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Biomedical subjects

K R Kenyon

Publications and source records attributed to K R Kenyon.

At least 163 records · Page 9Linked to original sources
PubMed1982

Traumatic wound dehiscence following penetrating keratoplasty.

Four young male patients with keratoconus had traumatic dehiscence of the surgical wound after penetrating keratoplasty. Two were rendered aphakic by the trauma, and in one patient the lens was dislocated posteriorly. In each case the dehiscence was repaired by resuturing the original corneal graft. Despite marked corneal oedema in the immediate postoperative period all four grafts deturgesced and subsequently cleared. The follow-up has been a minimum of 23 months. We recommend therefore primary resuturing of traumatic wound dehiscence after keratoplasty, anterior vitrectomy if the lens dislodged, and prophylactic antibiotics postoperatively. The clearing of the initially oedematous grafts in each case illustrates the resilience of the corneal endothelium.

Adult↗
PubMed1982

Studies on the source and release of collagenase in thermally burned corneas of vitamin A-deficient and control rats.

In previous studies we found that a mild thermal burn of the vitamin A-deficient rat cornea caused collagenase release into the medium of corneas placed in culture media 72 hr after applying the burn. Collagenase was released only on day 1 of culture and was not released from identically burned corneas of control rats. We now demonstrate that in deficient corneas, this collagenase release on day 1 of culture increased gradually with increasing time between burn and sacrifice, reaching a maximum at 16 hr after burning a remaining high up to 72 hr. In control rats day-1 collagenase release also increased to a maximum at 16 hr after the burn but then declined to almost zero at 72 hr. Trypsin treatment of day-1 media from both control and deficient corneas, taken at 72 hr after the burn, showed an almost complete absence of latent (inhibited) collagenase. Histologic observations revealed a close correlation between the presence of infiltrating polymorphonuclear neutrophils (PMNs) and the ulcerative lesions seen in burned, deficient corneas. When PMN infiltration was blocked by application of a tissue adhesive, no ulceration occurred and collagenase activity in the day-1 media dropped to almost zero. If burned and unburned areas of deficient corneas were separated and cultured separately, the burned area (containing most of the PMNs) was found to have 10 times the collagenase activity of the unburned area. In the controls, PMNs and some collagenase activity was detectable only 16 hr after the burn. We concluded that in the burned, vitamin A-deficient cornea there is increased attraction of PMNs to the lesion, resulting in collagenase release by these and possibly other cells, and ultimately resulting in ulceration.

Animals↗
PubMed1982

Iridoplasty for prevention of post-keratoplasty angle closure and glaucoma.

Twenty patients who had iridoplasties performed at the time of penetrating keratoplasty were followed for a minimum of nine months. Although 12 patients had peripheral anterior synechiae (PAS) preoperatively, only four developed progressive PAS and secondary angle closure glaucoma postoperatively. Our experience suggests that iris suturing, by producing a mechanically rigid iris diaphragm, may prevent postoperative anterior synechiae and appositional angle closure.

Corneal Transplantation↗
PubMed1982

Epithelial abrasion precipitates stromal ulceration in the vitamin A--deficient rat cornea.

Although the role of vitamin A deficiency in the development of xerophthalmia is well established, there is still some question as to whether the deficiency alone is sufficient cause for the development of keratomalacia. This article describes the clinical, histologic, and microbiologic changes occurring in eyes of vitamin A-deficient rats when keratomalacia-like stromal ulceration is induced by epithelial injury alone. The corneal epithelia of 21 severely vitamin A-deficient rats and 11 pair-fed controls were totally removed either by scraping or by n-heptanol. At 96 hr after epithelial removal, 93% of the deficient animals showed extensive epithelial defects and stromal ulceration. Histologically, an intense acute inflammatory response and abundant bacterial forms were consistently evident. Staphylococcus aureus and Streptococcus fecalis were the most frequent pathogens cultured from these ulcerating eyes. In contrast, the control corneas showed essentially complete re-epithelialization, with no ulceration, minimal inflammatory reaction, and an absence of morphologically demonstrable bacteria. Bacterial cultures from the control eyes showed abundant Pasteurella, with pathogens also present. These observations suggest that abnormal epithelial recovery, acute inflammation, and bacterial infection may be important factors for the development of keratomalacia-like corneal ulceration in experimental vitamin A deficiency.

Animals↗
PubMed1982

The corneal endothelium. Normal and pathologic structure and function.

A summary of normal and abnormal endothelial structure and function is presented. Endothelium originates from neural crest and it elaborates a banded basement membrane in utero. It is involved in mesenchymal dysgenesis of the anterior segment, like the central defect of Peters' anomaly. Cytoplasmic organelles include mitochondria that provide energy for the metabolic pump, rough endoplasmic reticulum that participate in secretion of extracellular matrix, and a terminal web that may participate in cell migration. The endothelium's main function is to control corneal hydration and nutrition with a leaky barrier formed by the apical gap and macula occludens junctions that keep some water out of the stroma but allow nutrients to pass, and with an ATPase-dependent metabolic pump that is located in the lateral plasma membranes. Endothelial wound healing involves flattening and enlargement of cells to maintain an intact monolayer as well as production of abnormal collagenous material posterior to Descemet's membrane. HLA antigens located in the plasma membrane may participate in corneal endothelial graft rejection. Clinical assessment of the endothelium involves three modalities: specular microscopy to study endothelial morphology, fluorophotometry to measure barrier function, and pachymetry to measure corneal thickness.

