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Biomedical subjects

R W Zabel

Publications and source records attributed to R W Zabel.

At least 19 recordsLinked to original sources
PubMed2001

The road to extinction is paved with good intentions: negative association of fish hatcheries with threatened salmon.

Hatchery programmes for supplementing depleted populations of fish are undergoing a worldwide expansion and have provoked concern about their ramifications for populations of wild fish. In particular, Pacific salmon are artificially propagated in enormous numbers in order to compensate for numerous human insults to their populations, yet the ecological impacts of this massive hatchery effort are poorly understood. Here we test the hypothesis that massive numbers of hatchery-raised chinook salmon reduce the marine survival of wild Snake River spring chinook, a threatened species in the USA. Based on a unique 25-year time-series, we demonstrated a strong, negative relationship between the survival of chinook salmon and the number of hatchery fish released, particularly during years of poor ocean conditions. Our results suggest that hatchery programmes that produce increasingly higher numbers of fish may hinder the recovery of depleted wild populations.

Animals↗
PubMed1997

X-ray diffraction and transmission electron microscopy of Morquio syndrome type A cornea: a structural analysis.

PURPOSE: This case report describes the structural characterization of the corneal stroma from a patient with Morquio syndrome type A. METHODS: A left penetrating keratoplasty was performed, and the cornea was examined using transmission electron microscopy and synchrotron x-ray diffraction. The interfibrillar proteoglycans were visualized in the electron microscope by using cuprolinic blue. RESULTS: Stromal collagen fibrils showed a bimodal distribution of diameters: 70% had a distribution comparable to that in normal tissue (20-30 nm) and 30% contained larger fibrils (30-42 nm) as seen by electron microscopy. Both electron microscopy and x-ray diffraction showed that the bulk numeric density of fibrils per unit area in cross-section (number density) was higher than normal in the Morquio syndrome cornea. The arrangement of proteoglycans throughout most of the Morquio syndrome cornea appeared normal, but many of the filaments were twice their normal length. In the anterior stroma, very large proteoglycan filaments (< or = 400 nm long) were found. Other ultrastructural differences also were noted, including abnormal keratocytes and long spacing collagen. CONCLUSION: The variation in fibril diameter and number density were modeled to account for only a 5% decrease in light scattering compared with the normal cornea. The extensive corneal clouding seen in the Morquio syndrome cornea cannot therefore be attributed to the variation in fibril diameters; collagen-free areas and expanded cells seem to be the most likely cause.

Adult↗
PubMed1993

Multifocal intraocular lenses and glare.

In a previous paper, we reported finding deficits in the contrast sensitivity functions of patients with diffractive multifocal intraocular lenses (IOL's). The results were consistent with optical measurements of the modulation transfer function (MTF) of the IOL. When this MTF is treated as a linear spatial frequency filter, it predicts the existence of a glare effect; contrast threshold for the recognition of target letters should be elevated by a bright, adjacent stimulus. We tested this prediction by measuring contrast thresholds for recognizing 0.2 degrees Sloan letters on a background luminance of 11.2 cd/m2. The letters were presented inside bright (300 cd/m2) annular rings with inner diameters ranging from 0.42 to 1.22 degrees. Thresholds were measured for seven multifocal subjects, age-matched groups of monofocal subjects and phakic-control subjects, and a young group. Multifocal subjects exhibited a greater glare effect than monofocal subjects, and they in turn exhibited a greater effect than phakic-control subjects. The observed glare effect for multifocal subjects was about twice that expected from the spatial filtering property of the multifocal IOL.

Adult↗
PubMed1993

Scheie's syndrome: the architecture of corneal collagen and distribution of corneal proteoglycans.

Processes that modulate the regular architecture and, hence, transparency of the cornea are poorly understood, although proteoglycans are thought to be involved. Scheie's syndrome displays corneal opacification and systemic accumulation of glycosaminoglycans. The manifestations of these two occurrences were examined in relation to the corneal stroma. Collagen architecture was investigated by transmission electron microscopy and synchroton x-ray diffraction. Cuprolinic blue staining located sulfated glycosaminoglycan deposits that disrupted the extracellular matrix. Unlike normal cornea, which contained collagen fibrils of remarkably uniform diameter (26.0 +/- 2.4 nm), there was a large range of fibril sizes in the Scheie's syndrome stroma (19.9 to 52.0 nm). Moreover, the distribution of fibril diameters appeared bimodal. X-ray diffraction confirmed the discovery of abnormally large stromal collagen. The results suggest a link in Scheie's syndrome between proteoglycan content/distribution and stromal disruption, and between stromal disruption and corneal opacification.

