Comitant strabismus

This review reports on articles written on comitant strabismus during the past year. Congenital esotropia was a recurring theme in these publications. Included in this review are articles that provide an insight into the basis for motor epiphenomena such as optokinetic nystagmus asymmetry and latent nystagmus. The optimum window of opportunity to achieve quality binocular vision by surgical alignment in congenital esotropia is discussed. We also report on articles that address various aspects of the management of comitant strabismus including the amount of medial rectus recession for esotropia, the target angle for best results in accommodative esotropia with high accommodation convergence/accommodation ratio, and issues related to comitant exotropia.     

Should accommodative strabismus be operated on?]

Hypermetropia is probably not the real cause of accommodative squint. The arguments for this view are the absence of binocular vision in more than half and of the presence of a vertical deviation in about one third of cases of accommodative strabismus. Furthermore, after reduction of this vertical deviation by means of simultaneous surgery upon the horizontal and oblique muscles, binocular vision recovers spontaneously, the accommodative component of the squint disappears and visual acuity improves without glasses. Recent neurophysiologic research explains the beneficial effect of simultaneous surgery. According to these investigations there are two systems of accommodation and convergence; a quick phasic one, where accommodation is linked with convergence and a slow tonic one without interaction. The tonic system is responsible for the neutralization of the excess of convergence induced by hyperaccommodation. Tonic vergence depends on fixation disparity which is eliminated by a vertical deviation and restored by the surgical reduction of this vertical deviation. The fact of wearing positive correction produces and consolidates a hypo-accommodation, revealing a latent hypermetropia which could compromise emmetropisation. Furthermore, this correction being associated with squint, is a source of psychological complexes and the cost of an optical treatment is high, considering that spectacles need to be renewed frequently and many times during lifetime. On the other hand, simultaneous surgery removes an important obstacle to fusion and makes the patient independent of spectacles, not only regarding the squint, but also visual acuity.     

汉语发展性阅读障碍儿童调节功能与眼位的研究

目的 探讨汉语发展性阅读障碍儿童与正常儿童调节功能与眼位各参数的变化,明确影响汉语发展性阅读障碍儿童视觉效率的关键视觉因素.方法 病例对照研究.选取天津市12所小学五年级学生1458名.根据识字量和瑞文智力的测验结果,筛选出98名汉语发展性阅读障碍儿童为试验组,随机选取年龄、性别、瑞文智力与之匹配的98名正常儿童为对照...     

Exotropia associated with defective accommodation

Despite the close association of convergence and accommodation, accommodative dysfunction is not often associated etiologically with exotropia. We studied 13 adolescent and young adults having intermittent exotropia and severely reduced accommodative function. Most patients had a prolonged history of visual symptoms that had not responded to therapy in the past. Clinical testing indicated that the patients had severely reduced amplitudes of accommodation and difficulty sustaining accommodation. Exotropia was manifest when the accommodative response was inadequate; relative orthophoria existed when the accommodative response was adequate. Treatment of the accommodative defect as well as the strabismus was successful for some patients. We recommend careful evaluation of accommodation for adolescent and young adults with exotropia to rule out an accommodative defect as a contributing cause.     

飞秒激光制瓣LASIK术对近视性屈光参差患者调节功能的影响

目的：探讨飞秒激光制瓣LASIK术对屈光参差患者调节功能的影响。

方法：采用系列病例观察试验设计。收集行飞秒激光制瓣LASIK术的近视性屈光参差患者35例70眼,分别于术前和术后1、3mo进行随访观察,检测裸眼远视力、远用等效球镜度、双眼屈光度差值、单眼调节幅度、正负相对调节、调节滞后量。

结果：术后1、3mo的裸眼远视力明显提高,远用等效球镜度、双眼屈光度差值较术前明显降低; 术后3mo的单眼调节幅度和正相对调节较术前戴镜明显提高(P<0.05); 术前戴镜、术后1mo裸眼、术后3mo裸眼的负相对调节、调节滞后量差异无统计学意义(P>0.05)。

