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Biomedical subjects

R W Beuerman

Publications and source records attributed to R W Beuerman.

At least 55 records · Page 3Linked to original sources
PubMed1995

Confocal microscopy of corneal graft rejection.

Corneal allografts were transplanted into inflamed and vascularized graft beds in rabbit eyes. The grafts were examined every 4 days by slit-lamp biomicroscopy and scanning confocal microscopy. Confocal images were recorded with a video camera and computer enhanced in real-time. Layers of the cornea were visualized in serial optical sections parallel to the epithelium. In the third postoperative week, signs of graft rejection were observed; slit-lamp examination revealed a circumferential line of epithelial rejection, along with cloudiness and edema. Vessels were observed growing into the graft. By confocal microscopy, infiltrating cells were seen in the graft stroma. Foci of cells were especially pronounced around the sutures. Scattered leukocyte infiltrates were prominent at capillary terminals. There was an accompanying reduction in the stromal keratocyte density in the region of the infiltrate. Additionally, various degrees of fibrosis were noted around each suture and at the host-graft interface. Confocal microscopy may provide a valuable clinical tool for determining the earliest indicators of an antigraft immune response, and as an aid in the differential diagnosis of other inflammatory conditions of the cornea.

Animals↗
PubMed1995

In vivo confocal microscopy of corneal wound healing after excimer laser photorefractive keratectomy.

We used real-time scanning confocal microscopy to evaluate early changes in corneal wound healing after excimer laser photorefractive keratectomy (PRK). Adult New Zealand White rabbits were given photorefractive keratectomy treatments appropriate for 5.00 to 8.00 D of myopia (44.5 to 71.0 micros depth, with a 5-mm diameter treatment zone). Daily confocal microscopic examinations showed acute loss of keratocytes in the anterior corneal stroma by 5 hours; losses were maximal between 24 and 48 hours for 5.00 D and 6.00 D ablations and between 72 and 96 hours for 7.00 D and 8.00 D ablations. The oval nuclei of normal keratocytes gave way to spindle-shaped fibroblasts accompanied by an accumulation of fibrillary extracellular matrix. Fibroblasts density increased toward the end of the week. Deeper ablations resulted in a longer period of keratocyte depletion and delayed onset of fibroblast activity. No epithelial, deep stromal, or endothelial abnormalities were detected, nor was stromal inflammation found. Light microscopy 1 week after PRK revealed superficial fibroplasia, which correlated with the en face images obtained with real-time in vivo confocal microscopy. The confocal microscope has a number of advantages as a clinical tool for investigation of laser-induced changes in corneal keratocytes and the stromal matrix, which may play a role in determining visual outcome after PRK.

Animals↗
PubMed1995

A new form of primary, localized, corneal amyloidosis: a case report with confocal microscopy.

We present a case of bilateral, primary, localized, corneal amyloid deposition with a unique appearance not, to our knowledge, previously described. The patient was a 73-year-old white man who complained of glare. Best corrected visual acuity was 20/25 in both eyes. Slit lamp examination revealed subepithelial/anterior stromal white-gray deposits in the peripheral cornea in both eyes. The corneal surface was smooth with no elevated areas. Superficial corneal scrapings showed focal deposits of an amorphous, glass-like material below the epithelial surface and within Bowman's membrane, which stained with Congo red. We examined the amyloid deposits using the confocal microscope to obtain high magnification images in vivo. The confocal microscopic views showed intercellular, cotton candy-like, fibrillar amyloid material scattered throughout the anterior stroma. The use of this instrument may permit clinical diagnosis of this rare disorder without the need for biopsy.

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PubMed1994

Quantitative histological studies of primate corneas after excimer laser photorefractive keratectomy.

