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Biomedical subjects

J M Parel

Publications and source records attributed to J M Parel.

At least 19 recordsLinked to original sources
PubMed1992

Photogrammetric analysis of corneal trephination.

We used a high-magnification shadow photogrammetric system to evaluate corneal buttons trephined from human donor globes. Whole eyes were trephined with one of five instruments: nonguarded blades held by hand or placed on a handle, Barraquer-Mateus motorized trephine, Hessberg-Barron suction trephine, or Hanna microkeratotrephine. Corneoscleral buttons were punched with one of three punches: Cottingham, Katena Lieberman guillotine, or a modified Lieberman guillotine with an increased impact force (BPEI 2). The precision (how closely buttons approximated the trephine diameter), accuracy (repeatability), acircularity (deviation from roundness), and straightness (verticality of edges) of cut were calculated from the diameter and edge profile angle measurements of buttons cut by the different instruments. These results were statistically compared. The Hanna microkeratotrephine instrument had the greatest precision and accuracy, least acircularity, and straightest edges. Of the corneal punches evaluated, the Cottingham instrument had the greatest precision; however, the BPEI 2 punch cut with the greatest accuracy and the straightest edges.

Cornea↗
PubMed1991

Gel injection adjustable keratoplasty.

Gel injection adjustable keratoplasty (GIAK) is a new refractive surgical procedure designed for the correction of myopia by injection of a gel substance into the peripheral corneal stroma. This paper describes the GIAK technique and reports the results obtained in 21 fresh cadaveric eyes using the procedure. After a deep interlamellar canal has been dissected with a helicoid spatula surrounding the visual axis, the gel is injected under keratometric control. In the 1st group of 14 eyes, the degree of correction varied from 2.2 to 12.8 D; there was a direct relationship between the amount of gel injected and the keratometric change. In the 2nd group of 7 eyes, the adjustability of the procedure was demonstrated. Through partial extraction of the gel and subsequent modification of the corneal curvature, the previously induced keratometric changes could be reversed or altered to a specific extent. Following the initial injection of gel to a targeted flattest meridian power of 35 D, an average value of 35.8 +/- 0.5 D was achieved in these eyes. We subsequently attempted to increase the flattest meridian to 40 D by partial removal of the gel and achieved a mean value of 40.2 +/- 0.4 D. Average presurgical astigmatism of 1.497 +/- 0.737 D was reduced to a postsurgical reading of 0.941 +/- 0.590 D (P = 0.005, Student's paired t-test), indicating an autocorrection by autodistribution of the gel inside the canaliculus (Laplace's law). GIAK is a simple, inexpensive procedure designed for the correction of myopia that has the added advantage of reducing preexisting astigmatism without encroaching on the visual axis.

Astigmatism↗
PubMed1990

Artificial orbit system for experimental surgery with enucleated globes.

A portable system for holding, accurately positioning, and restoring the physiologic integrity of enucleated globes during experimental anterior segment procedures and pars plana vitrectomy is described. A 0 to 500-mm Hg vacuum fixation ring and positioning apparatus mechanically locks globes into known spatial position while they are supported in a 2 to 6-mm Hg pressurized, pliable socket designed to match the size and pressure of a natural orbit. A gravity infusion system and an implantable piezoelectric pressure sensor in conjunction with a syringe and stopcock assembly allow for controlled inflation of globes to intraocular pressure (IOP) levels from 0 to 70 mm Hg, and to over 300 mm Hg. The fixation vacuum level, and intraocular and extraocular pressures are simultaneously monitored on 3-digit LED displays, and permanent records of each can be generated by routing data to storage devices. The anterior segment remains accessible at all times for surgical procedures and diagnostic measurements. The entire system is portable, allowing globes to be transported to multiple experimental stations, while all pressure settings and the position of the globe are maintained. To demonstrate applications of the artificial orbit system, we describe experiments using it to calibrate applanation tonometers, and to study the relationship between IOP and corneal curvature as well as the effect of trephination procedures and limbal vacuum fixation on IOP.

Animals↗
PubMed1989

Transient hypopyon with marked anterior chamber fibrin following pars plana vitrectomy and silicone oil injection.

In a retrospective review of 30 cases of complex retinal detachment, which had been managed by pars plana vitrectomy techniques together with silicone oil injection, we found that two patients developed marked postoperative anterior chamber fibrin and hypopyon. In all 30 cases, the same silicone oil was used: purified and heat-sterilized trimethylsiloxy-terminated, polydimethylsiloxane of 1000-centistoke viscosity. Although the silicone oil itself remained clear and without emulsification, the differential diagnosis of this postoperative inflammation included microbial endophthalmitis. These two cases were treated with frequent topical steroids and antibiotics while we closely monitored the retraction of the anterior chamber fibrin. In both cases, clinical improvement and long-term retinal reattachment with satisfactory visual function were achieved. The use of intense scatter laser endophotocoagulation and the presence of impurities in the silicone oil may have contributed to the excessive postoperative inflammation in these cases.

Anterior Chamber↗
PubMed1989

Biodegradable mechanical retinal fixation. A pilot study.

Mechanical retinal fixation is a useful tool in the armamentarium of vitreoretinal surgeons. Unfortunately, the use of metallic retinal tacks on a permanent basic mandates a retained intraocular foreign body that poses some potential for long-range toxic effects. Herein, we report the results of our initial experience with a temporary, biodegradable mechanical retinal fixation device ("biopin") in rabbits. When compared with metallic tacks, the biopins appeared to be well tolerated intraocularly, with minimal damage detectable at the light microscopic level. Disinsertion of the biopins occurred in 46% of the eyes within two weeks and in all eyes by four weeks. Initial signs of degradation of the biopins were observed at six weeks (median) in the ensectomized/vitrectomized eyes and at 12 weeks (median) in the nonvitrectomized eyes. Differences were found in the occurrence of retinal detachment between animals that underwent lensectomy/vitrectomy with insertion of two metallic tacks and animals that underwent insertion of one biopin without vitrectomy. The biopin has a potential as a vehicle for sustained release of pharmacologic agents to inhibit directly the development of vitreoretinal proliferation, thereby retarding or preventing subsequent retinal traction and detachment.