结论：飞秒激光制瓣LASIK术治疗近视性屈光参差是一种安全有效的术式,手术未对患者的调节功能产生不良影响,可能有助于恢复双眼协调一致的调节功能。     

Eyestrain induced by stereogram on 3-D display--differences between types of correction

PURPOSE: We investigated eyestrain in normal subjects induced by gazing at a random-dot stereogram on a parallax barrier system 3-D display. METHODS: The 41 subjects were divided into 4 groups according to the type of correction. Near point of accommodation, accommodative relaxation, and contraction times were measured with an accommodo-polyrecorder before and after a stereoscopic visual load, and 15 min and 30 min after a rest. The subjective symptoms were assessed by a 7-point rating questionnaire at the same time as the measurements. RESULTS: After 15 min of sustained visual load, the near point of accommodation was prolonged significantly in the groups without correction and with soft contact lenses(SCL), and accommodative contraction and relaxation times were significant delayed in the groups without correction, with hard contact lenses(HCL), and with SCL but not in the group with spectacles. These changed values of accommodation returned to their previous value following the rest. Significant increase in the rating questionnaire was found in the subjective symptoms of "eyestrain", "eye heaviness", "clouding", "eye dryness" and "irritation of eyes" after loading in the groups without correction, with HCL, and with SCL. In the spectacle group, there was no significant change in the subjective symptoms of "clouding" and "eye dryness". CONCLUSION: From these results, it is concluded that gazing at stereoscopic images on the parallax barrier system 3-D display causes severer eyestrain in cases of correction with contact lenses and in uncorrected cases than in cases with spectacles.     

Clinical method for measuring adaptation of tonic accommodation and vergence accommodation

Previous work indicates that tonic adapters of accommodation and vergence have indirect effects on accommodative vergence and vergence accommodation and that these crosslink responses interact with one another to produce clear and single vision. Clinical measurements of tonic accommodation, tonic vergence, vergence accommodation (CA/C ratio), and accommodative vergence (AC/A ratio) are therefore of value in determining possible binocular vision abnormalities. Currently, clinical methods are only available for measuring the tonic vergence (phoria) and the AC/A ratio. We have determined a fast and accurate method for evaluating both tonic accommodation (accommodative phoria) and vergence accommodation (CA/C ratio). In both procedures, the loop of accommodation was opened with a 0.2 cpd difference of Gaussian (DOG) target. This target was found to be incapable of stimulating any reflex accommodation, yet it is localized in space and can easily stimulate binocular fixation. Our results indicate that opening the loop of accommodation with a pinhole Maxwellian view or with a 0.2 cpd DOG produces similar response values for tonic accommodative aftereffects and vergence accommodation responses. The decay rate of tonic accommodative aftereffects as well as changes in the resting focus of accommodation caused by vergence accommodation (CA/C) can be measured clinically using dynamic retinoscopy in combination with the DOG target. Clinical values of the CA/C ratio obtained with these techniques were highly correlated (r = 0.92) with laboratory measures obtained with an objective infrared optometer and eye trac monitor.     

Experimental evidence for separate mechanisms mediating accommodative vergence and vergence accommodation

An experiment is described which qualitatively measures the state of accommodative vergence under binocular viewing conditions. Results show that under conditions of forced vergence, accommodative vergence maintains a value considerably different from vergence accommodation. These results indicated that accommodative vergence and vergence accommodation are mediated by separate neural processes.     

影响屈光性调节性内斜视立体视锐度发育因素分析

目的分析影响屈光性调节性内斜视患者立体视锐度发育的因素。方法对100例屈光性调节性内斜视按斜、弱视常规戴镜的原则进行治疗;采用同视机测量斜视度数;用颜少明的立体视觉检查图测量近立体视锐度。结果屈光性调节性内斜视患者发病年龄越小、戴镜前斜视度越大、两眼视力差距越大,立体视锐度的发育越差。结论屈光性调节性内斜视患者的立体视锐度发育与发病年龄、戴镜前斜视度、两眼视力有关。     

Serial measurements of accommodation by open-field Hartmann–Shack wavefront aberrometer in eyes with accommodative spasm

Purpose

To investigate the serial changes of accommodation and spherical aberration in eyes with accommodative spasm.