OBJECTIVE: To evaluate histological changes in the primate cornea after excimer laser photorefractive keratectomy (PRK) and to correlate them with clinical observations. METHODS: Sixteen African green monkey (Cercopithecus aethiops sabaeus) corneas were examined by light and transmission electron microscopy 6 weeks to 18 months after 1.5- or 3-diopter PRK. RESULTS: All specimens had a smooth stromal surface surrounded by a smooth, centrally tapered Bowman's layer. Epithelial thickness appeared to peak 12 months after PRK. The trend was for the epithelium to be thickest in the central-treated area; this phenomenon was more obvious in the 3-diopter-treated corneas. The numbers of activated keratocytes beneath the treated zone peaked at 4 months and decreased thereafter, while the numbers in the untreated areas decreased in the first 2 months after surgery, increased by 4 months, and did not change thereafter. Regenerated basal lamina averaged 86% intact over ablated areas; thickness was normal and no duplications were seen. Overall, the density of hemidesmosomes was significantly less in ablated areas compared with unablated areas. CONCLUSIONS: These findings support the relationship between clinical observations of corneal haze after PRK, reestablishment of the epithelial cell layer, and the potential for stromal remodeling by active fibroblastic keratocytes beneath the ablation zone. Overall, quantification of several morphological parameters indicated that the values for the treated zone tended, with time, to approach those of the untreated cornea after PRK.

Animals↗
PubMed1994

Quantification of real-time confocal images of the human cornea.

Real-time confocal microscopy was used to obtain images of the surface cells of the cornea in vivo in human subjects and in non-human primates. The surface cells represent the barrier between the tear layer and the internal cellular environment and as such, the state of these cells is indicative of the health of the cornea. In our study, confocal microscopy of the surface cells revealed prominent, centrally located nuclei. With the use of a series of image analysis procedures, the nuclei were located automatically and distances to the nearest neighbors were determined. Comparison of these procedures in 8 human corneas and 1 non-human primate cornea showed that unaided computer analysis of the surface cells was as accurate as manual location of the cell nuclei. The distribution of nearest-neighbor distances was found to be best fitted by a gamma distribution. Simulation of a condition marked by loss of surface cells demonstrated that the alpha (shape) and beta (scale) parameters could be used to compare the distribution of nearest-neighbor distances. Thus, confocal microscopy coupled with these image analysis and statistical procedures could provide an objective, quantitative approach to monitoring the epithelial barrier under clinical and experimental conditions, for example during post-surgical or post-traumatic healing or in the evaluation of the efficacy of topical therapeutic agents.

Animals↗
PubMed1994

Effect of topical beta blockers on corneal epithelial wound healing in the rabbit.

Topical beta adrenergic receptor blocking agents (beta blockers) are among the most frequently prescribed ophthalmic drugs. It has been suggested that some of these agents have a toxic effect on the corneal epithelium. In the present study, four beta blockers in common therapeutic concentrations, as well as their vehicles, were applied to rabbit corneas that had undergone mechanical removal of epithelium from a 6 mm diameter corneal wound. The tested drugs (0.25% timolol, 0.25% levobunolol, 0.25% betaxolol, and 0.3% metipranolol) were found significantly to accelerate wound closure, compared with saline treatment in controls. Eyes treated with two of the vehicles (betaxolol vehicle and metipranolol vehicle) also demonstrated more rapid healing than controls, but the magnitude of the effect was not as great as that seen with the drugs. Only the beta blockers were responsible for wound closure before 60 hours, whereas the saline treated controls and vehicle treated eyes required longer times for wound closure. In this model of wound healing, beta blockers appear to have no deleterious effect on corneal epithelial wound healing.

Administration, Topical↗
PubMed1993

Somatosensory evoked potentials induced by stimulating a variable number of nerve fibers in rat.

Somatosensory evoked potentials (SEPs) were recorded from rat spinal cord (sSEPs) and cerebral cortex (cSEPs). Stimulus sites included either one or both sural nerve branches having different fiber populations (group A), or distal to a lesion of controlled size of the sural nerve made 1 week earlier (group B). In the two groups of animals, amplitudes of SEPs correlated with the quantity of large myelinated nerve fibers. Peak latencies of sSEPs in group A related to the ratio of sizes of transmitting fibers. sSEPs and cSEPs in both groups A and B could be recorded in a reproducible fashion by stimulating sural nerve branches or lesioned nerve trunks containing only 100 or less nerve fibers greater than 4 microns in size. Thus, presence of sSEPs or cSEPs after stimulation distal to a lesion site does not insure that many nerve fibers have continuity with the central nervous system (CNS).

