Af. Spencer et al., VERTICAL OPTIC DISK DIAMETER - DISCREPANCY BETWEEN PLANIMETRIC AND SLO MEASUREMENTS, Investigative ophthalmology & visual science, 36(5), 1995, pp. 796-803
Purpose. To compare measurements of the vertical diameter of the optic
disk using the Heidelberg Retinal Tomograph (HRT) and planimetric met
hods. Methods. On the HRT, three measurements of the vertical disk dia
meter were made on 32 eyes from a composite image using the circle dra
w facility and were compared with three measurements of the central im
age of the 32 tomographic cuts. These were repeated by a second observ
er. Measurements were compared with those obtained from photographs us
ing the three corrections described by Bengtsson and Krakau. Results.
For the HRT, there was minimal intraobserver variation, coefficient of
variation (1.515% to 1.882% for the two observers). Interobserver var
iation was also small (CoV 1.969%). The authors found the closest agre
ement with the HRT measurements using regression analysis was obtained
using correction 3 (r = 0.8258). HRT measurements were significantly
smaller (P < 0.0001) by a constant amount of 0.13 mm across the range
of optic disk size. There was a significant difference between the HRT
measurement of the composite image and the central cut (P = 0.0003 fo
r observer 1). Conclusions. HRT measurements are significantly smaller
than those from photographs and, therefore, are not interchangeable.