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Biomedical subjects

J M Parel

Publications and source records attributed to J M Parel.

At least 37 records · Page 2Linked to original sources
PubMed1998

Reduction of corneal edema in endotoxin-induced uveitis after application of L-NAME as nitric oxide synthase inhibitor in rats by iontophoresis.

PURPOSE: To investigate the involvement of the cornea during endotoxin-induced uveitis (EIU) in the rat and the effect of Ngamma-nitro-L-arginine methyl ester (L-NAME) as nitric oxide synthase (NOS) inhibitor, administered by iontophoresis. METHODS: EIU was induced in Lewis rats that were killed at 8 and 16 hours after lipopolysaccharide (LPS) injection. The severity of uveitis was evaluated clinically at 16 hours, and nitrite levels were evaluated in the aqueous humor at 8 hours. Corneal thickness was measured, 16 hours after LPS injection, on histologic sections using an image analyzer. Transmission electron microscopy (TEM) was used for fine analysis of the cornea. Transcorneoscleral iontophoresis of L-NAME (100 mM) was performed either at LPS injection or at 1 and 2 hours after LPS injection. RESULTS: At 16 hours after LPS injection, mean corneal thickness was 153.7+/-5.58 microm in the group of rats injected with LPS (n=8) compared with 126.89+/-11.11 microm in the saline-injected rats (n=8) (P < 0.01). TEM showed stromal edema and signs of damage in the endothelial and epithelial layers. In the group of rats treated by three successive iontophoreses of L-NAME (n=8), corneal thickness was 125.24+/-10.36 microm compared with 146.76+/-7.52 microm in the group of rats treated with iontophoresis of saline (n=8), (P=0.015). TEM observation showed a reduction of stromal edema and a normal endothelium. Nitrite levels in the aqueous humor were significantly reduced at 8 hours by L-NAME treatment (P=0.03). No effect on corneal edema was observed after a single iontophoresis of L-NAME at LPS injection (P=0.19). Iontophoresis of saline by itself induced no change in corneal thickness nor in TEM structure analysis compared with normal rats. CONCLUSIONS: Corneal edema is observed during EIU. This edema is significantly reduced by three successive iontophoreses of L-NAME, which partially inhibited the inflammation. A role of nitric oxide in the corneal endothelium functions may explain the antiedematous effect of L-NAME.

Animals↗
PubMed1998

Quantification of holmium: YAG and thulium: YAG laser-induced scleral shrinkage for buckling procedures.

BACKGROUND AND OBJECTIVE: To quantify and compare holmium:YAG (2.1 microns) and thulium:YAG (2.0 microns) laser-induced scleral shrinkage for retinal buckling procedures. MATERIALS AND METHODS: Two overlapping spots of either laser radiation were applied at the equatorial sclera of 50 human cadaver eyes. Scleral shrinkage was expressed as a relative change of length between two reference points on the scleral surface, and quantified as a function of energy per pulse, total energy, scleral thickness, and intraocular pressure (IOP). Tissue effects were studied histopathologically. RESULTS: Shrinkage was most dependent on total fluence and attained a maximum of 27% to 30% with an IOP of 4 mm Hg, regardless of scleral thickness or laser parameters, but decreased with increasing IOP. The thulium:YAG laser produced more efficient scleral shrinkage and less collagen damage than the holmium:YAG laser. CONCLUSION: The recommended parameters for laser-induced scleral shrinkage are the thulium:YAG laser, with 2.4 J/cm2 per pulse and 12.0 to 14.4 J/cm2 total fluence (5 to 6 pulses). IOP control (< or = 4 mm Hg) is crucial during laser scleral buckling.

Humans↗
PubMed1998

Synthetic meshwork implant for glaucoma filtering surgery: effect of adjunct heparin and sodium hyaluronate in rabbits.

