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Biomedical subjects

G O Waring

Publications and source records attributed to G O Waring.

At least 91 records · Page 5Linked to original sources
PubMed1990

Healing of excimer laser ablated monkey corneas. An immunohistochemical evaluation.

The healing response of the cornea following excimer laser anterior keratomileusis (a 4-mm-diameter ablation to a depth of 11, 23, or 46 microns) was analyzed immunohistochemically in adult rhesus monkeys. The ablated surface had reepithelialized and the synthesis of type VII collagen (a major component of anchoring fibrils) was evident by 7 days; the reestablishment of a nearly continuous anchoring fibril zone was evident after 12 weeks. Stromal fibroblasts, activated in response to wounding, expressed a fetal antigen for approximately 6 weeks. Although fibronectin and type VII collagen were present only transiently in the regenerating subepithelial stromal matrix in the subepithelial regions, some other alterations, including the presence of type III collagen, increased levels of keratan sulfates, and discontinuities in the anchoring fibril zone were evident even 18 months after wounding. The depths of the regenerated stroma, which were estimated from the depths of remnant staining for type VII collagen in the stromal matrix, generally, but not always, corresponded to the depths of the calculated ablation.

Animals↗
PubMed1990

Inadequacy of a polyester (Mersilene) suture for the reduction of astigmatism after penetrating keratoplasty.

Through two prospective studies, we evaluated the use of polyester (Mersilene) sutures in penetrating keratoplasty. Study 1 was a randomized comparison of combined running and interrupted Mersilene and nylon sutures (n = 45). Study 2 was a case series of single running Mersilene with postoperative adjustment of suture tension to manage astigmatism (n = 23). Study 1 demonstrated that Mersilene interrupted sutures were 5.5 times more likely to have handling-related complications compared to nylon (P = 0.01); in addition, they were 3 times as likely to have tissue-related complications as nylon interrupted sutures (P = 0.16). Study 2 demonstrated a complication rate of 69% when Mersilene was used as a single adjustable running suture. At 6 months postoperatively, the median refractive astigmatism for the adjustable cases was 3.37 D (mean, 4.03 +/- 2.37 D). Eyes in Study 2 with significant suture-related complications were 2.85 times more likely to have greater than 4 D of refractive astigmatism than were eyes without suture-related complications. We concluded that Mersilene is an undesirable suture for use in penetrating keratoplasty.

Adult↗
PubMed1990

Recent developments in radial keratotomy.

The Scientific Board of the California Medical Association presents the following inventory of items of progress in ophthalmology. Each item, in the judgment of a panel of knowledgeable physicians, has recently become reasonably firmly established, both as to scientific fact and important clinical significance. The items are presented in simple epitome and an authoritative reference, both to the item itself and to the subject as a whole, is generally given for those who may be unfamiliar with a particular item. The purpose is to assist busy practitioners, students, research workers, or scholars to stay abreast of these items of progress in ophthalmology that have recently achieved a substantial degree of authoritative acceptance, whether in their own field of special interest or another. The items of progress listed below were selected by the Advisory Panel to the Section on Ophthalmology of the California Medical Association, and the summaries were prepared under its direction.

Humans↗
PubMed1989

Corneal stromal wound healing in rabbits after 193-nm excimer laser surface ablation.

An argon fluoride excimer laser (193 nm) with a moving slit delivery system was used to perform anterior myopic keratomileusis in both eyes of 24 New Zealand white rabbits. Rabbits were killed immediately after ablation and at intervals up to 100 days. By slit-lamp microscopy, four rabbits at day 100 exhibited four clear corneas and four corneas had central, spotty, subepithelial haze. Light and electron microscopy documented corneal healing. In the early stages a transient acellular zone in the anterior stroma appeared over a period of three weeks, followed by an increased number of fibrocytes. In the corneas with opacification, focal areas of 20-microns-thick subepithelial scarring were present. An unexpected finding was transient damage to posterior stromal keratocytes and endothelial cells. The endothelium produced a layer of granular material that migrated anteriorly across Descemet's membrane. Immunochemistry at day 6 showed a marked staining for collagen IV, proteoglycans, fibronectin, and laminin.

Animals↗
PubMed1989

Preliminary computer simulation of the effects of radial keratotomy.

We created a computerized mathematical model of the eye for the simulation of refractive surgery. This model used a slightly prolate shape for a moderately myopic eye and an idealized aspheric profile for the cornea. The finite element method and the nonlinear Mooney-Rivelin law were used to analyze stress-strain relationships. Radial keratotomy changes stress distribution in the cornea and the anterior sclera, with major changes at the paracentral and peripheral ends of the incisions. The model predicted that there would be a flattening of the central cornea with a posterior displacement, which increased with an increase in intraocular pressure. A change in the length of the incision of 0.5 mm produced a significant change in correction. For small clear zones (3 to 4 mm), incisions of equal length produced comparable changes in refraction. We found that the effect of the corneal radius of curvature on the amount of refractive change was negligible. We studied the effect of elasticity coefficients and corneal anisotropia.

