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Effect of the cardiac cycle on topographic measurements using confocal scanning laser tomography
1Department of Ophthalmology, Dalhousie University, Halifax, Nova Scotia, Canada.
Background:
This study was carried out to investigate the effect of the cardiac cycle on topographic measurements of the optic nerve head and peripapillary retina with confocal scanning laser tomography.
Methods:
The sample comprised 25 healthy subjects (mean age 40.44 years, range 23-67 years). Using a random crossover design, we obtained a set of three images using the Heidelberg Retina Tomograph (Heidelberg Engineering GmbH, Heidelberg, Germany) under each of two conditions. In the first, the images were obtained normally, while in the second, image acquisition was pulse-synchronised using an electrocardiographic signal. We compared the variability of topographic measurements under the two conditions in the whole image, in the optic nerve head and in the peripapillary retina free of visible vessels.
Results:
Nineteen subjects (76%) showed a decrease in variability in the whole image under the pulse-synchronised condition. The respective numbers for the optic nerve head and peripapillary retina were 20 (80%) and 21 (84%). The decrease in variability ranged widely, with a mean of 13.62% in the whole image, 12.26% in the optic nerve head and 18.51% in the peripapillary retina. These decreases were highly significant. There was no relationship between the decrease in variability and age, intraocular pressure, blood pressure, heart rate or the area of the image occupied by blood vessels.
Conclusion:
Detecting structural change depends on the accurate assessment of each subject's variability. Because the cardiac cycle confounds this assessment by varying and unpredictable amounts, it may be necessary to obtain pulse-synchronised images routinely.