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Shriji Patel, Ben Szirth, Anton Kolomeyer, Albert Khouri; Software Assisted Depth Analysis Of Normal Optic Nerve Simultaneous Non-Mydriatic Stereoscopic Images. Invest. Ophthalmol. Vis. Sci. 2012;53(14):642.
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To test the ability of a depth analysis software to assess optic nerve cup-to-disc ratio from simultaneous stereoscopic images of normal optic nerves.
Simultaneous stereoscopic optic nerve images from normal subjects (IOP < 21 mm Hg, normal anterior and posterior segment) were collected during community telemedicine screenings. Images were acquired using a Kowa 3Wx non-mydriatic simultaneous stereoscopic retinal camera (Tokyo, Japan) with a resolution of 12.3 Mega Pixels and a field of view equal to 34 degrees. Images were assessed following established protocol on a high-resolution monitor (1080 pixels) in a dark room. Optic nerve vertical cup-to-disc ratio was determined on the right channel of a stereo pair for non-stereoscopic view and from stereoscopic image pairs using a Berezin viewer at a distance of 18 inches. Green channel and negative image views were used to assist in rim and disc margin assessment. A proprietary pixel depth analysis software (Tokyo, Japan), based on right and left image channel discrepancy, was used to determine vertical cup-to-disc ratio after disc and cup contour line placement. All images were acquired without dilation. Age, race, and iris color were recorded. Mean, standard deviation, T-test, and the Intra-class correlation coefficient were used for analysis.
Thirty two patients’ optic nerve stereoscopic images were used for the analysis (mean age 39 +/- 13 yrs, 28 females, 4 males, 14 Caucasian, 13 Hispanic, 3 Asian, and 2 African American). Iris color was 23 brown, 5 hazel, and 4 blue. Image stereoscopic quality was adequate in all subjects. The mean vertical cup-to-disc ratio on non-stereoscopic images was 0.29 +/-0.12, on stereoscopic images 0.36 +/- 0.09, and with depth analysis software 0.38 +/- 0.08. The difference in mean vertical cup-to-disc ratio between the stereoscopic and non-stereoscopic recordings was significant (p < 0.05), while between stereoscopic and depth analysis software assisted recordings was not significant (p=0.45). The intra-class correlation coefficient (r) between stereoscopic and software assisted recordings was 0.88.
Depth analysis software assessment of stereoscopic optic nerve images was possible and showed no statistical difference from physician stereoscopic assessment of vertical cup-to-disc ratio. There was a high degree of agreement between software and stereoscopic assessment in normal optic nerves. Future applications of depth analysis software in glaucoma and during tele-screening warrants further study.
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