontal fusional amplitudes after adaptation to prism

Horizontal fusional limits and lateral phorias were measured subjectively on five normal subjects after adaptation to increments of base-in and base-out prism. Both the phoria and the fusional limits were found to change by approximately the amount of the adapting prism. The fusional amplitudes (the difference between the phoria and the fusional limits) were relatively unaffected by vergence adaptation except at the largest values of adapting prism. These results are in agreement with current models of disparity vergence eye movement control which suggest that there are independent fast and slow fusional vergence mechanisms, each with its own saturation limit.     

Reliability of rotary prism fusional vergence ranges.

BACKGROUND: The measurement of fusional vergence ranges is an important clinical test in the assessment of binocular vision status. Fusional vergence ranges are typically measured by recording a patient's reports of blur, break, and recovery to base-in (BI) and base-out (BO) prism. Published reliability data on fusional vergence ranges are very limited. METHODS: Eight subjects underwent four testing sessions, at which repeated measurements of fusional vergence ranges were taken. Near ranges were tested at the first session only Distance ranges were tested at all four sessions. Intra-examiner standard deviations were calculated for each fusional vergence test result (BI and BO; blur, break, and recovery) for each session. Intra-examiner standard deviations were averaged. These values were used to determine 95% limits of agreement. RESULTS: The 95% limits of agreement were between 2 delta and 2.5 delta for the distance BI break and recovery and for the near BI recovery; between 3 and 4 delta for near BI break and near BO break; between 4 and 5 delta for distance BO blur and recovery and for near BI blur; and between 5 and 5.5 delta for distance BO break and near BO blur and recovery.     

The relationship between fusional vergence eye movements and fixation disparity

The fusional vergence system is under the control of a fast neural integrator which aligns the eyes and a slow neural integrator which maintains binocular alignment. These controllers are distinguished by their decay time constants and their stimuli. Previous studies indicate that the fast fusional vergence controller responds to retinal image disparity and the slow fusional vergence controller responds to the output of the fast neural integrator. Slow fusional vergence as evidenced by adaptation of the phoria is unaffected by accommodative vergence when disparity vergence is open loop. Under closed loop conditions both accommodation and disparity induced vergence influence slow fusional vergence. These results indicate that the slow vergence controller is located before the site of interaction between convergence and accommodation. Fixation disparity is described as a steady-state error of the neural integrator controlling fast fusional vergence and its amplitude is shown to be inversely related to adaptation of the phoria to prism.     

[In Press] Visual efficiency among teenaged athletes and non-athletes

AIM: To compare visual efficiency, specifically accommodation, vergence, and oculomotor functions among athletes and non-athletes. METHODS: A cross-sectional study on sports vision screening was used to evaluate the visual skills of 214 elementary students (107 athletes, 107 non-athletes), aged between 13 and 16 years. The visual screening assessed visual parameters such as ocular motor alignment, accommodation, and vergence functions. RESULTS: Mean visual parameters were compared between age-group matched athletes (mean age 14.82±0.98y) and non-athletes (mean age 15.00±1.04y). The refractive errors of all participants were corrected to maximal attainable best corrected visual acuity of logMAR 0.0. Accommodation function assessment evaluated amplitude of accommodation and accommodation facility. Vergence functions measured the near point of convergence, vergence facility, and distance fusional vergence at break and recovery point. Ocular motor alignment was not statistically significant between both groups. Athletes had a statistically significant amplitude of accommodation for both the right eye (t=2.30, P=0.02) and the left eye (t=1.99, P=0.05). Conversely, non-athletes had better accommodation facility (t=-2.54, P=0.01) and near point of convergence (t=4.39, P<0.001) when compared to athletes. Vergence facility was found to be better among athletes (t=2.47, P=0.01). Nevertheless, non-athletes were significantly better for both distance negative and positive fusional vergence. CONCLUSION: Although the findings are still inconclusive as to whether athletes had superior visual skills as compared to non-athletes; it remains important to identify and elucidate the key visual skills needed by athletes in order for them to achieve higher performance in their sports.     

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。     

Sighting dominance and monovision distance binocular fusional ranges.

Clinicians typically apply the distance correction to the dominant sighting eye in fitting presbyopic patients with monovision (MV) contact lenses. We evaluated the effect of this fitting strategy on distance binocular fusional ranges for 23 presbyopic subjects. This sample was composed of successful and unsuccessful MV wearers. Fusional ranges for the two MV fitting possibilities (distance lens on the dominant eye, near lens on the dominant eye) were compared to fusional ranges in which both eyes were fitted with the distance correction. A greater esophoric shift and greater reduction in vergence ranges were demonstrated when the non-dominant eye received the clear image compared to when the dominant eye received the clear image. Successful MV patients demonstrated these effects to a lesser degree than did unsuccessful patients. In general, effects of MV on distance binocular fusional ranges were fewer when successful MV subjects received the clear image in the dominant eye.     

