Intermittent Distance Exotropia Research Articles

Intermittent Divergent Squint in Prematurity and Its Neurophysiological Aspects.

Intermittent distance exotropia is a deviation characterized by an exophoria at near fixation and manifest exotropia at distance fixation. There is normal binocular fusional vergence and stereoacuity at near fixation, but the eyes tend to diverge in bright sunlight, tiredness, day dreaming and the patient may close one eye in such circumstances. Prematurity is associated with numerous eye pathology, besides retinopathy of prematurity, amblyopia, refractive errors, it is also associated with a higher risk esotropia and exotropia. We report a case of a 5-year-old girl (preterm and very low birth weight) with an intermittent deviation of both eyes since three years. On her detailed ocular examination diagnosis of divergence excess intermittent exotropia with normal accommodative convergence to accommodation ratio was made. Bilateral lateral rectus recession was done using hang back technique. Postoperatively, the eyes were aligned normally thereby achieving orthotropia. This article reviews various neurophysiological aspects of intermittent divergent squint delineating the etiopathogenesis, classification system, and management options in intermittent exotropia.

Treating childhood intermittent distance exotropia: a qualitative study of decision making.

BackgroundEngaging patients (parents/families) in treatment decisions is increasingly recognised as important and beneficial. Yet where the evidence base for treatment options is limited, as with intermittent distance exotropia (X(T)), this presents a challenge for families and clinicians. The purpose of this study was to explore how decisions are made in the management and treatment of X(T) and what can be done to support decision-making for clinicians, parents and children.MethodsThis was a qualitative study using face to face interviews with consultant ophthalmologists and orthoptists, and parents of children with X(T). Interview data were analysed using the constant comparative method.ResultsThe drivers for clinicians in treatment decision-making for X(T) were the proportion of time the strabismus is manifest and parents’ views. For parents, decisions were influenced by: fear of bullying and, to a lesser degree, concerns around the impact of the strabismus on their child’s vision. Uncertainty around the effectiveness of treatment options caused difficulties for some clinicians when communicating with parents. Parental understanding of the nature of X(T) and rationale for treatment often differed from that of the clinicians, and this affected their involvement in decision-making. Though there were good examples of shared decision-making and parent and child engagement some parents said the process felt rushed and they felt excluded. Parents reported that clinicians provided sufficient information in consultations but they had difficulties in retaining verbal information to convey to other family members.ConclusionsOverall parents were happy with the care their child received but there is scope for better parent and (where appropriate) child engagement in decision-making. There was an expressed need for written information about X(T) to reinforce what was given verbally in consultations and to share with other family members. Access could be via the hospital website, along with videos or blogs from parents and children who have undergone the various management options. A method of assisting clinicians to explain the treatment options, together with the uncertainties, in a clear and concise way could be of particular benefit to orthoptists who have the most regular contact with parents and children, and are more likely to suggest conservative treatments such as occlusion and minus lenses.Electronic supplementary materialThe online version of this article (doi:10.1186/s12886-015-0087-y) contains supplementary material, which is available to authorized users.

Survey of British and Irish orthoptists in the measurement of the AC/A ratio

Aims: To determine what practising orthoptists consider to be a normal AC/A ratio and on what evidence this is based. To assess which method of measurement is most commonly used and whether the ratio itself contributes to the diagnosis and management of strabismus in current practice. Methods: A prospective cross-sectional survey was designed and distributed to all orthoptists registered with the British and Irish Orthoptic Society (BIOS). The survey was web-based and consisted of 17 questions relating to the measurement of the accommodative convergence/accommodation (AC/A) ratio and its application to clinical practice. Prior to the survey being distributed nationally, a pilot survey was sent to a small group of practising orthoptists for validation. Results: There was a significant difference ( p < 0.05) in orthoptists’ perception of the normal AC/A ratio (gradient and heterophoria) compared with published research. Ninety-three per cent stated that their definition of ‘normal’ was based on either clinical experience or what they were taught during training, with the gradient method at 33 cm being most commonly used (92.79%). The AC/A ratio is widely used (either ‘always’ or ‘sometimes’) in the diagnosis of convergence excess esotropia (CXS) (97.26%) and intermittent distance exotropia (IDEX) (93.75%) and (either ‘always’ or ‘sometimes’) in the management of CXS (88.89%) and IDEX (79.02%). Conclusion: The majority of orthoptists who participated are primarily measuring the stimulus AC/A ratio clinically. There is a discrepancy between participants’ perception of a normal AC/A ratio and published research, yet the ratio is still used in the diagnosis and management of certain types of strabismus.

