Jean Marie Parel

Axonal regeneration into Schwann cell grafts within resorbable poly(α-hydroxyacid) guidance channels in the adult rat spinal cord

Axonal growth and myelination in a SC graft contained in a resorbable tubular scaffold made of poly(D,L-lactic acid) (PLA50) or high molecular weight poly(L-lactic acid) mixed with 10% poly(L-lactic acid) oligomers (PLA(100/10)) were studied for up to 4 months after implantation in the completely transected adult rat thoracic spinal cord. The PLA50 tubes collapsed soon after implantation and, consequently, compressed the graft inside, leading to only occasional thin cables with SCs and a low number of myelinated axons: 17 +/- 6 at 1 and 158 +/- 11 at 2 months post-grafting. The cable contained 32 +/- 23 blood vessels at 2 weeks, 55 +/- 33 at 1 month and 46 +/- 30 at 2 months after implantation. PLA(100/10) tubes, on the other hand, were found to break up into large pieces, which compressed and sometimes protruded into the tissue cable inside. At all time points studied, however, cables contained SCs and were well vascularized with 414 +/- 47 blood vessels at 2 weeks, 437 +/- 139 at 1, 609 +/- 134 at 2 and 396 +/- 95 at 4 months post-grafting. The number of myelinated axons was 712 +/- 509 at 1 month, 1819 +/- 837 at 2 months and 609 +/- 132 at 4 months post implantation. These results demonstrated that fiber growth and myelination into a SC graft contained in a resorbable PLA(100/10) tube increases over the first 2 months post-implantation but decreases thereafter. Changes in geometry of both types of polymer tubes were detrimental to axonal regeneration. Future research should explore the use of polymers that better retain the appropriate mechanical, geometrical and permeability properties over time.

Reticulated hyaluronic acid implant in nonperforating trabecular surgery

PURPOSE To evaluate experimentally and clinically the tolerance and efficacy of a reticulated hyaluronic acid implant in nonperforating trabecular surgery (NPTS). SETTING Bascom Palmer Eye Institute, Miami, Florida, USA, and Clinique Sourdille and Clinique Ophtalmologique Universitaire, Nantes, France. METHODS In experimental surgery, NPTS was performed with and without a hyaluronic acid implant in 25 rabbit eyes. In a pilot study, the results of NPTS with a hyaluronic acid implant in 72 human eyes were retrospectively analyzed in terms of visual acuity, intraocular pressure (IOP), external filtration, postoperative inflammation, and gonioscopy. Mean follow-up was 13.8 months (range 6 to 24 months). RESULTS In the experimental surgery, the rabbit eyes with the implant showed a different healing process than the eyes without the implant. The implant was slowly bioabsorbed and remnants were seen at the operative site (where the tissue was removed) up to day 56 postoperatively. This site was detectable at all histology study periods. Intraocular pressure reduction was longer in the implant group: greater than 5 months versus 3 weeks (P < .05). In the pilot study, visual acuity remained stable, IOP decreased from a mean preoperative level of 26.3 mm Hg +/- 5.22 (SD) to a mean postoperative level without treatment of 15.4 +/- 3.1 mm Hg (P < .0001). No external filtration was detected in 60 eyes, a slightly elevated conjunctiva was noted in 12 eyes. Postoperative inflammation (laser flare and cell measurements) was low. Gonioscopy consistently demonstrated the persistence of a decompression space behind the trabeculum. CONCLUSION Comparative experimental surgery results showed excellent tolerance and efficacy in the rabbit eyes with a hyaluronic acid implant. Clinical results, to be confirmed by a randomized comparative study, also showed excellent biocompatibility and encouraging efficacy.

Corneal Mechanical Thresholds Negatively Associate With Dry Eye and Ocular Pain Symptoms.

Purpose To examine associations between corneal mechanical thresholds and metrics of dry eye. Methods This was a cross-sectional study of individuals seen in the Miami Veterans Affairs eye clinic. The evaluation consisted of questionnaires regarding dry eye symptoms and ocular pain, corneal mechanical detection and pain thresholds, and a comprehensive ocular surface examination. The main outcome measures were correlations between corneal thresholds and signs and symptoms of dry eye and ocular pain. Results A total of 129 subjects participated in the study (mean age 64 ± 10 years). Mechanical detection and pain thresholds on the cornea correlated with age (Spearmans ρ = 0.26, 0.23, respectively; both P < 0.05), implying decreased corneal sensitivity with age. Dry eye symptom severity scores and Neuropathic Pain Symptom Inventory (modified for the eye) scores negatively correlated with corneal detection and pain thresholds (range, r = −0.13 to −0.27, P < 0.05 for values between −0.18 and −0.27), suggesting increased corneal sensitivity in those with more severe ocular complaints. Ocular signs, on the other hand, correlated poorly and nonsignificantly with mechanical detection and pain thresholds on the cornea. A multivariable linear regression model found that both posttraumatic stress disorder (PTSD) score (β = 0.21, SE = 0.03) and corneal pain threshold (β = −0.03, SE = 0.01) were significantly associated with self-reported evoked eye pain (pain to wind, light, temperature) and explained approximately 32% of measurement variability (R = 0.57). Conclusions Mechanical detection and pain thresholds measured on the cornea are correlated with dry eye symptoms and ocular pain. This suggests hypersensitivity within the corneal somatosensory pathways in patients with greater dry eye and ocular pain complaints.