Binocular function in school children with reading difficulties

Introduction  

Prior findings suggest that poor readers tend to have poor binocular vision skills, but data on the binocular abilities of children with poor reading skills are lacking. Our aim was to characterize distance and near horizontal heterophoria, distance and near horizontal fusional vergence ranges, accommodative convergence/accommodation (AC/A) ratio, near point of convergence, and stereopsis in poor-reading school-age children without dyslexia selected from a non-clinical population.     

Visual efficiency among teenaged athletes and non-athletes

AIM: To compare visual efficiency, specifically accom-modation, vergence, and oculomotor functions among athletes and non-athletes. METHODS: A cross-sectional study on sports vision screening was used to evaluate the visual skills of 214 elementary students (107 athletes, 107 non-athletes), aged between 13 and 16y. The visual screening assessed visual parameters such as ocular motor alignment, accommodation, and vergence functions. RESULTS: Mean visual parameters were compared between age-group matched athletes (mean age 14.82±0.98y) and non-athletes (mean age 15.00±1.04y). The refractive errors of all participants were corrected to maximal attainable best corrected visual acuity of logMAR 0.0. Accommodation function assessment evaluated amplitude of accommodation and accommodation facility. Vergence functions measured the near point of convergence, vergence facility, and distance fusional vergence at break and recovery point. Ocular motor alignment was not statistically significant between both groups. Athletes had a statistically significant amplitude of accommodation for both the right eye (t=2.30, P=0.02) and the left eye (t=1.99, P=0.05). Conversely, non-athletes had better accommodation facility (t=-2.54, P=0.01) and near point of convergence (t=4.39, P<0.001) when compared to athletes. Vergence facility was found to be better among athletes (t=2.47, P=0.01). Nevertheless, non-athletes were significantly better for both distance negative and positive fusional vergence. CONCLUSION: Although the findings are still inconclusive as to whether athletes had superior visual skills as compared to non-athletes, it remains important to identify and elucidate the key visual skills needed by athletes in order for them to achieve higher performance in their sports.     

角膜塑形镜对近视性屈光参差儿童双眼视功能的影响

目的　探究角膜塑形镜（OK镜）对近视性屈光参差儿童双眼视功能的影响。方法　收集2018年至2019年于北京大学第三医院眼科视光中心就诊的60例近视性屈光参差儿童资料,随机分为OK组（配戴OK镜）和SP组（配戴普通框架眼镜）,每组各30例。基线时（配戴OK镜或框架眼镜前）和戴镜后6个月、12个月时,分别对受试儿童进行远距斜视度、远距融合范围、远近距立体视的检查。比较OK组和SP组儿童双眼视功能参数的差异,以及两组儿童双眼视功能参数随戴镜时间的变化情况。结果　与基线时相比,戴镜后6个月、12个月时,OK组儿童的远距融合范围、远距集合范围显著减小,近距立体视显著提高（均为P<0.05）,而远距斜视度、远距融合点、远距散开范围、远距立体视差异均无统计学意义（均为P>0.05）。与基线时相比,戴镜后6个月、12个月时,SP组儿童的近距立体视均显著提高（均为P<0.05）,而远距斜视度、远距融合点、远距融合范围、远距集合范围、远距散开范围、远距立体视差异均无统计学意义（均为P>0.05）。OK组和SP组儿童基线时和戴镜后6个月时的远距斜视度、远距融合范围、远距融合点、远距集合范围、远近距立体视差异均无统计学意义（均为P>0.05）。戴镜后12个月时,OK组儿童的远近距立体视均优于SP组（均为P<0.05）,而两组儿童其余指标差异均无统计学意义（均为P>0.05）。结论　近视性屈光参差儿童配戴OK镜后,远距融合范围减小,近距立体视提高。与框架眼镜相比,OK镜改善近视性屈光参差儿童远近距立体视的作用更好。     

Vergence Exercises for Six Weeks Induce Faster Recovery of Convergence Insufficiency Than Accommodation Exercises in School Children

