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Biomedical subjects

K R Kenyon

Publications and source records attributed to K R Kenyon.

At least 109 records · Page 6Linked to original sources
PubMed1987

Experimental drusen formation induced by intravitreal aminoglycoside injection.

A single intravitreal injection of aminoglycoside antibiotics in the rabbit induces changes in the retinal pigment epithelial layer that consist of disseminated yellow-white dots that are apparent six to ten months after injection. With fluorescein angiography, these dots have the characteristics of window defects or drusen. Histologic examination disclosed subepithelial amorphous material that stained positively with both periodic acid-Schiff and oil red O. Ultrastructural examination disclosed lipidic inclusions in the retinal pigment epithelial cells, basally directed cellular evagination, and basal accumulation of granular material, findings consistent with the reported morphologic features of hard drusen. These findings suggest that aminoglycoside-induced lesions may represent a model for retinal pigment epithelial degeneration and drusen formation.

Amikacin↗
PubMed1987

The role of vitrectomy in the treatment of postoperative bacterial endophthalmitis. An experimental study.

While the diagnostic value of vitreous culture in the management of bacterial endophthalmitis is well established, the therapeutic value of vitrectomy in this condition is debated. The present experimental study uses an aphakic model of Staphylococcus aureus endophthalmitis in the rabbit. Animals were treated with the following: (1) intravitreal antibiotics alone; (2) intravitreal antibiotics with vitrectomy; (3) vitrectomy alone; and (4) no treatment. Eyes treated with antibiotics and vitrectomy displayed significantly clearer media at 14 days after therapy compared with eyes treated with antibiotics alone. There was also a greater tendency for eyes treated with antibiotics and vitrectomy to have negative cultures at 14 days, although this difference was not statistically significant. These findings are consistent with beneficial effects of therapeutic vitrectomy as an adjunct to intravitreal antibiotic therapy in an animal model of aphakic bacterial endophthalmitis.

Animals↗
PubMed1987

Hydrogel contact lens-induced Pseudomonas keratitis in a rabbit model.

Unused soft contact lenses (SCL) containing 38.6% water (polymacon) and 70% water (lidofilcon A) were exposed to Pseudomonas aeruginosa (10(8) CFU/ml) for 60 min and washed. The contaminated lenses were used on rabbit eyes under the following conditions: for 1 h on a scratched corneal epithelium (16 eyes, four infected), for 24 h on normal cornea (eight eyes, none infected), and for 7 days on normal cornea (eight eyes, three bacterial infections and two noninfected epithelial defects). A control group of rabbits used an uncontaminated lens for 7 days (eight eyes, four noninfected epithelial defects). The control group and groups that wore contaminated lenses for 24 h and 7 days underwent tarsorrhaphy to keep the contact lens in place. In addition, three drops of the bacterial suspension were instilled in eyes with normal corneal epithelium (eight eyes, none infected) and scratched corneal epithelium (16 eyes, 13 infected). Results suggest that Pseudomonas-contaminated SCL give rise to keratitis only on an injured corneal epithelium and that a bacterial suspension is more pathogenic to the rabbit cornea than is a similar amount of bacteria on an SCL.

Animals↗
PubMed1987

Lacrimal gland, cornea, and tear film in the NZB/NZW F1 hybrid mouse.

The NZB/NZW F1 hybrid mouse has been reported to contract a disease similar to Sjögren's syndrome in man. We studied lacrimal gland morphology, corneal morphology, and tear osmolarity in this mouse as a function of age. Lacrimal glands of hybrid mice contained abnormal periductal infiltrates of lymphocytes and plasma cells. Maximum infiltration of the lacrimal gland occurred in the 29-week-old female hybrid mouse and was estimated to involve 12% of the gland, but was insufficient to alter tear osmolarity relative to DBA and Balb/c control mice. Nevertheless, both NZB/NZW F1 hybrid mice and DBA and Balb/c control mice had tear osmolarity and corneal surface morphology similar to that reported for keratoconjunctivitis sicca in man. Although the NZB/NZW F1 hybrid mouse may provide a valuable model for the study of lacrimal gland infiltration, since its tear osmolarity and ocular surface remain normal for a mouse, its usefulness as a model for ocular surface disease in human keratoconjunctivitis sicca may be more limited than previously thought.

