Abstract
Abstract: :
Background: The size of the binocular visual field (BVF) is determined by the extent to which the monocular visual fields (MVF) summate. Although the BVF is reduced in patients with esotropic amblyopia due to suppression of all or part of the visual field of the amblyopic eye, the BVF may improve following surgery. It is unclear however, which factors can be used to predict a postoperative improvement in the BVF. Purpose: To determine in children, the extent to which the BVF changes following surgery for large angle esotropia and whether this change can be predicted preoperatively. Methods: To assess the effect of a prism on the visual field using Goldman kinetic perimetry, the MVF and BVF in healthy adults (n=5) was measured using a range of prisms (-10PD to +30PD). Visual fields were measured in normal children (n=10) and in children with large angle esotropic amblyopia (n=22) in order to quantify and assess the variation in MVF and BVF. In those children undergoing surgery (n=11), the visual fields were measured preoperatively both with and without a prism equivalent to the size of the esotropia and then postoperatively without a prism or in addition, with a prism if there was a significant postoperative residual angle. Subjects were excluded if they were unable to complete the set of tests or showed unreliability on retesting. Results: In healthy adults there was no significant effect of varying the power of a prism on either the horizontal extent of MVF or BVF. Although there was no significant difference in the MVF in children with and without strabismus, there was a significant reduction in the BVF and in the ratio of the BVF to MVF between normal children (0.66) and children with esotropic amblyopia (0.61) (p=0.014). Following surgery, there was a significant overall improvement (p=0.01) in the BVF/MVF ratio from 0.58 (0.08) to 0.67 (0.07). The size of the preoperative BVF with a prism correlated with the postoperative BVF (r=0.81 p=0.001). Approximately 65% of the change in BVF could be predicted from the pre-operative BVF using a prism to correct the deviation. There was a significant negative correlation between the BVF/MVF ratio and angle of esotropia (r=0.40,p=0.03). Conclusion: Children with strabismic esotropic amblyopia demonstrate a significant reduction in their BVF. The potential increase in the BVF following surgery can be predicted by using a prism to correct the preoperative angle. Patients with a BVF/MVF approaching that found in normal children (0.66) may not show any improvement in the extent of their BVF following surgery.
Keywords: 588 strabismus • 624 visual fields • 313 amblyopia