Improving the repeatability of Heidelberg retina tomograph and Heidelberg retina tomograph II rim area measurements

Strouthidis, N G
White, E T
Owen, V M F
Ho, T A
Garway-Heath, D F

¹Glaucoma Research Unit, Moorfields Eye Hospital, London, UK
²Institute of Ophthalmology, London, UK
³School of Biomedical and Natural Sciences, Nottingham Trent University, Nottingham, UK

Correspondence to: D F Garway-Heath MD, FRCOphth, Glaucoma Research Unit, Moorfields Eye Hospital, 162 City Road, London EC1V 2PD, UK; [email protected]

Accepted 25 June 2005

Competing interests: NGS was funded by a Friends of Moorfields research fellowship and through an unrestricted grant from Heidelberg Engineering.

British Journal of Ophthalmology 89(11):p 1433-1437, November 2005.

Aims:

To devise and test strategies for improving Heidelberg retina tomograph (HRT and HRT-II) rim area (RA) repeatability and assess the benefit of the strategies in time series of HRT images.

Methods:

The effect of the standard and 320 μm reference planes and image quality on RA repeatability was assessed in a test-retest HRT image dataset from 74 subjects. A longitudinal HRT image dataset from 30 ocular hypertensive subjects was analysed by linear regression of RA over time, with each of the reference planes and using a manual image alignment facility. RA variability was estimated by comparing the standard deviation of residuals (RSD) generated by each linear regression.

Results:

RA repeatability was better with the 320 μm reference plane (repeatability coefficient 0.17 mm²), improving further with only good quality images (repeatability coefficient 0.08 mm²). For the longitudinal data, a significant (p<0.0001) reduction in the RSD from 0.10 to 0.05 mm² was obtained with the 320 μm reference plane. Manual alignment led to a further significant (p<0.0001) reduction in the RSD to 0.04 mm².

Conclusions:

The findings support the use of a 320 μm reference plane and manual image alignment to analyse RA over time. The estimates of RA repeatability may be used to define thresholds for glaucomatous change.