Measurement of fusional vergence: a systematic review

ABSTRACT

Background: Fusional amplitudes are important for clinical practice in diagnosing and managing binocular vision anomalies. Several measurement methods can be used to assess fusional amplitudes. However, those methods are not interchangeable, and measurement repeatability has been questioned.

Objectives: To compare the normative values of tests for the measurement of fusional vergence and to investigate sources of heterogeneity of diagnostic accuracy including: age, variation in method of assessment, study design and size, type (convergent, divergent, vertical, cyclo) and severity of strabismus (constant/intermittent/latent).

Data sources: Bibliographic databases were searched up to March 2018, including Cochrane registers, PubMed, Web of Science^TM, Google Scholar and Science Citation Index. Trial registers and conference proceedings were hand searched.

Review methods: The review observed and reported according to the PRISMA guidelines and was registered with PROSPERO. The I² was used to show the percentage of observed total variation across studies that is due to real heterogeneity rather than chance. The results of the different studies and the overall effect (meta-analysis under the random effects model) are shown.

Results: Eighty-one studies were included in the review. Heterogenous information about break vergence amplitudes is reported for the step vergence method (I² > 50%; p < 0.05) in children. Four parameters were reported consistently to affect measurements; age, method of assessment, order of testing and target size. For the smooth vergence technique break vergence values heterogeneity was not present in children and adults (I² = 0%; p > 0.05).

Limitations: The results are based on cross-sectional studies that were performed independently of each other, with different examiners, methods of examination and different populations.

Conclusions: The source of heterogeneity between studies for vergence break points measured with the step vergence method seems to be linked with age. Normal vergences reported in children had considerable heterogeneity compared with adults. In clinical practice, the population-based vergence ranges measured with the step vergence method in children should not be used as one single criterion. For the smooth vergence technique, normative population data can be used.     

Evaluation of distance and near stereoacuity and fusional vergence in intermittent exotropia

Aim: To evaluate the role of distance and near stereoacuity and fusional vergence in patients with intermittent exotropia [X(T)] and their change after surgery. Materials and Methods: This prospective interventional institution-based clinical study included 31 cases of X(T) requiring surgery and 33 age, sex-matched controls. All subjects underwent complete orthoptic assessment including near stereopsis (Randot stereogram) and distance stereopsis by polaroid stereo-projector apparatus using special paired slides and fusional vergence assessment at distance and near prism bar at baseline and one week, one month, three months and six months after surgery in X(T). Results: The successful surgical alignment rate was 74.2%. Preoperatively, cases demonstrated significantly poor distance and near stereoacuity, compared to controls ( P P Conclusion: Early detection of abnormal stereoacuity (near and if possible distance) and near fusional vergence amplitudes may help to decide proper timing of surgery in X(T).     

Repeatability and agreement in the measurement of horizontal fusional vergences

PURPOSE: This study was designed to determine the repeatability of fusional vergence ranges measured using the rotary prisms in the phoropter and in free space using the prism bar. The level of agreement between the two methods was also investigated. METHODS: In two separate sessions, negative and positive fusional vergence ranges (NFV and PFV, respectively) were measured at distance and near in 61 young adults (mean age 19.74, S.D. 2.5 years) who were unfamiliar with the methods used. Base-in and base-out blur, break and recovery points were sequentially determined. Both sets of measurements were obtained by the same examiner. At each distance, NFV was determined first and then PFV. The repeatability of the tests and agreement between measurements made with the phoropter rotary prisms and the prism bar were estimated by the Bland and Altman method. RESULTS: For both the phoropter rotary prisms and prism bar, NFV measurements showed better repeatability than PFV at both near and distance. Mean differences recorded for the NFV break and recovery points were non-significant (under 0.5Delta), while those observed for PFV were generally greater than 2Delta. When agreement between the two tests was assessed, it was found that break points were higher when determined using the phoropter rotary prisms, while recovery points were generally higher for the prism bar method. In clinical terms, according to the expected values of the NFV and PFV, agreement between the two techniques can be described as fair, because although mean differences were never greater than 5.5Delta, 95% agreement intervals were as wide as +/-8.00Delta for NFV and +/-13.19Delta for PFV. CONCLUSIONS: The two methods used to measure fusional vergences showed fairly good inter-session repeatability for measuring NFV but repeatability was reduced for PFV measurements. The level of agreement observed between the two methods was such that their interchangeable use in clinical practice is not recommended.     