PurposeConvergence insufficiency (CI) is characterized by abnormal vergence eye movement frequently accompanied by abnormal accommodation and subjective symptoms, such as headache, blurred vision, and diplopia. CI is treated with vergence and accommodation exercises that are integrated so that the relative contributions of vergence and accommodation exercises to the outcome are concealed. The purpose of the present study was to determine the individual contributions of vergence and accommodation exercises for the treatment of CI in school children.MethodsIn a prospective crossover study 44 children aged 9 to 13 years with CI were randomized to perform either vergence exercises followed by accommodation exercises each for 6 weeks or the 2 treatment regimes in the reverse order. The outcome measures were recovery from CI and the parameters vergence facility, positive fusional vergence, near point of convergence, monocular amplitude, and facility of accommodation.ResultsAfter the first 6-week period, full recovery from CI was significantly more frequent in the group commencing vergence exercises than in the group commencing monocular accommodation exercises (p = 0.01), whereas there was no significant difference between these proportions after the second 6-week period (p = 0.45). Vergence facility and positive fusional vergence improved significantly more after the period with vergence exercises than after the accommodation exercises, whereas there was no significant difference between the effects of the two types of exercises on the other studied parameters.ConclusionsVergence treatment induces a faster recovery of CI than accommodation treatment in school children. This may be used to improve compliance and success rate of the treatment.     

Effect of luminance on the relation between accommodation and convergence

When luminance is lowered, both vergence and accommodation tend to shift toward different and individually characteristic resting postures, commonly referred to as dark-vergence and dark-focus. In order to determine the luminance level at which these two mechanisms correspond to a target distance, subjects viewed a light spot 0.4 mm in diameter, corresponding to 1.4 to 2.7 min arc, located at the individually determined dark-focus position. As the luminance of a binocularly viewed spot increased, accommodation did not change significantly from the target distance. However, fusional vergence gradually shifted from the dark-vergence to the target position. The critical luminance level at which the 2 responses were coupled for the 12 observers ranged from 0.01 to 0.45 cd/m2, with distinct individual differences. In a second experiment, the target was positioned at distances different from the dark-focus and luminance was set at 0.5 and 1.0 log unit higher than the subject's critical luminance level. At lower luminance levels, mononuclear focus tended to remain at the individual dark-focus, whereas the binocular focus tended to correspond to the target distance. These differences can be attributed to vergence accommodation. Previous studies on night myopia reported that a negative correction based on one-half of the individual dark focus was superior to a full dark-focus correction. The present results suggest that this difference is due to vergence accommodation and that the optimum correction for night myopia depends, in part, on the critical luminance level for activation of fusional vergence.     

Binocular anomalies and reading problems

This paper reviews and evaluates the research literature on the relationship of binocular anomalies to reading problems. The weight of the evidence supports a positive relationship between certain binocular anomalies and reading problems. The evidence is positive for exophoria at near, fusional vergence reserves, aniseikonia, anisometropia, convergence insufficiency, and fixation disparity. There is some weak positive evidence for esophoria at near and mixed evidence for stereopsis. The evidence on lateral phorias at distance is negative.     

应用Sheard准则评估集合不足患者的临床研究

目的:运用Sheard准则对集合不足的屈光不正患者的双眼视失平衡症状进行评估和诊治。方法:对2009-06以来18例集合不足的患者进行眼屈光检查,同时检测远近分离性隐斜,远近辐辏,正相对调节,调节状态,负相对调节,辐辏近点,调节幅度等眼动参数。计算AC/A参数,检测其对Sheard准则符合性,并利用该准则计算所需的棱镜处方。结果:近距棱镜不符合Sheard准则有14例(78%),其所需的基底朝内棱镜度数为(3.47±2.83)△。结论:临床上运用Sheard准则可有效地评估和诊治近距离用眼不适的集合不足患者。     

使用计算机终端及不同休息方案对调节聚散功能影响分析

目的 研究使用计算机终端及不同的休息方案对调节、聚散功能的影响.方法 30名受试者均接受5种不同阅读方案:(1)连续计算机终端阅读2h后休息10min.(2)连续书本阅读2h后休息10min.(3)连续计算机终端阅读1h后休息10min(休息1方案).(4)计算机终端阅读总时间1h,每30min间隔休息5min(休息2方案).(5)计算机终端阅读总时间1h,每15min间隔休息2min(休息3方案).每次阅读前后分别查眼部屈光、调节反应(调节滞后度)、单眼调节幅度、聚散功能(集合近点、调节性集合/调节[accommodative convergence/accommodation,AC/A]、远近距水平隐斜、远近距融像性水平聚散力).结果 (1)连续2h计算机终端阅读后较书本阅读更易出现调节滞后值增加、调节幅度下降、集合近点远移、近距水平外隐斜增加内隐斜减小、近距融像性水平聚合力减弱(P＜0.05).(2)连续计算机终端阅读2h较1h更易出现调节滞后值增加、调节幅度下降、集合近点远移(P＜0.05).(3)调节滞后值、调节幅度、集合近点、近距离水平内外隐斜在三种休息方案之间的差异具有统计学意义(P＜0.05),休息3方案优于其它方案.结论 使用计算机终端阅读较书本阅读更易对调节、聚散功能产生影响,且随时间的不同出现差异.三种不同休息方案比较,每使用计算机终端阅读15min间隔休息2min对调节、聚散功能影响最小.     

