Effects of Head-Down Tilt on Optic Nerve Sheath Diameter in Healthy Subjects

dc.contributor.advisorCheng, Han
dc.contributor.committeeMemberPardon, Laura P.
dc.contributor.committeeMemberPatel, Nimesh B.
dc.creatorUstick, Jessica Jordan
dc.date.createdMay 2023
dc.description.abstractPURPOSE Intracranial pressure increases in head-down tilt (HDT) body posture. This study evaluates the effect of HDT on optic nerve sheath diameter (ONSD) in normal subjects. METHODS Twenty-six healthy adults (age 28 (4.7) years) participated in seated and 6° HDT visits. For each visit, subjects presented at 11am for baseline seated scans and then maintained a seated or 6° HDT posture from 12pm to 3pm. In both visits, three horizontal axial and three vertical axial scans were obtained at 11am, 12pm and 3pm with a 10 MHz ultrasonography probe on the same eye, randomly chosen per subject. At each time point, horizontal and vertical ONSD (mm) were quantified by averaging three measures taken 3mm behind the globe. Repeated-measures ANOVA and Tukey HSD test compared means across time. Paired t-tests compared horizontal vs vertical ONSD and changes from baseline between visits. RESULTS In the seated visit, ONSDs were similar across time (p>0.05), with an overall mean (SD) of 4.71 (0.48) horizontally and 5.08 (0.44) vertically. ONSD was larger vertically than horizontally at each time point (p<0.001). In the HDT visit, ONSD was significantly enlarged from baseline at 12pm and 3pm (p<0.001 horizontal, p<0.05 vertical). Mean (SE) horizontal ONSD change from baseline was 0.37 (0.07) HDT vs 0.10 (0.05) seated at 12pm (p=0.002), 0.41 (0.09) HDT vs 0.12 (0.06) seated at 3pm (p=0.002); mean vertical ONSD change was 0.14 (0.07) HDT vs -0.07 (0.04) seated at 12pm (p=0.016), 0.19 (0.06) HDT vs -0.03 (0.04) seated at 3pm (p=0.013). ONSD change in HDT was similar between 12pm and 3pm (p≥0.30). Changes at 12pm correlated with those at 3pm for horizontal (r=0.78, p<0.001) and vertical ONSD (r=0.73, p<0.001). CONCLUSION The ONSD significantly increased when body posture transitioned from seated to HDT position without further change at the end of the 3 hours in HDT.
dc.description.departmentOptometry, College of
dc.format.digitalOriginborn digital
dc.rightsThe author of this work is the copyright owner. UH Libraries and the Texas Digital Library have their permission to store and provide access to this work. Further transmission, reproduction, or presentation of this work is prohibited except with permission of the author(s).
dc.subjectOptic nerve sheath diameter
dc.subjectHead-down tilt
dc.subjectOphthalmic ultrasound
dc.subjectIntracranial pressure
dc.subjectTranslaminar pressure
dc.titleEffects of Head-Down Tilt on Optic Nerve Sheath Diameter in Healthy Subjects
dcterms.accessRightsThe full text of this item is not available at this time because the student has placed this item under an embargo for a period of time. The Libraries are not authorized to provide a copy of this work during the embargo period.
thesis.degree.collegeCollege of Optometry
thesis.degree.departmentOptometry, College of
thesis.degree.disciplinePhysiological Optics and Vision Science
thesis.degree.grantorUniversity of Houston
thesis.degree.nameMaster of Science


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