Contrasting the beam interaction characteristics of selected lasers with a partially stabilised zirconia (PSZ) bio-ceramic

Differences in the beam interaction characteristics of a CO2 laser, a Nd:YAG laser, a high power diode laser (HPDL) and an excimer laser with a partially stabilised zirconia (PSZ) bio-ceramic have been studied. A derivative of Beer-Lambert’s law was applied and the laser beam absorption lengths of the four lasers were calculated as 33.55 x 10-3 cm for the CO2 laser, 18.22 x 10-3 cm for the Nd:YAG laser, 17.17 x 10-3 cm for the HPDL and 8.41 x 10-6 cm for the excimer laser. It was determined graphically that the fluence threshold values at which significant material removal was effected by the CO2 laser, the Nd:YAG laser, the HPDL and the excimer laser were 52 J/cm2, 97 J/cm2, 115 J/cm2 and 0.48 J/cm2 respectively. The thermal loading value for the CO2 laser, the Nd:YAG laser, the HPDL and the excimer laser were calculated as being 1.55 kJ/cm3, 5.32 kJ/cm3, 6.69 kJ/cm3 and 57.04 kJ/cm3 respectively

Wettability characteristics of an Al2O3/SiO2-based ceramic modified with CO2, Nd:YAG, excimer and high-power diode lasers

Interaction of CO2, Nd:YAG, excimer and high power diode laser (HPDL) radiation with the surface of an Al2O3/SiO2 based ceramic was found to effect significant changes in the wettability characteristics of the material. It was observed that interaction with CO2, Nd:YAG and HPDL radiation reduced the enamel contact angle from 1180 to 310, 340 and 330 respectively. In contrast, interaction with excimer laser radiation resulted an increase in the contact angle to 1210. Such changes were identified as being due to: (i) the melting and partial vitrification of the Al2O3/SiO2 based ceramic surface as a result of interaction with CO2, Nd:YAG HPDL radiation. (ii) the surface roughness of the Al2O3/SiO2 based ceramic increasing after interaction with excimer laser radiation. (iii) the surface oxygen content of the Al2O3/SiO2 based ceramic increasing after interaction with CO2, Nd:YAG and HPDL radiation. The work has shown that the wettability characteristics of the Al2O3/SiO2 based ceramic could be controlled and/or modified with laser surface treatment. In particular, whether the laser radiation had the propensity to cause surface melting. However, a wavelength dependance of the change of the wetting properties could not be deduced from the findings of this work

Photoablation of human vitreous opacities by light-induced vapor nanobubbles

Myopia, diabetes, and aging are the main causes of progressive vitreous collagen aggregation, resulting in vitreous opacities, which can significantly disturb vision. As vitreous opacities, which induce the visual phenomenon of "floaters", are accessible with nanomaterials and light, we propose a nanotechnology-based approach to locally ablate them with highly reduced light energy compared to the more traditional YAG laser therapy. Our strategy relies on the plasmon properties of gold nanoparticles that generate vapor nanobubbles upon pulsed-laser illumination whose mechanical force can ablate vitreous opacities. We designed gold nanoparticles coated with hyaluronic acid (HA), which have excellent diffusional mobility in human vitreous, an essential requirement to reach the vitreous opacities. In addition, we found that HA-coated gold nanoparticles can accumulate extensively on human vitreous opacities that were obtained by vitrectomy from patients with vision-degrading myodesopsia. When subsequently applying nanosecond laser pulses, the collagen aggregates were efficiently destroyed with similar to 1000 times less light energy than typically used in YAG laser therapy. This low-energy "floater-specific destruction", which is due to the accumulation of the small gold nanoparticles on the opacities, is attractive, as it may be safer to the surrounding ocular tissues while at the same time being easier and faster to apply compared to YAG laser therapy, where the opacities need to be ablated piece by piece by a tightly focused laser beam. Gold nanoparticle-assisted photoablation may therefore provide a safer, faster, and more reliable destruction of vitreous opacities in the treatment of ophthalmologic diseases