Local Ischemia and Increased Expression of Vascular Endothelial Growth Factor Following Ocular Dissemination of Mycobacterium tuberculosis

The pathogenesis of intraocular tuberculosis remains poorly understood partly due to the lack of adequate animal models that accurately simulate human disease. Using a recently developed model of ocular tuberculosis following aerosol infection of guinea pigs with Mycobacterium tuberculosis, we studied the microbiological, histological, and clinical features of intraocular tuberculosis infection. Viable tubercle bacilli were cultivated from all eyes by Day 56 after aerosol delivery of ∼200 bacilli to guinea pig lungs. Choroidal tuberculous granulomas showed reduced oxygen tension, as evidenced by staining with the hypoxia-specific probe pimonidazole, and expression of vascular endothelial growth factor (VEGF) was detected in the retinal pigment epithelium (RPE) and photoreceptors. Fundoscopic examination of M. tuberculosis-infected guinea pig eyes revealed altered vascular architecture and chorioretinal hemorrhage by Day 56 after infection. This model may be useful in further elucidating the pathogenesis of ocular tuberculosis, as well as in developing tools for diagnosis and assessment of antituberculosis treatment responses in the eye.

OPTICAL PROFILOMETRY OF POLY(METHYLMETHACRYLATE) SURFACES AFTER RESHAPING WITH A SCANNING PHOTOREFRACTIVE KERATECTOMY (SPRK) SYSTEM

A prototype frequency-quintupled Nd:YAG laser was used with a scanning system to create, on poly(methylmethacrylate) (PMMA) blocks, ablations corresponding to a correction of 6 diopters of myopia by photorefractive keratectomy. The topography of the ablated samples was measured with an optical profilometer to evaluate the smoothness and accuracy of the ablations. The ablation depth was larger than expected. With a 50% to 70% spot overlap, large valleylike variations with a maximum peak-to-peak amplitude of 20 µm were observed. With an 80% spot overlap, the rms surface roughness was 1.3 µm, and the central flattening was 7 diopters. This study shows that optical profilometry can be used to determine precisely the ablation per pulse and the smoothness and accuracy of surface ablations. Knowing the exact ablation per pulse is necessary to produce a smooth and accurate corneal surface by scanning photorefractive keratectomy.

Preliminary study on the closure of the lens capsule by laser welding

We present a preliminary study of a new method, based on the laser welding of suitably prepared patches of capsular tissue for the closure of capsulorhexes in the lens capsule. This technique is proposed for the repair capsular breaks or tears caused by accidental traumas or ones produced intraoperatively during standard IOL implantation. Experiments were carried out ex vivo on freshly enucleated porcine eyes. Patches of anterior capsular tissue, collected from donor eyes, were stained with a solution of Indocyanine Green (ICG) in sterile water. Closure tests on a capsulorhexis were performed by welding a stained patch onto the recipient capsule, using diode laser radiation at 810 nm, which greatly absorbed by the ICG-stained tissue. Laser radiation was delivered by means of a 200-micron-core-fiber, the tip of which was gently pressed onto the patch surface (contact welding technique) so as to produce effective tissue welding in underwater conditions. Laser-welded capsular tissue was found to have good resistance to mechanical load, comparable in fact to that of healthy tissue.