Crossed and uncrossed stereoacuity at distance and the effect from heterophoria

BACKGROUND: Previous studies have found that crossed disparities give better stereoacuity than uncrossed. When near phoria is considered, exophores had a better crossed stereoacuity and esophores had a better uncrossed stereoacuity. The current study investigated the effect of heterophoria on distant crossed and uncrossed stereoacuity. METHODS: Seventy-two subjects were recruited and their distant heterophoria measured. Heterophoria within two prism dioptres was considered as orthophoric. Esophoric group had esophoria greater than two prism dioptres. Exophoric group had exophoria greater than two prism dioptres. There were 40 orthophores, 23 exophores and nine esophores. Their stereoacuity was measured with a three-rod apparatus at 6 m. RESULTS: The mean crossed stereoacuity was 4.8" and uncrossed stereoacuity was 7.2" (t = -3.03, p < 0.01). The mean stereoacuity for orthophoric subjects was 5.31", 6.02" for exophores and 8.91" for esophores. The distant crossed stereoacuity is better than uncrossed stereoacuity in all three groups but the difference is only significant for the exophores. Exophoric subjects demonstrated a significant difference between crossed (4.10") and uncrossed (7.95") stereoacuity. CONCLUSIONS: Orthophores have the best stereoacuity, followed by exophores and esophores. Exophoric subjects have a better crossed than uncrossed stereoacuity. More esophoric subjects should be recruited to confirm the difference between crossed and uncrossed stereoacuity.     

融像性聚散功能障碍者观看3D影像后视疲劳和动眼参数的变化

目的　观察融像性聚散功能障碍者在观看３Ｄ影像后动眼参数的变化情况,并探讨其与视疲劳的相关性。方法　本研究为病例对照研究,选取３７名青年受试者,按其融像性聚散能力分为２组:视功能正常（ｎｏｒｍａｌｖｉｓｕａｌｆｕｎｃｔｉｏｎ,ＮＶＦ）组２１人,融像性聚散功能障碍（ｆｕｓｉｏｎａｌｖｅｒｇｅｎｃｅｄｙｓｆｕｎｃｔｉｏｎＦＶＤ）组１６例。两组受试者观看４０ｃｍ处３Ｄ影像前和观影１ｈ后分别行动眼参数的测量,包括单眼调节幅度、梯度性调节性集合／调节（ａｃｃｏｍｍｏｄａｔｉｏｎｃｏｎｖｅｒｇｅｎｃｅ／ａｃｃｏｍｍｏｄａｔｉｏｎ,ＡＣ／Ａ）值、观看距离所对应的近距隐斜量、融像幅度以及视疲劳的主观问卷。结果　两组人观看３Ｄ影像后均出现视疲劳,ＦＶＤ组视疲劳问卷得分高于ＮＶＦ组（Ｐ＝０．０１２）。ＮＶＦ组观影前后的单眼调节幅度分别为（１２．４９±１．３７）Ｄ、（１２．０７ ±１．３１）Ｄ;近距隐斜量分别为－３．０２△ ±１．７０△、－４．７１△ ±１．５１△,差异均有统计学意义（均为Ｐ＜０．００１）;融像幅度分别为５１．８１△ ±６．９３△、５０．９０△ ±７．５７△,差异无统计学意义（Ｐ＝０．０５９）。ＦＶＤ组观影前后的单眼调节幅度分别为（１２．３３±１．７０）Ｄ、（１１．６６±１．８１）Ｄ;近距隐斜量分别为－３．１３△ ±２．３１△、－４．４１△ ±２．５９△,差异均有统计学意义（均为Ｐ＜０．００１）;融像幅度分别为３７．７５△ ±６．７２△、３４．２５△ ±７．３７△,差异有统计学意义（Ｐ＜０．００１）。ＮＶＦ组与ＦＶＤ组观影前后ＡＣ／Ａ均未发生显著性变化（Ｐ＝０．６３１,Ｐ＝０．２４５）。观影前后单眼调节幅度改变量、近距隐斜量改变量、ＡＣ／Ａ改变量在ＮＶＦ组和ＦＶＤ组间差异均无统计学意义（均为Ｐ＞０．０５）,且所有受试者观影前后近距隐斜量改变量与视疲劳程度无相关性（ｒｓ＝０．０２１,Ｐ＝０．９０４）。而观影前后融像幅度的改变量在ＮＶＦ组－１．００△（－２．５０△ ～１．５０△）和ＦＶＤ组－３．５０△（－５．００△ ～－２．２５△）间差异有统计学意义（Ｐ＝０．００１）。结论　观看３Ｄ影像会导致视疲劳及单眼调节幅度、近距隐斜量和融像幅度的变化;融像性聚散障碍者较视功能正常者观影后融像幅度下降更明显,视疲劳更严重。融像幅度可作为预测和评估观影像后视疲劳程度的一项指标。     

