Abstract
BackgroundPrecise optic disc size measurements based on anatomically exact disc margins are fundamental for a correct assessment of glaucoma suspects. Computerized imaging techniques, such as confocal-scanning-laser-tomography (CSLT), which applies operator defined boundaries and optical-coherence-tomography (OCT), which incorporates an alternative detectable landmark (Bruch’s-membrane-opening (BMO)), have simplified the planimetry of the optic disc and BMO-area, respectively. This study’s objectives are to compare both modalities for area and to define a threshold for macro-BMO using BMO-OCT.MethodsRetrospectively, patients that simultaneously received CSLT and BMO-OCT scans were included. Their images were correlated and agreement was determined using Bland-Altman-analysis. The diagnostic power of a macro-BMO threshold using OCT was derived after creating a receiver-operating-characteristics-curve using the well-established analogous CSLT threshold (2.43 mm2).ResultsOur study included 373 eyes with a median optic disc area by CSLT/ BMO-area by OCT of 2.56 mm2 and 2.19 mm2 respectively. The Bland-Altman-analysis revealed a systematic deviation with a diverging tendency with increasing area, which enabled the creation of the following mathematical relation: disc-area (CSLT)*0.73 + 0.3 = BMO-area (OCT). BMO-area of 2.19 mm2 showed the best diagnostic power for identifying macro-BMOs using OCT (sensitivity: 75%, specificity: 86%).ConclusionsArea measurements (CSLT optic disc area vs. BMO-area by OCT) showed a systematic deviation with a divergent tendency with increasing size. Our mathematical equation offers an estimated comparison of these anatomically diverse entities. Considering BMO-OCT´ anatomical accuracy, the 2.19 mm2 threshold may improve discernment between glaucoma suspects and norm variants.
Highlights
Precise optic disc size measurements based on anatomically exact disc margins are fundamental for a correct assessment of glaucoma suspects
While some consider the ring of Elschnig, a dense connective tissue rising up from the anterior segment of the sclera to join Bruch’s membrane and thereby enclosing the choroid, to be the real margin of the optic nerve head (ONH) [6,7,8], others regard Bruch’s membrane opening (BMO), which can sometimes extend beyond the border tissue, to be the clinically visible margin as shown in monkeys [9,10,11]
Our study presents the first comparison between disc area measurements by CSLT versus BMO-area by OCT
Summary
Precise optic disc size measurements based on anatomically exact disc margins are fundamental for a correct assessment of glaucoma suspects Computerized imaging techniques, such as confocal-scanning-lasertomography (CSLT), which applies operator defined boundaries and optical-coherence-tomography (OCT), which incorporates an alternative detectable landmark (Bruch’s-membrane-opening (BMO)), have simplified the planimetry of the optic disc and BMO-area, respectively. Several measuring techniques (histomorphometry, slit-lamp biomicroscopy, planimetry based on stereophotographs, and computerized imaging), with differing strengths and limitations, have to date been employed Imaging methods such as confocal-scanning-laser-tomography (CSLT), which applies operator defined boundaries based on the ring of Elsching and optical-coherencetomography (OCT), which incorporates an alternative detectable landmark (BMO), have automated segmentation and have simplified the planimetry of the area. It is the purpose of our study to put the two imaging modalities (CSLT and BMO-OCT) in direct comparison for area
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