Short- and Long Term Repeatability of Point- and Sector Wise Measurements of the Parapapillary Retina Using the Heidelberg Spectralis OCT

Abstract

Purpose: : To investigate short- and long term repeatability of parapapillary measurements obtained with gaze controlled optical coherence tomography and to investigate the effect of covariables on repeatability.

Methods: : 43 normal healthy young volunteers were recruited. One random eye from each subject underwent 5 repeated OCT measurements (Heidelberg Spectralis^TM) by one observer on each of 3 sessions at an interval of 4 weeks. Image alignment (TruTrack^TM) was activated after the first session to control for gaze. Circular- (3.4 mm) and radial scans (12 sections) were centered at the papilla. Point measurements of the retinal thickness were obtained 500 µm distal to the scleral ring at 18 locations (RT) and at corresponding points along the circular scan (CRT). From the latter scan, average measurements of nerve fiber thickness (NFT) were recorded from 6 sectors. All measurements were graded according to the vicinity of blood vessels, size of blood vessels, deviation from a perpendicular section, and agreement between subjectively assessed and instrument defined retinal layers at the measured point. In addition, all scans were graded for quality based on the IR image and the OCT scan. Short-term repeatability (within sessions) was analyzed using Coefficient of Repeatability (CR) and Coefficient of Variability, whereas CR and Intraclass Correlation Coefficient were used for long-term repeatability (between sessions). Multivariate analyses were used to assess the effect of covariables.

Results: : Preliminary analyses (n = 7) indicated a general improvement of repeatability for the majority of measurements after the 1^st session (average CR_RT = -7.4 µm (-51 %); average CR_CRT = -3.0 µm (-30 %); average CR_NFT = -3.0 µm (-47 %)). Supra- and infratemporal sectors were associated with higher frequencies of poor layer definitions and higher variability of scan angle deviations than elsewhere around the papilla.

Conclusions: : Early results indicate improvement of repeatability when image alignment function is activated. Further analyses will provide information on additional factors that influence the repeatability using the Heidelberg Spectralis.

Keywords: imaging methods (CT, FA, ICG, MRI, OCT, RTA, SLO, ultrasound) • optic nerve