BACKGROUND AND OBJECTIVE: To evaluate the efficacy of a novel filtering implant, a synthetic meshwork (MESH), with or without heparin or sodium hyaluronate amendment. MATERIALS AND METHODS: Eighteen eyes of 18 rabbits received MESH surgery. The eyes were divided into three subgroups. Six eyes received the MESH implant with no modification (group 1), 6 eyes received MESH saturated with heparin (group 2), and 6 eyes received MESH with sodium hyaluronate administration into the anterior chamber during surgery (group 3). Intraocular pressure (IOP) and outflow facility were measured during a period of 6 months. RESULTS: The MESH-implanted eyes showed lower IOP and higher outflow facility than control eyes up to postoperative days 119 and 49, respectively (P > .05). Earliest functional failure was seen in group 3 and latest in group 2. CONCLUSION: MESH implant surgery showed a long-term efficacy in reducing IOP. The beneficial effects of added heparin were limited. Sodium hyaluronate administration reduced the efficacy of the implant device.

Animals↗
PubMed1998

[Artificial trabeculum (MESH). Clinical and histological study in the rabbit].

PURPOSE: Designed to avoid postoperative hypotony that often occurs after trabeculectomy and to maintain long lasting filtration, the MESH is a thin porous expended polytetrafluoroethylene (ePTFE) implant that mimics the physiological meshwork. The aim of this study is to assess the tolerance, biocompatibility and effectiveness of this device during 6 months in the rabbit. MATERIAL AND METHODS: We used an ePTFE with about 5 microns pore size (Zytex). The head of the implant is 3,0 mm wide and 1,5 mm long and fits in the anterior chamber. The tail is 2,0 mm wide and 3,0 mm long and fits in the subconjunctival space. The MESH is 250 microns thick. 24 Dutch pigmented rabbits were selected because their dark pigmented iris contrasts with the ePTFE implant giving a better visualization. All the animals were cared for in accordance with ARVO resolutions. Surgery was performed on the right eye by the same surgeon (P.H.), the left eye serving as control for IOP measurements. The animals were distributed in 3 groups: one with MESH alone (MESH), one with MESH and Mitomycin C (MMC), one with MESH and 5-FU (5-FU). Follow-up was performed every week (W) during 6 months including IOP measurement, slit lamp observation, photography and bleb assessment. Histological study was done at POD 0, 15, 30, 90 and 180 one eye in each group. Student t test and alternate Welch t test were used for statistics. RESULTS: Filtering bleb: no bleb was visible before W3. A bleb was found between W3 and W6, decreasing between W6 and W9 with no more change after W10. The MESH implant: no change appears in the color of the MESH during the study. Some iris pigments or synechiae were seen in some cases. No extrusion occurred. Intraocular pressure: IOP was lower than in the control eye. The statistical analysis showed a significant lower pressure for the MESH alone at W5 (p = 0.0069), for the 5-FU group at W1 (p = 0.0326), W2 (p = 0.0488), W4 (p = 0.0312). With Mitomycine C we found very significant results at W1 (p = 0.0073), W2 (p = 0.0136), W4 (p = 0.0497), W9 and W11 (p = 0.0174). After W12 the groups were joined and IOP was significantly decreased at W17 (p = 0.0376) and W23 (p = 0.0462). Histology confirmed the correct position of the MESH, its biocompatibility and its ability to drain aqueous humor even if there is colonization of the pores by fibroblast-like cells. CONCLUSION: The present study has shown that the filtering bleb appeared after 3 weeks without major hypotony. The material was integrated only in the intrascleral tunnel and was stable. After 6 months the Mesh was well tolerated. The new concept has a simple surgical technique, less invasive than trabeculectomy and required less surgical time. This technique reduced IOP and produced long survival blebs in rabbits. This device appears suitable for the surgical treatment of open angle glaucoma.

Animals↗
PubMed1998

[Keratoprosthesis by posterior fixation and mechanical biocompatibility: determination of intraocular pressure provoking aqueous humor leak and/or extrusion].

