Stability of a non-applanating handheld liquid patient interface for femtosecond laser-assisted cataract surgery.

PURPOSE: A stable and reliable vacuum is crucial for the correct planning and performance of femtosecond laser-assisted cataract surgery (FLACS) in order to avoid complications such as suction loss and cyclorotation. This study investigates, for the first time, the impact of different vacuum levels on the stability of the application of a liquid patient interface for FLACS in view of break-away forces. METHODS: Break-away forces were measured using a multifunctional material testing machine with a mounted digital manometer. Sixteen porcine eyes were docked to the patient interface of a femtosecond laser platform (FEMTO LDV Z8), and the impact of different vacuum levels between 300 and 500 mbar investigated. RESULTS: Mean break-away forces for each vacuum level were as follows: 1.78 N (± 0.58 N) for 300 mbar; 2.24 N (± 0.68 N) for 350 mbar; 2.66 N (± 0.68 N) for 400 mbar; 2.86 N (± 0.77 N) for 420 mbar; and 3.49 N (± 0.86 N) for 500 mbar. CONCLUSION: The stability increases with the vacuum in a nearly linear manner. Vacuum levels higher than 500 mmHg and lower than 350 mmHg are not recommended for FLACS.

Novel Liquid Interface for Femtosecond Laser-Assisted Penetrating Keratoplasty.

PURPOSE: To introduce a methodical description and to investigate first clinical safety of a novel liquid interface technology for femtosecond laser-assisted perforating keratoplasty, maintaining the corneal curvature without applanation of the cornea. METHODS: In this pilot study six patients received a femtosecond laser keratoplasty using a new liquid interface providing a non-applanating trephination. Clinical outcomes were evaluated 1, 3 and 6 months after surgery. RESULTS: All procedures were performed without complications and donor and recipient corneas could be aligned without problems, even in cases of advanced keratoconus. Although this initial pilot study investigated clinical safety, a positive effect on postoperative astigmatism was observed. CONCLUSION: We could show in this first pilot study that a hand-held liquid patient interface in combination with a femtosecond laser has a preliminary safety and reliability in penetrating keratoplasty.

Significant differences between specular microscopy and corneal bank endothelial cell counts - a pilot study.

BACKGROUND: It was shown recently that endothelial cell count performed by cornea banks overestimates the real number of endothelial cells. The aim of this study was to investigate the internal quality of preclinical ECD in human donor corneas using two widely used methods for endothelial cell counting, transmitted light microscopy used in organ culture tissue bank and clinically used specular microscopy. METHODS: Twenty human donor corneas that could not be transplanted were included in this analysis. Differences in evaluating endothelial cell density (ECD) and hexagonal endothelial cell ratio (HEX) between clinical specular microscopy (CSM) and corneal bank transmitted light microscope (CBLM) were evaluated as well as differences between automated and manual cell counts. RESULTS: Automated CBLM showed a higher ECD of 31.85% compared to automated CSM, while manual CBLM counting is 10.51% higher compared to manual CSM (p < 0.01). Further, higher average ECD values result in a higher difference between CSM and CBLM measurements. The manual CBLM ECDs were significantly higher compared to automated derived ECD from CSM (p < 0.01). However, no systematic bias can be detected when comparing the differences of the measurements with the average ECD measurements of both methods. CONCLUSION: This preclinical pilot study confirmed a significant higher ECD using transmitted light microscopy in organ culture compared to clinical specular microscopy. This indicates that the early rapid decrease of EC universally observed after surgery might be partly artefactual.

Decreased contrast sensitivity at high altitude.

BACKGROUND/AIMS: The aim of this study was to investigate a change in visual acuity and contrast sensitivity (CS) during high altitude exposure in healthy subjects due to the effects of hypobaric hypoxia. This study is related to the Tübingen High Altitude Ophthalmology study. METHODS: Visual acuity and Weber CS were tested monocularly using the Freiburger Visual Acuity and Contrast Test under standardised conditions in 14 healthy subjects at high altitude at the Capanna Margherita (4559 m, Italy) and compared with baseline measurements in Tübingen (341 m, Germany). Intraindividual differences between baseline and follow-up examinations were calculated by multivariate analysis of variance for repeated measures. Clinical parameters of peripheral oxygen saturation (SpO2) and heart rate (HR) as well as scores for acute mountain sickness (AMS) were correlated to psychophysical tests by Pearson's correlation coefficient. RESULTS: A significant decrease in CS with a mean effect size of -0.13 logCS was found for Weber CS (day 1=-0.16±0.22, p=0.01; day 2=-0.10±0.2, p=0.049; day 3=-0.12±0.19, p=0.03) at high altitude compared with baseline. Visual acuity remained unchanged. Decreased CS correlated with SpO2 (r=0.53, p=0.046) but not with HR (r=- 0.16, p=0.59) and occurred irrespective of AMS at high altitude. CONCLUSION: High altitude exposure leads to decreased CS. Changes occur independent of AMS. This finding is of clinical importance to trekkers and mountaineers exposed to high altitude as visual processing in particular under mesopic conditions at dusk and dawn is altered. Furthermore, it provides novel insight into hypoxia related changes in CS function.

