Ultrasound biomicroscopy in viscocanalostomy

Purpose: To evaluate by high frequency ultrasound biomicroscopy (UBM) the anatomical characteristics of viscocanalostomy and their relationship with the intraocular pressure (IOP) lowering. Methods: A transversal study which included 9 eyes (7 patients) undergoing viscocanalostomy and examined by high frequency UBM (80 MHz). Several UBM variables were evaluated, including the presence of the intrascleral space, the maximum length and height of the intrascleral space and the minimum thickness of residual trabeculo-Descemet membrane (TDM). Surgical success was considered to be achieved when IOP was <22mmHg or the IOP was lowered 20% or more without the use of any medication. The possible association between UBM variables and the surgical outcome was determined. Results: The mean time between surgery and the UBM examination was 15.5 +/- 8.8 months (range 6-29). The mean IOP decreased from a preoperative value of 23.5 +/- 6.9 mmHg (range 13.7-32.0) to 14.5 +/- 2.4 mmHg (range 10.7-17.3) postoperative (p<0.05). The presence of an intrascleral space was a constant finding. The mean length of the intrascleral space was 1.83 +/- 0.51mm, the mean height was 0,36 +/- 0,17mm; and the mean TDM thickness was 0.14 +/- 0.07mm. There were a poor correlation between the level of IOP at the time of UBM and the lenght of the intrascleral space (r(2)=0.359), the height of the intrascleral space (r(2)=0.017) or the thickness of the remaining TDM (r(2)=0.003). Conclusion: In patients undergoing viscocanalostomy, UBM examination after a minimum of 6-month follow-up period showed the presence of an intrascleral space in all patients. There was no statiscally significant relationship between the level of IOP and the anatomical characteristics of the intrascleral space.