The use of cues to convergence and accommodation in naive, uninstructed participants

A remote haploscopic video refractor was used to assess vergence and accommodation responses in a group of 32 emmetropic, orthophoric, symptom free, young adults naïve to vision experiments in a minimally instructed setting. Picture targets were presented at four positions between 2 m and 33 cm. Blur, disparity and looming cues were presented in combination or separately to asses their contributions to the total near response in a within-subjects design. Response gain for both vergence and accommodation reduced markedly whenever disparity was excluded, with much smaller effects when blur and proximity were excluded. Despite the clinical homogeneity of the participant group there were also some individual differences

Independent and reciprocal accommodation in anisometropic amblyopia

Accommodation is considered to be a symmetrical response and to be driven by the least ametropic and nonamblyopic eye in anisometropia. We report the case of a 4-year-old child with anisometropic amblyopia who accommodates asymmetrically, reliably demonstrating normal accommodation in the nonamblyopic eye and antiaccommodation of the amblyopic eye to near targets. The abnormal accommodation of the amblyopic eye remained largely unchanged during 7 subsequent testing sessions undertaken over the course of therapy. We suggest that a congenital dysinnervation syndrome may result in relaxation of accommodation in relation to near cues and might be a hitherto unconsidered additional etiological factor in anisometropic amblyopia

What do we expect new graduate orthoptists to do?

Aims: To validate the content of an updated orthoptic curriculum for the British & Irish Orthoptic Society (BIOS), BIOS members were surveyed about their views on what an orthoptist should be able to do soon after entering the profession. Methods: An online survey of all practicing members of BIOS was carried out. In 35 questions across 5 domains (professional behaviour, foundation knowledge and theory, investigation, management and research and literature skills) covering the range of orthoptic practice, orthoptists were asked about the breadth and depth of knowledge required. Results were analysed by the respondents’ working environment, experience, geographical region and teaching involvement. Results: 325 orthoptists (27% of the membership) provided useable data, and 265 provided a full dataset. Orthoptists are frequently required to exercise considerable autonomy and responsibility for patient care from very early in their careers across many domains, often in the least-supervised environments. There was broad agreement across most core topics but wider variation in opinion in more peripheral domains. More experienced orthoptists value the wider medical aspects of orthoptic practice more highly. Conclusions: The survey confirmed that there is generally a good match between current undergraduate teaching and clinicians’ expectations of newly graduated orthoptists. It is clear that training must prepare graduates for a high level of professional autonomy from the earliest stages of their careers. There may be a place for targeting CPD provision for professionals at different stages in their careers

Typical and atypical development of ocular alignment and binocular vision in infants – the background

These pages cover the outcomes of research into the typical motor aspects of development of binocular vision in very early childhood. Separate pages on the clinical Examination of Ocular Alignment and Binocular Vision in Infants under six months of age deals with the their clinical assessment and the recognition of atypical signs. The development and assessment of visual acuity, stereopsis, refraction and the process of emmetropization has a large literature, are only covered here where they affect motor systems. Specific ocular motor anomalies such as esotropia, exotropia, incomitant strabismus, congenital dysinnervation syndromes and paralytic strabismus are also not be covered as their management extends well beyond infancy

Disparity-driven vs blur-driven models of accommodation and convergence in binocular vision and intermittent strabismus

Background. Current models of concomitant, intermittent strabismus, heterophoria, convergence and accommodation anomalies are either theoretically complex or incomplete. We propose an alternative and more practical way to conceptualize clinical patterns. Methods. In each of three hypothetical scenarios (normal; high AC/A and low CA/C ratios; low AC/A and high CA/C ratios) there can be a disparity-biased or blur-biased “style”, despite identical ratios. We calculated a disparity bias index (DBI) to reflect these biases. We suggest how clinical patterns fit these scenarios and provide early objective data from small illustrative clinical groups. Results. Normal adults and children showed disparity bias (adult DBI 0.43 (95%CI 0.50-0.36), child DBI 0.20 (95%CI 0.31-0.07) (p=0.001). Accommodative esotropes showed less disparity-bias (DBI 0.03). In the high AC/A and low CA/C scenario, early presbyopes had mean DBI of 0.17 (95%CI 0.28-0.06), compared to DBI of -0.31 in convergence excess esotropes. In the low AC/A and high CA/C scenario near exotropes had mean DBI of 0.27, while we predict that non-strabismic, non-amblyopic hyperopes with good vision without spectacles will show lower DBIs. Disparity bias ranged between 1.25 and -1.67. Conclusions. Establishing disparity or blur bias, together with knowing whether convergence to target demand exceeds accommodation or vice versa explains clinical patterns more effectively than AC/A and CA/C ratios alone. Excessive bias or inflexibility in near-cue use increases risk of clinical problems. We suggest clinicians look carefully at details of accommodation and convergence changes induced by lenses, dissociation and prisms and use these to plan treatment in relation to the model