Methods

Four patients with accommodative spasm and ten healthy subjects were studied. The ocular refractive power (spherical equivalent) and spherical aberration were measured serially with an open-field, binocular Hartmann–Shack wavefront aberrometer. Patients and subjects wore full-correction lenses and were instructed to fixate a target set at 50?cm from the eye. The time-average of the refractive power, spherical aberration, and fluctuations of accommodation analyzed by the fast Fourier transform (FFT) of the two groups were compared.

Results

The average?±?standard deviation refractive power in the patients was significantly more negative than that in the healthy subject (?3.12?±?1.06 vs. ?1.49?±?0.17?D). The integrated intensity of the FFT from 1 to 4?Hz was significantly higher in the patients than in the healthy subjects. The spherical aberration in patients was more negative than that in the healthy subjects (?0.033?±?0.048?μm vs. 0.002?±?0.027?μm).

Conclusions

Eyes with accommodative spasm are characterized by a lead of accommodation with greater fluctuations and negative spherical aberrations. Excessive accommodation can be measured objectively in such eyes with a binocular wavefront aberrometer without cycloplegics.     

The binocular accommodative response in uncorrected ametropia.

PURPOSE: To measure the changes in astigmatism and in the degree of anisometropia when ametropes respond to accommodative stimulation. METHODS: The accommodative responses of ametropes were binocularly measured with an improved photorefractometer (PR-1100), which objectively measured binocular refraction in all meridians simultaneously, when a visual fixation target was shown in natural space at 5 and 0.5 m. RESULTS: (1) Changes of astigmatism and anisometropia occur during binocular accommodation. (2) Changes of astigmatism mainly result from lag of accommodation in the horizontal meridian. (3) Changes of anisometropia result from the effort to focus. (4) The interaction of both eyes is suggested as the cause of the changes of astigmatism and anisometropia with accommodation. (5) In the majority of strong anisometropes (nonoverlapping group in this paper), the magnitude of anisometropia decreases (approaching isometropia) with accommodation. CONCLUSION: Changes in astigmatism and anisometropia can occur during accommodation, and these interactions of both eyes with accommodation may contribute to the development and maintenance of binocular function.     

Strabisme Alternant - Etude clinique - traitement

The author defines motor and sensory alternation: the term alternation should not be used in isolation, it should always be accompanied by the name of the parameter concerned. Sensory alternation is always found together with motor alternation but the reverse is not true.The examining criteria for a diagnosis of sensory alternation are given, sensory alternation must not be confused with alternating inhibition. Working from clinical observations of cases of motor alternating strabismus, the author selects 2 types of binocular sensory relations which allow one to differentiate between:- cases of primary alternating strabismus- cases of secondary alternating strabismusThese forms will develop in different ways; in both cases a cure is possible providing that the right treatment is prescribed and once prescribed carefully followed, etc. It is always a case of serious forms of strabismus whose developmental period is spread over several years.According to the authors, the frequency of cases of true primary strabismus is from 1–3%, the frequency of cases of secondary alternating strabismus varies according to the type of therapy practised on cases of monocular strabismus with amblyopia. These latter will become cases of alternating strabismus under the influence of certain types of therapy carried out over several years (penalization, rocking, alternated occlusion, etc...).Experimental data on kittens confirm clinical data; kittens placed in abnormal environments during the sensitive period will show modification in the distribution of cortical cells and the absence of binocular cells (either because the excitation of the two eyes was not simultaneous, or not identical: artificial strabismus, occlusion, opaque glasses). This disturbances become irreversible after a certain period of exposure (a function of age, length of exposure, etc...).It is thus necessary to bear in mind: 1) the iatrogenic risks of certain orthoptic treatments, 2) the necessity for a binocular form of treatment as soon as possible, as once a certain stage is passed, cortical plasticity diminishes and the elaboration of normal binocular relations becomes impossible.

