AIM: To explore the safe movement angle of a 23-gauge(G)cannula in double-channel silicone oil(SO)removal surgery.

METHODS: From March 2017 to September 2017, 15 patients with SO filled eyes were enrolled in this retrospective analysis. Based on ultrasound biomicroscopy(UBM), the distance from the front surface of the sclera at the 2 o'clock and the 10 o'clock positions to the SO bubble at 4 mm behind the corneal limbus was measured and defined as “A”. The length of the 23G cannula(4 mm)was defined as “C”. The width of the scleral inner wall at the maximum operating angle of the scleral trocar was defined as “B”. The safe movement angle of the 23G cannula was determined according to the trigonometric function table. Using the self-made SO removal device connected to the 23G puncture cannula, the SO was successfully removed from all patients.

RESULTS: The average SO removal time for all patients was 4.78±0.13min. The trigonometric function was used to work out the distance from the scleral front surface to the SO bubble, which was 0.82-2.81(1.62±0.41)mm at the 2 o'clock position, and 0.98-2.19(1.71±0.34)mm at the 10 o'clock position. Finally, the verification analysis using geometric model calculation showed that the optimal movement angle of the cannula was 52°.

CONCLUSION:Combining the trigonometric function and UBM measurement to calculate the safe movement angle of a 23G cannula can effectively guide the moving range of the trocar during SO removal. A movement angle of the cannula larger than 50° may avoid the occurrence of a retinal tear.