Return to sport decisions after an acute lateral ankle sprain injury : introducing the PAASS framework - an international multidisciplinary consensus

Background Despite being the most commonly incurred sports injury with a high recurrence rate, there are no guidelines to inform return to sport (RTS) decisions following acute lateral ankle sprain injuries. We aimed to develop a list of assessment items to address this gap. Methods We used a three-round Delphi survey approach to develop consensus of opinion among 155 globally diverse health professionals working in elite field or court sports. This involved surveys that were structured in question format with both closed-response and open-response options. We asked panellists to indicate their agreement about whether or not assessment items should support the RTS decision after an acute lateral ankle sprain injury. The second and third round surveys included quantitative and qualitative feedback from the previous round. We defined a priori consensus being reached at >70% agree or disagree responses. Results Sixteen assessment items reached consensus to be included in the RTS decision after an acute lateral ankle sprain injury. They were mapped to five domains with 98% panellist agreement-PAASS: ain (during sport participation and over the last 24 hours), nkle impairments (range of motion; muscle strength, endurance and power), athlete perception (perceived ankle confidence/reassurance and stability; psychological readiness), ensorimotor control (proprioception; dynamic postural control/balance), port/functional performance (hopping, jumping and agility; sport-specific drills; ability to complete a full training session). Conclusion Expert opinion indicated that pain severity, ankle impairments, sensorimotor control, athlete perception/readiness and sport/functional performance should be assessed to inform the RTS decision following an acute lateral ankle sprain injury. Trial registration number ACTRN12619000522112. [Abstract copyright: © Author(s) (or their employer(s)) 2021. No commercial re-use. See rights and permissions. Published by BMJ.

The changes of shape of the human cornea with age

Póster presentado al 6th EOS Topical Meeting on Visual and Physiological Optics celebrado en Dublin (Irlanda) del 20 al 22 de agosto de 2012.The shape of the aging cornea was studied in a group of 407 nor-mal eyes. The most significant changes found were: a small increase of the curvature, eccentricity and irregularity of the anterior surface with age. For both the anterior and posterior surfaces the misalign-ment with the keratometric axis increased with age. [Introduction]: There are several studies on the mean corneal shape based on fit-ting the surface topography to a given model. The most popular models divide the surface elevation S into a regular basis surface, B (with a straightforward optical interpretation, such as spheres, coni-coids, 3 axes ellipsoids or biconics) plus a residual R = S – B which accounts for local irregularities and departures from the basis sur-face B. It is also common to fit the residual to a Zernike polynomial expansion. In an earlier study the geometry and optical proper-ties of the mean cornea were analyzed using a general 3-axis ellip-soid, so that we could determine the position (x0, y0, z0) and orienta-tion (α, β, γ) of the optical axis in the 3D space. The strength of that B model was patent as it provided significant lower fitting errors than standard (canonical) models. Here we apply a similar approach to a larger set (407 corneas), covering a wide range of ages (4 - 79 years). The measurements were taken with a Scheimpflug system (PentacamTM) which provides topographies of both front and back surfaces. The B model was also improved and generalized to a general biconic defined by 10 parameters: apex radii (RMax, Rmin), conic constants (QMax, Qmin) plus position and orientation in space. The residual R was analyzed by a 8th order Zernike polynomial expansion.[Discussion]: The RMS residual (fit error) shows marked differences between the anterior ( = 5.7 μm) and posterior ( = 14.6 μm) surfaces (Sant and Spos). This suggests that the biconic is a good model but only for the anterior surface. Interestingly, this residual slightly increases with age for Sant but shows the opposite trend for Spos. Fig. 1 shows the evolution of the horizontal (β) and vertical (α) angles between the biconic and keratometric axes. The linear regression shows a clear trend to increase both angles (misalignment) with age. Even though the predictability is poor due to a high intersubject variability, such trend has a high statistical significance (p-values 0.0236 and 0.0033 for βant, and βpos; and even lower p-values for α). In addition there is a clear misalignment between Sant and Spos of ~2.5º for both angles. Similar plots were obtained for radii, conic constants and apex coordinates for both surfaces. The radii of the anterior surface were found to decrease slightly but significantly (P ant = 7.85 - 0.0047·age mm; ant = 7.70 - 0.0040·age), as well as the conic constant along the meridian of maximum curvature for both surfaces (ant = -0.30-0.0025·age; pos = - 0.55 -0.0024·age). Several parameters, on the other hand, remained constant with age, such as the apical radii of the back surface (pos = 6.27 ± 0.26 mm; pos = 5.92 ± 0.30 mm); the conic constant along the axis of minimum cur-vature for both anterior and posterior surfaces (ant = -0.38 ± 0.13; pos = -0.49 ± 0.14 mm) do not change significantly with age; and Euler angle γ, corresponding with the astigmatism axis, which on average is close to vertical, but shows a large inter-subject variability. The statistical analysis presented so far is somewhat preliminary in the sense that it is based on the complete set without removing out-liers. Nevertheless, it is worth noting that this will probably affect the exact values of parameters, but the main trends and conclusions are expected to be basically the same.[Conclusions]: These results confirm previous findings, such as the increase of the corneal power, or the tendency of the cornea to become more prolate with age. In addition, the biconic model permits to iden-tify that the conic constant has a maximum change along the merid-ian of maximum curvature (no change in the orthogonal one). A new finding (to our knowledge) is that our results suggest a significant progressive tip/tilt of the optical axis of the (best fit) biconic with age, for both anterior and posterior corneal surfaces.Supported by the Spanish MEC, grant FIS2011-22496 to Rafael Navarro and by the Flemish IWT, grant 110684 to Jos Rozema.Peer reviewe

