Stereoacuity and Fusional Vergence Ranges of Siblings of Children with Familial Strabismus

Donna Ferguson
Alison Mayo
Elaine Cornell
Robert Heard

Genetic factors play an integral role in the cause of many cases of strabismus and it is currently believed that the mode of transmission Is multifactorial with a threefold effect, that is, that specific genes must be present above a certain threshold before a strabismus Is produced.
If this is the case, then it is likely that close relatives of those with strabismus may also possess some of these ‘abnormal’ genes, but to a lesser extent, and therefore have subtler abnormalities of binocular vision without eliciting a manifest strabismus. This assumption was tested by measuring the stereoacuity and fusional vergence range of 16 non-squinting siblings of children with early onset strabismus. Analysis of the data showed that compared with a control group of children with no family history of strabismus, there was a significant decrease in the stereoacuity of the experimental group (p=0.0245) but no significant difference in the fusional vergence ranges.
It is possible that defects of the vergence response may be too subtle to be elicited by this method and more information may be gained by studying the dynamics of the response. Nevertheless, the reduced stereoacuity supports the multifactorial theory for the inheritance of strabismus.