Animals↗
PubMed1989

Design features and surgical use of a cannulated extrusion needle.

A cannulated extrusion needle was designed as a modification of the standard 20-gauge extrusion by including an inner 24-gauge flexible cannula that can be extended up to 18 mm beyond the metal tip. Indications for use of the instrument are reviewed along with selected case histories demonstrating its use. The instrument is used primarily for internal subretinal fluid drainage in eyes with complex retinal detachments caused by proliferative vitreoretinopathy. The flexible cannula is guided into the subretinal space through an open peripheral retinal break and the subretinal fluid is evacuated during a simultaneous fluid/air exchange. The positive pressure of the automated air pump creates a pressure gradient sufficient to achieve passive egress of subretinal fluid through the cannula. Active suction is avoided because of the risk of posterior retinal incarceration into the cannula tip. In addition, the cannula can be used to remove hemorrhage, gas, or silicone oil in the subretinal space.

Adult↗
PubMed1989

Potential use of lasers for penetrating keratoplasty.

Experimental corneal trephination has been achieved with the 193 nm argon fluoride excimer and 2.9 microns hydrogen fluoride and Er:YAG laser systems. Compared with metal blades and other lasers, the 193 nm excimer laser creates the best quality corneal excision, but has a relatively slow etch rate through the stroma, and its use requires toxic gas. The mid-infrared laser systems trephine the cornea in less than 10 seconds, but cause a 10 microns to 15 microns zone of adjacent stromal damage and create wounds that are approximately 2.5 times larger than wounds made by metal scalpels. The wavelength and laser pulse duration influence the cutting characteristics of the laser. Optical delivery systems using an axicon lens, a rotating slit, and a computer controlled scanning optical system have been developed for penetrating keratoplasty. Selection of the optimal laser system for penetrating keratoplasty must await further experimental studies. Refinements of the laser cavity and delivery system are necessary before clinical studies can begin. A carefully controlled randomized clinical trial comparing laser trephination with conventional mechanical trephines will be necessary to determine the safety and efficacy of a laser trephination system.

Cornea↗
PubMed1989

Shadow photogrammetric apparatus for the quantitative evaluation of corneal buttons.

We have developed a technique for the accurate, quantitative, geometric evaluation of trephined and punched corneal buttons. A magnified shadow of the frontal and edge views of a corneal button mounted on the rotary stage of a modified optical comparator is projected onto the screen of the comparator and photographed. This process takes approximately three minutes. The diameters and edge profile at any meridian photographed can subsequently be analyzed from the film. The precision in measuring the diameters of well cut corneal buttons is +/- 23 microns, and in measuring the angle of the edge profile is +/- 1 degree. Statistical analysis of inter observer variability indicated excellent reproducibility of measurements. Shadow photogrammetry offers a standardized, accurate, and reproducible method for analysis of corneal trephination.

Calibration↗
PubMed1989

Novel technology in microsurgery.

Several of the latest technical advances in microsurgical technology employing conventional engineering are briefly summarized. New scientific fields are introduced: injectable soft polymeric gels for cataract implants and vitreous substitution, controlled drug release and temporary tissue fixation via polymeric biodegradation, photodynamic therapy via intraoperative use of photosensitizers and surgical photoablation via short pulsed laser surgical instrumentation. Clinical examples covering the anterior and posterior segment of the eye are described. The potential uses of these technologies involve procedures for cataract, vitrectomy, strabismus, glaucoma and keratoplasty as well as therapeutics.

Biopolymers↗
PubMed1978

An improved microsurgical ceiling-mounted unit and automated television.

To increase the versatility of a ceiling-mounted microsurgical unit, we instructed an instrument company to redesign an existant unit according to our requirements. The modified instrument has improved microscope supporting arms capable of supporting an inserted X-Y translation stage. The unit houses diathermy, cautery, fiberoptic light source, and suction devices. Most of these devices can be exchanged for other to adapt to individual requirements. Mirror image design increases versatility. Floor-mounted outlets avoid a multitude of cables. A double color television system for automatic recording of surgery has been installed.

Humans↗
PubMed1978

Simultaneous stereophotogrammetric and angiographic fundus camera.

We developed an apparatus for serial, simultaneous stereophotogrammetric fundus angiography by modifying a fundus camera. The paired stereoangiograms obtained by this system provided satisfactory stereoscopy and fair depth of field. With this system, mounting and filing of slides were easy. Accurate photogrammetric analysis of the fundus can be performed. Clinical results were impressive in both young and old subjects with fully dilated pupils.

Fluorescein Angiography↗
PubMedDate not supplied

Contact lens filter for macular photocoagulation with monochromatic green argon laser.

Safer and more effective macular photocoagulation can be performed with monochromatic green light, thereby avoiding the energy absorption by the xanthophyll pigment in the inner retina in the blue portion (488 nm line) of the argon laser radiation. While an appropriate laser filter has been built into commercially available laser systems to provide a "green-only option," a contact lens filter which provides monochromatic green energy with a standard argon laser delivery system has been evaluated. The filter requires twice as much laser energy output from the laser, and may allow higher levels of energy to reflect off the filter towards observers.

Choroid↗