Abstract
Purpose: :
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.
Methods: :
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.
Results: :
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.
Conclusions: :
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.
Keywords: optic disc • imaging/image analysis: clinical • computational modeling