Intra-Examiner And Inter-Examiner Variability With Stereoscopic And Monoscopic Optic Nerve Head Evaluation.

Background: There is variability in the criteria used by optometrists when measuring cup
to disc ratios (C/D) during optic nerve head evaluation. The present "gold-standard" for
optic disc assessment is stereoscopic ophthalmoscopy, yet the variety of methods used
along with the inherent variability of a subjective assessment makes intra and interexaminer
repeatability a challenging task. This demonstrates the need for a study to determine the repeatability of subjective estimates of C/D ratio. Methods: A sample of sixteen photographs, eight stereoscopic and their identical non-stereoscopic (monoscopic) photographs were presented to both students and practicing optometrists for evaluation. A total of 43 participants' responses for each image were used for statistical study in order to compare the intra and inter-examiner repeatability while judging the value of stereoscopic versus monoscopic views. Results: For nearly all of the photographs, each group consistently rated the C/D ratio larger when viewed stereoscopically. Interexaminer variability was found to be consistent using monoscopic and stereoscopic conditions, although the variability with stereopsis was slightly increased. Conclusion: Monoscopic and stereoscopic viewing have similar variability when evaluating C/D ratio of digital optic nerve photographs. Also, C/D ratio is larger when viewed with stereopsis.