The GDx variables used in the present study
| Symmetry: | the ratio of the average 1500 thickest pixels in the superior quadrant divided by the average of the 1500 thickest pixels in the inferior quadrant. |
| Superior ratio: | the ratio of the average of the 1500 thickest pixels in the superior quadrant divided by the average of the 1500 median pixels in the temporal quadrant. |
| Inferior ratio: | the ratio of the average of the 1500 thickest pixels in the inferior quadrant divided by the average of the 1500 median pixels in the temporal quadrant. |
| Superior/nasal: | the average of the 1500 thickest pixels in the superior quadrant divided by the average of the 1500 median pixels in the nasal quadrant. |
| Average thickness: | the average of all pixels outside the disc margin. |
| Max modulation: | first, the average of the 1500 thickest points in the superior and inferior quadrants was calculated, then the average of 1500 median points in the nasal and temporal quadrants were calculated and the lowest of these four values was subtracted from the highest, then that value divided by the lowest value. |
| Ellipse modulation: | thinnest pixel within the elliptical band was subtracted from the thickest pixels within the elliptical band, then the total divided by the value of the thinnest pixel. |
| Ellipse average: | average thickness of the pixels within the elliptical band surrounding the optic nerve. |
| Superior average: | the average thickness of the pixels within the elliptical band in the superior quadrant. |
| Inferior average: | the average thickness of the pixels within the elliptical band in the inferior quadrant |
| Superior integral: | the total area under the curve and within the superior portion of the elliptical band surrounding the optic nerve. |