This investigation was based on the database of POAG patients included in the Investigating Glaucoma Progression Study (IGPS), which is an ongoing prospective study at the Seoul National University Bundang Hospital Glaucoma Clinic. Written informed consent was obtained from all subjects, and the study protocol was approved by the Institutional Review Board of Seoul National University Bundang Hospital and followed the tenets of the Declaration of Helsinki.
Subjects who were enrolled in the IGPS underwent a comprehensive ophthalmic examination, including visual acuity assessment, Goldmann applanation tonometry, refraction tests, slit-lamp biomicroscopy, gonioscopy, and dilated stereoscopic examination of the optic disc. All subjects also underwent disc photography and red-free fundus photography (EOS D60 digital camera; Canon, Utsunomiyashi, Tochigiken, Japan), circumpapillary RNFL scanning and enhanced depth imaging (EDI) of the optic nerve head by spectral-domain optical coherence tomography (SD-OCT, Spectralis; Heidelberg Engineering, Heidelberg, Germany), and standard automated perimetry (Humphrey Field Analyzer II 750; 24–2 Swedish interactive threshold algorithm; Carl Zeiss Meditec, Dublin, CA, USA). In addition, all subjects underwent measurements of corneal curvature (KR-1800; Topcon, Tokyo, Japan), central corneal thickness (CCT, Orbscan II; Bausch & Lomb Surgical, Rochester, NY, USA), and axial length (IOL Master version 5; Carl Zeiss Meditec). Although initial enrollment in the IGPS began in 2011, additional tests have been added as new instruments have become available. Since September 2014, CH has been measured in the treatment-naïve POAG patients using the Ocular Response Analyzer (ORA v. 2.02; Reichert Ophthalmic Instruments, Depew, NY, USA).
The IGPS excluded subjects with a best-corrected visual acuity of <20/40, a history of intraocular surgery other than cataract extraction and glaucoma surgery, or any intraocular disease (e.g., diabetic retinopathy or retinal vein occlusion) or neurologic disease (e.g., pituitary tumor) that could cause visual field loss.
Patients included in the present study were required to be newly diagnosed with POAG. POAG was defined as the presence of glaucomatous optic nerve damage and associated visual field defect without ocular disease or conditions that might elevate IOP, and an open angle on gonioscopy. A glaucomatous visual field change was defined as (1) outside normal limit on glaucoma hemifield test, (2) three abnormal points with a <5% probability of being normal, including 1 with a probability <1% by pattern deviation, or (3) a pattern standard deviation of 5% if the visual field was otherwise normal, as confirmed on two consecutive tests. Visual field measurements were considered reliable when the rate of false-positive/negative results was <25% and the rate of fixation losses was <20%.
Eyes that had undergone corneal refractive surgery, coexisting corneal dystrophy that could affect CH, or those with optic disc torsion >15° or a tilt ratio (minimum-to-maximum optic disc diameter) <0.75 were excluded.
14,15 Eyes were also excluded when good-quality images (i.e., quality score >15) could not be obtained at more than five sections of EDI SD-OCT disc scans (if the quality score did not reach 15, the image-acquisition process automatically stopped and the image of that section was not obtained), or when the images did not allow clear delineation of the anterior LC border at the measurement points on more than two selected B-scans. If both eyes were eligible, one was randomly chosen for analysis.