A Novel Method Of Measuring Optic Disc Tilt

Abstract

Purpose: To describe a new method of measuring optic nerve head tilt assessed using the Heidelberg Retinal Tomograph (HRT), and arrive at a definition of optic disc tilt.

Methods: A new program was developed to calculate the horizontal disc tilt from a reference plane using the retinal plane. It estimates the degree of horizontal disc tilt using 35 HRT scans of Chinese eyes with clinically-detectable disc tilt. We applied the same program to 2,927 eyes from the Singapore Malay Eye Study (SiMES), a population study and determine the optimal tilt cut-off based on the area under the receiver operating characteristic curve (AUC) (adjusting for age, gender, diabetes mellitus, hypertension and smoking) for a range of ocular and HRT parameters. Lastly, we apply the program to 300 Malay and 300 Chinese normal eyes which were randomly selected from population studies as controls for comparison to the tilt cases.

Results: The median horizontal disc tilt from the 35 HRT scans of eyes with clinically-detectable disc tilt is 3.8 degrees. The median of optimal cut-offs derived from 2,927 eyes (SiMES) with adjusted AUCs greater than 0.6 from a range of risk factors associated with disc tilt (i.e. glaucoma, IOP) and HRT parameters (i.e. disc area, rim area) is 3.8, which corresponds to the 90th percentile horizontal tilt value of the 216 Malay and 224 Indian control eyes.

Conclusions: We found a method of measuring disc tilt and also correlated the measurements with a population based sample. Based on these measurements, we aim to define the degree of disc tilt which will allow us to classify cases into those which have significant tilt and the severity of tilt. This will allow us to then measure the amount of disc tilt in the population and assess the risk factors and associations with other ocular diseases.

Keywords: 550 imaging/image analysis: clinical • 629 optic nerve