Measurement of two-photon-absorption spectra through nonlinear fluorescence produced by a line-shaped excitation beam.

We propose an innovative experimental approach to estimate the two-photon absorption (TPA) spectrum of a fluorescent material. Our method develops the standard indirect fluorescence-based method for the TPA measurement by employing a line-shaped excitation beam, generating a line-shaped fluorescence emission. Such a configuration, which requires a relatively high amount of optical power, permits to have a greatly increased fluorescence signal, thus avoiding the photon counterdetection devices usually used in these measurements, and allowing to employ detectors such as charge-coupled device (CCD) cameras. The method is finally tested on a fluorescent isothiocyanate sample, whose TPA spectrum, which is measured with the proposed technique, is compared with the TPA spectra reported in the literature, confirming the validity of our experimental approach.

Direct costs of glaucoma: Relationship between cost and severity of the disease.

OBJECTIVES: To estimate the direct medical costs associated with the management of patients with primary open-angle glaucoma and to compare the costs of patients according to the degree of severity. METHODS: A longitudinal retrospective study was carried out using all patients with primary open-angle glaucoma that recorded follow-up from May 2010 to June 2013 at the Hospital Privado de Córdoba. We estimated the cost of the disease from the perspectives of the institution, with a bottom-up approach. RESULTS: The three-year follow-up after treatment of 104 patients revealed that the average cost of care for a patient with primary open-angle glaucoma was US$2746 ± 1560. The first year of treatment was significantly more expensive than subsequent ones (US$1100-$810-$827). Cost was related to the degree of severity of glaucoma; patients in "Stage 0" had significantly lower costs than those in other groups (Kruskal-Wallis test, p < 0.01). This was a consequence of lower costs associated with medication and a lower percentage of patients undergoing surgery. DISCUSSION: The direct medical costs of a patient with primary open-angle glaucoma vary according to the severity of their disease and the year of treatment. We found that costs increased with disease severity, but decreased over time.

Triamcinolone acetonide-loaded lipid nanocapsules for ophthalmic applications.

Triamcinolone acetonide (TA) is an effective drug widely (off-label) used in the treatment of several ocular diseases involving inflammation and angiogenic processes. However, the use of TA ocular presents some limitations mainly related to its excipient composition, as in the case of benzyl alcohol. Thus, the aim of this work was to obtain an alternative TA formulation based on lipid nanocapsules (LNCs). Triamcinolone acetonide-loaded lipid nanocapsules (TA-LNCs) were obtained by the phase inversion temperature process without the use of irritating excipients, by combining lipids and surfactants generally recognized as safe. Pre-formulation studies were carried out to evaluate the TA solubility in different co-surfactants and to optimize the lipid core composition in order to enhance the drug loading and encapsulation rate in the LNCs. A stable final TA-LNC formulation was obtained with a mean particle size (MPS) of below 50 nm, a narrow size distribution (PDI < 0.2), a negative zeta potential (ZP) and a high encapsulation efficiency (%EE > 98%). In vitro cellular viability assays revealed that blank LNCs and TA-LNCs at 0.1 µg/mL did not affect the viability of the human corneal epithelial (HCE) cells. TA-LNCs showed a high anti-inflammatory activity below the toxicity level, with a reduction of 30% in interleukin (IL)-6 secretion observed in an in vitro model using the same cell line. More importantly, the TA-LNCs revealed a therapeutic efficacy in the endotoxin-induced uveitis (EIU) rabbit model with a significant attenuation of clinical signs of an inflammatory response. These findings make the TA-LNCs a safer and more efficient alternative for the treatment of eye disorders.

Bound electronic and free carrier nonlinearities in Silicon nanocrystals at 1550nm.

We present a detailed investigation of the different processes responsible for the optical nonlinearities of silicon nanocrystals at 1550 nm. Through z-scan measurements, the bound-electronic and excited carrier contributions to the nonlinear refraction were measured in presence of two-photon absorption. A study of the nonlinear response at different excitation powers has permitted to determine the change in the refractive index per unit of photo-excited carrier density sigma(r) and the value of the real bound-electronic nonlinear refraction n(2be) as a function of the nanocrystals size. Moreover at high excitation power, a saturation of the nonlinear absorption was observed due to band-filling effects.

Supercontinuum generation by higher-order mode excitation in a photonic crystal fiber.

We describe an experiment in which a train of femtosecond pulses is coupled into a photonic crystal fiber (PCF) by means of an offset pumping technique that can selectively excite either the mode LP(01) or LP(11) or LP(21). The PCF presents a wide range of wavelengths in which the fundamental mode experiences normal dispersion, whereas LP(11) and LP(21) propagate in the anomalous dispersion regime, generating a supercontinuum based on the soliton fission mechanism. We find that the existence of a cut-off wavelength for the higher-order modes makes the spectral broadening asymmetrical. This latter effect is particularly dramatic in the case of the LP(21) mode, in which, by using a pump wavelength slightly below cut-off, the spectral broadening occurs only on the blue side of the pump wavelength. Our experimental results are successfully compared to numerical solutions of the nonlinear Schrödinger equation.