Biomechanical Phenomena↗
PubMed1989

Accuracy and precision of keratometry, photokeratoscopy, and corneal modeling on calibrated steel balls.

Surgical manipulation of corneal shape requires an accurate and precise method of measuring anterior corneal curvature from apex to limbus. We evaluated the accuracy and precision of the Bausch & Lomb Keratometer, Kera Corneascope, and Computed Anatomy Corneal Modeling System by measuring comparable locations on four calibrated steel test balls. The Keratometer and Corneal Modeling System were more accurate and precise than the Corneascope. No statistically significant difference was found between the Keratometer and Corneal Modeling System with respect to accuracy or precision. In addition, the accuracy and precision of all 31 rings of the Corneal Modeling System were studied. Rings 2 through 26 were read accurately and precisely within +/- 0.25 diopter on three of the four balls. Values on the steepest ball were within +/- 0.37 diopter.

Calibration↗
PubMed1989

The Hanna suction punch block and trephine system for penetrating keratoplasty.

We describe a new system for corneal trephination. The system for cutting donor buttons consists of a concave Teflon well in which the donor corneoscleral shell is secured by gentle suction. A cylindrical guide ensures that the disposable razor blade trephine is centered and is perpendicular during punching from the endothelium. The suction mechanical trephine used for the host has the following features: (1) a gun-sight alignment system for reliable centering, (2) a 360 degrees limbal suction ring that secures the trephine to the eye and ensures perpendicularity of the cut, (3) support surfaces on either side of the disposable razor blade that support the cornea during cutting to create near-vertical uniform wound margins, (4) rotation of the trephine with a manually operated gear system for smooth cutting, and (5) a calibration device that governs the extension of the blade and also allows cutting without descent of the blade.

Corneal Transplantation↗
PubMed1989

Effect of excimer laser radiant exposure on uniformity of ablated corneal surface.

The argon fluoride (193 nm) excimer laser is being used to change the anterior corneal curvature for correction of refractive errors. Uniformity of the surface following laser ablation may play an important role in the rate of epithelial healing and amount and type of stromal scarring. To test the effect of radiant exposure (fluence) on surface smoothness, we ablated rabbit corneas with the 193 nm argon fluoride excimer laser at nine radiant exposures from 50 to 850 mJ/cm2. A total energy of 100 J/cm2 was used for each ablation at a frequency of 1 Hz. Scanning electron microscopy demonstrated progressive improvement of surface smoothness with increasing radiant exposures. Transmission electron microscopy demonstrated no consistent increase in thickness to the surface condensate (pseudomembrane) with increasing radiant exposure. Improvement in surface quality associated with increasing radiant exposures may result from a more uniform depth of ablation per pulse in the corneal lamellae that absorb laser wavelengths differently. Radiant exposures at levels where the depth of ablation is the same regardless of increasing energy densities achieve a more uniform surface because inhomogeneities in the beam and variation in energy from pulse to pulse do not affect the ablation rate.

Animals↗
PubMed1989

Keratography as a guide to selective suture removal for the reduction of astigmatism after penetrating keratoplasty.

After penetrating keratoplasty in 52 eyes, keratography refraction and keratometry were used to select appropriate interrupted sutures for removal in order to reduce astigmatism. All eyes had one continuous and either 12 or 16 interrupted nylon sutures. The keratographs were examined retrospectively and separated into six groups on the basis of similar mire patterns. The removal of single sutures associated with three of these patterns reduced astigmatism by the following average amounts: symmetrical oval pattern, 0.44 diopters (D); D-shaped oval pattern, 2.07 D; and focal indentation pattern, 6.60 D. The other three patterns--mildly disrupted mires, incomplete mires, and uninterpretable mires--did not allow quantification of results. Examples of these keratographic patterns are presented and recommendations are made for their use in the management of astigmatism following penetrating keratoplasty.

Astigmatism↗
PubMed1989

Scanning slit delivery system.

We describe the structure and function of a delivery system designed for use with an argon fluoride excimer laser for corneal surgery. The basic principle of the delivery system is to shape the laser beam with a slit mask to a defined configuration. The image of the slit is moved across the cornea in a mathematically defined pattern to ablate a given amount of tissue, creating a new anterior radius of curvature for the cornea. The location of the beam on the cornea is determined by a rotating dove prism and a translating spherical lens, each of which is controlled by computer-regulated servomotors. The system is versatile and can be used for laser myopic or hyperopic keratomileusis, for correction of astigmatism by surface ablation, for creation of radial or transverse linear cuts, for excision of corneal buttons, and for uniform lamellar corneal smoothing procedures. The delivery system is currently used in the laboratory for the ablation of nonhuman primate corneas.

