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Amirhossein Hariri, Sun Young Lee, Muneeswar Gupta Nittala, Florian M. Heussen, Srinivas R. Sadda; Effect Of Angle Of Incidence On Macular Thickness And Volume Measurements Obtained By Cirrus High Definition Spectral-Domain Optical Coherence Tomography (Cirrus HD OCT). Invest. Ophthalmol. Vis. Sci. 2012;53(14):4077.
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To evaluate the effect of angle of incidence on macular thickness and volume measurements obtained by Cirrus High Definition spectral-domain optical coherence tomography (Cirrus HD OCT).
A total of 18 eyes from 9 healthy young subjects underwent macular cube volume scans (512 x 128 protocol) following dilation using the Cirrus HD OCT. For each eye, scans were obtained by positioning the scanning beam in the center of the dilated pupil, as well as in four eccentric positions (approximately 3 mm from the center), superior, inferior, nasal, and temporal to the pupillary center, in order to create oblique angles of incidence between the light beam and the retina. In all cases, the region scanned by the volume cube was centered on the fovea. Macular thickness and volume measurements were computed for volume scan acquisitions and differences in values between eccentric scans and the central scan were analyzed.
Retinal thickness and volume values were observed to increase significantly in all subfields for all eccentrically-obtained scans compared with scans obtained through the center of the pupil. The increases in thickness and volume are shown in table 1. ( All p values were < 0.05 ). Scans which were temporally displaced showed the greatest increase in thickness and volume, whereas nasally positioned scans showed the least increase. Amounts of changes in angle of incidence were 14.33 ± 1.21 degrees for temporal eccenteric position,12.03 ± 0.76 degrees for upward eccenteric position,10.11 ± 0.84 degrees for downward eccenteric position, and 8.19 ± 0.91 degrees for nasal eccenteric position. Using Pearson Correlation Coefficient we found that correlations between angle of incidence and increase in measured thickness and volume are statistically significant in all subfields ( All p values were <0.05).
Macular thickness and volume results may be significantly affected by positioning of the scanning beam in the pupil and resultant angle of incidence on the retina. These findings suggest that care should be taken to consistently position the scanning beam in the center of the pupil in order to achieve reliable measurements.
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