Kerr-induced spontaneous Bessel beam formation in the regime of strong two-photon absorption.

We study the effect of Two-Photon Absorption (TPA) nonlinear losses on Gaussian pulses, with power that exceeds the critical power for self-focusing, propagating in bulk kerr media. Experiments performed in fused silica and silicon highlight a spontaneous reshaping of the input pulse into a pulsed Bessel beam. A filament is formed in which sub-diffractive propagation is sustained by the Bessel-nature of the pulse.

Acanthamoeba in the eye, can the parasite hide even more? Latest developments on the disease.

Acanthamoeba spp. is a free living protozoan in the environment, but can cause serious diseases. Acanthamoeba keratitis (AK), a severe and painful eye infection, must be treated as soon as possible to prevent ulceration of the cornea, loss of visual acuity, and eventually blindness or enucleation. Although the disease affects principally contact lens (CLs) wearers, it is recognized nowadays as a cause of keratitis also in non-CLs wearers. Although the number of infections caused by these amoebae is low, AK is an emerging disease presenting an extended number of cases each year worldwide mostly due to the increasing use of CLs, but also to better diagnostic methods and awareness. There are two principal causes that lead to severe outcomes: misdiagnosis or late diagnosis of the causal agent, and lack of a fully effective therapy due to the existence of a highly resistant cyst stage of Acanthamoeba. Recent studies have reported different genotypes that have not been previously associated with this disease. In addition, Acanthamoeba can act as a reservoir for phylogenetically diverse microorganisms. In this regard, recently giant viruses called Pandoravirus have been found within genotypes producing keratitis. What potential risk this poses is not yet known. This review focuses on an overview of the present status and future prospects of this re-emerging pathology, including features of the parasite, epidemiology, clinical aspects, diagnosis, and treatment.

The role of hyaluronan as a drug carrier to enhance the bioavailability of extended release ophthalmic formulations. Hyaluronan-timolol ionic complexes as a model case.

The aim of this work was to obtain information concerning the properties of ophthalmic formulations based on hyaluronic-drug ionic complexes, to identify the factors that determine the onset, intensity and duration of the pharmacotherapeutic effect. Dispersions of a complex of 0.5% w/v of sodium hyaluronate (HyNa) loaded with 0.5% w/v of timolol maleate (TM) were obtained and presented a counterionic condensation higher than 75%. For comparison a similar complex obtained with hyaluronic acid (HyH) was also prepared. Although the viscosity of HyNa-TM was significantly higher than that of HyH-TM, in vitro release of TM from both complexes showed a similar extended drug release profile (20-31% over 5h) controlled by diffusion and ionic exchange. Ocular pharmacokinetic study performed in normotensive rabbits showed that HyNa-TM complex exhibited attractive bioavailability properties in the aqueous humor (AUC and Cmax significantly higher and later Tmax) compared to commercial TM eye-drops. Moreover, a more prolonged period of lowered intra-ocular pressure (10h) and a more intense hypotensive activity was observed after instillation of a drop of HyNa-TM as compared to the eye-drops. Such behavior was related to the longer pre-corneal residence times (400%) observed with HyNa-TM complex. No significant changes in rabbit transcorneal permeation were detected upon complexation. These results demonstrate that the ability of HyNa to modulate TM release, together with its mucoadhesiveness related to the viscosity, affected both the pharmacokinetic and pharmacodynamic parameters. The HyNa-TM complex is a potentially useful carrier for ocular drug delivery, which could improve the TM efficacy and reduce the frequency of administration to improve patient compliance.

[Treatment of corneal ulcers with platelet rich plasma]. / Tratamiento de úlceras corneales con plasma rico en plaquetas.

OBJECTIVE: To assess the efficacy of platelet rich plasma (PRP) in the treatment of extensive corneal ulcers in albino rabbits. METHODS: New Zealand rabbits, divided in 3 groups, were used for the study. Corneal ulcers of 10mm diameter were made. Rabbits blood was extracted for the preparation of the PRP of the corresponding group. The blood was processed by differential centrifugation. The first group, named control, was treated with sterile saline every 8h. The second group, named gel, was treated with deproteinized extract gel beef fat every 8h, and the third group, named PRP received one PRP drop on the first and third day of monitoring. The rabbits were monitored, by taking photographs, each day for the 7 days that the study lasted. RESULTS: A better outcome was observed in the group with deproteinized extract gel beef fat (GE group), and the PRP group (PL group), in comparison with the control group (CO group) (P<.05). CONCLUSION: The PRP showed to be just as effective as the commercial product (Solcoseryl®), for the regeneration of the extensive and deep corneal ulcers. Besides, it stands out as a no surgical procedure is required, and there is easy access, low cost and reduced doses.

Novel bioadhesive hyaluronan-itaconic acid crosslinked films for ocular therapy.