SyntEyes: A higher-order statistical eye model for healthy eyes

[Purpose]: Stochastic eye models are a method to generate random biometry data with the variability found in the general population for use in optical calculations. This work improves the accuracy of a previous model by including the higher-order shape parameters of the cornea. [Methods]: The right eye biometry of 312 subjects (40.8 ± 11.0 years of age) were measured with an autorefractometer, a Scheimpflug camera, an optical biometer, and a ray tracing aberrometer. The corneal shape parameters, exported as Zernike coefficients, were converted to eigenvectors for dimensional reduction. The remaining 18 parameters were modeled as a sum of two multivariate Gaussians, from which an unlimited number of synthetic data sets (SyntEyes) were generated. After conversion back to Zernike coefficients, the data were introduced into ray tracing software. [Results]: The mean values of nearly all SyntEyes parameters were statistically equal to those of the original data (two one-sided t-test, P > 0.05/109, Bonferroni correction). The variability of the SyntEyes parameters was similar to the original data for most important shape parameters and intraocular distances (F-test, P 0.05/109). The same was seen for the correlations between higher-order shape parameters. After applying simulated cataract or refractive surgery to the SyntEyes model, a very close resemblance to previously published clinical outcome data was seen. [Conclusions]: The SyntEyes model produces synthetic biometry that closely resembles clinically measured data, including the normal biological variations in the general population.Supported by research grants from the Flemish government agency for Innovation by Science and Technology (Grant IWT/110684) and the Spanish Ministry of Economy and Competitiveness (FIS2014-58303-P).Peer Reviewe

Higher order statistical eye model for keratoconus

Trabajo presentado al 8th European Meeting on Visual and Physiological Optics, celebrado en Antwerp (Bélgica) del 22 al 24 de agosto de 2016.This work presents and validates a stochastic eye model for keratoconus that may be used to develop new optical corrective strategies in these patients. This could be particularly useful for researchers that do not have access to original keratoconic data.This project was supported by research grants by the Flemish government agency for Innovation by Science and Technology (grant nr IWT/110684) and the Spanish Ministry of Economy and Competitiveness (FIS2014-58303-P).Peer Reviewe