The effect of a sudden increase in intraocular pressure (IOP) on Eye Bank eyes implanted with a posterior fixation keratoprosthesis PCL5 type (Lacombe) is evaluated. The IOP was artificially increased at a rate close to that observed in direct eye trauma. The critical pressure values causing aqueous humor leak and/or keratoprosthesis extrusion were compared to those found to blow up unoperated eyes. No statistical difference was found between operated and control eyes (6 pairs of eyes). This KPro type showed its efficacy for keratoprosthesis fixation.

Aqueous Humor↗
PubMed1997

Iontophoresis of dexamethasone in the treatment of endotoxin-induced-uveitis in rats.

The purpose of this study was to evaluate the efficacy of a Coulomb Controlled Iontophoresis system (CCI) in the local delivery of corticosteroids for the treatment of uveitis. The therapeutic efficacy of Dexamethasone (Dex) administered by CCI was compared to systemic injection and to topical application with the iontophoresis apparatus in the absence of electrical current. The evaluation was done in the treatment of the endotoxin-induced uveitis (EIU) model, and in the effect on TNF gene expression in the iris/ciliary body as well as in the retina and on TNF levels in aqueous humor and vitreous. Dex was administered either at the time of LPS injection or 5 hours later. For iontophoresis, we used a 1 ml reservoir-electrode covering the cornea, the limbus, and the first millimeter of the sclera. The applied electrical current was of 400 microA during four minutes with a total surface charge of 0.4 C cm-2. EIU was evaluated by clinical examination, by counts of intraocular inflammatory cells on histological sections, and by measuring the protein levels in the aqueous humor and in the vitreous. The TNF-alpha gene expression in the iris and ciliary body, and in the retina was evaluated by RT-PCR. The systemic effect of Dex delivered by CCI was evaluated on the level of serum TNF-alpha in EIU. Our results demonstrated that local administration of Dex by CCI inhibited anterior and posterior signs of intraocular inflammation as effectively as systemic administration, with no effect on systemic level of TNF. In the anterior and posterior segments of the eye, the protein exudation. TNF levels and the cellular infiltration were inhibited. The TNF-alpha gene expression was inhibited in the anterior as well as the posterior segment of the eye. No clinical nor histological damage were caused by the CCI apparatus. In conclusion, CCI administration of Dex allows for a therapeutic effect on the posterior as well as the anterior segment of the eye, and may present a viable alternative to systemic administration of glucocorticoids in severe ocular inflammations.

Animals↗
PubMed1997

[Reticulated polyethylene oxide for gel injection adjustable keratoplasty. Biocompatibility in critical situation].

BACKGROUND: GIAK is a surgical technique developed for the correction of myopia. We evaluated the biocompatibility of a gamma-ray crosslinked poly(ethylene oxide) gel in two critical situations. MATERIALS AND METHODS: In 3 rabbits, a 5 mm inner diameter annular channel of 1 mm width was delaminated at 80% corneal depth and a sterile gamma-ray crosslinked polyethylene oxide gel was injected in the channel. In cornea 1 (control), the annulus was centered on the corneal apex and the channel was fully filled with gel. In cornea 2, the delamination was purposely decentered and the channel was approximately 1 mm from the limbus at its closest point. In cornea 3, the centered channel was purposely partially filled. After a 6 month follow-up, the rabbits were sacrificed for histology. RESULTS: Histopathology showed the oval channel walls to be irregular and a slight thinning of the epithelium located above the implant but no abnormalities in the stromal thickness. No mononuclear, polynuclear cells or other signs of encapsulation or rejection were found around the polymer in any of the animals. In cornea 3, fibroblasts were found on the lateral sides of the hydrogel globules. No limbal neovascularization was observed over the 6 month period in any of the animals. CONCLUSIONS: The injected PEO gel followed intimately the delaminated stromal channel and was well tolerated in the cornea. The fibroblastic reaction found in partially filled channels is caused by the normal wound healing process and not by the hydrogel chemical properties.

Animals↗
PubMed1996

Stereotactic uses beyond core biopsy: model development for minimally invasive treatment of breast cancer through interstitial laser hyperthermia.