The Clinical Near Gradient Stimulus AC/A Ratio Correlates Better With the Response CA/C Ratio Than With the Response AC/A Ratio

Aim: To provide evidence that a near clinical gradient AC/A ratio could instead reflect the CA/C relationship (the accommodation driven by response to disparity).Design: Case control study.Methodology: 27 emmetropic participants with heterophoria <4 PD, 19 with intermittent distance exotropia, and 17 with near exophoria >6 PD were tested. A remote haploscopic photorefractor, which can measure simultaneous convergence and accommodation to a range of targets containing all combinations of presence or absence of binocular disparity, blur, and proximal (looming) cues, was used to assess response AC/A and CA/C relationships. These were compared with clinical gradient AC/A ratios at near and distance fixation using alternate prism cover test and plus or minus lenses.Results: Although the near and distance clinical AC/A ratios correlated weakly with each other (p = 0.03), neither clinical method correlated with the more accurate response AC/A ratio from the laboratory method (p = 0.88 and p = 0.93, respectively). The laboratory CA/C ratio correlated strongly with the near clinical AC/A ratio (p = 0.004) but only very weakly with the distance ratio (p = 0.16).Conclusions: The “near gradient AC/A ratio” may actually reflect the CA/C linkage as the dissociation of the prism cover test disrupts vergence accommodation. If the near deviation diverges more with plus lenses, it may be because the lenses allow clear near vision without needing to recruit convergence accommodation to achieve it.

Evidence that convergence rather than accommodation controls intermittent distance exotropia

This study considered whether vergence drives accommodation or accommodation drives vergence during the control of distance exotropia for near fixation. High accommodative convergence to accommodation (AC/A) ratios are often used to explain this control, but the role of convergence to drive accommodation (the CA/C relationship) is rarely considered. Atypical CA/C characteristics could equally, or better, explain common clinical findings. Nineteen distance exotropes, aged 4-11 years, were compared while controlling their deviation with 27 non-exotropic controls aged 5-9 years. Simultaneous vergence and accommodation responses were measured to a range of targets incorporating different combinations of blur, disparity and looming cues at four fixation distances between 2 m and 33 cm. Stimulus and response AC/A and CA/C ratios were calculated. Accommodation responses for near targets (p = 0.017) and response gains (p = 0.026) were greater in the exotropes than in the controls. Despite higher clinical stimulus AC/A ratios, the distance exotropes showed lower laboratory response AC/A ratios (p = 0.02), but significantly higher CA/C ratios (p = 0.02). All the exotropes, whether the angle changed most with lenses ('controlled by accommodation') or on occlusion ('controlled by fusion'), used binocular disparity not blur as their main cue to target distance. Increased vergence demand to control intermittent distance exotropia for near also drives significantly more accommodation. Minus lens therapy is more likely to act by correcting overaccommodation driven by controlling convergence, rather than by inducing blur-driven vergence. The use of convergence as a major drive to accommodation explains many clinical characteristics of distance exotropia, including apparently high near stimulus AC/A ratios.

The improving outcomes in intermittent exotropia study: outcomes at 2 years after diagnosis in an observational cohort

BackgroundThe purpose of this study was to investigate current patterns of management and outcomes of intermittent distance exotropia [X(T)] in the UK.MethodsThis was an observational cohort study which recruited 460 children aged < 12 years with previously untreated X(T). Eligible subjects were enrolled from 26 UK hospital ophthalmology clinics between May 2005 and December 2006. Over a 2-year period of follow-up, clinical data were prospectively recorded at standard intervals from enrolment. Data collected included angle, near stereoacuity, visual acuity, control of X(T) measured with the Newcastle Control Score (NCS), and treatment. The main outcome measures were change in clinical outcomes (angle, stereoacuity, visual acuity and NCS) in treated and untreated X(T), 2 years from enrolment (or, where applicable, 6 months after surgery). Change over time was tested using the chi-square test for categorical, Wilcoxon test for non-parametric and paired-samples t-test for parametric data.ResultsAt follow-up, data were available for 371 children (81% of the original cohort). Of these: 53% (195) had no treatment; 17% (63) had treatment for reduced visual acuity only (pure refractive error and amblyopia); 13% (50) had non surgical treatment for control (spectacle lenses, occlusion, prisms, exercises) and 17% (63) had surgery. Only 0.5% (2/371) children developed constant exotropia. The surgically treated group was the only group with clinically significant improvements in angle or NCS. However, 8% (5) of those treated surgically required second procedures for overcorrection within 6 months of the initial procedure and at 6-month follow-up 21% (13) were overcorrected.ConclusionsMany children in the UK with X(T) receive active monitoring only. Deterioration to constant exotropia, with or without treatment, is rare. Surgery appears effective in improving angle of X(T) and NCS, but rates of overcorrection are high.

Conservative Management of Intermittent Distance Exotropia: A Review

Background and PurposeIntermittent distance exotropia is difficult to conservatively manage, with techniques varying widely between institutions. This review aims to examine current literature on conservative management for intermittent distance exotropia, investigate its impact upon current clinical practice, and identify areas for further research.MethodA literature search was performed using PubMed, Web of Knowledge, LILACS, and the University of Liverpool Orthoptic Journals and Conference Transactions Database. All English-language papers published between 1950 and the present day were considered.ResultsIntermittent distance exotropia is a difficult condition to manage because of its variability/uncertain natural history, although control scores can facilitate management decisions. Research is required to establish recommended dosages for antisuppression occlusion and determine whether other treatments such as minus lenses are more effective. Use of orthoptic exercises has declined, but recently certain exercises have been shown to improve surgical outcomes if applied preoperatively. Prisms are mainly used postoperatively. Minus lens therapy is recommended as a first line treatment, but may not always be successful.ConclusionConservative management techniques for intermittent distance exotropia have their place as both an alternative and an adjunct to surgery. However, further research needs to be conducted to determine which techniques are appropriate for which patients.