Animals↗
PubMed1989

Computer simulation of arcuate and radial incisions involving the corneoscleral limbus.

We have created a computer model of the eye that improves upon previous models with two assumptions: (1) the cornea is considered anisotropic, and (2) the strain tensor is non-linear for large displacements. Values used include those for Young's modulus, Poisson's ratio, and three coefficients of anisotropia. A finite element computer program was used to stimulate the behaviour of the eye. Four simulations were done: (1) a full thickness arcuate limbal cataract incision, (2) a partial thickness arcuate corneal relaxing incision, (3) a partial thickness radial incision extending across the limbus, (4) a partial thickness radial incision confined to the cornea. A full thickness corneal arcuate incision for cataract induced more change in corneal shape than a limbal incision. However, the gaping is more important in the limbal incision. Partial thickness arcuate corneal relaxing incisions were found to be more effective with a clear zone 3-5 mm in diameter. Radial incision simulation demonstrated little enhancement of the effect of the incisions when across the limbus.

Astigmatism↗
PubMed1989

Penetrating keratoplasty in the management of iridocorneal endothelial syndrome.

The clinical results of penetrating keratoplasty for iridocorneal endothelial (ICE) syndrome are presented. Nine cases of penetrating keratoplasty for ICE syndrome were reviewed retrospectively. All grafts remain clear, with posterior corneal changes occurring in only one case, after a mean follow-up of 43 months. Penetrating keratoplasty produced visual improvement in 7 of the 9 cases, relief of pain in 6 of 6 cases, and prevention of further corneal infection in 1 case. We believe that penetrating keratoplasty has a place in the treatment regimen of this disease, not only to achieve improvement in vision, but also for relief of pain, and avoidance of recurrent corneal infections, and to allow a clear media for careful monitoring of optic disc and field changes in the associated glaucoma.

Adult↗
PubMed1988

Laser trabeculoplasty for glaucoma in aphakic and pseudophakic eyes after penetrating keratoplasty.

We used argon laser trabeculoplasty to treat medically uncontrolled glaucoma after penetrating keratoplasty in ten eyes that were aphakic or pseudophakic. These patients were examined over an average of 22.8 months (range, 12 to 37 months) after treatment. We found an average decrease in intraocular pressure of 9.1 mm Hg (range, +8 to -19), from an average of 30.6 mm Hg before treatment to an average of 21.5 mm Hg after treatment. Eight of ten eyes had a reduction of greater than 5 mm Hg, and six of ten eyes had intraocular pressure of less than 20 mm Hg. Visual function remained stable, and complications were rare. We now prefer argon laser trabeculoplasty to cyclocryotherapy for the initial treatment of patients with medically uncontrolled glaucoma who have predominantly open angles and a clear penetrating keratoplasty.

Aged↗
PubMed1988

Excimer laser keratectomy for myopia with a rotating-slit delivery system.

We performed argon fluoride excimer laser (193-nm) superficial keratectomy for myopia on human donor eyes and on a resected corneal disc. The laser beam was shaped by a rotating slit to produce a circular ablation 7.5 mm in diameter, with a mathematically defined profile to correct myopia. The fluence at the surface of the cornea was 200 mJ/cm2; the laser was fired at 20 Hz. Each 4.5-mJ laser pulse etched a 0.17-micron deep image of the slit in the cornea. Since the slit moved (0.03 Hz), each successive pulse etched an area adjacent to the previous one, reducing damage from repetitive pulses striking the same area. The slit scanned the cornea many times and the summation of these individual ablations produced the smooth myopic ablation profile, as shown by computerized keratographs and light and electron microscopy.

Cornea↗
PubMed1988

Effect of diameter and depth on the response to solid polysulfone intracorneal lenses in cats.

Impermeable, solid polysulfone intracorneal lenses (ICLs) can change corneal refractive power but will not allow diffusion of nutrients from the aqueous to the anterior stroma. Lenses of 4, 5, 6, and 7 mm in diameter were implanted in 50 cat eyes at depths ranging from 45% to 95% of corneal thickness to determine the effect of depth and diameter. Two types of stromal opacities occurred during follow-up: peripheral amorphous opacity (100%) and crystalline-granular lipid central opacity (79%). No eyes implanted with a 4-mm ICL ulcerated, but ulceration occurred in 28% of the eyes overall. Because opacification occurred with all lens diameters and implantation depths, metabolic demands of the cornea are not met. No safe limit exists at which these ICLs can be predictably used in cat eyes.

Animals↗