Direction-of-Motion Detection and Motion VEP Asymmetries in Normal Children and Children with Infantile Esotropia Invest. Ophthalmol. Vis. Sci :

Repeated tests

Types of Strabismus

Angle with or without glasses

Onset ? reliable

Onset after the development of normal binocularity

Reduced vision (amblyopia)

Background Infantile esotropia –Large angle convergent squint with onset before 6 months of age Usual definition is “observed by qualified eyecare professional” before 6 months –Consequences Poor cosmesis Loss of binocular vision & stereopsis * Risk of developing amblyopia (lazy eye) Long term cosmetic & social effects

Infantile Esotropia

Fully Accommodative Esotropia

Infantile esotropia vs neonatal misalignments –Initially IE thought to be “congenital” Now known to develop between 2 & 4 months Before 4 months many TD babies show brief large angle misalignments that resolve from one month When TD infants’ eyes becoming more reliably aligned, squinting infants show more frequent and increasingly large angle deviations Eventually become constant

Definition of treatment “Success” Alignment to within 8 pd (prism dioptres)(approx 4  ) –But doesn’t differentiate between those with normal, abnormal or absent binocular vision Convergent and divergent Orthophoria (no deviation detectable) –Still doesn’t mean they have binocular vision Restoration of binocular vision –not considered here Doesn’t say – whether deviation measured for near or distance –Whether the angle is the same near and distance

Background –Suggested theories for aetiology Muscle anomaly Innervation anomaly Secondary to absence of binocular vision Motion processing problem

Development Monocular asymmetry in TD in early infancy until 7 months Asymmetry disappears in TDs by four months Older individuals without binocular vision retain asymmetry into adulthood Correction of squint can restore some symmetry monkeys (Tychsen et al 2004)

Motion processing Nasal / temporal asymmetries for –Monocular OKN (Atkinson 1979) Disrupted when stripes moving temporal→nasal –Smooth pursuit –Velocity judgements (Brosnahan et al 1998) D.. Motion detection nasalward moving targets rated as slower than temporalward targets –mVEP Inconclusive perceptual correlates (Birch et al 2000, Mason et al., 2001 ) Correlates to bifoveal fusion at cortical level

Motivation for study Is mVEP asymmetry similarly observed in psychophysical measures of motion processing within individuals To examine the effects of surgical alignment and patching (occlusion)on motion detection and mVEP asymmetries

Methods Conventional paradigms mVEP –1cyc/ deg grating jittering at 6Hz –5-10 trials per eye –Fourier analysis to extract 6Hz(F 1 ) & 12Hz(F 2 ) –Vector averages calculated for at least 5 trials R&L eyes and for F 1 & F 2 Uniocular

Polar plots of mVEP Length of line = amplitude Angle of line = phase Symmetric mVEP mainly F2 Asymmetric if mainly F1 “bow tie” effect – interocular phase difference of 180  (+/- 40  )

Asymmetry index F 1 F 1 + F 2 Large AI indicate larger F 1 asymmetric component than the F 2 symmetric component