Association between the function of Schlemm canal and outcome following selective laser trabeculoplasty for primary open-angle glaucoma

Objective

To investigate the relationship between the function of Schlemm canal and the efficacy of selective laser trabeculoplasty (SLT) in patients with primary open-angle glaucoma (POAG).

Methods

An observational case series study was conducted.Seventeen POAG patients (25 eyes), including 12 males (18 eyes) and 5 females (7 eyes), were enrolled in Tongji Hospital, Tongji Medical College, Huazhong University of Science and Technology from March to December, 2017.The three-mirror contact lens was adopted to observe the presence of blood reflux in Schlemm canal before aerobic exercise, and positive referred to that blood reflux was observed in any region of Schlemm canal, and negative was defined as that no blood reflux was observed in Schlemm canal.The intraocular pressure (IOP) and blood pressure of subjects were measured before and after exercise test by the non-contact tonometer and automatic blood pressure monitor respectively.Positive referred to the IOP reduction ≥4.6 mmHg (1 mmHg=0.133 kPa) and negative was defined as the IOP reduction <4.6 mmHg.Optical coherence tomography (OCT) was used to observe whether Schlemm canal was dilated or not and the dilated area before and after exercise test.Positive referred to the opening clock position of Schlemm canal was larger and/or the Schlemm canal was dilated at one or more clock position.The subjects presenting positive in above three indicators were classified as the positive Schlemm canal function group (8 eyes). The subjects presenting positive in above one or two indicators were classified as the mixed Schlemm canal function group (11 eyes). The subjects presenting negative in above three indicators were classified as the negative Schlemm canal function group (6 eyes). All subjects received SLT treatment.The IOP was examined at postoperative 1 week, 2 weeks and 1 month.The IOP, IOP reduction and rate of IOP reduction were compared among the three groups at various time points.This study adhered to the Declaration of Helsinki.The study protocol was approved by an Ethics Committee of Tongji Hospital, Tongji Medical College, Huazhong University of Science and Technology (No.TJ-IRB20160306). Written informed consent was obtained from each subject.

Results

The preoperative IOP and postoperative 1-week, 2-week and 1-month IOP were (20.33±9.22), (17.10±2.98), (19.00±3.94) and (19.33±4.32) mmHg of negative Schlemm canal function group, (25.75±9.03), (20.00±7.60), (19.18±4.46) and (18.00±3.63) mmHg of mixed Schlemm canal function group and (22.28±4.78), (18.75±8.53), (15.50±4.98) and (14.38±3.24) mmHg of positive Schlemm canal function group, respectively.There was no statistical significance in the IOP value among the three groups (F_group=1.028, P=0.374). The difference in IOP before and after surgery was statistically significant (F_time=6.751, P=0.002). Compared with preoperative IOP, the postoperative 1-week IOP of the negative Schlemm canal function group, the postoperative 1-week, 2-week and 1-month IOP of the mixed Schlemm canal function group, and the postoperative 2-week and 1-month IOP of positive Schlemm canal function group were significantly decreased (all at P<0.05). There was no significant difference in IOP reduction or the rate of IOP reduction among the three groups after operation (F_group=0.952, P=0.401; F_time=0.828, P=0.402; F_group=1.840, P=0.182; F_time=0.419, P=0.660).

Conclusions

POAG patients with better function of Schlemm canal have a better IOP-lowering efficacy after SLT treatment.Blood reflux in Schlemm canal before exercise, reduced IOP and dilated Schlemm canal after exercise can be considered as indicators to evaluate Schlemm canal function.

Selective laser trabeculoplasty; Primary open angle glaucoma/surgery; Schlemm canal; Function; Outcome