Animals↗
PubMed1993

Vitreoretinal toxicity of basic fibroblast growth factor.

Basic fibroblast growth factor (b-FGF) is one of the multifunctional growth factors with important therapeutic potential in the field of ophthalmology. It is also implicated in pathogenesis of vitreoretinal proliferative diseases. In the present study, we evaluated its vitreoretinal toxicity by means of clinical observation, electroretinography (ERG), and histopathology after injection of different doses of b-FGF into the vitreous of rabbit eyes. Doses of b-FGF up to 2 micrograms per eye caused no toxicity; however, injection of 4 micrograms or more resulted in sight-threatening vitreoretinal proliferative changes. This information is important for studies aimed at evaluating the therapeutic potential of b-FGF in retinal diseases. Despite some degree of vitreous organization and opacification, retinal folds, and small areas of traction retinal detachment, the amplitudes of ERGs were normal or even increased (hyperpolarization) in eyes which received 8 micrograms of b-FGF.

Animals↗
PubMed1993

Assessment of the long-term corneal response to hydrogel intrastromal lenses implanted in monkey eyes for up to five years.

The biocompatibility of hydrogel intracorneal lenses (ICLs) implanted in monkey eyes was evaluated for periods ranging up to five years. Seventy-three plus or minus powered ICLs made of Lidofilcon A (68% water) or Lidofilcon B (79% water) were implanted following lamellar dissection with a microkeratome. Ten sham surgical procedures were performed without ICL implantation as controls. Eyes were followed for up to five years by slitlamp biomicroscopy and specular microscopy. Light and transmission electron microscopic evaluations of enucleated eyes were performed at various intervals. Minimal tissue reaction was noted; both hydrogel materials appeared to be equally well tolerated. Failures usually occurred as a result of microkeratome problems encountered during surgery. Histopathological changes to the cornea included epithelial thinning anterior to the thickest portion of the ICL, fibroblastic activity along the ICL-stromal interface, and deposition of an amorphous extracellular material adjacent to the ICL. These observations did not appear to be clinically significant as the eyes were quiet by slitlamp examination. Removal of three ICLs eight to ten months prior to enucleation restored the normal histological characteristics of the cornea. The endothelial cell density of ICL-implanted eyes decreased by 4.3% (n = 17) six months after surgery but remained stable thereafter. The variation in endothelial cell area and percentage of hexagonal cells did not change over 50 months. The results appear to demonstrate that high water content synthetic ICLs can be well tolerated in the monkey cornea for up to five years.

Animals↗
PubMed1993

Comparison of macropore, semipermeable, and nonpermeable collagen conduits in nerve repair.

Twelve rabbits were used to study functional nerve regeneration through macropore, semipermeable, and nonpermeable collagen conduits. Each animal underwent a 10-mm bilateral resection of posterior tibial nerve. Lesions were repaired with a macropore collagen tube in one leg, and with a semipermeable or a nonpermeable collagen tube contralaterally. Functional nerve regeneration was evaluated at 6 and 12 weeks post-repair periods. Functional recovery was assessed by electrophysiologic analysis of nerve conduction velocity, amplitude of nerve action potential, amplitude and area of muscle action potential, and by quantitative and qualitative histologic analysis of myelinated nerve fibers from the distal nerve stumps. The macropore-collagen-tube group showed significantly greater functional recoveries than semipermeable or nonpermeable collagen-tube groups, based on electrophysiologic and histologic analyses.

Animals↗
PubMed1993

Topical bupivacaine and proparacaine: a comparison of toxicity, onset of action, and duration of action.

