The Institutional Review Board of Hanyang University Hospital approved this study (IRB No. 2020-04-057-001). The study design followed the tenets of the Declaration of Helsinki for biomedical research.
A total of 27 patients with PAC who were followed-up for more than five years at the Department of Ophthalmology of Hanyang University Hospital from January 2002 to December 2010 were enrolled in this study and their medical charts were retrospectively reviewed. Only the patients with PAC were included in the study. Clinical definitions of PAC and its disease spectrums are further described in oncoming section. Exclusion criteria included secondary angle closure due to any possible causes, such as neovascular, uveitic glaucoma or trauma, corneal disorders that prevent accurate measurements, previous history of ocular surgery, trauma and other ocular disorders after intraocular surgery. Patients with less than 5-year follow-up period were also excluded from the study.
All subjects underwent a complete ophthalmologic examination, including visual acuity testing, manifest refraction assessment, slit-lamp examination, IOP measurements using Goldmann applanation tonometry, gonioscopy, dilated fundus examination, axial length measurement (IOLMaster; Carl Zeiss Meditec, Dublin, Ca, USA, Aviso; Quantel medical, Quebec, Canada), stereo-disc photography and red-free RNFL photography (TRC-50X; Topcon Corporation, Tokyo, Japan, F-10; Nidek, Gamagori, Japan), and Swedish interactive thresholding algorithm (SITA) 30-2 perimetry (Humphrey Field Analyzer II; Carl Zeiss Meditec, Jena, Germany). The CCT measurements were performed using an ultrasound pachymeter (Tomey SP-3000; Tomey Corporation, Nagoya, Japan) by the same technician, recording a mean of ten consecutive readings. Above explained ophthalmologic examinations were performed every year for all study patients.
PAC and its disease spectrum
The latest classification scheme by the International Society of Geographical and Epidemiological Ophthalmology (ISGEO) describes features of the PAC spectrum (PACS, PAC, PACG). Accordingly, PAC was defined as present in an eye with an “occludable angle” with normal IOP, less than 21 mmHg. The occludable angle was defined as when the posterior trabecular meshwork was not visible on the nonindentation gonioscopy for at least two quadrants at the primary position. PAC was defined as PACS eye with features of increased IOP, trabecular obstruction, such as peripheral anterior synechiae (PAS), increased IOP, iris whirling, and glaucomflecken. Both PAC and PACS should not have had glaucomatous optic damage. PACG was defined as the presence of glaucomatous optic neuropathy with compatible visual field loss in an association with occludable angle.
In this study, a single glaucoma specialist (KBU) made clinical diagnoses using non-indentation gonioscopy. All surgical and laser treatment decisions were made and undertaken by a glaucoma specialist (KBU). The laser peripheral iridotomy (PI) was done for patients with acute angle closure by the trained doctor mentioned above. Furthermore, prophylactic PI was performed for patients without an attack, who were considered to have PAC in a broad sense. Trabeculectomy was performed in cases with severe corneal edema or failed PI, such as persistent IIOP or progression of glaucomatous damage after PI.
PI was performed in a standard manner. After administration of 2% pilocarpine eye drops, PI was done using argon and Nd:YAG lasers, sequentially. The argon laser was used to irradiate the iris, using an Abraham lens. First, 3-6 pulses at a power of 200 mW and a spot diameter of 200 micron with a duration of 0.2 seconds for iris extension, was performed. Then, 10-40 pulses at 800 mW power, the spot diameter of 50 micron, and a duration of 0.05 to create perforation in the iris were done. Irradiations were applied to the superior iris in order to avoid corneal complications. Finally, pulses of 3.5 to 5.0 mJ of the Nd:YAG laser was used for complete perforation of the wound. Preoperatively, the administration of anti-glaucoma medications and steroid medications were used for one week. When IOP was not adequately controlled, even after surgical or laser procedures, additional anti-glaucoma medications were prescribed by the single glaucoma specialist (KBU).
Calculation of Central Corneal Thickness Changing Rates & Statistical Analyses
All statistical tests were performed using SAS version 9.4 (SAS Institute Inc., Cary, NC, USA). Patient characteristics with continuous variables were expressed as the mean ± SD, and nominal variables were expressed as frequencies and percentages. The normality of the distribution of the CCT scores was verified using the Shapiro-Wilk’s test. The rate of CCT changes from baseline was determined from the serial measurements using repeated linear mixed model analysis (expressed in µm per year), with a restricted maximum likelihood estimation. Fixed effects were treatment group (trabeculectomy vs. PI and angle closure attack vs. no attack), time of measurement, and the treatment group by time interaction. The rates of change were compared among groups through testing of the interaction term in the linear mixed models. In this model, the treatment by time interaction was not statistically significant. It indicates that there were no differential changes in CCT over time, depending on treatment groups. The covariance pattern between the repeated measurements was assumed to be compound symmetry. We considered different forms of the random effects terms ranging from the simplest model with no random effects to the largest model with random intercepts and random slopes. We computed the Akaike information criterion (AIC) for a set of candidate models with different forms of random effects and selected the one with the smallest AIC value indicating better fitting model. Finally, we applied eye-specific random effects model. Additionally, we analyzed the associated CCT change rate in PAC patients with clinicopathological factors of interest using a linear mixed model, and estimate, SE, and its P-values were calculated. The level of significance was set at P-value < 0.05.