Collagen↗
PubMed1992

Contrast sensitivity and reading through multifocal intraocular lenses.

Multifocal intraocular lenses are intended to increase depth of focus for patients with cataracts, but optical considerations predict reduced retinal-image contrast. We evaluated visual performance through multifocal intraocular lenses by measuring contrast sensitivity functions and reading speed for age-matched groups with multifocal and monofocal intraocular lenses and two normal control groups. Contrast sensitivity functions of the patients with multifocal lenses did not differ significantly for optical distances differing by 2.5 diopters, indicating substantial depth of focus. Normal and monofocal contrast sensitivity functions were nearly identical, and both were about a factor of two higher than multifocal contrast sensitivity functions. Patients with multifocal lenses showed deficits in reading speed only for low-contrast text (less than 30%) and small letters (0.2 degree and 1.0 degree).

Aging↗
PubMed1992

A morphological study of rabbit corneas after laser keratectomy.

We have examined the morphology of the collagen and proteoglycans in rabbit corneas that have undergone excimer laser photorefractive keratectomy using a clinical, 193 nm excimer laser. The photoablation was carried out to a stromal depth of 100 microns and a diameter of 6 mm. All ablated corneas developed a haze that was most intense between week 4 and week 8 and which showed no improvement after week 16. The corneas were stained with the cationic dye cuprolinic blue to visualise proteoglycans and were then processed for transmission electron microscopy. The ultrastructural location of proteoglycans (keratan sulphate and dermatan sulphate) was observed in the corneal wounds at different time intervals. Corneas that had undergone steroid treatment post-operatively were also examined. In the healing tissue proteoglycan filaments of abnormal size were observed, which became most prominent after 2 weeks. As healing progressed these abnormal filaments decreased but after 45 weeks some were still present, indicating that the proteoglycan content had not returned to normal.

Animals↗
PubMed1991

Clinical use of the 193-nm excimer laser in the treatment of corneal scars.

Phototherapeutic keratectomy using a 193-nm excimer laser was performed at four centers on 33 sighted patients with corneal opacity and/or irregular astigmatism. Pathologic conditions included anterior stromal and superficial scarring from postinfectious and posttraumatic causes, including inactive herpes simplex virus, anterior corneal dystrophies, recurrent erosions, granular dystrophy, and band keratopathy. Most patients received peribulbar anesthesia and underwent removal of the epithelium prior to laser ablation. A majority of patients had a reduction in the amount of corneal scarring and approximately half had improved visual acuity. No intraocular reaction or changes in endothelial counts were seen, and some patients avoided the need for penetrating keratoplasty. Reepithelialization usually occurred within 4 or 5 days and we noted no significant scarring secondary to use of the laser. It was difficult to eliminate preexisting irregular astigmatism despite the use of surface modulators, such as methylcellulose. A hyperopic shift secondary to corneal flattening was encountered in approximately 50% of the patients. A combination of myopic ablation, followed immediately by a secondary hyperopic steepening, may minimize this refractive change. The 193-nm excimer laser is an effective new tool in the treatment of selected patients with superficial corneal opacity from a variety of conditions.

Adult↗
PubMed1991

Corneal endothelial decompensation after argon laser iridotomy.

Focal corneal edema overlying the site of argon laser iridotomy followed by generalized corneal decompensation developed in six eyes of five patients. The average interval between the iridotomy and the development of focal edema was 3 years, with generalized edema appearing an average of 3.5 months later. Light, scanning and transmission electron microscopy of tissue removed at the time of corneal transplantation showed abnormalities characteristic of Fuchs' dystrophy in two patients. Possible contributing factors include episodes of intraocular pressure elevation, cornea guttata and the use of high total amounts of energy during laser iridotomy.

Argon↗
PubMed1990

Multifocal intraocular lenses.

Current multifocal intraocular lens designs incorporate refractive or diffractive optical principles to achieve increased depth of focus. Information about four basic design concepts is presented. Early clinical results with two of these, the IOLAB Nuvue two-zone refractive multifocal and the 3M diffractive multifocal, are summarized.

Clinical Trials as Topic↗
PubMed1989

Scheie's syndrome. An ultrastructural analysis of the cornea.

