Study design and patients enrollment
This is a prospective, hospital-based, observational study that was approved by the Ethics Committee of Tianjin Medical University Eye Hospital [202KY(L)-52]. The study enrolled 28 patients (52 eyes), who underwent LPI for PAC state at the glaucoma clinic of Tianjin Medical University Eye Hospital in April 2020. The informed consent was signed before entering the study.
All enrolled eyes fulfilled the diagnosis criteria of PAC: 1. Narrow angles were found by gonioscopy (at least 180° of trabecular meshwork was invisible, Spaeth grade A or B); 2. One or more IOP lowering drugs were used or peripheral anterior synechiae (PAS) was found; 3. No glaucomatous damage of the optic nerve was found (visual field was normal and vertical cup-to-disc ratio was no more than 0.6). The exclusion criteria were as follows: 1. subjects unable to tolerate LPI treatment, for example, those with severe systemic diseases; 2. subjects unable to cooperate well with the conductor to receive all the examinations; 3. subjects not suitable for gonioscopy, for example, those with infectious conjunctivitis; 4. eyes with apparent ocular diseases except for cataract; 5. eyes with a history of laser procedure or intraocular surgery; 6. eyes diagnosed as secondary angle closure; 7. eyes with acute PAC or other conditions which needed surgery intervention.
All participants underwent baseline ophthalmic examination including slit-lamp biomicroscopy, non-mydriatic fundus examination, gonioscopy, Goldmann applanation tonometer, visual field test. Slit-lamp biomicroscopy was done by a trained ophthalmologist to exclude subjects with other ocular diseases or abnormal cup-to-disc ratio. Static and dynamic gonioscopy were performed by an experienced gonioscopist to assess the condition of anterior chamber angle, to diagnose PAC and to identify the presence of PAS. The angle widths were graded using the Spaeth gonioscopic grading scale: A. open to Schwalbe’s line; B. open to anterior trabecular meshwork; C. open to posterior trabecular meshwork; D. open to scleral spur; E. open to ciliary body band in each of 4 quadrants . Visual field tests were done with the 24-2 pattern on the Humphrey Field Analyzer (Carl Zeiss Meditec, Dublin, CA). To avoid learning effect, the second reliable visual field result was accepted as the final one. Visual field results were considered abnormal if one of the following criteria was met: having a glaucoma hemifield test “outside normal limits”, or pattern standard deviation (PSD) at a P<5% level, or a cluster of three non-edge locations worse than a P level of 5% with at least one worse than a P level of 1% on the pattern deviation plot (PDP) .
LPI was performed after all baseline examination being finished. Before LPI, miotic drops were given four times in half an hour. IOP was measured again 20 minutes after LPI. Prednisolone acetate and pranoprofen eye drops were administered 4 times a day for a week. IOP lowering drugs used by the patients remained unchanged before and after LPI. AS-OCT were performed before and 1 week after LPI for each subject. IOP was measured again 1 week after LPI.
Image acquisition and parameter measurement
AS-OCT was performed by an experienced ophthalmic imaging technician. All subjects underwent AS-OCT (Tomey CASIA2) under ambient room lighting conditions. The CASIA2 uses a 1310 nm swept-source laser wavelength at a frequency of 0.3 seconds. With a high scan speed, it produces12 images from 12 different angles in less than 2 seconds. Three consecutive scans were performed under “anterior chamber angle” mode. All patients had an AS-OCT scan performed by the same technician 1 week after LPI treatment.
The obtained images were analysed by the software provided by the manufacturer. This build-in software can automatically analyse the anterior segment structures and provide measurement results after scleral spurs (SSs) were marked. The SS was defined as the inward protrusion of the sclera where a change in curvature of the corneoscleral junction was observed. A trained technician who was masked to the gonioscopic grading marked SSs according to the rule. The analysed parameters included average angle opening distance (AOD500, defined as AOD at 500μm from the marked SSs), AOD500 area (defined as the area formed by 360° AOD500), average trabecular iris space area (TISA500, defined as the area formed by the following four points: trabecular meshwork at 500μm from the marked SSs, angle recess, intersection of trabecular meshwork at 500μm from the marked SSs perpendicular line and iris anterior surface, intersection of angle recess perpendicular line and iris anterior surface), TISA500 volume, (defined as the volume formed by 360° TISA500), trabecular iris angle (TIA500, defined as the angle formed by trabecular meshwork at 500μm from the marked SSs, angle recess and intersection of trabecular meshwork at 500μm from the marked SSs perpendicular line and iris anterior surface), iridotrabecular contact index (ITCI, defined as the percentage of iridotrabecular contact areas to all measured areas), ITC area, anterior chamber volume (ACV), anterior chamber depth (ACD), lens vault (LV, defined as the distance between the intersection of perpendicular bisector of SSs connection and lens and the midpoint of SSs connection) and lens thickness (LT).
Statistical analysis was performed by SPSS (Version 22). Continuous data were presented as mean ± SD. Parameter variable before and after LPI analysis was performed using paired t-test. P<0.05 was considered statistically significant. Correlation between parameter variables was evaluated by the Pearson correlation analysis. The strength of the association was designated as no correlation for 0.0 < r < 0.2, weak correlation for 0.2 < r < 0.4, moderate correlation for 0.4 < r < 0.6, and strong correlation for 0.6 < r < 1.0.