Objective: Filtration in the area subjected to CO2 laser-assisted sclerectomy surgery (CLASS) is described using ultrasound biomicroscopy (UBM) and the clinical grading scale to evaluate the mechanism of intraocular pressure (IOP) reduction.
Methods: Twenty-eight patients with open-angle glaucoma underwent CLASS. The Indiana Bleb Appearance Grading Scale evaluation was performed 1 month after surgery to determine bleb height, extent, vascularity, and leakage. UBM was used to describe and measure the surgical area. Bleb morphology, the size of the scleral lake, scleral route, and trabeculodescemetic membrane (TDM) thickness were examined.
Results: One month after CLASS, IOP significantly decreased from 20.46 ± 3.92 mmHg to 12.71 ± 2.99 mmHg, and the anterior chamber depth significantly more shallow, from 2.75 ± 0.36 mm to 2.61 ± 0.33 mm(p < 0.05). Shallow uplift occurred in 71.43% of the blebs, and 64.29% of the blebs were within 1 to 2 h; 82.15% showed mild or moderate vascular hyperemia, and the Seidel test was negative. UBM showed that all eyes had an intact TDM, with a mean thickness of 99.3 ± 22.2 μm; 21 eyes (75%) had L-type (low reflective). The scleral lake anteroposterior length, height, and transversal length were 2.247 ± 1.831 mm, 0.520 ± 0.234 mm, and 3.312 ± 0.423 mm, respectively. The TDM thickness and postoperative IOP were positively correlated, and the size of the scleral lake was not correlated with IOP reduction. Four eyes (14.29%) exhibited cyclodialysis.
Conclusion: UBM examination indicated the aqueous humor drainage route. In the early stage after CLASS, subconjunctival and choroidal drainage routes might be the major mechanism underlying IOP reduction. Mild and moderate congestion of bleb blood vessels warrant attention to avoid early bleb scarring.
Keywords: CO2 laser-assisted sclerectomy surgery; Filtration canal; open-angle glaucoma; ultrasound biomicroscopy.