Participants and Examinations

All study subjects were recruited from the Glaucoma Service at the Massachusetts Eye and Ear Infirmary between January 2009 and July 2013, as part of the prospective SIG (Spectral Domain OCT in Glaucoma) Study, which was approved by the Massachusetts Eye and Ear Infirmary institutional review board. Informed consent form was obtained from all the subjects participating in the study. All methods adhered to the tenets of the Declaration of Helsinki for research involving human subjects, and the study was conducted in accordance with Health Insurance Portability and Accountability Act regulations. All study subjects underwent a complete eye examination by a glaucoma specialist (T.C.C.), and this included history, visual acuity testing, refraction, Goldmann applanation tonometry, slit-lamp biomicroscopy, gonioscopy, ultrasonic pachymetry, dilated ophthalmoscopy, stereo disc photography (Visucam Pro NM; Carl Zeiss Meditec, Inc), visual field (VF) testing (Swedish Interactive Threshold Algorithm 24-2 test of the Humphrey visual field analyzer 750i; Carl Zeiss Meditec, Inc), and volume scans using Spectralis OCT (HRA/Spectralis software version 5.4.8.0, Heidelberg Engineering GmbH, Heidelberg, Germany).

Patients were included if they had a spherical equivalent between −5.0 and +5.0 diopters and a best-corrected visual acuity of 20/40 or better. Only patients with reliable VF testing were included, with less than 33% fixation losses, less than 20% false-positive results, and less than 20% false-negative results. Patients were excluded if they had discernible congenital anomalies of the anterior chamber, corneal scarring or opacities, diabetic proliferative or severe nonproliferative retinopathy, VF loss attributable to a non-glaucoma condition, or a dilated pupil diameter of less than 2 mm.

Glaucoma patients were defined as having characteristic changes of the ONH with corresponding abnormal VF defects. The VF was considered to be abnormal if 3 or more contiguous test locations in the pattern standard deviation plot were depressed significantly at the P < .05 level with at least 1 at the P < .01 level on the same side of the horizontal meridian and if the VF defect corresponded to the optic nerve appearance. Only POAG patients were included. VF abnormalities were classified as early (mean deviation [MD] >−6 decibels [dB]), moderate (−12 dB< MD ≤−6 dB), or severe (MD ≤−12 dB).

Normal subjects were those without ocular disease, except for mild cataract, and those with normal VF test results, as defined by a pattern standard deviation of more than 5% and glaucoma hemifield test results within normal limits. If both eyes were eligible for the study, 1 eye was selected randomly by using the RANDBETWEEN (min,max) function in Microsoft Office Excel 2007. We defined “1” for the “min” and “2” for the “max.” We ran the command = RANDBETWEEN (1,2) for every row of patients whose both eyes were eligible. We picked the right eye for the result “1” and left eye for the result “2.”

Spectralis Optical Coherence Tomography Peripapillary Retinal Volume Scan

After pupillary dilation, all SD OCT imaging was performed with the Spectralis OCT machine, which uses an 870-nm superluminescent diode source. Additional details of the SD OCT technique have been described elsewhere. Spectralis OCT provides an automatic real-time (ART) function with an eye-tracking system that can increase image quality. With the ART function activated, multiple frames of the same scanning location are obtained. These data then are averaged for noise reduction, and eye-motion artifacts are reduced. As suggested by the manufacturer, scans with signal strength of less than 15 dB (range, 0–40) were excluded from the analysis. In addition, the criteria for determining adequate scan quality were as follows: a clear fundus image with good optic disc and scan area visibility before and during image acquisition, overlay of volume scan visible and without interruptions, and a continuous scan pattern without missing or blank areas. The Spectralis OCT software enables volume scans, which are performed with a 20 × 20-degree field and which are centered on the ONH. One-hundred ninety-three sections were taken with the high speed rate and 3 frames for ART. All 193 B-scans for each subject were checked for algorithm artifacts and errors.

