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Biomedical subjects

M J Mannis

Publications and source records attributed to M J Mannis.

At least 19 recordsLinked to original sources
PubMed1992

Corneal topography of posterior keratoconus.

Posterior keratoconus is an unusual abnormality of the cornea generally classified as one of the anterior chamber cleavage anomalies. It is characterized clinically by the presence of a circumscribed or generalized corneal thinning with posterior depression of the cornea and is considered distinct from keratoconus. Although patients with posterior keratoconus may have visual complaints clearly related to their abnormal corneas, the surface topography of these corneas has not been studied in detail. Keratometry and photokeratoscopy provide an incomplete picture of the surface geometry of posterior keratoconus. We utilized computer assisted topographic analysis to study the cornea of a patient with posterior keratoconus. The Topographic Modeling System demonstrated that the patient's cornea showed a central steepened "cone" coincident with the area of circumscribed posterior keratoconus as well as paracentral flattening. This report documents the topographic abnormality in this rare disorder.

Anterior Chamber↗
PubMed1992

The effect of trabeculectomy on corneal topography.

Trabeculectomy is increasingly being performed earlier in the treatment of primary open-angle glaucoma (POAG). Surgically-induced alterations in corneal curvature resulting from filtering surgery may have a significant impact on patients, especially younger ones, whose vision may already be compromised by visual-field loss. Using data obtained by computer-assisted topographic analysis performed preoperatively and at 12 weeks postoperatively, we longitudinally studied the corneal surface changes induced by primary trabeculectomy in eight eyes undergoing surgery for POAG or normal-tension glaucoma. Additional data collected included refraction, keratometry, axial length, intraocular pressure, and pachometry. Five of eight eyes developed 1.50 to 2.50 diopters of steepening in the 90-degree meridian. One patient developed flattening in the 180-degree meridian without vertical steepening. Two patients had little change in the central optical zone. Of the six eyes with induced with-the-rule astigmatism, keratometry was less sensitive than topographic analysis in detecting the changes induced by trabeculectomy. Our data indicate that changes in corneal curvature are induced by filtering surgery, but may be undetectable without topographic analysis.

Astigmatism↗
PubMed1992

Myopia and refractive error in dogs.

The refractive error of 240 phakic dogs of various breeds was measured using streak retinoscopy and averaged (-0.27 +/- 1.41 D relative to infinity). Analysis by breed showed that the German Shepherd, Rottweiler, and Miniature Schnauzer breeds had an increased prevalence of myopia with an average refractive error of -0.86 +/- 1.31 D, -1.77 +/- 1.84 D, and -0.66 +/- 1.05 D, respectively. Myopia also was found in older dogs with marked nuclear sclerosis of the crystalline lens. Fifty-three percent of all German Shepherd dogs in a veterinary clinic population (n = 58 eyes) had a myopic refraction of greater than or equal to -0.50 D; 64% of all Rottweiler dogs (n = 28 eyes) were myopic. An in-depth investigation of German Shepherd dogs, using A-scan ultrasonography, photokeratoscopy, and streak retinoscopy, was done at Guide Dogs for the Blind (San Rafael, CA). By contrast with the results obtained in the veterinary clinic population, the overall average refractive error of guide dog German Shepherd dogs (n = 106 eyes) was +0.19 +/- 0.81 D, and only 15% of these dogs were myopic. The axial length and corneal curvature of myopic eyes did not differ significantly from nonmyopic eyes.

Animals↗
PubMed1991

Herpes simplex dendritic keratitis after keratoplasty.

We treated three patients with herpes simplex dendritic keratitis that occurred between three and 11 months after keratoplasty. The patients had no history of herpetic infection. The eyes of two of the patients were grafted for corneal scarring of undetermined origin. The eye of the third patient was grafted for pseudophakic bullous keratopathy. At the time of onset of dendritic keratitis, all three patients were receiving either maintenance or higher doses of topical corticosteroids. All infections responded to topical antiviral treatment. The findings in these patients illustrate the importance of considering herpes simplex keratitis in the differential diagnosis of all late-onset epithelial defects in the corneal graft, even in the absence of a history of herpes simplex keratitis.

Administration, Topical↗
PubMed1990

In vitro antimicrobial activity of defensins against ocular pathogens.

