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Comparison of Confocal Laser Scanning Tomographic Measurements with Planimetric Photographic Measurements of the Optic Disc in an average South Indian Population
1Thomas R., 1George R., 1Muliyil J., 2Berenstein T.,
1Christian Medical College Vellore, Department of Ophthalmology (Vellore)
2Ruprecht-Karls-Universität Heidelberg, Fakultät für klinische Medizin Mannheim, Augenklinik (Mannheim)
Purpose: To compare confocal laser scanning tomographic measurements of the optic nerve head with planimetric measurements of optic disc photographs of a normal South Indian population.
Methods: The study included 63 subjects (39 females, 24 males) forming a population based sample, selected in a random manner. Mean age was 48.0 ± 9.1 years (range, 35.3 - 69.5 years), mean refractive error measured -0.07 ± 1.11 diopters (range, -4.50 to +2.50 diopters). Confocal laser scanning tomographic images of the optic nerve head as well as stereoscopic optic disc slides were taken and morphometrically analyzed.
Results: Measured by confocal laser scanning tomography, mean optic disc area was significantly (p<0.001) smaller than as determined by planimetric assessment of optic disc photographs. For both techniques, optic disc area was statistically independent of age (p>0.20). In a similar manner, mean neuroretinal rim area as measured by confocal laser scanning tomography was significantly (p<0.001) than as assessed by planimetry of photographs. For both techniques, it was significantly and positively correlated with the optic disc size (p<0.001). For both methods, the neuroretinal rim was smallest in the temporal horizontal optic disc sector. The widest section of the rim, however, was located in the inferior disc sector when measured by planimetry of photographs, and it was in the nasal region of the optic nerve head when determined by confocal laser scanning tomography. For both techniques, optic cup area was significantly and positively correlated with optic disc size (p<0.001).
Conclusions: As in Caucasians so for South Indians, confocal laser scanning tomographic measurements of the optic nerve head results in smaller size of the optic disc and neuroretinal rim than as if measured by planimetry of optic disc photographs. Additionally, the shape of the neuroretinal rim is measured in a different way, with the widest rim part in the inferior disc region when determined planimetrically, and with the widest rim part in the nasal disc region when measured by tomography. These differences may have clinical importance.