Non-invasive Measurement of the Viscoelasticity of the Optic Nerve and Sclera for Assessing Papilledema: A Pilot Clinical Study.

Objective: The purposeofthisstudywastoevaluateournovelultrasoundvibro-elastography(UVE) techniquefor assessing patientswithpapilledemabynon-invasivelymeasuringshearwavespeed(SWS), elasticityandviscosity properties oftheopticnerveandsclera. Methods: Shear wavespeedsweremeasuredatthreefrequencies-100, 150and200Hz-on theopticnerveand sclera tissuesforassessingpatientswithpapilledemaresultingfromidiopathicintracranialhypertension(IIH). The methodwasevaluatedinsixpapilledemapatientsandsixcontrolsontwoseparatelocationsforeachparticipant (i.e., optic nerveandposteriorsclera). SWSsoftheopticnerveandsclerawereanalyzedbyusinga2-Dspeed map techniquewithinacircularregionofinterest(ROI)(i.e., the diameteroftheROIwas1.5mm x 3.0 mmatthe optic nerveandsclera, respectively). Elasticityandviscositywerethenanalyzedusingthewavespeeddispersion over thethreefrequencies. Results: We measuredvaluesofSWSatbothlocations, opticnerveandsclera, oftherighteyeandlefteyeatthree different frequenciesinIIHpatientsandcontrols. TheSWS(mean +/- standard deviation[m/s]) oftherighteye was significantly higheratthesclerainIIHpatientscomparedwithcontrols(i.e., patients vs. controls: 5.91 +/- 0.54 vs. 3.86 +/- 0.56, p < 0.0001 at100Hz), buttherewasnosignificant differenceattheopticnerve(i.e., patients vs. controls: 3.62 +/- 0.39 vs. 3.36 +/- 0.35, p = 0.1100at100Hz). Weobservedincreasedelasticity(kPa) inIIH patients, indicatingtherearesignificant differencesinelasticitybetweenpatientsandcontrolsattheopticnerve and sclera(i.e., right eye[patientsvs. controls]: 14.42 +/- 6.59 vs. 6.5 +/- 5.71, p = 0.0065[opticnerve]; 33.04 +/- 10.62 vs. 9.16 +/- 7.15, p < 0.0001 [sclera]). Viscositywasalso(Pa.s) higherinthescleraandopticnerveofthe left eye(i.e., left eye[patientvs. control]: 8.89 +/- 4.37 vs. 7.27 +/- 5.01, p = 0.3790(opticnerve); 16.05 +/- 10.79 vs. 8.49 +/- 6.09, p < 0.0194 [sclera]).