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Yvonne M Buys, Avner Belkin, Rana Greene, Graham Eric Trope, Yaping Jin, Fred Gentili; EFFECT OF POSTURAL CHANGES ON THE TRANS LAMINA CRIBROSA PRESSURE DIFFERENCE – A PILOT STUDY. Invest. Ophthalmol. Vis. Sci. 2018;59(9):2684.
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Intraocular pressure (IOP), the only modifiable risk factor for glaucoma, is thought to be a surrogate measure for trans-laminar pressure difference (TLPD), defined as IOP-intracranial pressure (ICP). A recent meta-analysis has found a higher TLPD in glaucoma patients as compared to healthy controls. This same study found that a that higher TLPD was associated with larger optic disc changes in glaucoma patients. It has been suggested that sleeping with ones’ head slightly elevated, decreases the postural IOP rise, and therefore could be considered in progressive glaucoma with ‘normal’ daytime pressures. If however, ICP and IOP are similarly influenced by posture this recommendation may be flawed. This study aims to evaluate the effect of changes in position on TLPD by measuring ICP and IOP simultaneously in the seated and supine positions.
This was a prospective cohort study. Patients admitted to the neurosurgery unit at Toronto Western Hospital with an External Ventricular Drain (EVD) placed for ICP monitoring were recruited after obtaining informed consent. Exclusion criteria were any ophthalmic surgical procedures within the preceding 6 months, history of glaucoma and corneal abnormalities affecting IOP measurement. IOP and ICP were recorded in both the supine and seated positions with the order of positions randomized. Measurements were made 10 minutes after assuming each position. TLPD was calculated for the sitting and supine positions.
Our interim results include 10 patients, 6 female and 4 male (planned total enrollment is 20 subjects). The average age was 51.3. Results for the left and right eye were similar. Data is shown for right eyes only. IOP, ICP and TLPD are in mmHg. Average sitting and supine IOPs were 16.4 ± 4 and 16.6 ± 4.3 respectively. Average sitting and supine ICPs were 13.75 ± 7.13 and 11.4 ± 4.6 respectively. Average TLPD was 2.85 ± 5.7 in the sitting position and 5.2 ± 6.8 in the supine position, p=0.26. In 6 of the 10 patients the posture response of IOP and ICP was in the same direction – a supine increase in 4 patients, and a supine decrease in 2. In the other 4 patients, the posture response of the IOP and ICP were in opposite directions.
Our interim results found no statistically significant difference in sitting and supine TLPD suggesting that TLPD is unaffected by body position.
This is an abstract that was submitted for the 2018 ARVO Annual Meeting, held in Honolulu, Hawaii, April 29 - May 3, 2018.
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