Light of a Nd:YAG laser presented through a fiberoptic cable to a diffusing tip can be adapted to mammographic stereotactic instruments now used for core biopsy in the hyperthermic endoablation of breast cancer. This approach to cancer destruction extends breast preservation to the point of no observable surface skin change. The initial analysis characterizes the effects of laser endohyperthermia in a physical model as well as in tissue, both ex vivo and in vivo, to create a reliable technique that will lead to human trials. A fiberoptic cable with a diffusing quartz tip placed deep within soft tissue can pass light of a neodymium laser and consequent thermal energy for the destruction of surrounding soft tissues. Because breast cancer occurs with greatest frequency in the involuted breasts of women more than 50 years of age and because this tissue is predominantly fibro-fatty in nature, our work has concentrated on model development and the determination of heat distribution and destruction of fat and fibro-fatty tissue. Following the development of a physical model, time-temperature courses were found to be similar in ex vivo human breast tissue and subcutaneous porcine fat. This led to in vivo porcine studies that confirmed similar time-temperature courses. For tissues brought to a range of 60 degrees C to 80 degrees C and sustained for the better part of 20 minutes, gross and histological analyses reveal complete destruction over a 1 1/2 cm radial region around the laser tip. This approach offers great promise for the treatment of stereotactically biopsied small T1 breast carcinomas.

Animals↗
PubMed1996

[Biodegradable controlled-release 5-FU implant in the surgery for glaucoma. Experimental study].

BACKGROUND: 5-Fluorouracil (5-FU) is useful as an adjunct treatment for glaucoma filtering surgery. However, efficacy depends upon maintaining sustained drug levels, currently achieved by repeated daily injections of the drug for several days. To overcome this limitation, we designed a biodegradable implant for the sustained release of 5-FU. MATERIAL AND METHODS: The implant (0.79 mm diameter, 6 mm long, 2.2 mg weight) contains 0.66 mg of 5-FU and is loaded in a needle coupled to a custom-made instrument to permit subconjonctival insertion of the implant through a 2 mm wide snip incision. The in vitro and in vivo pharmacokinetics as well as the biocompatibility studies of the implants were assessed in the rabbit. RESULTS: No infection, inflammatory reaction or extrusion occurred. The implant released the drug at a constant rate of 1.20 micrograms/hr for over 18 days and totally biodegraded in less than 86 days. CONCLUSION: Implantation of the device, after laser sclerostomy or conventional trabeculectomy shows great potential for the treatment of glaucoma. To determine the implant's efficacy, additional studies in the cat are underway.

Animals↗
PubMed1995

Keratoprosthesis with biocolonizable microporous fluorocarbon haptic. Preliminary results in a 24-patient study.

BACKGROUND: Most complications of a keratoprosthesis occur at the tissue-to-implant interface. The ideal prosthesis would eliminate this interface by having the tissue actually grow into the supporting material. We present a prospective clinical human study of a novel biocolonizable keratoprosthesis in 24 eyes of 24 patients. DESIGN: To promote implant stability, the 9-mm-diameter haptic was fashioned using a custom-made microporous fluorocarbon with a 4-mm-diameter, 2.67-mm-long, central optic made of medical grade polymethylmethacrylate, giving a global visual field of 110 degrees to 130 degrees. Only bilaterally blind patients with untreatable corneal diseases were included in the study. The haptic was inserted into a lamellar pocket delaminated in the stroma, and the optic was positioned through a hole trephined in the central cornea. RESULTS: The average follow-up was 15.7 months (range, 4 to 28 months). The host corneal fibroblasts penetrated and proliferated into the peripheral microporous fluorocarbon and provided anchorage between the cornea and prosthesis. Seventeen patients (70.8%) had visual acuity improvements. Mean corrected final visual acuity was 20/100 (range, 20/30 to 20/400). Five anatomic failures occurred in the first 6 months (three extrusions, one dislocation of the optic, and one endophthalmitis). We had one case (4.1%) of treatable glaucoma. We successfully removed four of five retroprosthetic membranes that had occurred. No retinal detachment occurred. CONCLUSION: The biocompatible inert microporous polymer did not eliminate all mechanical complications associated with a keratoprosthesis.