Intravitreale applikation von azetylsalizylsäure mittels silikonöltamponade

ZusammenfassungDer Transfer von Azetylsalizylsäure (Aspirin®) mittels intravitrealer Silikonöltamponade wurde hinsichtlich Pharmakokinetik und Sicherheit geprüft.Material und MethodikDie Azetylsalizylsäure wurde mit Silikonöl in einer Konzentration von 1,67 mg/ml suspendiert. Fünfzehn New Zealand White Kaninchen erhielten diese Suspension als intravitreale Tamponade nach Vitrektomie. Die Konzentrationen von Salizylsäure, dem Hauptmetaboliten der Azetylsalizylsäure, wurden in der Retina, Chorioidea, Vitreus, Nervus opticus und Blutplasma 6 und 24 Stunden sowie 5 Tage nach Operation mittels Hochdruckflüssigkeitschromatographie (HPLC) ermittelt. Zusätzlich zu den klinischen Nachuntersuchungen wurden prä- und postoperativ Elektroretinogramme durchgeführt. Ein, zwei und drei Monate nach der Tamponade wurden histologische Präparate hergestellt.ErgebnisseIn der klinischen Nachuntersuchung und in den histologischen Schnitten ergab sich kein Hinweis auf Nebenwirkungen oder Toxizität. Die Elektroretinogramme zeigten keine signifikanten Unterschiede zwischen prä- und postoperativen Ergebnissen. Die Salizylsäurekonzentrationen zeigten Höchstwerte im Rest-Vitreus (640,0 μg/ml), in der (Chorioidea (446,0 ng/ml) und in der Retina (281,3 ng/ml) nach 6 Stunden. Nach 24 Stunden konnten Salizylsäurespiegel von 20,9 μg/ml im Rest-Vitreus und 38,5 ng/mg in der Retina gemessen werden. Noch nach 5 Tagen konnten 48,1 ng/mg Salizylsäure in der Retina nachgewiesen werden.DiskussionDer Transport von Azetylsalizylsäure mittels intravitrealem Silikonöl ist eine sichere Methode, die zur Anreicherung von hohen Salizylsäurespiegeln bei geringfügiger systemischer Belastung führt.SummaryDelivery of acetylsalicylic acid by intravitreal silicone oil was investigated for safety and for its pharmacokinetics in the posterior pole of the eye.MethodsThe acetylsalicylic acid was mixed in silicone oil to a concentration of 1.67 mg/ml. After vitrectomy, 15 NZW rabbits received an intravitreal injection of acetylsalicylic acid /silicone oil suspension. Clinical examination pre- and postoperative electroretinography (ERG) and histology were performed. The pharmacokinetics of the distribution of salicylic acid were determined by HPLC analysis at 6 hours, 24 hours and 5 days in optic nerve, retina, choroid, vitreous, and blood.ResultsClinical examination and histology revealed no adverse effects or signs of toxicity. The ERGs showed no significant difference between the pre- and postoperative results. The salicylic concentrations demonstrated peak values in the residual vitreous (640.0 μg/ml), choroid (446.0 ng/mg) and retina (281.3 ng/mg) at 6 hours. At 24 hours, the salicylic acid concentration decreased to 20.9 μg/ml in the residual vitreous and to 38.5 ng/mg in the retina. At 5 days the retinal level was still 48.1 ng/mg.DiscussionDelivery of acetylsalicylic acid by intravitreal administration of loaded silicone oil is a safe method and results in high concentrations of salicylic acid in the posterior segment of the eye while maintaining low blood levels.

Scleral heating with pulsed midinfrared lasers and temperature-dependent absorption coefficient

We studied the effect of the temperature-dependence of the scleral absorption coefficient on the accuracy of thermal models of laser-induced scleral heating. The scleral surface temperature increase during pulsed Holmium:YAG and Thulium:YAG laser irradiation was calculated with a constant (static model) and temperature-dependent (dynamic model) absorption coefficient. The 1D heat equation was solved with the assumption that thermal diffusion during the pulse is negligible. We found that the dynamic model yields lower temperatures than the static model. For the sclera, the overestimation becomes significant when the surface temperature is above 70 degree(s)C. This study shows that the temperature-dependence of the absorption coefficient must be taken into account to accurately predict laser-induced scleral or corneal heating.

Spectral properties of common intraocular lens (IOL) types

Currently over 50 kinds of intraocular lenses (IOLs) are approved for patient use in the treatment of cataracts and ametropia. These lenses are manufactured from at least 2 kinds of silicones as well as several kinds of acrylic polymers including polyHEMA, Poly HOXEMA, a range of polymethacrylate and polyacrylate formulations. We sought to measure spectral transmission curves of a range of IOLS in the UV-visible and near IR spectral regions in order to better characterize their optical properties and to provide a baseline from which to assess their alteration following implantation over time. Consideration of how this may best be achieved are discussed. The variable ability of both explained IOLs and some samples from a range of manufacturers to block UV wavelengths is commented upon.

Optical comparison of multizone and single-zone photorefractive keratectomy

The purpose is to calculate and compare the point-spread function and the central ablation depth (CAD) of a paraxial eye model after photo-refractive keratectomy (PRK), with single and multizone treatments. A modified Le Grand-El Hage paraxial eye model, with a pupil diameter ranging from 2 to 8 mm was used. Ray-tracing was performed for initial myopia ranging from 1 to 10D; after single zone PRK; after double zone PRK; and after tripe zone PRK. The ray-tracing of a parallel incident beam was calculated by using the paraxial matrix method. At equal CAD, the optical image quality is better after single zone treatments. Multizone treatments do not seem to be advantageous optically.