Aging↗
PubMed1987

Residual bodies in the retinal pigment epithelium induced by intravitreal netilmicin.

Intravitreal injection of aminoglycoside antibiotics is known to induce morphological changes in the retinal pigment epithelium (RPE) resembling a lipidosis. The RPE of netilmicin-treated rabbits displays a dose-related increase in autofluorescence compared to untreated controls. Netilmicin produces an accumulation of membrane-limited osmiophilic lamellated inclusions in the pigment epithelial cell. These inclusions measure from 1 to 3 microns in diameter, and have acid hydrolase activity demonstrated by cytidine monophosphate cytochemistry. These findings suggest that netilmicin-induced inclusions are residual bodies and that the accumulation of these residual bodies is responsible for the observed cellular lipidosis.

Animals↗
PubMed1987

A new donor cornea marker and punch for penetrating keratoplasty.

We describe a new device to mark and punch donor corneas for penetrating keratoplasty. The device contains eight marking-suction holes that make circular marks in the periphery of the donor cornea and fix the tissue in position during trephination. The eight peripheral marks correspond in location to meridians of an eight-blade radial keratotomy marker. When used in conjunction with this marker for the host bed, the donor cornea marker facilitates alignment of meridians on donor and host tissues, radial placement of sutures, and quantitative placement of sutures equi-distant from the wound margin.

Corneal Transplantation↗
PubMed1987

Anterior segment reconstruction following trauma.

In summary, this discussion reiterates the basic principles and techniques of reconstructive surgery following severe anterior segment trauma. Clearly, visual rehabilitation is a direct concomitant of anatomical restoration. Thus, definitive efforts to remove and replace damaged ocular surface tissue, as by conjunctival transplantation or pannus stripping, followed by penetrating keratoplasty with particular attention to restoration of iris and angle structures are well within the capability of anterior segment surgeons. Given the remarkable plasticity of ocular anterior segment tissues, particularly conjunctiva and iris, the straight forward application of these techniques can frequently yield both aesthetically satisfying and visually satisfactory results.

Anterior Eye Segment↗
PubMed1987

Noninvasive measurements of pyridine nucleotide and flavoprotein in the lens.

Abnormalities in glucose metabolism are thought to be among the main causes of cataract formation. The authors have made noninvasive biochemical measurements of the lens that provide information concerning glucose metabolism in the lens epithelium. The autofluorescence of reduced pyridine nucleotides (PN) and oxidized flavoproteins (Fp) within the rabbit lens were noninvasively measured as a function of depth using redox fluorometry. The peak of the autofluorescence at 440 nm (excited at 360 nm) and 540 nm (excited at 460 nm) were determined at the lens epithelium. When 8 mM sodium pentobarbital, a known inhibitor of mitochondrial respiration, was applied to the lens, the autofluorescence peak at 440 nm increased and that at 540 nm decreased. The 440 nm autofluorescence is thought to be from reduced pyridine nucleotides, whereas the 540 nm autofluorescence is from the oxidized flavoprotein. Blocking lens respiration with pentobarbital caused an increase in the PN/Fp ratio by a factor of 3 within 3.5 hr after pentobarbital application.

Animals↗
PubMed1986

Corneal changes during pilocarpine gel therapy.

Fifteen of 53 patients (28%) receiving long-term pilocarpine gel therapy were noted to have a subtle, diffuse superficial corneal haze. Results of a masked examination of patients using pilocarpine gel vs pilocarpine eyedrops and the finding of the haze unilaterally in patients using the gel unilaterally suggested that the haze is related to the pilocarpine gel. In most patients the haze persisted for two years after gel treatment was discontinued; the haze disappeared in two patients. Although patients remain asymptomatic with unaltered visual acuities, the long-term effect of this corneal change is unknown.

Conjunctiva↗
PubMed1986

Intravitreal amikacin in the treatment of bacterial endophthalmitis.

Intravitreal administration of broad-spectrum antibiotics is a widely accepted component of initial therapy for bacterial endophthalmitis. Four cases of culture-proved bacterial endophthalmitis are reported to demonstrate the safety of intravitreal administration of amikacin sulfate in conjunction with cephalosporins in patients. The benefits of using amikacin rather than gentamicin sulfate in intravitreal drug therapy are discussed, and a wider role for amikacin as the aminoglycoside of choice for initial intravitreal injection in presumed bacterial endophthalmitis is suggested.