New approaches to antimicrobial therapy for ocular pathogens must overcome organisms that are resistant to current therapeutic modalities. This investigation examined the antimicrobial activity of novel antimicrobial neutrophil peptides (defensins NP-1 and NP-5) against isolates from clinical ocular microbial infections in humans and horses. The test panel of human clinical isolates included Candida albicans, an alpha-hemolytic Streptococcus, Streptococcus pneumoniae, Pseudomonas aeruginosa, and Morganella morganii. The test panel of equine pathogens included three clinical isolates of P aeruginosa and two clinical isolates of Staphylococcus aureus. The equine isolates were chosen for their relative resistance to commonly employed antimicrobial therapy. The two defensins differed markedly in their bactericidal activity. Defensin NP-5, at a 50-micrograms/mL concentration, exhibited minimal bactericidal activity against the majority of isolates of the test panel. The inferior microbicidal activity of NP-5 is consistent with previously published results. However, at this concentration, NP-5 did exhibit appreciable bacteriostatic activity against human ocular pathogens M morganii (74%), alpha-hemolytic Streptococcus (57%), and P aeruginosa (93%) during the 2-hour incubation period. In contrast, defensin NP-1 at 10 micrograms/mL exerted potent microbicidal activity against all isolates, effecting a 2 to 3 log10 decrease in colony-forming units within a 60-minute incubation period. Under the assay conditions employed, these findings demonstrate: (1) two distinct mechanisms by which defensins exert their antimicrobial activity against microbial pathogens associated with clinical ocular disease in humans and horses, and (2) that rabbit defensin NP-1 is a potent antimicrobial agent against a wide array of ocular pathogens.

Animals↗
PubMed1988

Intracameral thrombin and the corneal endothelium.

We perfused the endothelia of isolated human corneas mounted in the specular microscope with BSS Plus containing 1,000-U/ml or 100-U/ml dilutions of two commercially available topical thrombin preparations. Corneas perfused with thrombin at 1,000 U/ml showed intracellular and intercellular vacuole formation and altered junctional complexes. As listed on the package inserts, the thrombin preparations contained preservatives and other additives that present a significant osmotic load in 1,000-U/ml preparations. Corneas perfused with 100-U/ml thrombin solutions showed a significant attenuation in their deswelling rate but no ultrastructural alterations. One available thrombin preparation when diluted to 100 U/ml had a glycine concentration associated with previous retinal electroretinography changes. Polyacrylamide gel electrophoresis of one manufacturer's thrombin solution showed multiple high and low molecular weight constituents. Analysis of particulate contamination showed one 100-U/ml thrombin preparation to have a large quantity of particulates. Although thrombin may be useful when applied topically as an aid in surgical hemostasis, its use intraocularly presents substantial concern regarding the preparation's purity, additives, contaminants, and adverse effects on ocular tissues.

Aged↗
PubMed1988

Corneal fistulas and their management.

We reviewed three representative cases of chronic corneal fistula formation and provide a systematic approach to the assessment and therapeutic alternatives for this problem. In two of our patients, the fistula was managed surgically. The third patient developed endophthalmitis, which resulted in loss of light perception. Chronic corneal fistulization is a rare clinical entity resulting from malapposition of corneal tissue after traumatic, surgical, or infectious perforation. Fistulas may result in prolonged or recurrent hypotony, peripheral anterior synechia formation, or endophthalmitis. Accurate assessment of the risks associated with corneal fistula formation takes into account the type of fistula, its location in the cornea, and the condition of the ocular adnexae. We reviewed the risk factors that will determine the urgency and type of therapy used.

Aged↗
PubMed1988

Uses of thrombin in ocular surgery. Effect on the corneal endothelium.

Thrombin is a hemostatic factor that induces platelet aggregation and catalyzes the conversion of fibrinogen to fibrin. The potential for its increasing application to a variety of anterior and posterior segment surgery led us to investigate the in vitro effect of thrombin on the corneal endothelium in a sheep model. We examined freshly excised sheep corneas stained with alizarin red and trypan blue after exposure to two different concentrations of thrombin for four hours. The structure of the corneal endothelium appeared to be intact even after prolonged exposure to thrombin at concentrations of 100 and 1000 U/mL. Thrombin appears to be nontoxic to the corneal endothelium in this experimental model.

Adult↗
PubMed1988

The effect of fluorouracil on the corneal endothelium.

The utility of the antiproliferative agent fluorouracil has been demonstrated recently in glaucoma-filtering surgery and in the management of proliferative vitreoretinopathy after vitrectomy. Because of the potential for contact with the corneal endothelium, its toxicity to the endothelium is an important consideration. The effect of fluorouracil on corneal endothelial integrity in an in vitro animal model was studied. Freshly excised sheep corneal buttons were exposed to increasing concentrations of fluorouracil for four hours and were subsequently evaluated microscopically using vital staining with alizarin red and trypan blue. Exposure to normal saline and chlorhexidine gluconate was used to establish negative- and positive-staining controls. Corneal buttons exposed to normal saline or to 1.0 mg/mL or less of fluorouracil had intact endothelial monolayers that completely excluded trypan blue. Corneal buttons exposed to chlorhexidine gluconate or to 10 mg/mL of fluorouracil, however, had severely or totally disrupted endothelial monolayers in which the remaining cells, if any, all had blue-staining nuclei. These results suggest that the threshold concentration for fluorouracil toxicity to corneal endothelium lies between 1 and 10 mg/mL when exposure time is four hours.

Animals↗