Statistical normal values of visual parameters that characterize binocular function in children

A wide range of visual parameters used to evaluate binocular function were evaluated in a paediatric population (1056 subjects aged 6-12 years). Mean values are provided for these ages in optometric tests that directly assess the vergence system, horizontal phorias for near and far vision (measured by a modified version of the Thorington method), negative and positive vergence amplitude for near and far vision (step vergence testing), vergence facility (flippers 8 Delta BI/8 Delta BO), and near-point of convergence (penlight push-up technique and red-lens push-up technique), as well as stimulus accommodative convergence/accommodation ratio and stereoacuity (Randot test) which provide an overall evaluation of the vergence, accommodative and oculomotor systems. A statistical comparison (anova and Bonferroni post hoc test) of these values between ages was performed. The differences, although statistically significant, were not clinically meaningful, and therefore we identified two trends in the behaviour of these parameters. For all parameters, except for vergence facility, we established a single mean reference value for the age range studied. The difference between the means for vergence facility indicated the need to divide the population into two age ranges (6-8 and 8-12 years). This study establishes statistical normal values for these parameters in a paediatric population and their means are a valuable instrument for separating children with binocular anomalies from those with normal binocular vision.     

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.     

Normal values of distance heterophoria and fusional vergence ranges and effects of age

Background Although it is well known that age affects visual function, we still have much to learn about the impact of aging on binocular vision. Our aim was to establish distance heterophoria and distance fusional vergence ranges in a large non-clinical population of wide age range, to provide normal values for comparisons.Methods A cross-sectional study was performed on 271 non-clinical subjects stratified into six age groups. Distance heterophoria measurements were obtained using the von Graefe technique and distance horizontal fusional vergence ranges using Risley rotary prisms in each subject, with best spectacle correction.Results The mean heterophoria value for distance fixation was exophoric except for the 71–80 year age group, which was esophoric. No effects of age were observed on distance heterophoria and distance base-in and base-out break means. However, a significant effect of age was noted on base-in recovery and base-out recovery. Between the youngest and oldest age groups, mean base-in recovery decreased by 2.5 Δ and mean base-out recovery by 3.3 Δ.Conclusions Distance base-in and base-out recovery means diminished significantly with age such that recovery values fell outside the norm in subjects in the 61–70 year age group and older. This study establishes statistical normal values for distance heterophoria and fusional vergence in a non-clinical population. Mean values such as these are valuable tools for identifying subjects with far binocular anomalies.     

Influence of target color and vergence of light on ocular accommodation during binocular fixation

In an earlier study we reported large discrepancies between ocular refraction and perception of blur for black/white letters. In the present study we report on the influence of target color and vergence of light on the human focusing system. Twenty visually normal volunteers between 14 and 25 years of age participated in this experiment. Targets were brightness-matched red, yellow, green, blue or white 21 minarc letters displayed on the black background of a high resolution RGB monitor, at a 40 cm observation distance. Changes in the vergence of light were effected via increasing amounts of positive and negative power spherical lenses placed binocularly in front of the subject's eyes. Our results showed that: 1) the accommodative level varied as a function of the color of a target, 2) the vergence of light was not an infallible cue for accurate accommodation and 3) the inter-subject variability seen in response to the vergence of light was not linked with the chromaticity of test targets. All subjects showed a decreasing ability to fully relax accommodation with increasing plus power lenses. For minus power lenses, accommodative response profiles were divided into 3 categories, category 1 having accurate accommodation for the test target, category 2 showing a low level lag of accommodation and category 3 being totally unresponsive to increasing divergence of light. While subjects across response categories showed differential endpoints in clinical estimates of positive relative accommodation, other clinical measurements related to refractive error, accommodative amplitude and fusional ability failed to predict the accommodative behavior of our subjects as did measurements of the resting focus of accommodation.