Correlation Between Optic Disc Size and the RNFL in GDx VCC Examination

Abstract

Abstract: : Purpose: To investigate the correlation between retinal nerve fiber layer (RNFL) distribution and optic disc size, and assess the impact of ocular magnification correction in GDx VCC measurement. Methods: GDx VCC images of 256 normal eyes were collected from 5 clinical centers in China. A MatLab program performed ocular magnification correction of GDx VCC images based on the axial eye length (AEL) from ultrasound A–scan. After correction, the optic disc area was measured from the GDx VCC image, and the RNFL retardation values were obtained from a fixed 3.5 mm diameter measurement circle. Correlation between RNFL retardation and disc area was investigated and RNFL normal ranges from a fixed measurement circle before and after magnification correction were compared. Results: Age of normal subjects ranged from 15 to 80 (48 ±16.2). Visual field MD distribution was –0.16 ± 1.48 dB. AEL distribution was from 20 to 26.5 mm (23.97±1.22mm). Disc area distribution was from 1.5 to 4.5 mm2 (2.44 ± 0.49 mm2). Horizontal disc diameter was 1.67±0.19 mm; vertical disc diameter was 1.84±0.18 mm. Almost no correlation was found in Chinese eyes between disc size and GDx VCC RNFL measurements (R2=0.0048). TSNIT normal range was slightly reduced with ocular magnification correction. Conclusions: Normal eyes with large discs do not necessarily have more RNFL. Ocular magnification correction makes a small difference in normal range. The correction has no impact on the ability to track progression.

Keywords: imaging/image analysis: clinical • optic disc • imaging methods (CT, FA, ICG, MRI, OCT, RTA, SLO, ultrasound)