Effect of Head Elevation on Intraocular Pressure and Retinal Imaging in the Prone Position

Asymmetric postoperative visual loss after spine surgery in the lateral decubitus position

“…In the prone position, slight head elevation has been demonstrated to reduce chemosis, 4 but not choroidal venous congestion as seen on retinal imaging. 5 This patient had visually impressive facial oedema at the conclusion of the procedure as had some of the other reported patients with POVL. Some authors have implicated facial oedema in the pathophysiology of PION, 6 but a causal association between facial oedema and POVL has not been substantiated.…”

Effects of Prone and Reverse Trendelenburg Positioning on Ocular Parameters

“…Thus, we were unable to show an attenuation of IOP with a 4-degree (15 cm) RT table inclination as was shown for an immediate change in table inclination in two previous studies for a 10degree elevation 15,16 and over 1 h at a 4-degree elevation. 18 However, in the second patient study, 16 this immediate attenuation could not be translated into differences when either horizontal or RT (10 degrees) were used for the duration of the surgery. Thus, if a difference could not be shown over time for a 10-degree elevation, it is likely that a 4-degree elevation is too small to show consistent comparative improvement in these parameters over a prolonged period.…”

“…A 10-degree elevation in a one-piece table is equivalent to 37-cm head versus foot height, 17 which theoretically may cause increased venous pooling at the lumbar surgical site. One preliminary study on awake volunteers showed that an increase in table inclination of only 4 degrees (15 cm) would attenuate the increase in IOP over 1 h 18 whereas a pilot study on two awake volunteers over 5 h showed a trend but not a significant difference. 19 With the exception of the pilot study, no volunteer study in the prone position, evaluating this degree of head elevation and eliminating the effects of anesthetics and fluid administration, has been conducted beyond 1 h. The thickness of the choroid layer also increased significantly over time but not significantly with table position.…”