Gauti Jóhannesson

Pascal, ICare and Goldmann applanation tonometry - a comparative study

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.

Kinetics of γ-cyclodextrin nanoparticle suspension eye drops in tear fluid.

We have developed nanoparticle γ‐cyclodextrin dexamethasone (DexNP) and dorzolamide (DorzNP) eye drops that provide sustained high drug concentrations on the eye surface. To test these characteristics, we measured dexamethasone and dorzolamide levels in tear fluid in humans following eye drop administration.

Topical dexamethasone γ-cyclodextrin nanoparticle eye drops increase visual acuity and decrease macular thickness in diabetic macular oedema.

To compare in a randomized, controlled trial topical 1.5% dexamethasone γ‐cyclodextrin nanoparticle eye drops (DexNP) with posterior subtenon injection of triamcinolone acetonide in diabetic macular oedema (DME).

γ-Cyclodextrin Nanoparticle Eye Drops with Dorzolamide: Effect on Intraocular Pressure in Man

PURPOSE To test a new drug delivery platform with dorzolamide γ-cyclodextrin (γCD) nanoparticle eye drops for intraocular pressure (IOP) control and safety and compare with Trusopt.(®) METHODS Self-aggregating γCD nanoparticle eye drops containing 3% dorzolamide were given once a day (QD) and compared with Trusopt given three times a day (TID) in a prospective randomized single masked crossover trial over 24 h. Seventeen subjects with IOP over 18 mmHg were recruited. IOP was measured with an Icare Tonometer Pro.(®) RESULTS There was no statistically significant difference in the IOP lowering effect of dorzolamide nanoparticle eye drops QD and Trusopt TID. At peak (4 h), the IOP reduction from baseline was 3.8±2.6 mmHg (18%, P<0.05) in the nanoparticle eye drop group and 3.1±3.7 mmHg in the Trusopt group (14%, P<0.05, P=0.97 between groups). At trough (24 h), the IOP reduction was 1.4±2.8 mmHg (6%, P>0.05) in nanoparticle eye drop group and 1.5±2.0 mmHg (7%, P>0.05) in the Trusopt group (P=0.23 between groups). Burning sensation measured on the visual analogue scale (1-100) was less from the nanoparticle eye drops (12±15) than from the Trusopt (37±30), (P=0.0038). Visual acuity and conjunctival hyperemia did not differ between the two groups. CONCLUSIONS Dorzolamide cyclodextrin nanoparticle eye drops QD lower IOP and the effect seems comparable to Trusopt given TID. The nanoparticle eye drops are well tolerated and seem to have a better safety profile than Trusopt.

Blood flow of ophthalmic artery in healthy individuals determined by phase-contrast magnetic resonance imaging

PURPOSE Recent development of magnetic resonance imaging (MRI) offers new possibilities to assess ocular blood flow. This prospective study evaluates the feasibility of phase-contrast MRI (PCMRI) to measure flow rate in the ophthalmic artery (OA) and establish reference values in healthy young (HY) and elderly (HE) subjects. METHODS Fifty HY subjects (28 females, 21-30 years of age) and 44 HE (23 females, 64-80 years of age) were scanned on a 3-Tesla MR system. The PCMRI sequence had a spatial resolution of 0.35 mm per pixel, with the measurement plan placed perpendicularly to the OA. Mean flow rate (Qmean), resistive index (RI), and arterial volume pulsatility of OA (ΔVmax) were measured from the flow rate curve. Accuracy of PCMRI measures was investigated using a vessel-phantom mimicking the diameter and the flow rate range of the human OA. RESULTS Flow rate could be assessed in 97% of the OAs. Phantom investigations showed good agreement between the reference and PCMRI measurements with an error of <7%. No statistical difference was found in Qmean between HY and HE individuals (HY: mean ± SD = 10.37 ± 4.45 mL/min; HE: 10.81 ± 5.15 mL/min, P = 0.655). The mean of ΔVmax (HY: 18.70 ± 7.24 μL; HE: 26.27 ± 12.59 μL, P < 0.001) and RI (HY: 0.62 ± 0.08; HE: 0.67 ± 0.1, P = 0.012) were significantly different between HY and HE. CONCLUSIONS This study demonstrated that the flow rate of OA can be quantified using PCMRI. There was an age difference in the pulsatility parameters; however, the mean flow rate appeared independent of age. The primary difference in flow curves between HE and HY was in the relaxation phase of the systolic peak.

The Pressure Difference between Eye and Brain Changes with Posture

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.

Effects of topical anaesthetics and repeated tonometry on intraocular pressure

Purpose:  To investigate the effects of repeated measurements of intraocular pressure (IOP) using Goldmann applanation tonometry (GAT) and applanation resonance tonometry (ART) to identify mechanisms contributing to the expected IOP reduction.

Change in intraocular pressure measurement after myopic LASEK: a study evaluating goldmann, pascal and applanation resonance tonometry.

PurposeTo prospectively evaluate 3 tonometry methods—the gold standard, Goldmann applanation tonometry, a new method, Pascal dynamic contour tonometry (PDCT), and a method under development, applanation resonance tonometry (ART)—with respect to intraocular pressure (IOP) measurements before, 3 and 6 months after laser-assisted subepithelial keratectomy (LASEK). Materials and MethodsOne randomly assigned eye of each of 53 healthy individuals, who underwent LASEK surgery for myopia was studied. Visual acuity, central corneal thickness, corneal curvature, and IOP were measured at each visit. Six IOP measurements/methods with 5 minutes pause between methods were performed. ResultsAll tonometry methods measured a significantly lower IOP after LASEK correction by a mean of −3.1 diopters. The IOP reduction was largest after 6 months for Goldmann applanation tonometry (−1.7±1.8 mm Hg) followed by ARTstat (−1.2±1.5 mm Hg), PDCT (−1.1±1.6 mm Hg), and ARTdyn (−1.0±1.5 mm Hg). The reduction of IOP did not differ significantly between different methods (P=0.11). There was a significant further reduction of measured IOP for PDCT between 3 and 6 months (−0.5±1.0 mm Hg). Uncorrected visual acuity improved significantly between 3 and 6 months postoperatively from 1.32±0.28 to 1.43±0.27. ConclusionsAll tonometry methods measured a significant, but low, reduction of IOP 3 and 6 months after LASEK. Further change in visual acuity and IOP measurements between 3 and 6 months suggest a still ongoing postoperative process.

Topical dexamethasone-cyclodextrin nanoparticle eye drops for non-infectious Uveitic macular oedema and vitritis : a pilot study

To evaluate the safety and efficacy of 1.5% dexamethasone nanoparticle (DexNP) drops in eyes with non‐infectious uveitic macular oedema and vitritis.

Introduction and clinical evaluation of servo-controlled applanation resonance tonometry

Purpose:  In recent years, Applanation Resonance Tonometry (ART) has been suggested for intraocular pressure (IOP) measurements. The manual version of ART (ARTmanual) has been further developed, and to improve usability, an automatic servo‐controlled prototype (ARTservo) has been proposed. The aim of this study was to assess the limits of agreement (LoA) of ARTmanual and ARTservo as compared with the reference method, Goldmann Applanation Tonometry (GAT).