Bupivacaine is a local ocular anesthetic with a long duration of action when administered by retrobulbar injection. To determine the potential for the use of bupivacaine as a topical ocular anesthetic, the onset and duration of action and toxicity of various concentrations of bupivacaine were studied after instillation in rabbit eyes. The onset and duration of action were not significantly different from that of topical 0.5% proparacaine. Increasing the pH of the bupivacaine solution from 5.7 to 6.5 nearly doubled the duration of action, but the increase was not sufficient to be clinically important. Slit lamp biomicroscopic examination and scanning electron microscopy showed that bupivacaine was less toxic to the corneal epithelium than 0.5% proparacaine. Healing after keratectomy was significantly more rapid in eyes treated with 0.75% bupivacaine, compared with eyes treated with 0.5% proparacaine. These results suggest that bupivacaine may be less toxic to the corneal epithelium than proparacaine and could be clinically useful for topical ocular anesthesia, particularly if pharmacologic modifications can increase the duration of anesthesia provided by this drug.

Administration, Topical↗
PubMed1993

Histochemical distribution of carbonic anhydrase in rat and rabbit lacrimal gland.

PURPOSE: The purpose of this study was to examine the histochemical distribution of carbonic anhydrase (CA) in lacrimal glands from rats and rabbits; and to determine if age- and/or sex-related differences exist in the amount and distribution of CA in the rat lacrimal gland. METHODS: Lacrimal glands from young (3-12 wk) and aged (2-2.5 yr), male and female F344 rats and male rabbits were fixed in 1% paraformaldehyde and embedded in glycolmethacrylate. CA histochemistry was performed on 2-microns sections. The distribution of CA activity was determined by morphometric analysis. RESULTS: In rat lacrimal gland, CA activity was distributed in a discontinuous, mosaic fashion among the acinar cells. In tissue from young males and females as well as from aged females, about 10% of the acinar tissue displayed CA activity. Significantly more activity was present in tissue from aged male rats. CA was present in the ductal lumina, suggesting that it is a secretory product of the acinar cells. In rabbits, CA activity was associated with the basolateral membranes of the terminal acinar cells only. CONCLUSIONS: In rat, the presence of CA activity in certain acinar cells and in ductal lumina suggests that CA is actively secreted by the lacrimal gland. An age-related increase in the amount of CA activity in the male glands exists that may be under gender-specific hormonal influences. In the rabbit lacrimal gland, the membrane-associated CA found uniquely with the terminal acinar cells suggests that these cells have special transport functions associated with the primary secretion of lacrimal fluid.

Animals↗
PubMed1992

Vancomycin-enriched corneal storage medium.

Antibiotics in a corneal preservation solution probably have little effect during storage at 4 C, but are effective as the tissue is warmed. The tissue acts as a sponge, soaking up the antibiotic from the solution and releasing it into the eye, where the bactericidal effect is achieved. Currently, high concentrations of gentamicin (relative to the minimal inhibitory concentration) are used in the preserving solution for this purpose. Presumably, proportionately high concentrations of any proposed new antibiotic added to supplement the bactericidal effect of gentamicin, such as the vancomycin used in this study, would be required. However, neither the ability of donor tissue to tolerate high concentrations of vancomycin nor the stability of vancomycin at neutral pH in appropriate storage media has been documented. We evaluated the addition of vancomycin (100 micrograms/ml) to two corneal storage media that contained gentamicin in terms of stability of the antibiotic in solution and the effect on the endothelial cells of donor tissue stored for two weeks at 4 C. Vancomycin was stable in solution at neutral pH (7.2) during the five-month period of the study; the concentration exceeded 90 micrograms/ml for the first five weeks. The endothelial cells from donor tissue stored in the vancomycin-enriched media showed no notable differences from those stored in the same media without vancomycin in terms of cell shape, cell borders, cell swelling, and apical holes. The stability of vancomycin in storage and the absence of endothelial toxicity in vitro support the potential use of this antibiotic as a supplement to gentamicin for the prevention of endophthalmitis in patients receiving corneal transplants.

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