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J M Parel

Publications and source records attributed to J M Parel.

At least 55 records · Page 3Linked to original sources
PubMed1993

[Radial keratotomy, corneal hydration and intraocular pressure. Experimental study].

Radial keratotomy reduces myopia by flattening the central cornea. The role of wound hydration, length and depth of incisions, intraocular pressure and general weakening of the cornea play a part in this process. The relative importance of these factors is not clear. We examined the effect of wound hydration on an 8 incision radial keratotomy (RK) procedure performed on cadaver eyes. The cornea was moistened with balanced salt solution. A mean change of 10 D was achieved after 30 minutes. The corneal dehydration induced by Dextran B was associated with a significant reduction (10 D) in RK induced corneal flattening. It would appear that the radial incision induced keratometric change is a preliminary result of wound hydration. Intraocular pressure within the physiological range had very minimal influence (< 1.5 D) on corneal flattening.

Body Water↗
PubMed1993

[Optical power of the corneal epithelium].

The refracting power of the corneal epithelium is relatively unknown. We measured the keratometric refracting power of the cornea in two series of 10 fresh bank eyes and on five cat eyes with and without epithelium. The readings were performed at the 2 and 3.6 mm optical zones with an automated keratometer and with a videokeratoscope (TMS-1). The mean change was +1.30 D (0.55-1.85 D) at the 2 mm optical zone and 0.85 D (0.2-1.6 D) at the 3.6 mm optical zone in the first series of 10 eyes. The optical power of the epithelium was most significant within the central cornea. By removing the epithelium there was an increase in corneal refracting power and a change in the power and axis of astigmatism. We discuss the consequences of these findings and how they might affect the outcome of photorefractive keratectomy or other similar keratorefractive procedures.

Animals↗
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↗
PubMed1988

Hypodermic stainless steel tacks and companion inserter designed for peripheral fixation of retina.

Mechanical fixation of the torn or cut edge of retina with 30-gauge hypodermic stainless steel tacks has been performed in 15 patients at the Bascom Palmer Eye Institute, Miami, and Miami Veterans Administration Medical Center with six to 18 months of follow-up. The companion tack inserter allows the surgeon to select an angle for the shaft of the tack in relation to the inserter to allow the tack to be driven perpendicularly into sclera even when the insertion is anterior to the equator. If residual detachment remains following fluid-gas exchange after preliminary placement of the retinal tacks, a given tack may be removed and reinserted to facilitate complete retinal reattachment. This utilitarian feature allows the surgeon to eliminate residual anteroposterior traction following complete membrane peeling by extending relaxing retinotomies and tacking the posterior cut edge of the retina securely between the ora serrata and the equator.

Adult↗
PubMed1988

A suction trephine block for marking donor corneal buttons.

We describe a technique to accurately align the circumferences of the donor button and host cornea during penetrating keratoplasty. The donor cornea is trephined on a block into which four narrow, intersecting, equally spaced radial cuts are made. Suction is applied to the donor cornea through the four cuts, resulting in four radial marks in the donor corneal epithelium. Four radial marks are also made in the host cornea before trephination, using a radial keratotomy marker. When the donor button is placed within the recipient opening, the radial marks are aligned and used as guides for the cardinal sutures. This simple technique allows for matching of the donor and host circumferences, even if there is some collapse of the peripheral host cornea and sclera at surgery, and should minimize astigmatism resulting from donor/host misalignment.

Astigmatism↗
PubMed1988

Internal sclerectomy with an automated trephine for advanced glaucoma.

An automated trephine (trabecuphine) was used to perform an internal sclerectomy in seven glaucoma patients who were aphakic or had undergone previous filtering surgery that had failed or both. A patent fistula was achieved intraoperatively in all seven eyes. Postoperatively, six patients received subconjunctival injection of 5-fluorouracil (5-FI) once daily for an average of 8 days. Five of seven patients have retained a functional bleb and a controlled intraocular pressure (IOP) after surgery (follow-up, 4-24 months). The only intraoperative complication was hemorrhage from the sclerectomy site in a patient with aniridia that resulted in a 20% hyphema. The hyphema cleared quickly, and the bleb has remained functional with a pressure of 12 mmHg for 9 months. The trabecuphine makes it possible to perform a glaucoma filtering operation safely from within the anterior chamber. This technique minimizes conjunctival trauma in the filtration area. The absence of a conjunctival incision overlying the fistula simplifies the adjunctive use of antimetabolites such as 5-FU.

Choroid↗
PubMed1988

Applications of a cannulated extrusion needle during vitreoretinal microsurgery.

A specially designed cannulated extrusion needle facilitates the internal drainage of subretinal fluid during vitreoretinal microsurgery. Case histories demonstrate the use of this instrument in the management of complex retinal detachments including eyes with preretinal and subretinal hemorrhage, proliferative vitreoretinopathy with open peripheral retinal breaks, retinal detachment with giant retinal tear, and combined traction-rhegmatogenous detachments due to diabetic retinopathy. This method of internal drainage appears to have specific advantages over standard techniques by allowing the removal of subretinal hemorrhage, the utilization of pre-existing peripheral breaks for internal drainage, and the complete reattachment of shallow posterior pole retinal detachments to allow laser endophotocoagulation.

Adult↗