Direction-of-Motion Detection and Motion VEP Asymmetries

in Normal Children and Children with Infantile

EsotropiaInvest. Ophthalmol. Vis. Sci.

2007 48: 5523-5531.

Bold acuities indicate values that were outside normal age-based monocular acuity limits. In these cases, an amblyopic correct factor was applied to the mVEP data; data were not noticeably changed by this. Letters (1a, 1b,...) indicate repeated, consecutive visits. ++, adopted; NA, not available.

Repeated tests

Bold acuities indicate values that were outside normal age-based monocular acuity limits. In these cases, an amblyopic correct factor was applied to the mVEP data; data were not noticeably changed by this. Letters (1a, 1b,...) indicate repeated, consecutive visits. ++, adopted; NA, not available.

Types of Strabismus

Bold acuities indicate values that were outside normal age-based monocular acuity limits. In these cases, an amblyopic correct factor was applied to the mVEP data; data were not noticeably changed by this. Letters (1a, 1b,...) indicate repeated, consecutive visits. ++, adopted; NA, not available.

Angle with or without glasses

Bold acuities indicate values that were outside normal age-based monocular acuity limits. In these cases, an amblyopic correct factor was applied to the mVEP data; data were not noticeably changed by this. Letters (1a, 1b,...) indicate repeated, consecutive visits. ++, adopted; NA, not available.

Onset ? reliable

Bold acuities indicate values that were outside normal age-based monocular acuity limits. In these cases, an amblyopic correct factor was applied to the mVEP data; data were not noticeably changed by this. Letters (1a, 1b,...) indicate repeated, consecutive visits. ++, adopted; NA, not available.

Onset after the development of normal binocularity

Bold acuities indicate values that were outside normal age-based monocular acuity limits. In these cases, an amblyopic correct factor was applied to the mVEP data; data were not noticeably changed by this. Letters (1a, 1b,...) indicate repeated, consecutive visits. ++, adopted; NA, not available.

Reduced vision (amblyopia)

Bold acuities indicate values that were outside normal age-based monocular acuity limits. In these cases, an amblyopic correct factor was applied to the mVEP data; data were not noticeably changed by this. Letters (1a, 1b,...) indicate repeated, consecutive visits. ++, adopted; NA, not available.

Bold acuities indicate values that were outside normal age-based monocular acuity limits. In these cases, an amblyopic correct factor was applied to the mVEP data; data were not noticeably changed by this. Letters (1a, 1b,...) indicate repeated, consecutive visits. ++, adopted; NA, not available.

Bold acuities indicate values that were outside normal age-based monocular acuity limits. In these cases, an amblyopic correct factor was applied to the mVEP data; data were not noticeably changed by this. Letters (1a, 1b,...) indicate repeated, consecutive visits. ++, adopted; NA, not available.

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(F1) & 12Hz(F2)

– Vector averages calculated for at least 5 trials R&L eyes and for F1 & F2

• 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

F1

F1 + F2

Large AI indicate larger F1 asymmetric component than the F2 symmetric component