1. Influence of Body Position on Intraocular Pressure and Lens Vault in Healthy Eyes
Handan Akil1,2, Vikas Chopra 1,2 , Brian A Francis 1,2, Sirinivas S Sadda1,2 , and Alex S Huang1,2
1 Doheny Eye Institute, Los Angeles, CA
2 Department of Ophthalmology, David Geffen School of Medicine at UCLA, Los Angeles, CA
Purpose
Changes in upright to horizontal body positions are well known to elevate intraocular pressure (IOP). Here we investigate position-related changes to the anterior chamber parameter of the lens vault simultaneous to IOP changes in normal, healthy eyes. 
Methods
Twenty eyes from 10 subjects underwent positional testing in this prospective, cross-sectional study. All subjects took a SEATED position for 10 minutes after which IOP was measured by a pneumotonometer (Reichert) and/or Tonopen. Then, anterior segment optical coherence tomography (OCT) for lens vault was performed. Next, all subjects took a horizontal position for 10 minutes. Six subjects (11 eyes) laid SUPINE on a flat examination chair under the flex arm (Fig. 1a) and 4 subjects (8 eyes) took a PRONE position on a customized table that supported the head with rubber straps on the forehead and lower chin (Fig. 1b).
OCT images were taken with the Spectralis HRA+OCT (Heidelberg Engineering GmBH) with FLEX module using the two-angle anterior segment horizontal scan centered on the pupil (ART = 60). The FLEX module is a modified surgical boom arm that orients the Spectralis for imaging in nearly any body position.
For image analysis, the lens vault was defined as the perpendicular distance between the anterior pole of the crystalline lens and a horizontal line joining the two scleral spurs, on horizontal anterior-segment optical coherence tomography scans.
Results
Figure 3. Representative anterior segment OCT images comparing SEATED and SUPINE positions.
Figure 4. Representative anterior segment OCT images comparing SEATED and PRONE positions.
Conclusions
Elevation of IOP in a horizontal body position compared to upright has been previously described and is thought to be due to increased episcleral venous pressure and return of fluid to the anterior chamber.
A SUPINE position led to a deeper anterior chamber by lens vault which could have been due to gravity or increased aqueous humor in the anterior chamber from episcleral venous reflux.
Therefore, we studied the lens vault in a PRONE position where fluid shifts would be similar but gravity reversed.
In a PRONE position, the lens vault did not change, suggesting that gravity is not the sole determinant of lens position or that the lens/iris/zonular complex only has native laxity in one direction but not the other.
Understanding normal positional anatomic changes may provide new insights into angle closure disease pathophysiology.
SEATED
SEATED VS.
SUPINE
SEATED
POSITION
p-value
Intraocular pressure (IOP) (mmHg)
17.7 ± 2.7
23.2 ± 2.2
0.01
Lens vault (mm)
-0.03±0.2
-0.3 ±0.3
0.04
Anterior chamber width (mm)
12.1±0.4
12.2±0.5
0.3
SUPINE
Table 1. SEATED vs. SUPINE Testing: Mean±SD values of intraocular pressure, lens vault and anterior chamber width of healthy subjects at seated and supine positions.
SEATED
PRONE
SEATED VS.
PRONE
SEATED
POSITION
p-value
IOP (mmHg) (T)
13 ± 1.3
20.6±2.1
<0.0001
IOP (mmHg) (P)
16.6±1.8
24.25±0.96
Lens vault (mm)
0.05±0.2
0.08± 0.18
0.7
Anterior chamber width (mm)
11.98±0.47
12.04±0.9
0.9
Table 2. SEATED vs. PRONE Testing: Mean±SD values of the IOP with tonometer (T) and pneumotonometer (P), lens vault, anterior chamber width of healthy subjects at seated and prone positions.
Fig. 1a
Fig. 1b
Fig. 2
Disclosures: Handan Akil (none); Vikas Chopra (F) Allergan, (C) Allergan; Brian A. Francis (F) Infocus, Allergan, Lumenis, Aquesys, Diopsys, (C) BVIEndooptiks; SriniVas R. Sadda (F) Genentech, Allergan, Optos, Carl Zeiss Meditec, (C) Genentech, Allergan, Regeneron, Novartis, Bayer, Thrombogenics, Stem Cells Inc., Iconic, Avalanche,  Optos.; Alex S. Huang (F) Heidelberg Engineering , (C) Allergan