Convergence and accommodation development is pre-programmed in premature infants

Purpose This study investigated whether vergence and accommodation development in pre-term infants is pre-programmed or is driven by experience. Methods 32 healthy infants, born at mean 34 weeks gestation (range 31.2-36 weeks) were compared with 45 healthy full-term infants (mean 40.0 weeks) over a 6 month period, starting at 4-6 weeks post-natally. Simultaneous accommodation and convergence to a detailed target were measured using a Plusoptix PowerRefII infra-red photorefractor as a target moved between 0.33m and 2m. Stimulus/response gains and responses at 0.33m and 2m were compared by both corrected (gestational) age and chronological (post-natal) age. Results When compared by their corrected age, pre-term and full-term infants showed few significant differences in vergence and accommodation responses after 6-7 weeks of age. However, when compared by chronological age, pre-term infants’ responses were more variable, with significantly reduced vergence gains, reduced vergence response at 0.33m, reduced accommodation gain, and increased accommodation at 2m, compared to full-term infants between 8-13 weeks after birth. Conclusions When matched by corrected age, vergence and accommodation in pre-term infants show few differences from full-term infants’ responses. Maturation appears pre-programmed and is not advanced by visual experience. Longer periods of immature visual responses might leave pre-term infants more at risk of development of oculomotor deficits such as strabismus

Asymmetrical accommodation in hyperopic anisometropic amblyopia

Background/Aims: To investigate the presence of asymmetrical accommodation in hyperopic anisometropic amblyopia. Methods: Accommodation in each eye and binocular vergence were measured simultaneously using a PlusoptiX SO4 photorefractor in 26 children aged 4 to 8 years with hyperopic anisometropic amblyopia and 13 controls (group age-matched) whilst they viewed a detailed target moving in depth. Results: Without spectacles, only 5 (19%) of anisometropes demonstrated symmetrical accommodation (within the 95%CI of the mean gain of the sound eye of the anisometropic group), whereas 81% demonstrated asymmetrical accommodation. Of those, 15 (58%) showed aniso-accommodation and 6 (23%) demonstrated “anti-accommodation” (greater accommodation for distance than for near). In those with anti-accommodation the response gain in the sound eye was (0.93 ±0.20) whilst that of the amblyopic eye showed a negative accommodation gain of (-0.44 ±0.23). Anti-accommodation resolved with spectacles. Vergence gains were typical in those with symmetrical and asymmetrical accommodation. Conclusion: The majority of hyperopic anisometropic amblyopes demonstrated non-consensual asymmetrical accommodation. Approximately one in four demonstrated anti-accommodation

Intermittent exotropia: are we underminusing by not overminusing?

In this invited commentary, the authors discuss whether the use of minus lenses to aid control of intermittent exotropia has an alternative method of action. Conventional theory suggests that the lenses induce accommodation and therefore accommodative convergence to reduce the angle of deviation. We discuss evidence which suggests that convergence is induced to control the primary deviation and that the minus lenses allow this control by correcting refractive blur caused by additional vergence accommodation

2016 International Orthoptic Congress Burian Lecture: folklore or evidence?

The theme of the 2016 Burian Lecture is how our understanding of strabismus has been changed by the research carried out in our laboratory in Reading over the years. Accommodation and convergence are fundamental to Orthoptics, but actual responses have often been very different to what we had expected. This paper outlines how our laboratory’s understanding of common issues such as normal development of accommodation and convergence, their linkage, intermittent strabismus, anisometropia, orthoptic exercises and risk factors for strabismus have changed. A new model of thinking about convergence and accommodation may help us to better understand and predict responses in our patients

Accommodation and vergence response gains to different near cues characterize specific esotropias

Aim. To describe preliminary findings of how the profile of the use of blur, disparity and proximal cues varies between non-strabismic groups and those with different types of esotropia. Design. Case control study Methodology. A remote haploscopic photorefractor measured simultaneous convergence and accommodation to a range of targets containing all combinations of binocular disparity, blur and proximal (looming) cues. 13 constant esotropes, 16 fully accommodative esotropes, and 8 convergence excess esotropes were compared with age and refractive error matched controls, and 27 young adult emmetropic controls. All wore full refractive correction if not emmetropic. Response AC/A and CA/C ratios were also assessed. Results. Cue use differed between the groups. Even esotropes with constant suppression and no binocular vision (BV) responded to disparity in cues. The constant esotropes with weak BV showed trends for more stable responses and better vergence and accommodation than those without any BV. The accommodative esotropes made less use of disparity cues to drive accommodation (p=0.04) and more use of blur to drive vergence (p=0.008) than controls. All esotropic groups failed to show the strong bias for better responses to disparity cues found in the controls, with convergence excess esotropes favoring blur cues. AC/A and CA/C ratios existed in an inverse relationship in the different groups. Accommodative lag of >1.0D at 33cm was common (46%) in the pooled esotropia groups compared with 11% in typical children (p=0.05). Conclusion. Esotropic children use near cues differently from matched non-esotropic children in ways characteristic to their deviations. Relatively higher weighting for blur cues was found in accommodative esotropia compared to matched controls