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B. D. Lima, F. Venzara, R. De Los Santos, L. M. Ventura, V. Porciatti; Postural Changes of Intraocular Pressure and Their Impact on Retinal Ganglion Cell Function. Invest. Ophthalmol. Vis. Sci. 2007;48(13):212.
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To evaluate changes of Retinal Ganglion Cell (RGC) activity as measured by the Pattern Electroretinogram (PERG) in response to posture-related autoregulatory changes of intraocular pressure (IOP) and ophthalmic perfusion pressure (OPP).
Subjects were 31 normal subjects (mean age 34 ± 12 years). IOP, systemic blood pressure (BP) and PERG were automatically and non-invasively measured at different angles of body position obtained with an electronically-adjustable tilting bed. IOP was measured by means of a non-contact tonometer (Reichert PT-100); PERG was recorded simultaneously from both eyes by means of skin electrodes (PERGLA paradigm, Porciatti and Ventura, 2004). OPP was calculated as the difference between the estimated mean ophthalmic artery pressure (OAPm) and the IOP.
Compared to sitting position, increased angle of body tilting resulted in a progressive increase of IOP (-10 deg head-down: +19%, SD 21; -30 deg head-down +111%, SD 38, n=8 subjects, 16 eyes). Sequential (10 minutes apart) measurements of IOP, PERG and BP were systematically (n=25 subjects, 50 eyes) carried out in 3 conditions: seated (baseline), -10 deg head-down (Trendelenburg), and seated (recovery). In the Trendelenburg condition, significant changes (paired t-test, P<0.01) were found for IOP (+2.83 ± 2.8 mm Hg, +20%) and PERG amplitude (-0.2 ± 0.29 µV, -16%). In the recovery condition, IOP and PERG were not significantly different from baseline. Estimated OPP changes critically depended on the coefficients used to calculate OAPm. Using Sayegh and Weigelin, 1983 ophthalmodynamometric coefficients, no significant changes in OPP occurred in Trendelenburg position.
Autoregulatory changes of IOP in response to changes of posture induce measurable and reversible reductions of RGC function in normal subjects. This non-invasive protocol may disclose impaired autoregulation in glaucoma suspects, which manifests as disproportionate PERG reduction and longer time to recovery.
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