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Accommodation functions: co-dependency and relationship to refractive error

We assessed the extent to which different accommodative functions are correlated and whether accommodative functions predict the refractive error or the progression of myopia over a 12 month period in 64 young adults (30 myopes and 34 non-myopes). The functions were: amplitude of accommodation; monocular and binocular accommodative facility (6 m and 40 cm); monocular and binocular accommodative response to target distance; AC/A and CA/C ratios, tonic accommodation (dark focus and pinhole), accommodative hysteresis, and nearwork-induced transient myopia. Within groups of related accommodative functions (such as facility measures or open-loop measures) measurements on individuals were generally significantly correlated, however correlations between functions from different groups were generally not significant. Although accommodative amplitude and pinhole (open loop) accommodation were significantly different in myopes than in non-myopes, these functions were unrelated to myopia progression. Facility of accommodation and accommodative lag was independent predictors of myopia progression.     

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.     

部分调节性内斜视屈光状态与双眼单视功能的相关性研究

目的研究部分调节性内斜视患儿的屈光状态与双眼单视功能的相关性。 方法回顾性分析36例部分调节性内斜视患儿，对患儿裸眼视力、矫正视力、阿托品散瞳后的屈光度数、戴镜半年的远近残余斜视度及双眼单视功能等进行记录和统计学分析。左右眼等效球镜用配对秩和检验比较，右眼等效球镜与视力、斜视度和视功能的相关性采用Spearman分析。 结果36例部分调节性内斜视患儿年龄3~14岁，平均(79.39±31.21)个月，右眼等效球镜(+4.45±1.73)D，左眼等效球镜(+4.75±1.68)D；33 cm裸眼斜视度(+53.19±18.05)△，6 m裸眼斜视度(+47.50±19.00)△；33 cm残余斜视度(+30.36±12.03)△，6 m残余斜视度(+25.53±9.59)△。右眼等效球镜与同视机Ⅰ级、Ⅱ级和Ⅲ级视功能无相关性(r＝-0.012，-0.058，-0.016；P>0.05)。右眼等效球镜与33 cm裸眼斜视度呈正相关(r＝0.344，P<0.05)，与裸眼视力呈负相关(r＝-0.456，P<0.05)。33 cm裸眼斜视度与同视机Ⅰ级、Ⅱ级和Ⅲ级功能均呈负相关(r＝-0.378，-0.678，-0.482；P<0.05)，与Titmus立体图亦呈负相关(r＝-0.477，P<0.05)。6 m裸眼斜视度与同视机Ⅰ级、Ⅱ级和Ⅲ级功能均呈负相关(r＝-0.453，-0.610，-0.430；P<0.05)。33 cm残余斜视度与同视机Ⅱ和Ⅲ级功能均呈负相关(r＝-0.651，-0.600；P<0.05)，与Titmus立体图、立体动物和立体圆圈亦呈负相关(r＝-0.688，-0.625，-0.462；P<0.05)。6 m残余斜视度与同视机Ⅱ和Ⅲ级功能均呈负相关(r＝-0.587，-0.543；P<0.05)，与Titmus立体图、立体动物和立体圆圈亦呈负相关(r＝-0.644，-0.514，-0.492；P<0.05)。 结论部分调节性内斜视患儿的屈光状态与双眼单视功能不相关，与裸眼视力负相关。影响双眼单视功能的是残余斜视度。     

Normative study of accommodative facility in elementary schoolchildren

Although accommodative facility testing is used widely in the evaluation of accommodation in children, published normative data are not available for this age group. Current values being used are based upon studies of adult populations. In order to establish norms, 542 elementary schoolchildren were screened. Those that passed a specific set of criteria were included in the accommodative facility assessment. We used a new target and instructional set, which took into consideration the problems associated with subjective testing of young children. The results revealed lower mean accommodative facility values for both monocular and binocular accommodative facility than the values obtained previously from adult populations. These new findings can be used as a clinical guide to evaluate accommodative facility in young children.     

