Effects of body posture on spontaneous retinal venous pulsatility

Abstract

Purpose : Glaucoma is associated with an increase in intraocular pressure (IOP) and recent evidence suggests that intracranial pressure (ICP) and translaminar pressure gradient (IOP-ICP) may also play a role in glaucoma pathogenesis. IOP and ICP have been shown to increase significantly from sitting to supine position, however, the effects of such postural changes on spontaneous retinal venous pulsatility (SVP), a marker for glaucoma severity, remains unclear. In this study, we quantified SVPs in healthy individuals during a postural change from sitting to supping position.

Methods : A total of twelve eyes from eleven healthy individuals (27±3 yrs, 5 females) were included. IOP, SVP and blood pressure (BP) was measured at sitting and supine position. IOP was measured using a calibrated Tono-Pen applanation tonometer and a 10 second video of retinal vessels at a 46^o field of view were obtained using a custom built handheld tablet ophthalmoscope. Mean arterial pressure (MAP) was calculated from systolic and diastolic BP measurements (i.e. MAP= (Systolic+2Diastolic)/3). SVP amplitudes were extracted from retinal videos using a custom written MATLAB algorithm. Student’s t-test was used to assess the difference in IOP , SVP and MAP between the two positions.

Results : Mean IOP and MAP in sitting and supine position were 14±2 mmHg , 18±2 mmHg and 95±13 mmHg, 92± 14 mmHg, respectively. SVP amplitudes were 4.6±1.4 um and 3.7±1.1 um in sitting and supine position. We observed a significant increase in IOP (p<0.001) and a significant decrease in SVP values (p<0.05). This was equivalent to a 20% increase in IOP levels and 20% decrease in SVP amplitudes. There were no significant differences in MAP values (p=0.3).

Conclusions : In this study we observed a significant decrease in SVPs from sitting to supine position. While we did not measure ICP , previous reports have shown an estimated 150% increase in ICP levels from sitting to supine position. Comparing those values to our IOP increase rate of 20% suggests that ICP variation, as a result of postural change, has a significant impact on the translaminar pressure gradient leading to decreased SVPs in supine position. This highlights the significance of studying ICP changes in glaucoma pathophysiology. Further studies are required to establish the role of trans-laminar pressure gradient on retinal circulation in glaucoma.

This is an abstract that was submitted for the 2018 ARVO Annual Meeting, held in Honolulu, Hawaii, April 29 - May 3, 2018.