New hyaluronic acid (HA)-itaconic acid (IT) films have been previously synthesized and used as potential topical drug delivery systems (DDS) for ocular administration. In this study we explored homogeneous and heterogeneous crosslinking reactions of HA using glutaraldehyde (GTA) and polyethylene glycol diglycidyl ether (PEGDE) in the presence of IT, a naturally occurring compound that is non-toxic and readily biodegradable. We have studied the morphology, mechanical properties and in vitro biocompatibility between these new materials and ocular surface cells (human corneal epithelial cell line) and evaluated the biopharmaceutical performance of the designed formulations. Although all the synthesized materials exhibited good mechanical properties, the PEGDE modified films exhibited the best biocompatibility, with in vivo assays showing good adhesive performance and minimal irritation. PEGDE films were also tested for their effects in the treatment of intraocular pressure (IOP) in rabbits using timolol maleate (TM) as the model drug. These results may be useful for further design of novel bioadhesive matrix containing drugs by topical application in ophthalmology.

Generation and amplification of pulsed Bessel beams by seeding an optical parametric amplifier.

By using two very different seed pulses we demonstrate that the spatiotemporal gain properties of a chi(2) optical parametric amplifier can be exploited as an efficient conical reshaping mechanism leading to the generation and amplification of a pulsed Bessel beam.

Complete retrieval of the field of ultrashort optical pulses using the angle-frequency spectrum.

We propose an experimental technique that allows for a complete characterization of the amplitude and phase of optical pulses in space and time. By the combination of a spatially resolved spectral measurement in the near and far fields and a frequency-resolved optical gating measurement, the electric field of the pulse is obtained through a fast, error-reduction algorithm.

Ultrashort-pulse investigation of the propagation properties of the LP(11) mode in 1.55-mum communication fibers.

The coupling of an ultrashort laser pulse into a single-mode optical communication fiber gives rise to two propagating pulses as a result of the excitation of two guided modes, the fundamental, LP(01) , and the leaky, LP(11) . Such a phenomenon provides a new approach to the study of the propagation properties of the LP(11) mode. An experiment with tunable 110-fs pulses at a wavelength near 1550 nm is described. Information about the group velocity, the polarization-rotation length, the attenuation coefficient, and the cutoff wavelength of the LP(11) mode is obtained in a simple and direct way for various fibers.

Tratamiento de úlceras corneales con plasma rico en plaquetas / Treatment of corneal ulcers with platelet rich plasma

OBJETIVO: Evaluar la eficacia del plasma rico en plaquetas (PRP) en el tratamiento de úlceras corneales no infecciosas extensas en conejos albinos. MÉTODOS: Para el estudio se utilizaron conejos New Zealand, divididos en 3 grupos. Se realizaron úlceras corneales de 10 mm de diámetro. Se extrajo sangre de los conejos para la preparación del PRP del grupo correspondiente. La misma fue procesada mediante centrifugación diferencial. El primer grupo, llamado control, fue tratado con solución salina estéril cada 8 h durante 7 días; el segundo grupo, llamado gel, fue tratado con un gel extracto desproteinizado de sangre de ternera (Solcoseryl®) cada 8 h durante 7 días y el tercer grupo, llamado PRP, recibió una gota del PRP el día 1 y el día 3 de seguimiento. Los controles fueron realizados diariamente durante los 7 días que duró el tratamiento. Se llevó a cabo un registro de los mismos a través de muestras fotográficas. RESULTADO: Se observó una mejor evolución en el grupo del gel extracto desproteinizado de sangre de ternera (grupo GE) y en el grupo de PRP (grupo PL), en comparación con el grupo control (grupo CO) (p < 0,05). CONCLUSIÓN: El PRP demostró ser tan efectivo como la muestra comercial (Solcoseryl®), para la regeneración de úlceras corneales profundas y extensas. Además se destaca su fácil acceso, costo y reducida posología

OBJECTIVE: To assess the efficacy of platelet rich plasma (PRP) in the treatment of extensive corneal ulcers in albino rabbits. METHODS: New Zealand rabbits, divided in 3 groups, were used for the study. Corneal ulcers of 10 mm diameter were made. Rabbits blood was extracted for the preparation of the PRP of the corresponding group. The blood was processed by differential centrifugation. The first group, named control, was treated with sterile saline every 8 h. The second group, named gel, was treated with deproteinized extract gel beef fat every 8 h, and the third group, named PRP received one PRP drop on the first and third day of monitoring. The rabbits were monitored, by taking photographs, each day for the 7 days that the study lasted. RESULTS: A better outcome was observed in the group with deproteinized extract gel beef fat (GE group), and the PRP group (PL group), in comparison with the control group (CO group) (P<0.05). CONCLUSION: The PRP showed to be just as effective as the commercial product (Solcoseryl®), for the regeneration of the extensive and deep corneal ulcers. Besides, it stands out as a no surgical procedure is required, and there is easy access, low cost and reduced doses