[Study on the near, middle and long distance stereopsis of normal and children with intermittent exotropia].

OBJECTIVE

To study the pre- and post-operative changes of stereopsis at different distances in normal and children with divergence in excess type of intermittent exotropia.

METHODS

TNO and new stereo tests (NST) and the middle and long distance stereotest were used for the evaluation of stereoacuity at 40 cm - 5 m in 844 normal and 35 children aged 4 - 12 years with divergence excess type of intermittent exotropia undergoing operative correction of strabismus.

RESULT

(1) Normal subjects: The TNO test showed that the near distance stereoacuity </= 60" was in 98% subjects aged 4 - 8 years. The stereoacuity was increased with the increase of age, the correlation being linear. The stereoacuity in children aged 10 - 11 years was the lowest. In the comparison of stereoacuity between children aged 4 - 8 years and 9 - 12 years, the difference in distribution was very significant (P < 0.01). The NST test showed that the near stereoacuity >/= 40" was in 97% subjects. The mean stereoacuity was 40" - 42" in children various in age. The middle and far distance stereoacuity was the greatest in children aged 4 years, along with the increase of age, it was gradually declined and at 9 - 10 years it was the lowest. (2) Divergence excess type of intermittent extropia: There was no significant difference between the pre- and post-operative near stereoacuity examined by TNO and NST (P > 0.05) The pre-operative middle and long distance stereoacuities were greater than that in the normal children, the difference being significant (P < 0.05). The post-operative middle distance stereoacuity was improved and approximately normal in comparison with that before the surgery, and the far distance stereoacuity was improved mildly.

CONCLUSIONS

(1) In the normal group, the development of stereopsis at different distances begins at 4 years, keeping on developing with the increase of age, and the stereoacuity is elevated after 8 years and in 9 - 11 years well developed. (2) In the group of divergence excess type of intermittent exotropia, the pre-operative near stereoacuity is well, but the middle and far distance stereoacuities are poor and the middle stereoacuity improves significantly after the surgery. The recovery of middle distance stereoacuity seems to be an objective criterion of the operative therapeutic effect.