Head-down tilt reverses neuroretinal rim thinning in healthy eyes

Abstract

Purpose : In healthy eyes, the neuroretinal rim tissue is thickest in the early morning and thins through mid-afternoon. We hypothesize that this change of the neuroretinal rim is a reflection of the translaminar pressure difference as one goes from a supine to sitting or standing position. The purpose of this study was to determine if head-down tilt (HDT) reverses this neuroretinal rim thinning.

Methods : Twenty-six healthy subjects presented to the lab on two separate days at 11 AM. Baseline measures included visual acuity, standard automated perimetry, optic nerve photos, and intraocular pressure (IOP with rebound tonometry), all performed in a seated position. Optic nerve head (ONH) and peripapillary tissue were imaged using radial and circular optical coherence tomography (OCT) scans centered on the ONH, aligned to the fovea-Bruch’s membrane opening (BMO) axis. Following 3 hrs in either a seated or 6° HDT, IOP and OCT scans were repeated in that position. OCT data were exported, and programs written in MATLAB were used to quantify global minimum rim width (MRW), peripapillary total retinal thickness (TRT), choroid thickness, retinal nerve fiber layer (RNFL) thickness, BMO area, and BMO position referenced to a 3.5mm plane aligned to the choroid-sclera junction (BMO height). Data are presented as mean ± SEM.

Results : Each of the 26 subjects completed both seated and HDT sessions and one randomized eye from each was used for analysis. Compared to seated baseline measures, IOP decreased by 1.7±0.5mmHg (p<0.01) in the seated position and increased by 3.1±0.7mmHg in the HDT position (p<0.01). The average BMO area was 2.1±0.1mm² and did not change with time or posture (p>0.05). The mean BMO height did not change in the seated condition but was anteriorly displaced in HDT (6.8±3.1µm, p=0.04). While there was no significant change in MRW in the seated position (0.8±0.8µm, p=0.3), MRW increased in HDT (4.2±1.7µm, p=0.02). Similarly, for an annulus of 250µm from the BMO, TRT in the seated position showed no significant change (p>0.05), but increased in HDT (3.4±1.1µm, p<0.01).

Conclusions : Thinning of the neuroretinal rim which occurs during waking hours is reversed in HDT. This provides support that changes in the translaminar pressure difference from supine to seated or standing are partly contributory to this diurnal change.

This is a 2021 ARVO Annual Meeting abstract.