Sources of variability of topometric data with a scanning laser ophthalmoscope
S. Orgul, G. A. Cioffi, D. R. Bacon and E. M. Van Buskirk
Devers Eye Institute, R. S. Dow Neurological Science Institute, Legacy Portland Hospitals, USA.
OBJECTIVE: To determine in a two-part study whether misalignment between
the patient and the laser scanner is a major source of variability with the
Heidelberg Retina Tomograph (Heidelberg [Germany] Engineering). METHODS:
Three topographic images of the right optic nerve were acquired with the
Heidelberg Retina Tomograph in eight patients with glaucoma. The
correlations between average cup volume, variability of cup volume
estimates, and direction of imaging were evaluated. Furthermore, the
correlations between average rim volume, variability of rim volume
estimates, and direction of imaging were evaluated. Next, the optic nerve
cup volume and rim volume estimates of a rabbit's left eye were compared
between three series of five topographic images acquired from three
slightly different directions. RESULTS: Average cup volume, variability of
cup volume estimates, and variability in the direction of imaging
correlated significantly among the patients with glaucoma (multiple R2 =
.95; P < .001). Average rim volume, variability of rim volume estimates,
variability in the direction of imaging, and variability in the mean height
of the contour line also correlated significantly (multiple R2 = .88; P =
.03). In the rabbit eye, the cup volume and the rim volume differed
significantly among the three image series (analysis of variance, P <
.001 and P = .04, respectively). CONCLUSION: Misalignment between the
patient and the laser scanner may account for significant variability with
the Heidelberg Retina Tomograph.