Adult↗
PubMed1994

Expanded fluorocarbon for keratoprosthesis cellular ingrowth and transparency.

The development of a synthetic material allowing increased cellular adhesion and ingrowth would improve keratoprosthetic devices and requires an understanding of cell colonization processes. Interlamellar implantation of hydrophobic synthetic material may lead to poor corneal nutrition with subsequent necrosis. The probability of necrosis increases with material which is more impermeable, larger in diameter and more anterior in its placement. In this study we demonstrated the importance of pore diameter in the rate and density of cell colonization. We demonstrated that an opaque hydrophobic material may become translucent and wettable with very low perturbation of flow through the cornea. We used an expanded polytetrafluoroethylene with either 20 microns or 50 microns pore diameter. Cellular ingrowth was significantly greater in the material with 50 microns pores, resulting in collagen deposition within the pores without corneal vascularization at 6 months follow-up. Immunohistochemical study with monoclonal antibody AE5 revealed normal epithelial differentiation on the surface of the cornea over the implanted polymer.

Animals↗
PubMed1994

Ultraviolet solid-state laser (213-nm) photorefractive keratectomy. In vivo study.

BACKGROUND: The pulsed ultraviolet 213-nm solid-state laser has been demonstrated as an alternative to the gas argon-fluoride 193-nm excimer laser for photorefractive keratectomy (PRK). The authors studied the clinical course and histopathologic changes occurring in rabbit corneas after PRK with a 213-nm solid-state laser. METHODS: The 213-nm output of neodymium:YAG frequency-quintupled laser was used to create 5-mm optical zone ablations in seven pigmented rabbit corneas. The radiant exposure was 250 mJ/cm2 delivered through a computer-controlled scanning delivery system with a spot size of 0.5 mm. The target ablation was 4.0 diopters with an estimated ablation depth of 40 microns. A clinical estimate of corneal epithelial healing and stromal haze was made at intervals over the 3-month study period. Animals were killed immediately after ablation, or at 10 days, 1 month, or 3 months after ablation. Corneal tissue was preserved for light microscopy and transmission electron microscopy at each study interval. RESULTS: All corneas re-epithelialized within 10 days postoperatively. Anterior stromal haze was clinically visible at 3 days, increased until approximately 1 month, and then gradually decreased over the succeeding 2 months. Residual subepithelial haze was visible at 3 months. Results of histopathologic study documented normal epithelium healing over time; the basement membrane retained its regular thickness and hemidesmosomes were abundant at 3 months. The anterior stroma had an increased number of fibroblasts at 10 days, many of which remained until 1 month. A mild, transient, cellular reaction occurred throughout the thickness of the stroma and the endothelium. CONCLUSION: Using the 213-nm ultraviolet solid-state laser with a scanning delivery system, PRK shows a similar clinical course and histopathologic findings to the 193-nm excimer PRK study in rabbits. It is a clinically viable procedure for refractive surgery and requires further human clinical trails to determine its efficacy.

Animals↗
PubMed1994

[Results of a 2-year animal experiment with reticulated polyethylene oxide intrastromal rings].

Gel Injection Adjustable Keratoplasty (GIAK) is a technique previously described by G. Simon for the correction of myopia. Following pachometry, a 0.8 mm wide, 80% deep linear incision is performed 2.5 mm from the apex. Using a guide, a 1 mm wide, 5 mm diameter annular spatula is introduced to dissect an interlamellar canal and the crosslinked polyethylene oxide hydrogel is injected with a modified 23 gauge needle. The biocompatibility to 13 PEO batches was studied on 21 albino rabbits (Follow up 15 to 135 days). In nineteen, the cornea remained perfectly transparent. Two animals presented an infection at POD 1. Histopathology showed no endothelial deterioration, no anomaly of the thickness or of the cellular morphology around the injected zone. However some mononuclear cells were noticed surrounding the hydrogel in some rabbits together with thinning of the corneal epithelium anterior to the injected zone. A pilot refractive study was conducted on 5 cats using 2 PEO gels. One cat developed an infection following surgery. A second developed an inflammatory response with corneal neovascularization at POD 8. Thus, these animals were not included in the follow-up study which ranged from 6 to 28 months. Immediately after surgery, the refractive effect, measured with the Canon SK-1 digital autokeratometer, was 5.22 +/- 0.46 D (SD) of flattening. The long term effect (26 months) of the GIAK procedure appears to be stable and safe when using sterile PEO gels made of highly purified materials.

