TY - JOUR
T1 - Does optic nerve head size variation affect circumpapillary retinal nerve fiber layer thickness measurement by optical coherence tomography?
AU - Huang, David
AU - Chopra, Vikas
AU - Lu, Ake Tzu Hui
AU - Tan, Ou
AU - Francis, Brian
AU - Varma, Rohit
PY - 2012/7
Y1 - 2012/7
N2 - PURPOSE. To determine the relationship between retinal nerve fiber layer (RNFL) thickness, optic disc size, and image magnification. METHODS. The cohort consisted of 196 normal eyes of 101 participants in the Advanced Imaging for Glaucoma Study (AIGS), a multicenter, prospective, longitudinal study to develop advanced imaging technologies for glaucoma diagnosis. Scanning laser tomography was used to measure disc size. Optical coherence tomography (OCT) was used to perform circumpapillary RNFL thickness measurements using the standard fixed 3.46-mm nominal scan diameter. A theoretical model of magnification effects was developed to relate RNFL thickness (overall average) with axial length and magnification. RESULTS. Multivariate regression showed no significant correlation between RNFL thickness and optic disc area (95% confidence interval [CI] = -0.9 to 4.1 μm/mm2, P = 0.21). Linear regression showed that RNFL thickness depended significantly on axial length (slope = -3.1 μm/mm, 95% CI = -4.9 to -1.3, P = 0.001) and age (slope = -0.3 μm/y, 95% CI = -0.5 to -0.2, P = 0.0002). The slope values agreed closely with the values predicted by the magnification model. CONCLUSIONS. There is no significant association between RNFL thickness and optic disc area. Previous publications that showed such an association may have been biased by the effect of axial length on fundus image magnification and, therefore, both measured RNFL thickness and apparent disc area. The true diameter of the circumpapillary OCT scan is larger for a longer eye (more myopic eye), leading to a thinner RNFL measurement. Adjustment of measured RNFL thickness by axial length, in addition to age, may lead to a tighter normative range and improve the detection of RNFL thinning due to glaucoma.
AB - PURPOSE. To determine the relationship between retinal nerve fiber layer (RNFL) thickness, optic disc size, and image magnification. METHODS. The cohort consisted of 196 normal eyes of 101 participants in the Advanced Imaging for Glaucoma Study (AIGS), a multicenter, prospective, longitudinal study to develop advanced imaging technologies for glaucoma diagnosis. Scanning laser tomography was used to measure disc size. Optical coherence tomography (OCT) was used to perform circumpapillary RNFL thickness measurements using the standard fixed 3.46-mm nominal scan diameter. A theoretical model of magnification effects was developed to relate RNFL thickness (overall average) with axial length and magnification. RESULTS. Multivariate regression showed no significant correlation between RNFL thickness and optic disc area (95% confidence interval [CI] = -0.9 to 4.1 μm/mm2, P = 0.21). Linear regression showed that RNFL thickness depended significantly on axial length (slope = -3.1 μm/mm, 95% CI = -4.9 to -1.3, P = 0.001) and age (slope = -0.3 μm/y, 95% CI = -0.5 to -0.2, P = 0.0002). The slope values agreed closely with the values predicted by the magnification model. CONCLUSIONS. There is no significant association between RNFL thickness and optic disc area. Previous publications that showed such an association may have been biased by the effect of axial length on fundus image magnification and, therefore, both measured RNFL thickness and apparent disc area. The true diameter of the circumpapillary OCT scan is larger for a longer eye (more myopic eye), leading to a thinner RNFL measurement. Adjustment of measured RNFL thickness by axial length, in addition to age, may lead to a tighter normative range and improve the detection of RNFL thinning due to glaucoma.
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U2 - 10.1167/iovs.11-8214
DO - 10.1167/iovs.11-8214
M3 - Article
C2 - 22743319
AN - SCOPUS:84867372679
SN - 0146-0404
VL - 53
SP - 4990
EP - 4997
JO - Investigative Ophthalmology and Visual Science
JF - Investigative Ophthalmology and Visual Science
IS - 8
ER -