Intervention for intermittent distance exotropia with overcorrecting minus lenses

There are numerous treatment options for intermittent distance exotropia. The aim of this study is to evaluate the use of overcorrecting minus lenses as a primary treatment option for intermittent distance exotropia (IDEX) and determine ocular alignment status after 5 years from commencement of the study. Prospective nonrandomised longitudinal cohort study in which 21 patients were recruited with a diagnosis of IDEX. Treatment was instigated with the minimum minus lens required to achieve control of the manifest deviation. The strength of lenses was reduced over time while monitoring the results of orthoptic measurements. The results were evaluated by nonparametric (Wilcoxon) and parametric (paired t-test) analysis. Thirteen female and eight male patients were recruited with a mean age of 5 years at the start of treatment. There was a significant reduction in angle of deviation after treatment. Overcorrecting lenses did not appear to induce myopia. Twenty-four per cent of the patients had a successful outcome, 28% had a good outcome, and 33% required surgery at a later date. Fifty-two per cent of the patients achieved a successful or good outcome with overcorrecting minus lenses alone, and this was maintained for at least 1 year follow-up. Those requiring surgery had been unable to wean out of lenses but had a successful outcome after one procedure. We recommend overcorrecting minus lenses as a primary treatment option for IDEX with the knowledge that surgery, if subsequently required, is safely delayed to an older age without prior loss of binocular vision.

Interventions for intermittent distance exotropia: review.

Management decisions in intermittent distance exotropia vary and lack well-defined clinical guidelines. We undertook a systematic review in an attempt to clarify the effects of various surgical and nonsurgical treatments and to establish the significance of factors such as age with respect to outcome. The review was undertaken in collaboration with the Cochrane Eyes and Vision Group. Electronic and manual searches were undertaken to identify randomised controlled trials of surgical or nonsurgical treatments for intermittent distance exotropia. We also contacted researchers active in this field for information about further published or unpublished studies. There were no language restrictions. Study abstracts identified from the searches were analysed independently by the two reviewers (SR and LG) and marked for inclusion, exclusion, or consideration. Reviewer analysis was compared and full papers for appropriate studies were requested. No randomised controlled trials were found that met our selection criteria. The current literature consists mainly of retrospective reviews. These are difficult to compare and analyse due to variations in definition, intervention criteria, and outcome measures. However, there appears to be an agreement that the nonsurgical treatment is more appropriate in small-angle deviations or as a supplement to surgery. Studies supporting both early and late surgical intervention were found, so the optimal timing of surgical intervention could not be concluded. There is a need for robust clinical trials to improve the evidence base for the management of this condition.

Interventions for intermittent distance exotropia.

The clinical management of intermittent distance exotropia has been discussed frequently in the literature but there is a lack of clarity regarding the indications for intervention, the most effective type and the optimum age at which it should be carried out. The objective of this review is to assess intervention criteria, the effects of various surgical and non-surgical treatments in people with intermittent distance exotropia and to determine the significance of factors such as age with respect to outcome. We searched the Cochrane Central Register of Controlled Trials - CENTRAL (which contains the Cochrane Eyes and Vision Group trials register) on the Cochrane Library (Issue 4 2002), MEDLINE (1966 to November 2002), EMBASE (1980 to November 2002) and LILACS (Latin American and Caribbean Literature on Health Sciences) (1966 to 2002). We manually searched the British Orthoptic Journal, proceedings of the European Strabismological Association (ESA), International Strabismological Association (ISA) and American Academy of Paediatric Ophthalmology and Strabismus meeting (AAPOS). We contacted researchers who are active in the field for information about further published or unpublished studies. There were no language restrictions in the manual or electronic searches. We planned to include randomised controlled trials of any surgical or non-surgical treatment for intermittent distance exotropia. Each reviewer independently assessed study abstracts identified from database and manual searches. Reviewer analysis was then compared and full papers for appropriate studies were obtained. No studies were found that met our selection criteria and therefore none were included for analysis. The available literature consists mainly of retrospective case reviews. These are difficult to compare and analyse due to a large variation in the definition of intermittent distance exotropia, intervention criteria and outcome measures. However there seems to be general agreement that non-surgical treatment is most appropriate in small angle deviations or as a supplement to surgery. Studies were found supporting both early and late surgical intervention so the optimal timing of surgical intervention cannot be concluded. Recent work indicates that bilateral surgery may be the most effective surgical procedure in these cases. There is clearly a need for carefully planned clinical trials to be undertaken to improve the evidence base for the management of this condition.