Guided Trocar Insertion in Highly Myopic Eyes

To demonstrate through a diagnostic test used as a new preoperative assessment that trocar insertion for pars plana vitrectomy could be safely placed at a distance >4.0 mm in highly myopic eyes to facilitate the surgical maneuvers.

Thirty eyes of 30 patients were tested with a biometer for the axial length measurement and with ultrasound biomicroscopy to measure the pars plana length. Pars plana lengths of highly myopic eyes were then compared with those of emmetropic eyes. The surgeon also measured the pars plana of highly myopic eyes intraoperatively and compared it with ultrasound measurements to assess ultrasound biomicroscopy reliability.

The mean axial length was 23.81 mm (SD ± 0.30) in the control group and 31.11 mm (SD ± 0.56) in the myopic group. The mean pars plana length was 4.96 mm (SD ± 0.19) in control eyes and 6.65 (SD ± 0.36) in myopic eyes. An extremely significant statistical difference ( P < 0.001) was obtained by comparing the length of pars plana between control eyes and myopic eyes. The results of pars plana measurements were 6.65 mm (SD ± 0.36, ultrasound biomicroscopy) and 6.66 mm (SD ± 0.34, intraoperative measurements) in myopic eyes. The statistical comparison of the measurements in these two groups did not give a statistically significant result ( P = 0.950).

Ultrasound biomicroscopy is a reliable technique to calculate the length of pars plana in highly myopic eyes, where this parameter is significantly greater than that of emmetropic eyes. Trocars insertion for pars plana vitrectomy may be performed, in eyes with axial length >30 mm, in relative safety at a distance to limbus higher than 4 mm.