Objective: The discovery of a posture-dependent effect on the difference between intraocular pressure (IOP) and intracranial pressure (ICP) at the level of lamina cribrosa could have important implications for understanding glaucoma and idiopathic intracranial hypertension and could help explain visual impairments in astronauts exposed to microgravity. The aim of this study was to determine the postural influence on the difference between simultaneously measured ICP and IOP.Methods: Eleven healthy adult volunteers (age 46±10 years) were investigated with simultaneous ICP, assessed through lumbar puncture, and IOP measurements when supine, sitting, and in 9° head down tilt (HDT). The trans-lamina cribrosa pressure difference (TLCPD) was calculated as the difference between the IOP and ICP. To estimate the pressures at the lamina cribrosa, geometrical distances were estimated from MRI and were used to adjust for hydrostatic effects. Results:The TLCPD (mm Hg) between IOP and ICP was 12.3±2.2 for supine, 19.8±4.6 for sitting and 6.6±2.5 for HDT. The expected 24-hour average TLCPD on earthassuming 8 h supine and 16 h upright-was estimated to be 17.3 mm Hg. By removing the hydrostatic effects on pressure, a corresponding 24 h-average TLCPD in microgravity environment was simulated to be 6.7 mmHg. Interpretation:We provide a possible physiological explanation for how microgravity can cause symptoms similar to those seen in patients with elevated ICP. The observed posture dependency of TLCPD also implies that assessment of the difference between IOP and ICP in upright may offer new understanding of the pathophysiology of idiopathic intracranial hypertension and glaucoma.

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ABSTRACT.Purpose: To compare intraocular pressure (IOP) measurements by Pascal, ICare and Goldmann applanation tonometry (GAT), to evaluate the effects of central corneal thickness (CCT) and curvature on IOP measurement and to estimate the intra-observer variability. Methods: A prospective, single-centre study of 150 eyes with a wide range of pressures. Six masked IOP measurements ⁄ method; corneal thickness and curvature were studied for each eye. GAT was the reference. Results: IOP Pascal and IOP ICare correlated with IOP GAT (r = 0.91, 0.89). Mean ICare measurement exceeded GAT by 2 mmHg. Pascal measured higher than GAT at low IOPs and lower at high IOPs. For every 10 mmHg increase in IOP above 31 mmHg, Pascal measured 2 mmHg lower than GAT and vice versa. CCT was correlated significantly with IOP GAT (r = 0.23) and IOP ICare (r = 0.43) but not with IOP Pascal (P = 0.12). CCT was correlated with age. In a subgroup (>50 years), ICare and the difference between IOP GAT and IOP Pascal were affected significantly by the CCT, whereas IOP GAT and IOP Pascal were not. Corneal curvature was correlated significantly with IOP GAT (r = )0.27) and IOP Pascal (r = )0.26) but not with IOP ICare (P = 0.60). Intra-observer variability within each set of six measurements was approximately 2 mmHg, irrespective of method. Conclusion: This study showed a reasonable overall correlation and concordance between the IOP obtained with the three instruments. None of the methods were completely independent of the biomechanical properties of the cornea. ICare showed a significant dependency upon CCT, whereas GAT and Pascal showed a significant dependency on corneal curvature. All methods showed intra-observer variability, which leaves room for further improvement of methods.

ABSTRACT.Purpose: To compare in a randomized, controlled trial topical 1.5% dexamethasone c-cyclodextrin nanoparticle eye drops (DexNP) with posterior subtenon injection of triamcinolone acetonide in diabetic macular oedema (DME). Methods: In this prospective, randomized, controlled trial, 22 eyes of 22 consecutive patients with DME were randomized to (i) topical treatment with DexNP 33/day (4 weeks), 32/day (4 weeks) and 31/day (4 weeks) or (ii) one posterior subtenon injection of 20 mg triamcinolone acetonide. Study visits were at baseline and 4, 8, 12 and 16 weeks. Results: The logMAR (Snellen) visual acuity (mean AE SD) improved significantly with DexNP from 0.41 AE 0.3 (Snellen 0.39) to 0.32 AE 0.25 (0.48) and 0.30 AE 0.26 (0.50) at 4 and 8 weeks, respectively. One-third of the DexNP group improved more than 0.3 logMAR units. For triamcinolone, logMAR changed significantly from 0.42 AE 0.28 (0.38) at baseline to 0.32 AE 0.29 (0.48) at 4w and 0.33 AE 0.37 (0.47) at 12w. The central macular thickness (CMT) decreased significantly with DexNP from 483 AE 141 lm to 384 AE 142 lm at 4w and 342 AE 114 lm at 8w. For triamcinolone, CMT decreased significantly at all time-points: 494 AE 94 lm, 388 AE 120, 388 AE 145, 390 AE 136 and 411 AE 104 lm at 0, 4, 8, 12 and 16 weeks, respectively. There was a modest increase in intraocular pressure (IOP) at all time-points with DexNP while no increase was seen with triamcinolone. Serum cortisol was affected by both treatments. Conclusion: Topical DexNP significantly improve visual acuity and decrease macular thickness in patients with DME. The effect is similar to that from subtenon triamcinolone. A modest increase in IOP was seen with the nanoparticle eye drops, but IOP normalized after the discontinuation of treatment.

There was no evidence of reduced ICP in NTG patients as compared with healthy controls, either in supine or in upright position. Consequently, the hypothesis that NTG is caused by an elevated TLCPD from low ICP was not supported.