Relationship between optic disc ovality and horizontal disc tilt in normal young subjects
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To investigate the relationship between optic disc ovality and horizontal disc tilt.
The ovality index (the ratio of minimum to maximum disc diameter), horizontal and vertical optic disc tilt, and optic disc torsion were measured on the Heidelberg Retina Tomograph 3 printout in 381 right eyes of 381 normal young subjects. Stereophotographically obvious horizontal tilt and the relationship between the ovality index and horizontal tilt were determined in non-torted discs with an absolute value of disc torsion ≤15°.
The median values of the ovality index, horizontal and vertical tilt, and disc torsion in all subjects were 0.92, 9.0°, 0.0°, and 0.0°, respectively. In the non-torted discs (205 eyes, 53.8 %), a horizontal tilt of ≥20° was stereoscopically obvious. The ovality index was significantly correlated with horizontal tilt (r = −0.276, P < 0.001). The area under the receiver operation curve for the ovality index to discriminate a disc with a horizontal tilt of ≥20° was 0.861. The horizontal disc tilt was significantly correlated with spherical equivalent (r = −0.369, P < 0.001) and axial length (r = 0.277, P < 0.001), but the ovality index was not.
Although the ovality index may be an indicator of stereoscopically obvious horizontal disc tilt, horizontal tilt is more closely related with myopia.
KeywordsOptic disc tilt Ovality index Heidelberg Retina Tomograph Stereophotograph Myopia
The authors thank Goji Tomita, MD. PhD., for permission to use the software for measuring PPA parameters on the HRT images.