Nine cases of esotropia occurring in deprivation amblyopia, where exotropia rather than esotropia is usually found, showed a refractive error of hypermetropia. This fact suggested that an accommodative factor is largely responsible for the development of esotropia. A- or V-pattern strabismus was encountered in a higher incidence in deprivation amblyopia than in ordinary strabismus. Pattern-reversal VEP showed more prominent abnormality than flash VEP did. Studies of the sensitive period of the visual system revealed that the sensitivity is likely to be low for a month or two after birth and increases with a peak around the 18th month of age, decreasing thereafter with a waning slope to the end of the 8th year of life.