Variability of the Standard Reference Height and its Influence on the Stereometric Parameters of the Heidelberg Retina Tomograph 3

¹ Ophthalmology, University Hospitals Leuven, Kapucijnenvoer 33, Leuven, 3000, Belgium
² Ophthalmology, University Hospitals Leuven, Leuven, Belgium

^* To whom correspondence should be addressed. E-mail: christophe.breusegem{at}gmail.com.

	Abstract

Purpose: To investigate the variability of the standard reference height (SRH) in consecutive Heidelberg Retina Tomograph 3 (HRT3) examinations and its influence on 5 main stereometric parameters. Methods: The HRT3 results of all patients attending our glaucoma center from August to October 2007 were retrospectively reviewed. Only one eye per patient with at least 3 consecutive HRT's with a quality control label of acceptable or better was selected. A SRH difference 10% compared to baseline was considered as excess SRH variability. Results: A review of 641 patients yielded 150 patients (150 eyes) who met the inclusion criteria representing a total of 556 examinations. The mean total number of HRT's per patient was 3.7 (range 3-7), and the mean follow-up time was 3.5 years (range 1.4-6.7). The mean proportion of consecutive HRT3 examinations with intra-individual excess SRH variability was 46% (95%CI [40;52]), while the mean intra-individual excess SRH variability was 24% (95%CI [20;28]). The median absolute SRH difference was 8.6% (interquartile range [IQR] 3.9%-16.2%). Furthermore, 55.5%, 75.3%, 74.7%, 0.0% and 19.4% of the variability in Rim Area (RA), Rim Volume (RV), Retinal Nerve Fiber Layer (RNFL) thickness, Cup Shape Measure (CSM), and Height Variation Contour (HVC), respectively, could be attributed to SRH variability. Conclusions: There is considerable SRH variability between HRT3 examinations of the same eye and this could explain more than half of the variability of the parameters RA, RV, and RNFL. These findings indicate that changes of HRT3 parameters should be considered with caution when excess SRH variability is present.

Key Words: glaucoma, image analysis, scanning laser ophthalmoscopy, optic neuropathy, optic nerve head, optic disc

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