压贴三棱镜辅助治疗部分调节性内斜视儿童的临床观察

目的探讨压贴三棱镜在儿童部分调节性内斜视治疗中的应用及效果。方法对53例3～13岁部分调节性内斜视患儿,在全部屈光矫正的基础上,依据同视机及三棱镜检查结果,配戴压贴三棱镜矫正残余斜视度,观察3～6月后,在配戴压贴三棱镜状态下,斜视度矫正及双眼视功能改善情况。结果配戴压贴三棱镜后,患儿残余斜视度矫正,双眼视功能改善,改善率在年龄≤6岁组（81.58%）高于〉6岁组（46.67%）（χ2=6.46,P〈0.05）。结论压贴三棱镜在临床部分调节性内斜视的治疗中,可以矫正残留斜视度,帮助重建双眼视功能,且年龄越小,效果越好。     

Accuracy of accommodation in heterophoric patients: testing an interaction model in a large clinical sample

A model of the cross-link interactions between accommodation and convergence predicted that heterophoria can induce large accommodation errors (Schor, Ophthalmic Physiol. Opt. 1999;19:134-150). In 99 consecutive patients with intermittent tropia or decompensated phoria, we tested these interactions by comparing their accommodative responses to a 2.50-D target under binocular fused conditions (BFC) and monocular occluded conditions (MOC). The accommodative response in BFC frequently differed from that in MOC. The magnitude of the accommodative errors in BFC, ranging from an accommodative lag of 1.80 D (in an esophoric patient) to an accommodative lead of 1.56 D (in an exophoric patient), was correlated with distance heterophoria and uncorrected refractive errors. These results indicate that heterophoria affects the accuracy of accommodation to various degrees, as the model predicted, and that an accommodative error larger than the depth of focus of the eye occurs in exchange for binocular single vision in some heterophoric patients.     

Strabismus management

In this article, three topics of current interest in strabismus are covered. These include strabismus after glaucoma implant surgery, management of accommodative esotropia, and the timing of treatment for strabismic amblyopia. Glaucoma implants have improved our results with difficult glaucoma syndromes, however, a high incidence of postoperative strabismus has been associated with this procedure. The mechanism of the strabismus has not been clearly defined in previous literature, but in this article we describe three mechanisms that cause strabismus after glaucoma implant surgery and describe methods for managing this problem. The standard management of accommodative esotropia has historically resulted in a large number of undercorrections. Patients with accommodative esotropia have good fusion potential as the strabismus is acquired and binocular visual development occurred during the critical period. Recent studies indicate that we should increase our surgical numbers when managing patients with accommodative esotropia. Various treatment strategies are covered in the section on accommodative esotropia. Finally, a discussion on the management of strabismic amblyopia is presented. The importance of treating amblyopia first, then secondarily correcting the strabismus is emphasized.     

Motion VEPs, stereopsis, and bifoveal fusion in children with strabismus

PURPOSE: The link between nasal-temporal motion asymmetries and anomalous binocular sensory function in infantile esotropia (ET) has led to the idea that visual evoked potential responses to horizontal motion (mVE) is an alternative measure of sensory binocularity to stereopsis. A second hypothesis is that the mVEP response is a marker for bifoveal fusion. The purpose of this study was to directly evaluate these two hypotheses by examining the correspondence between the mVEP response and both stereoacuity and bifoveal fusion in a cohort of strabismic patients with variable binocular sensory function. METHODS: Motion VEPs, random dot stereopsis, and bifoveal fusion were measured in 94 children: 20 with infantile ET, 16 with infantile accommodative ET, 22 with late-onset accommodative ET, 10 with intermittent infantile strabismus, and 26 normal control participants. RESULTS: Patients with infantile ET and infantile accommodative ET had high concordance between mVEP responses and stereoacuity and mVEP responses and bifoveal fusion. Asymmetric mVEP responses were highly concordant with both no measurable stereopsis and an absence of fusional vergence. Patients with late-onset accommodative ET and intermittent infantile strabismus revealed discordance between the mVEP response and stereoacuity and high concordance between the mVEP response and bifoveal fusion. Asymmetric mVEP responses were highly concordant with the absence of bifoveal fusion and the minimum-size prism to elicit fusional vergence. CONCLUSIONS: The qualitative and quantitative relationship between the mVEP response and fusional vergence suggests that the mVEP response is an objective measure of bifoveal fusion. The availability of such a test will facilitate studies of normal development of bifoveal fusion and development of monofixation syndrome in strabismus.