聚散灵敏度与融像性聚散的相关性研究

目的 探讨聚散灵敏度与融像性聚散的相关性,为临床聚散系统异常的诊断提供更直接、更有意义的指标.方法 临床病例自身对照研究.对2012年10～12月在天津医科大学眼科中心志愿随机抽取50名20～28周岁在校近视大学生,应用电脑验光仪和综合验光仪行规范验光后,在屈光不正全矫的基础上分别进行聚散灵敏度检测和融像性聚散检测,并利用Flashed Von Graefe法测量视近隐斜,利用SPSS 13.0统计软件对相关数据进行分析,确定聚散灵敏度与融像性聚散的相关性.结果 (1)视近隐斜偏高组(＞6EXO)和视近隐斜正常组(0-6EXO)的聚散灵敏度差异显著有统计学意义(P＜0.05),而融合性聚散(BI)恢复点数值差异无统计学意义(P＞0.05).(2) BI模糊点和破裂点与聚散灵敏度无相关性,而其恢复点与聚散灵敏度有相关性.结论 可以通过被检者的恢复点数值推测患者的聚散灵敏度是否异常,可使聚散检测中恢复点数据得到充分的使用,从而减少了专项的聚散灵敏度检查,使双眼视异常的诊断更为简便.     

LASIK前后水平隐斜度的对比研究

目的 探讨LAISK对近视患者水平隐斜度的影响.方法 对行LASIK术患者45例(90只眼),应用综合验光仪用Von Grafefa法分别测量手术前、后视远及视近的水平隐斜度,将所得数据用单因素方法及t检验进行统计学分析.结果 术前戴镜与术后1月、3月裸眼的水平隐斜度比较,差异均无显著性(P＞0.05).术前戴镜视近时,中、低度近视组与高度近视组相比较,水平隐斜度差异有显著性(P＜0.05).结论 LASIK手术对患者的视远及视近水平隐斜度无明显影响.     

The effects of sustained vertical gaze deviation on the resting state of the vergence system

Vergence of the eyes in the dark depends on the vertical direction of gaze. In three experiments this phenomenon was studied using eye inclinations and head tilts of 5 min duration during which monocular or binocular near and distant stimuli were inspected. The effects of eye inclination and head tilt on dark vergence were temporally stable; they exhibited even a tendency to increase with the passage of time. On return to horizontal gaze, positive aftereffects were found, that is dark vergence was biased towards its value with a vertically deviated gaze. The effect of vertical gaze direction turned out to be additive to the effect of binocular near fixation. These findings represent evidence against the hypothesis that the effect of vertical gaze direction on dark vergence is mediated by a feedforward signal that is related to voluntary effort in raising or depressing the eyes.     

