Methods

This was an observational cohort study. Patients were recruited from the Diagnostic Innovations in Glaucoma Study conducted at the Hamilton Glaucoma Center (University of California, San Diego). The Diagnostic Innovations in Glaucoma Study is registered at http://www.clinicaltrials.gov under the identifier NCT00221897 . Participants were longitudinally evaluated according to a protocol that included visits with a comprehensive clinical examination and several imaging and functional tests. All participants who met the inclusion criteria described below were enrolled and all data were entered in a computer database. Informed consent was obtained from all participants. The University of California San Diego Human Subjects Committee approved all protocols, and methods adhered to the Declaration of Helsinki.

Each subject underwent a comprehensive ophthalmic examination, including review of medical history, best-corrected visual acuity, slit-lamp biomicroscopy, intraocular pressure measurement using Goldmann applanation tonometry, gonioscopy, dilated fundoscopy examination using a 78-diopter (D) lens, stereoscopic optic disc photography, and standard automated perimetry with 24-2 Swedish Interactive Threshold Algorithm (Carl Zeiss Meditec, Inc, Dublin, California, USA). To be included, subjects had to have best-corrected visual acuity of 20/40 or better, spherical refraction within ±5.0 D, cylinder correction less than 3.0 D, and open angle with gonioscopy. Subjects with coexisting retinal disease, uveitis, or nonglaucomatous optic disc neuropathy were excluded from the study.

Eyes were classified as glaucomatous if they had repeatable (at least 3 consecutive) abnormal visual field test results, defined as pattern standard deviation with a P value <5% and/or a glaucoma hemifield test result outside normal limits, regardless of the appearance of the optic disc. Visual fields with more than 33% fixation losses, more than 33% false-negative errors, or more than 15% false-positive errors were excluded. The only exception was the inclusion of patients with more than 33% of false-negative errors and advanced disease stage (mean deviation lower than minus 12 dB). In addition, all visual fields were reviewed by the Visual Field Assessment Center (University of California at San Diego) and masked to the results of other tests. Visual fields were reviewed and excluded in the presence of artifacts such as eyelid or rim artifacts, fatigue effects, inattention, or inappropriate fixation. Visual fields were also reviewed for the presence of abnormalities that could indicate diseases other than glaucoma, such as homonymous hemianopia.

We also included in the glaucoma group patients with preperimetric glaucomatous damage. The inclusion of these eyes required longitudinal follow-up to determine their ultimate diagnosis, as described in previous publications. These eyes had normal visual field examinations at the time of imaging, but had history of documented evidence of progressive glaucomatous change in the appearance of the optic disc, as assessed by simultaneous stereoscopic photographs (Topcon Instrument Corporation of America, Paramus, New Jersey, USA). The evidence of progressive glaucomatous damage had to be present before the imaging test date. For evaluation of progressive optic disc damage, stereoscopic sets were examined using a stereoscopic viewer (Asahi; Pentax, Tokyo, Japan). All stereophotographs were evaluated by 2 experienced graders masked to the subject’s identity, chronological sequence of the stereophotographs, and other test results. For inclusion, stereophotographs needed to be graded adequate or better. Definition of change was based on focal or diffuse thinning of the neuroretinal rim, increased excavation, or enlargement of the RNFL defects. Changes on rim color, presence of disc hemorrhages, or progressive peripapillary atrophy were not sufficient for characterization of progression. Discrepancies between the 2 graders were resolved by either consensus or adjudication of a third experienced grader. The use of this composite reference standard for glaucoma diagnosis allowed us to evaluate likelihood ratios for continuous RNFL thickness measurements in patients with a broad spectrum of disease severity, as patients with visual field loss and patients with normal visual fields but confirmed progressive glaucomatous damage were included.

Healthy eyes had intraocular pressures of 21 mm Hg or less with no history of increased intraocular pressure, a normal clinical examination, and at least 2 reliable baseline normal visual field tests. A normal visual field was defined as a mean deviation and pattern standard deviation within 95% confidence limits and a glaucoma hemifield test result within normal limits. Healthy subjects were recruited from the general population or from spouses and relatives of patients.