Impact of 10% SF6 Gas Compared to 100% Air Tamponade in Descemet's Membrane Endothelial Keratoplasty.

PURPOSE: To compare the clinical outcomes following Descemet's membrane endothelial keratoplasty (DMEK) with 100% air tamponade versus 10% sulfur hexafluoride (SF6) tamponade. METHODS: Retrospective analysis of 108 consecutive DMEK cases subdivided by anterior chamber tamponade with 54 eyes receiving 10% SF6 and 54 eyes receiving 100% air injection. A post-hoc matched analysis revealed no statistically significant differences between the groups. The main outcome measurements were the complication rate, including intra- and postoperative complications and graft detachment rate requiring re-bubbling. Clinical outcome included best-corrected visual acuity (BCVA), endothelial cell count (ECC), and central corneal thickness (CCT) measured 1, 3, and 6 months after DMEK surgery. RESULTS: The graft detachment rate with consecutive re-bubbling was 18.5% in the air group and 22.2% in the SF6 group (p = 0.2). Remaining small peripheral graft detachments with a clear cornea occurred more often in the 100% air group (air: 22.2%; 12/54, 6/12 inferior compared to SF6: 7.4%; 4/54, 2/4 inferior; p = 0.06). The primary graft failure rate was comparable between the two groups. No complete graft detachment occurred. Outcome results for BCVA, ECC, and CCT at all follow-up time points were comparable between the two groups. CONCLUSION: The clinical outcomes (including re-bubbling rate, primary graft failure rate, and endothelial cell loss) were comparable with 100% air versus 10% SF6 tamponade, whereas other studies suggest that a higher SF6 concentration (20%) may result in a lower re-bubbling rate.

Comparison of intraocular pressure during the application of a liquid patient interface (FEMTO LDV Z8) for femtosecond laser-assisted cataract surgery using two different vacuum levels.

BACKGROUND: To evaluate intraocular pressure (IOP) using the application of a novel liquid patient interface for femtosecond laser-assisted cataract surgery with the FEMTO LDV Z8. METHODS: IOP was evaluated in enucleated porcine eyes prior, during and after the application of the Femto LDV Z8 liquid patient interface (Ziemer Ophthalmic Systems, Switzerland) using intracameral cannulation (n=20), intravitreal cannulation (n=20), rebound tonometry (n=20) and indentation tonometry (n=20). Pressure was assessed prior vacuum, during vacuum (30 s, 1 min, 2 min, 3 min) and after releasing the vacuum (1 min and 2 min). Two groups with different predefined vacuum levels (350 mbar, 420 mbar) were investigated. RESULTS: Mean intracameral pressure (±SD) increased during vacuum application from 20 mm Hg to 52.00 mm Hg (±6.35mm Hg; p=0.005) and 45.18 mmHg (±4.34 mm Hg; p=0.005) for the 420 mbar and the 350 mbar vacuum levels, respectively. Mean intravitreal pressure increased from 20 mm Hg to 25.60 mm Hg (±9.85 mm Hg; p=0.058) and 28.10 mm Hg (±2.54 mm Hg; p=0.059) for the 420 mbar and the 350 mbar vacuum levels, respectively. Pressure values from indentation and rebound tonometry were in between intracameral and intravitreal values. Mean intracameral IOP was 18.1% higher (p=0.019) in the 420 mbar group compared with the 350 mbar group. CONCLUSION: During vacuum application of the liquid patient interface of the Femto LDV Z8 for femtosecond laser-assisted cataract surgery, IOP values were higher in the anterior chamber compared with the intravitreal pressure measurements. The higher predefined vacuum level (350 mbar vs 420 mbar) resulted in significant higher intracameral IOP.