Static vergence and accommodation: population norms and orthoptics effects

The steady-state characteristics of the accommodation and vergence systems can be described by a model with six major oculomotor parameters. These include the system biases (tonic vergence and accommodation) and forward-loop gains (vergence and accommodative gains), as well as the interactive system gains (AC/A and CA/C ratios). We investigated these parameters in two populations: (1) 22 visually-normal asymptomatic individuals, and (2) 21 visually-abnormal symptomatic individuals before and after conventional orthoptic therapy. Two parameters related to system gain differentiated between the symptomatic and asymptomatic individuals: the slope of the fixation disparity curve with accommodation open-looped and the slope of the accommodative response/stimulus curve. Following orthoptic therapy, 4 static model parameters and 1 dynamic clinical parameter showed changes toward the normal mean; this included tonic accommodation, slope of the fixation disparity curve with accommodation closed-loop (2.5D), slope of the accommodative response/stimulus curve, the CA/C ratio, and the ± 2D monocular accommodative flipper rate.     

近距隐斜视与屈光不正的关系研究

目的 探讨近距隐斜视的发生、类型与屈光不正的关系.方法 连续收集近距隐斜视患者267例,男145例,女122例,年龄(8.05+5.0)岁(3～44岁),分别进行近距隐斜视检测,静态检影.结果 正视者63例,其中发生近距外隐斜60例,近距内隐斜3例,近距外隐斜所占比重明显高于内隐斜(P=0.000).近距内隐斜47例,其屈光状态构成分别为正视和近视各3例,远视41例;近距外隐斜220例,其屈光状态构成分别为正视60例,近视64例,远视96例,经卡方检验,近距隐斜视类型与屈光状态有关(X2=29.47,P=0.000).就137例远视患者而言,发牛近距内隐斜41例,其不同程度屈光构成分别为轻度远视12例,中度远视18例,重度远视11例;发生近距外隐斜96例,其不同程度屈光构成分别为轻度远视56例,中度远视27例,重度远视13例,经卡方检验,对远视患者而言,近距隐斜视类型与远视的程度有关(X2=16.61,P=0.000),近距内隐斜多发生于中度远视,而近距外隐斜多发生于轻度远视.结论 近距隐斜视类型与屈光状态相关,其中近距内隐斜主要为远视眼未经屈光矫正引致;一定范嗣内的近距外隐斜可能是一种,圭理性眼位,而近距内隐斜则可能是一种病理性眼位,并与近视的发生发展相关.     

Quantification of heterophoria and phoria adaptation using an automated objective system compared to clinical methods

Purpose:  To develop a system with which to quantify objectively the heterophoria to be measured throughout eye movement experiments. This study compared precision, resolution and accuracy characteristics of a limbus eye movement tracking system to the alternate cover test and the Maddox rod.
Methods:  Precision testing was performed using each technique with binocularly-normal subjects at different test sessions. Resolution was measured and compared between the three systems. The heterophoria or phoria was measured from 40 cm/16 inches objectively with the limbus eye movement system and the Maddox rod during a sustained convergence-induced phoria adaptation experiment using physical and haploscope visual targets to compare accuracy.
Results:  Precision testing quantified that the responses objectively recorded using the limbus tracking system exhibited similar standard deviations to the Maddox rod and the alternate cover test techniques. The limbus tracking method has the ability to quantify the response decay to phoria and has better resolution when compared to the clinical methods. When physical targets were used to induce phoria adaptation, the correlation was significant between the limbus eye movement tracking system and the Maddox rod after near and far adaptation, where the Maddox rod measurements were slightly more esophoric compared to those measured with the limbus tracking system.
Conclusion:  This objective limbus tracking system offers a better means by which to study the phoria and its adaptation throughout an eye movement experiment. The broader aim of this research is to establish a tool that will further the basic science of oculomotor control and binocular dysfunctions.     

Changes in the interpupillary distance with age and its effect on the near fusion free position

Purpose: The effect of the rate of the interpupillary distance (IPD) change with age on the near fusion free position was investigated in the present study. Methods: Three hundred and fifty-two children aged from 2 to 16 years of age were tested. Interpupillary distance was estimated with a modified Viktorin's method and the near fusion free position was measured with a modified Maddox Wing. Results: The results reveal a significant difference in IPD growth rate between females and males and between children aged below and above 5 years. Most children below 5 years of age were orthophoric, but heterophoria became more common above 5 years of age. Conclusion: The present study suggests that the oculomotor control system for convergence can compensate for age changes in IPD.     

