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Laura P Pardon, Pratik Chettry, Han Cheng, Nimesh Bhikhu Patel; Optic nerve head morphological changes over a 12-hour period in a seated vs. head-down tilt posture. Invest. Ophthalmol. Vis. Sci. 2019;60(9):4819. doi: https://doi.org/.
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© ARVO (1962-2015); The Authors (2016-present)
The optic nerve head (ONH) is sensitive to alterations in the translaminar pressure gradient (intraocular pressure [IOP] – intracranial pressure [ICP]). IOP is typically highest in the early morning and decreases throughout the day. Though diurnal variations in ICP are not well-established, ICP can be elevated relative to IOP using a head-down tilt (HDT) body posture. The goal of this study was to investigate how ONH morphology changes in a seated vs. 6-degree HDT posture over a 12-hour daytime period in young, healthy adults.
Ten eyes of ten healthy human subjects (mean age 29.4 ± 4.8 years) were included. Each subject presented for two sessions on different days: one session in a seated position and the other in 6-degree HDT. Radial OCT scans of the ONH, rebound tonometry, and blood pressure were acquired at 7 time points for each session (7AM, 9AM, 11AM, 1PM, 3PM, 5PM, 7PM); for the HDT session, baseline and endpoint measurements were also acquired in a seated position prior to and after HDT. Global values for the ONH minimum rim width (MRW) and location of Bruch’s membrane (BM) opening (BMO) relative to a 4 mm BM reference plane centered on the ONH were calculated after correction of ocular magnification using individualized biometry data.
In the seated position, MRW decreased from 7AM (median = 355.8 µm, interquartile range [IQR] = 297.2 to 424.9 µm) to 7PM (median = 347.9 µm, IQR = 292.2 to 403.8 µm; p < 0.01). While there was a decrease in IOP (median = –0.7 mmHg), it was not statistically significant (p = 0.18). The median change in MRW from 7AM to 7PM was –8.2 µm (range –1.09 µm to –28.52 µm). When changing from a seated to HDT posture, IOP initially increased (median = +3.9 mmHg; p < 0.01). Though MRW and BMO location changed over the 12 hours in HDT (p = 0.04), none of the HDT time points significantly differed from the 7AM baseline (p > 0.35); on average, MRW initially increased in HDT then decreased.
MRW decreases from morning to evening in young, healthy individuals, and this change cannot be explained by IOP. A HDT posture prevents MRW thinning during the day, suggesting that the translaminar pressure gradient influences ONH morphology/dynamics. These findings suggest that it is important to acquire neuroretinal rim measures at approximately the same time of day when diagnosing optic neuropathies.
This abstract was presented at the 2019 ARVO Annual Meeting, held in Vancouver, Canada, April 28 - May 2, 2019.
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