Animals↗
PubMed1993

Laser scleral buckling for retinal reattachment.

The holmium:yttrium aluminum garnet (Ho:YAG) laser produces infrared light that is absorbed inside scleral tissues, which increases local temperature, thereby shrinking collagen and inducing a buckle effect. Scleral indentation was induced in ten cadaver eyes by shrinkage of scleral collagen fibers by using a pulsed solid-state Ho:YAG (2.1-microns) laser with fiberoptic delivery. The amount of laser-induced buckling effect is controlled by selecting laser treatment settings such as beam spot, radiant exposure, and number of pulses. With treatment using 11.3 +/- 1.2 J/cm2 of laser radiant exposure and five pulses, laser-induced scleral shrinkage affected only the external two thirds of the scleral tissue. No thermal damage or disruption was observed in subjacent retinal pigment epithelium, choroid, or retina. The coupling of two appropriately selected lasers may allow laser-induced scleral buckling and transscleral retinal photocoagulation by using the same laser probe for retinal reattachment.

Collagen↗
PubMed1993

Keratotomy for astigmatism using an arcuate keratome.

We describe a new system for performing transverse arcuate corneal incisions for the correction of astigmatism. The instrument consists of a conical housing with suction and/or friction fixation to the limbus and two micrometric diamond knives mounted on a carrier that can be rotated by a gear mechanism. The depth, length, and location of the incisions can be predetermined. Light microscopy of donor eye corneas documented the achieved incision depth. One sweep at normal speed produced an incision depth 28% less deep than the preset depth. One sweep at low speed achieved depths of approximately 100% of the knife setting. Variability from one incision to another in the same cornea was related to blade sharpness. We report successful use of the instrument in five consecutive eyes with naturally occurring astigmatism.

Adolescent↗
PubMed1993

Ultraviolet solid-state laser (213-nm) photorefractive keratectomy. In vitro study.

BACKGROUND: Replacing the gas argon fluoride (193 nm) excimer laser with a solid-state laser source in the far-ultraviolet spectrum region would eliminate the hazards of a gas laser and would reduce its size, which is desirable for photorefractive keratectomy. The authors investigated corneal reshaping using a frequency-quintupled (213 nm) pulsed (10 ns) neodymium:YAG laser coupled to a computer-controlled optical scanning delivery system. METHODS: A 250 +/- 15-mJ/cm2 radiant exposure was used to ablate a 5-mm optical zone in human cadaver eyes and rabbit eyes. The 213-nm laser pulses were delivered through and shaped by a computer-controlled optical scanning delivery system, producing a 0.5-mm spot with a quasi-Guassian energy distribution on the cornea. Corneal surface changes were documented by computer-assisted corneal topography. Light microscopy, scanning electron microscopy, and transmission electron microscopy were performed to examine the effects on corneal surface quality and cellular components. RESULTS: Corneal topographic measurements showed myopic corrections ranging from 2.3 to 6.1 diopters. Results of postoperative examination with the slit lamp and operating microscope demonstrated a smoothly ablated surface without corneal haze. Histologic results showed a smoothly sloping surface without recognizable steps. The surface quality and cellular effects were similar to that of previously described excimer photorefractive keratectomy. CONCLUSION: The authors demonstrated that an ultraviolet (213-nm) solid-state laser coupled to an optical scanning delivery system is capable of reshaping the corneal surface with smooth transition. The scanning beam delivery system may offer the advantage of producing spatially resolved, customized, aspheric corrections to optimize the quality of vision after photorefractive keratectomy.

Animals↗