Accommodation and Vergence Response Gains to Different Near Cues Characterize Specific Esotropias

Abstract

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: This was a 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. Thirteen 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 >1.0 D at 33 cm 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.

• AC/A
• accommodation
• CA/C
• convergence
• esotropia

Acknowledgements

This research was supported by a Department of Health Research Capacity Development Fellowship award PDA 01/05/031 to AMH. These data formed the basis of a poster presented at the XIIth International Orthoptic Congress Toronto 2012.

Notes

¹The data from this target position were discarded for technical reasons not associated with the study.

²A clinical AC/A ratio of 6Δ:1D in a patient with an IPD of 6 cm is equivalent to our MA:D ratio of 1:1 (100% of vergence is driven by blur); a normal ratio would be 0.66 MA:1D (4Δ:1D), showing that two-thirds of the total vergence requirement is driven by blur.