Analysis of the volume scans was performed using Heidelberg Eye Explorer version 1.7.0.0 (Heidelberg Engineering GmbH). The scan area overlay was lowered to zero, and the circular grid pattern was centered on the ONH by one of the authors (H.S.). The mean retinal thickness, determined by an internal program algorithm, was recorded in regions we term circumpapillary annuli. For these circumpapillary annuli, mean retinal thickness values are shown in black ( Figure 1 , Bottom left). For this paper, we only analyzed the outer annulus (OCA) for each of the circular grid scan options (gray areas, Figure 2 ), because the inner circular region and inner annulus covered portions of the optic nerve. The outer annuli (gray areas, Figure 2 ) were further subdivided by quadrant: superior, temporal, inferior, and nasal. For circumpapillary annulus 1 ( Figure 1 , Top left and Figure 2 , Left), the inner area is bounded by circles of diameters 1.00 mm and 2.00 mm, and the outer area by circles of diameters 2.00 mm and 3.00 mm (gray area OCA1, Figure 2 , Left). For circumpapillary annulus 2 ( Figure 1 , Top middle and Figure 2 , Center), the inner area is bounded by circles of diameters 1.00 mm and 2.22 mm, and the outer area by circles of diameters 2.22 mm and 3.45 mm (gray area OCA2, Figure 2 , Center). For circumpapillary annulus 3 ( Figure 1 , Top right and Figure 2 , Right), the inner area was bounded by circles of diameters 1.00 mm and 3.00 mm, and the outer area by circles of diameters 3.00 mm and 6.00 mm (gray area OCA3, Figure 2 , Right). Throughout the rest of the paper, the outer circumpapillary annuli of circular grids 1, 2, and 3 will be called OCA1, OCA2, and OCA3, respectively. If parts of OCA1, OCA2, or OCA3 extended outside the 20 × 20-degree field, these areas were also excluded from the final data analysis.

The three scan protocols used for peripapillary retinal thickness analysis in glaucoma using 3D volume scans. This figure shows the infrared reflectance (IR) image of the 3D volume scans of the optic nerve and peripapillary region (Top left, middle, and right), a sample average retinal thickness map (Bottom left), a sample retinal thickness topography map (Bottom middle), and a sample B-scan image (Bottom right). The horizontal green arrow in the IR image represents the 97th of 193 B-scan measurements, and 97/193 is shown in green at the top left corner of the images (Top left, middle, and right). Scanned regions are depicted by the green translucent square areas in the IR images, which are centered over the optic nerve (Top left, middle, and right). The diameters of the blue circular grids of the top row are 1 mm, 2 mm, and 3 mm (Top left); 1 mm, 2.22 mm, and 3.45 mm (Top middle); and 1 mm, 3 mm, and 6 mm (Top right). The black-white small squares in the top row in the IR images show the retinal thickness values at the place called Marker whose value is shown in the left bottom image of the figure. The 97 ^th frame of the 193 B-scans is shown in the bottom left image of the figure. In the average thickness map (Bottom left), retinal thickness values are written in black and retinal volume parameters are written in red. Thickness and volume parameters are only shown for the outer circumpapillary annulus of the circular grid region.

Schematic representation of the 3 circular grids used for peripapillary retinal thickness determinations using 3D volume scans. The first scan grid has diameters of 1 mm, 2 mm, and 3 mm (Left); the second scan grid has diameters of 1 mm, 2.22 mm, and 3.45 mm (Center), and the third scan grid has diameters of 1 mm, 3 mm, and 6 mm (Right). The gray areas represent the outer circumpapillary annuli of circular grids (OCA) 1 (Left), OCA2 (Center), and OCA3 (Right).

The average RNFL thickness values for the overall RNFL (360 degrees), for each 90-degree quadrant (superior, temporal, inferior, and nasal), and for each sector (superior-temporal [TS], superior nasal [NS], inferior-temporal [TI], and inferior-nasal [NI]) were recorded from the Spectralis OCT RNFL printouts.

Statistical Analysis

All of the calculations in this article were performed using MedCalc for Windows, version 11.4.2 (MedCalc Software, Ostend, Belgium). Demographic characteristics of the normal and glaucoma groups were compared using χ ² tests for categorical variables and nonpaired 2-tailed Student t tests for continuous variables. Receiver operating characteristic (ROC) curves were created, and areas under the receiver operating characteristic (AUROC) curves were calculated for the retinal volume scans of the 4 quadrants (ie, superior, temporal, inferior, and nasal) for each of the OCA1, OCA2, and OCA3. Sensitivity, specificity, positive predictive value (PPV), negative predictive value (NPV), positive likelihood ratio (PLR), and negative likelihood ratio (NLR) were calculated. The cutoff value for each variable is calculated by the statistical program automatically, depending on the maximum value of the Youden index (J), which is equal to the maximum of [Sensitivity + Specificity − 1]. This value corresponds with the point on the ROC curve furthest from the diagonal line. Pair-wise comparisons of ROC curves were performed to determine which quadrant had higher accuracy in the diagnosis of glaucoma. False-positive and false-negative values were evaluated with respect to the cutoff value. Normal subjects who had RT values smaller than the cutoff value were counted as false positives, and POAG patients who had RT values larger than the cutoff were counted as false negatives. The effects of PPA on false-positive and false-negative determinations were calculated by χ ² tests.

ROC curves for RNFL thickness values were created, and AUROC curves were calculated for overall RNFL, the 4 quadrants, and the 4 sectors. Sensitivity, specificity, PPV, NPV, PLR, and NLR were calculated as described above. Pair-wise comparisons of ROC curves were performed for the best AUROC curve values for RT and RNFL thickness measurements, both for all POAG patients and for the early POAG patient subset. Differences were considered significant at P values <.05.