All subjects enrolled in the IGPS received comprehensive ophthalmic examinations, including measurements of visual acuity, Goldmann applanation tonometry, refraction tests, slit-lamp biomicroscopy, gonioscopy, dilated stereoscopic examination of the optic disc, and stereo disc photography (EOS D60 digital camera; Canon, Utsunomiya-shi, Tochigiken, Japan). They also underwent spectral-domain optical coherence tomography (SD-OCT; Spectralis OCT, Heidelberg, Engineering, Heidelberg, Germany) and measurements of central corneal thickness (CCT; Orbscan II, Bausch & Lomb Surgical, Rochester, NY, USA), corneal curvature (KR-1800; Topcon, Tokyo, Japan), axial length (AXL; IOL Master version 5; Carl Zeiss Meditec, Dublin, CA, USA), and standard automated perimetry (Humphrey Field Analyzer II 750, 24-2 Swedish interactive threshold algorithm; Carl Zeiss Meditec).
Eyes included in the present study were required to have clinically apparent γ-zone parapapillary atrophy (PPA) with a width > 100 µm on at least one horizontal optical coherence tomography (OCT) scan image, as measured by the built-in caliper tool of the Spectralis OCT.
19 Eyes with poor image quality preventing clear delineation of the γ-zone on SD-OCT images were excluded. Eyes were also excluded when images did not allow clear delineation of the anterior border of the central LC.
Eyes included in the present study were required to have POAG, best-corrected visual acuity of at least 20/40, spherical refraction < -3.0 diopters (D) or an AXL > 24.0 mm, and cylinder correction within –3.0 to +3.0 D with a tilted appearance (defined as a Bruch's membrane opening [BMO]-border tissue angle [BBA] < 70°;
Fig. 1). Subjects with a history of intraocular surgery other than cataract extraction, intraocular disease (e.g. diabetic retinopathy, retinal vein occlusion, or optic neuropathies), or neurologic disease (e.g. pituitary tumor) that could cause visual field loss were excluded. Eyes were also excluded when a good-quality image (i.e. quality score > 15) could not be obtained due to media opacity or lack of patient cooperation.
POAG was defined as the presence of glaucomatous optic nerve damage (i.e. focal thinning of the neuroretinal rim, notching, or a splinter hemorrhage) and associated visual field defect without ocular diseases or conditions that may result in elevated IOP. A glaucomatous visual field defect was defined as (1) outside the normal limits on glaucoma hemifield test; (2) three abnormal points with P values < 5% probability of being normal, including one with P values < 1% by pattern deviation; or (3) a pattern standard deviation < 5%, confirmed on two consecutive tests. Visual field measurements were considered reliable when false-positive/negative results were < 25% and fixation losses were < 20%.
Optic discs were examined by SD-OCT 1 day before surgery and 1–3 months after surgery. Pre- and postoperative IOPs were each defined as the average of at least two measurements on Goldmann applanation tonometry made within 2 weeks before surgery and at the time of follow-up SD-OCT scan, respectively. Indications for trabeculectomy were IOP deemed to be associated with a high risk for glaucomatous progression of the visual field or optic disc despite maximally tolerated medications.
3,5 If both eyes of a subject were eligible for the study, one eye was selected randomly.