The influence of tonometric technology and body position on the calculation of pulsatile translaminar pressure gradient

Abstract

Purpose : To investigate the mean translaminar pressure gradient (TLPG) and translaminar pulse amplitude (TPA) using 5 tonometric technologies and 3 body positions.

Methods : Right eyes of 53 subjects were prospectively enrolled in a study to investigate TLPG and TPA in primary open angle glaucoma (POAG: n = 19), normal tension glaucoma (NTG: n = 7), ocular hypertension (OHT; n = 5), and normal subjects (NRM: n = 22). Intraocular pressure (IOP) was measured using Goldmann Applanation Tonometry (GAT), Corneal Compensated IOP (IOPcc) from the Ocular Response Analyzer (ORA), and biomechanically corrected IOP (bIOP) from the Corvis ST. Both IOP and ocular pulse amplitude (OPA) were measured with PASCAL Dynamic Contour Tonometry (DCT), and Model 30 Pneumatonometry (PNT). All measurements were taken in the sitting position (sit), and only for the PNT, also supine (sup) and lateral decubitus (LD) during (dur) a lumbar puncture (LP). Cerebrospinal fluid pressure (CSFP) was measured during the LP using an electronic transducer with a 27 gauge spinal needle, to provide both mean CSFP and CSFP pulse amplitude (CPA). TLPG was calculated as IOP minus CSFP using all devices and positions. TPA was calculated as OPA minus CPA with both DCT and PNT, in 1 and 3 body positions, respectively. The PNT IOP acquired during the LP was used as the gold standard for comparison to other positions and technologies using Repeated Measures Analysis of Variance (ANOVA) with Analysis of Variance of Contrast Variables. T-tests were performed between mean values of NRM and POAG groups. Significance threshold was p < 0.05.

Results : TLPG and TPA were significantly different between the during LP measurement and other tonometric technologies and positions, with the exception of supine TLPG. TLPG (mmHg) in NRM (DCT: -1.0 ± 4.4; GAT: -4.3 ± 4.0; IOPcc: -1.1 ± 5.2; bIOP: -3.9 ± 3.8; PNTdur: 2.2 ± 4.2; PNTsup: 2.8 ± 4.3; PNTsit: 0.1 ± 3.7) was significantly lower than POAG (DCT: 2.2 ± 4.8, p=.03; GAT: 0.2 ± 4.3, p<.01; IOPcc: 2.2 ± 4.9, p<.04; bIOP: -1.8 ± 4.4, p<.10; PNTdur: 4.9 ± 4.6, p=.05; PNTsup: 4.8 ± 4.8, p=.16; PNTsit: 3.1 ± 5.2, p<.04) with most technologies.

Conclusions : TLPG is lower in normal than glaucoma subjects, but of different magnitude than previous reports. IOP measured in the sitting position with GAT and CSFP measured in the LD position, as used in the literature, may lead to inaccurate estimation.

This is an abstract that was submitted for the 2017 ARVO Annual Meeting, held in Baltimore, MD, May 7-11, 2017.