Comparison of vergence mechanisms between university students with good and poor sleep quality

AIM: To compare the vergence mechanisms between good and poor sleepers in university students. METHODS: A total of 64 university students were recruited in this study. The validated Malay version of Pittsburgh Sleep Quality Index questionnaire (PSQI-M) was used to measure the participants’ sleep quality over the past month. Participants were categorized as good sleepers (n=32) and poor sleepers (n=32) based on the PSQI-M scores. Heterophoria and fusional vergences were measured at distance and near. Mann-Whitney U test was used to compare heterophoria, negative fusional vergence (NFV), and positive fusional vergence (PFV) at distance and near between good and poor sleepers. Spearman correlation analysis was used to study the relationship between PSQI-M score and PFV at distance. RESULTS: Both distance and near heterophorias were not significantly different between good and poor sleepers (P>0.05). There was a difference in distance PFV (P<0.05) between good and poor sleepers, but not in distance NFV, near NFV, and near PFV (P>0.05). Distance PFV was negatively correlated with PSQI-M score (rs=-0.33, P<0.05). CONCLUSION: University students with poor sleep quality demonstrates a reduced ability to maintain fusion with increasing convergence demand at distance. Sleep quality assessment during binocular vision examination in university students is recommended.     

A comparison of the Red Plate Test and the Free-Space Near Phoria Card Test for heterophoria

Near lateral heterophoria and the gradient AC/A ratio were measured in 67 children (34 male and 33 female) using both the Red Plate Test and the Free-Space Near Phoria Card Test and the results were compared. Correlation between the two tests was 0.6128 for heterophoria measurements and 0.4385 for AC/A ratio measurements. Paired t-test showed significant differences between the tests in both heterophoria (t = 5.01, p < 0.01) and AC/A ratio (t = -7.07, p < 0.01) measurements.     

Effects of age, viewing distance and target complexity on static ocular counterroll

The ocular counterroll (OCR) reflex generates partially compensatory torsional eye movements during static head roll tilt. We assessed the influence of age, viewing distance and target complexity on the OCR across the age span (13-63 years; n = 47), by recording eye movements during head-on-body roll tilt (0 ± 40° in 5° steps) while subjects viewed simple vs. complex targets at 0.33 and 1 m. We found that subjects ?31 years had lower gains than those ?30 years, but only for far targets. Consistent with prior reports, far targets elicited higher OCR gains than near targets, and target complexity had no effect on gains, suggesting that visual input is primarily used to maintain vergence during OCR.     

近视学生的水平隐斜及屈光矫正对隐斜的影响

目的:了解近视学生同正常学生水平隐斜的差异,不同近视程度学生隐斜度的变化,屈光矫正对隐斜的影响。方法:采用隐斜仪(Maddox杆旋转三棱镜)测定825名青少年学生的远近隐斜度,比较近视与正常学生的隐斜发生率,再将近视学生按近视程度、矫正情况分类、分组,分别同正常学生进行隐斜度比较。结果:远外隐斜发生率:正常学生19.8%,近视学生28.8%;近外隐斜发生率:正常学生52.9%,近视学生64.7%。远隐斜均值:正常学生为1.97△;低、中、高度近视全体学生分别为1.76△,1.33△,-0.68△;矫正足度组分别为2.11△,1.75△,0△;不矫正组(低、中度近视)分别为1.29△,-0.78△。近隐斜均值:正常学生为-0.67△;低、中、高度近视全体学生分别为-2.43△,-3.02△,-5.71△;矫正足度组分别为-1.20△,-2.28△,-4.06△;不矫正组(低、中度近视)分别为-3.28△,-5.06△。近隐斜度产生显著差异的屈光度界线有两处:(1)-0.75～-2.00D,(2)-6.00D;矫正足度后仅有一处:-3.00～-6.00D。远隐斜度产生显著差异的屈光度界线有一处:-3.00～-6.00D;矫正足度后消失。结论:近视学生比正常学生外隐斜显著增多。学生近视如不矫正或矫正不足,对近隐斜度的影响在低度近视就已非常显著,对远隐斜度的影响是近视程度越高影响越大。