AIM: To investigate the differences in squint angle measured by right angle prism and isosceles angle prism.

METHODS: Case control study. A total of 176 cases of concomitant strabismus admitted to our hospital from June 2021 to April 2022 were selected, among which 79 cases were concomitant esotropia and 97 cases were concomitant exotropia. The squint angle of all patients was measured respectively by alternating cover right angle prism and isosceles angle prism.

RESULT: For patients with concomitant esotropia, the right angle prism degree was 49.167^△±13.573^△ and the isosceles angle prism degree was 38.250^△±10.756^△ (P<0.01), with a difference of 10.917^△±3.752^△; the measurement of right angle prism converted to circular degree was 19.096°±2.456°, and the isosceles angle prism value was 20.847°±5.364°(P<0.05), with a difference of 2.443°±2.702°. For patients with concomitant exotropia, the right angle prism degree was 51.875^△±13.567^△, and the isosceles angle prism degree was 40.492^△±11.753^△ (P<0.01), with a difference of 11.383^△±4.783^△; the measurement of right angle prism converted to circular degree was 19.589°±2.521°, and the isosceles angle prism value was 21.947°±5.864°(P<0.01), with a difference of 3.200°±3.077°. There was no significant statistical difference in the differences of the two prism degree and the circular degree for concomitant esotropia and concomitant exotropia(P>0.05).

CONCLUSIONS: The squint angle measured by different shaped prisms is different. The degree measured by right angle prism is larger than that by isosceles angle prism.