Paper 5

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Sparing of Vernier acuity in Children with Recent Onset Strabismus and Amblyopia Before and After Treatment

Arvind Chandna, MD, FRCOphth; Sean Chen, MD, PhD; Anthony M. Norcia, PhD, Spero Nicholas, PhD
1. C-Lab. The Smith-Kettlewell Eye Research Institute.  San Francisco, California. USA  2.Ophthalmology Dept., Alder Hey Children’s Hospital.  Liverpool. UK
3. Suite 22, The Galway Clinic. Doughiska, Galway, Ireland
4. Department of Psychology, Stanford University. Stanford University, California. USA

Introduction:  Almost everything we know about visual functions in amblyopia other than visual acuity comes from adults, studied long after initial onset and often treatment of the disorder. Studies indicate that vernier and optotype measures are correlated in amblyopic adults. Here, we report fundamental differences between children and adults with strabismic amblyopia.

Methods:  Prospective, longitudinal controlled study. Spectral analysis of swept Visual Evoked Potential (sVEP) responses were used to isolate vernier-offset related responses in children with recent onset strabismic amblyopia (strab-amb.) n=11, mean age 5.24 years, mean (SD) interocular acuity difference 0.27 (0.16) LogMAR. and typically developing children (control): n=16, mean age 5.14 years at presentation and following conventional treatment.

Results:  Despite significant optotype acuity deficits and favorable treatment response (p<0.05); vernier response functions were not significantly different between a) the preferred and amblyopic eyes of strab-amb. children; b) either eye of strab-amb. group vs. control children; and c) stable vernier response after treatment in strab-amb. group.

Discussion:  Vernier response in previously untreated strab-amb. children is unaffected, in contrast to the clear deficits reported in previously treated adults with the same amblyopia subtype and in children with anisometropic amblyopia of the same age. The difference between adult and child strabismic amblyopes may indicate differential amblyogenic processes at different stages of cortical involvement and in different etiologies.

Conclusion:  Vernier sVEP function is spared in children with reductions in optotype acuity in untreated recent onset strabismus.  These data underscore the need for caution when applying  ‘one size fits all’ treatment regimes – at least in developing visual systems.

References:  1. Hou C, Good WV, Norcia AM. Validation Study of VEP Vernier Acuity in Normal-Vision and Amblyopic Adults. Invest Ophthalmol Vis Sci. 2007;48: 4070-4078.
2. McKee SP, Levi DM, Movshon JA. The pattern of visual deficits in amblyopia. Journal of Vision. 2003;3:380-405.
3. Skoczenski AM and Norcia AM. Development of VEP Vernier acuity and grating acuity in human infants. Investigative Ophthalmology & Visual Science. 1999;40:2411-7.

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