Aged↗
PubMed1986

Aqueous to cornea fluorescein distribution ratio in normal and swollen cornea.

Intravitreal sodium fluorescein was used to simulate equilibrium fluorescein kinetics, thereby allowing simple measurement of the aqueous to cornea fluorescein distribution ratio. Two groups of rabbit corneas were studied: normal corneas and corneas wounded by freezing. The aqueous to cornea fluorescein distribution ratio was approximately 0.4, was not significantly different in groups of normal or wounded eyes and little variability was noted. In addition, a comparison of in vivo and in vitro measurements of corneal fluorescein concentration in wounded eyes suggests that in vivo protein-bound fluorescein in the cornea fluoresces less efficiently than free fluorescein.

Animals↗
PubMed1986

Systemic tetracycline hydrochloride as adjunctive therapy in the treatment of persistent epithelial defects.

Recent evidence shows tetracyclines have anticollagenolytic activity that may be clinically effective in disease treatment. This led us to use systemic tetracycline (oral tetracycline hydrochloride 1 g daily divided into 4 doses) as adjunctive therapy in treating 18 patients with persistent corneal epithelial defects. Fourteen of 18 patients healed their defects; within 48 hours (9 patients) and within two weeks (the other 5 responding patients). Two patients showed no effect and two showed disease progression.

Adolescent↗
PubMed1986

Treatment of superior limbic keratoconjunctivitis by thermocauterization of the superior bulbar conjunctiva.

Superior limbic keratoconjunctivitis (SLK) is a chronic and recurrent inflammatory disease of the superior tarsal, bulbar and limbal conjunctiva that often responds to topical treatment with silver nitrate. As an alternative treatment in 11 patients (13 eyes), we applied thermal cautery to the inflamed superior bulbar conjunctiva following subconjunctival injection of 2% xylocaine. The overall positive response rate to thermocautery was 73% (8 patients). Of the positive responders, 63% (5 patients) had been considered silver nitrate treatment failures. Keratitis sicca was additionally noted in 55% of the patients studied. Impression cytology of involved superior bulbar conjunctiva was nearly devoid of goblet cells during the acute stage of the disorder. Following successful cauterization, goblet cells returned. Thus, thermocauterization of the superior bulbar conjunctiva appears to be a safe and effective mode of therapy for SLK.

Adult↗
PubMed1985

The influence of aphakia and vitrectomy on experimental retinal toxicity of aminoglycoside antibiotics.

To study the effect of lens and vitreous surgery on the dose threshold of aminoglycoside-induced retinal toxicity, we performed extracapsular lens extraction (Group 1) or lensectomy and vitrectomy (Group 2) on Dutch Belted rabbits. A single dose of amikacin or gentamicin ranging from 100 to 4,000 micrograms was administered intravitreally. Retinal toxicity was examined by light and transmission electron microscopy seven days after injection. Both groups showed retinal toxicity after 400 micrograms of gentamicin or 1,500 micrograms of amikacin, doses identical to those causing toxicity in intact, phakic rabbit eyes. Thus, neither surgical procedure increased the toxic threshold of injected aminoglycoside. Given the accelerated aminoglycoside clearance reported in aphakic eyes, these findings imply that the mechanism of aminoglycoside toxicity may be related to peak drug concentration rather than duration of tissue exposure.

Aminoglycosides↗
PubMed1985

Comparative toxicity of intravitreal aminoglycoside antibiotics.

We compared the toxicity of the aminoglycoside antibiotics (tobramycin, amikacin, netilmicin, and kanamycin) by ophthalmoscopy, light and electron microscopy, and electro-retinography after intravitreal injection in rabbits in doses ranging from 100 to 3,000 micrograms. The earliest manifestations of toxicity were confined to the outer retina with each drug, with lamellar lysosomal inclusions in the retinal pigment epithelium as the earliest finding. However, the aminoglycosides displayed marked differences in the threshold dose required to produce toxic reactions, permitting the following ordering of toxicity: (most toxic) gentamicin greater than netilmicin = tobramycin greater than amikacin = kanamycin (least toxic).

Amikacin↗