The histopathology of a corneal graft specimen obtained from a patient with Scheie's syndrome (systemic mucopolysaccharidosis, type IS) is described with particular emphasis on the ultrastructural findings. Numerous vacuoles containing fibrillogranular material were found in the corneal epithelial cells, the keratocytes, and the endothelial cells. The basement membrane of the epithelium contained frequent breaks and peg-like undulations, and Bowman's layer was markedly attenuated. Fibrous long-spacing (FLS) collagen featured prominently in the stroma. Descemet's membrane was normal. The findings of a markedly attenuated Bowman's layer and FLS collagen may be abnormalities specific to Scheie's syndrome resulting from the altered glycosaminoglycan composition of the extracellular matrix.

Adolescent↗
PubMed1989

Corneal topography: a new photokeratoscope.

The assessment of the topography of the cornea is an important modality in the management of surgical procedures complicated by astigmatism. Additionally, the outcome of corneal refractive surgery is often best illustrated by photokeratoscopy. Currently available photokeratoscopes suffer from a number of deficiencies that include (i) the lack of topographic detail from the central cornea, (ii) the difficulty in transporting these units, (iii) the cost of such units. A photokeratoscope which addresses these shortcomings is described.

Cornea↗
PubMed1989

Corneal toxic changes after cataract extraction.

Over an 18-month period 10 patients (12 eyes) presented with severe corneal toxic changes after cataract extraction. Defined stages in the keratopathy included punctate epithelial keratopathy, pseudodendrite, central epithelial ulcer and central stromal ulcer. Periods of up to 13 months were required for resolution of the defects. Axial scarring and nonhealing epithelial defects resulted in a final visual acuity of counting fingers and hand movement in two patients. We believe that exposure during the postoperative period to benzalkonium chloride contained in ophthalmic medications represents the most likely cause of the toxic changes and that no single ophthalmic medication can be held responsible. The past ocular histories of the patients included chronic open-angle glaucoma, dry eye syndrome and anterior membrane dystrophy. Prior exposure to benzalkonium-containing antiglaucoma medications, tear film deficiencies or abnormalities of epithelial adhesion may have predisposed the corneas in these patients to the development of benzalkonium-related toxic changes.

Benzalkonium Compounds↗
PubMed1989

Corneal repair following keratectomy. A comparison between conventional surgery and laser photoablation.

We have used the fluorescent dye dichlorotriazinyl aminofluorescein (DTAF) to demonstrate corneal remodeling following keratectomy in the rabbit. The dye was applied to the surface of 3.5 mm diameter anterior keratectomy wounds produced by either lamellar dissection or photoablation with an excimer laser (193 nm) to a depth of 15, 50 or 75 microns. Stromal wounds that had been ablated in 12 concentric steps to produce a graded profile with a central depth of 15 or 30 microns were also studied. The repair process was followed for periods of up to 6 months. These results were compared to wounds of similar dimensions in which an intrastromal keratectomy was performed and the anterior stromal surface replaced. Sections examined by fluorescence microscopy showed that connective tissue was deposited beneath the epithelium of all anterior keratectomy wounds irrespective of their mode of induction or depth. The deposition of this new tissue, and an associated thickening of the epithelium over the wound surface, appeared to be complete by 1 month and tended to restore the original surface contour. The synthesis of connective tissue, but not the hyperplasia of the epithelium, was reduced by local steroid treatment. In contrast, an intrastromal keratectomy only stimulated the deposition of small amounts of new connective tissue at the wound junction without as marked a thickening of the overlying epithelium. These observations emphasize the importance of the epithelium in moderating repair after stromal loss, and suggest that remodeling may result in corneal haze and a change in the desired refraction if refractive surgery is attempted by anterior keratectomy.

Animals↗
PubMed1989

Hyperplastic precorneal membranes. Extending the spectrum of neurotrophic keratitis.

Neurotrophic keratitis is a recognized complication of the neurosurgical treatment of trigeminal neuralgia. Following a retrogasserian rhizotomy, our patient developed, in addition to the anterior segment abnormalities anticipated with neurotrophic keratitis, an actively growing hyperplastic precorneal membrane originating from the limbal area and overlying intact corneal epithelium. Growth of the membrane continued towards the visual axis until all but the central 3 mm of the corneal epithelium was covered. This previously undescribed observation may indicate that the epithelium of the conjunctival and limbal areas are maintained and regulated by a different physiologic mechanism than that of the central corneal epithelium following sensory deafferentation. The significance of the membrane is discussed in context with the X, Y, Z hypothesis of corneal epithelial maintenance.

Cornea↗