Adolescent↗
PubMed1982

Corneal epithelial regeneration and adhesion following acid burns in the rhesus monkey.

For study of corneal adhesion after chemical injury, sulfuric acid was used to burn the central and peripheral corneal epithelium in rhesus monkeys. The adhesion properties of the regenerating epithelium were sequentially followed by clinical assessment and by serial corneal biopsy specimens examined by transmission electron microscopy. The peripheral burns healed uneventfully, but the central corneal burns resulted in persistently loose adhesion for more than 8 weeks. The pathogenesis of the defective epithelial adhesion appeared to initially the persistence of the original basement membrane that could not be utilized by regenerating epithelium. Later, poor adhesion was related to the slow rate of basement membrane regeneration and also to fragmentation of the Bowman's layer substrate and to mild stromal edema.

Animals↗
PubMed1981

Amiodarone keratopathy: drug-induced lipid storage disease.

Therapeutic administration of amiodarone, an antiarrhythmic drug, to eight patients resulted in the formation of vortex-like figures within the anterior cornea. Clinical examination disclosed no visual loss or other ocular abnormality attributable to the drug. In one patient, light and transmission electron microscopy of corneal epithelium, bulbar conjunctiva, and cataractous lens revealed complex lipid deposits within lysosome-like intracytoplasmic inclusions in corneal, conjunctival, and lens epithelium, conjunctival fibrocytes, and conjunctival vascular endothelium. Amiodarone keratopathy is compared clinically and morphologically with the corneal alterations seen in Fabry's disease and in chloroquine use as an example of a drug-induced lipid storage disorder.

Aged↗
PubMed1981

Comparative studies of corneal surface injury in the monkey and rabbit.

This animal study of corneal surface injury using acid, alkali n-heptanol, iodine, keratectomy, or scraping, despite morphologic differences from the human, simulated the human response to these forms of trauma. The rabbit and monkey thus remain useful models for the study of the effects of chemical and physical injury on the corneal surface. Although abnormalities in the basement membrane complex seem to play an important role in corneal epithelial adhesion problems, the presence of a poor substratum on which adhesion complexes must in turn rely for their stromal attachment is also an important factor.

Alcohols↗
PubMed1981

Posterior corneal pigmentation and fibrous proliferation by iris melanocytes.

Pigmentation of the posterior corneal surface results either from endothelial phagocytosis of free melanin pigment or from the presence of iris melanocytes, iris pigment epithelial cells, or pigment-containing macrophages on the posterior corneal surface. Although this is occasionally seen clinically, it is more often noted at histopathologic evaluation after operative or accidental ocular trauma. Three cases of posterior corneal pigmentation by iris melanocytes are reported. In one case, the pigmented membrane was the major cause of considerable visual impairment and was documented with clinical photographs and specular microscopy. By light and electron microscopy, all three cases were consistent with findings of posterior corneal pigmentation by iris stromal melanocytes that had acquired endothelium-like morphologic characteristics. We also consider the possible contribution of these melanocytes to posterior collagen layers of the cornea.

Aged↗
PubMed1981

Mast cell ultrastructure. Comparison in contact lens-associated giant papillary conjunctivitis and vernal conjunctivitis.

Mast cells from the upper tarsal conjunctiva of six normal subjects, seven persons with contact lens-associated persons with contact lens-associated giant papillary conjunctivitis (CL-GPC), and six persons with vernal conjunctivitis were examined by electron microscopy. Most mast cells from normal subjects were fully granulated and showed granule forms previously reported for conjunctiva. All mast cells from patients with CL-GPC had some degree of degranulation. The number of granules in approximately 30% of mast cells from patients with CL-GPC was sufficiently reduced that the cells probably would not have been recognized as mast cells using light microscopy. Mast cells from vernal conjunctivitis patients had the most extensive degranulation. The vast majority of these cells, at least 80%, had so few granules that it is unlikely they would have been recognized as mast cells if light microscopy alone were used.

Conjunctiva↗
PubMed1981

Epiretinal and vitreous membranes. Comparative study of 56 cases.

Five morphologically distinguishable cell types were observed in 56 epiretinal and vitreous membranes obtained surgically from eyes with various ocular diseases: (1) retinal pigment epithelial (RPE) cells that were evident only in association with retinal detachment, (2)(macrophages, (3) fibrocytes, (4) fibrous astrocytes that were characteristic of all disease groups, and (5) myofibroblast-like cells that had mostly the characteristics of fibrocytes and, occasionally, of RPE cells or fibrous astrocytes. The combination of cell types varied in different types of epiretinal membranes, but the formation of collagen and the development of cells with myofibroblast-like properties were common features and seemed to be within the capacity of several cell types. These two common features seem to be the basis for the contractile properties of epiretinal and vitreous membranes.

Astrocytes↗
PubMed1981

Bitot's spots responsive and nonresponsive to vitamin A. Clinicopathologic correlations.

Conjunctival biopsy specimens from patients with Bitot's spot responsive and nonresponsive to vitamin A were studied by light and electron microscopy. In both types, the lesions demonstrated keratinization with granular cells, irregular maturation, inflammatory infiltration of the conjunctival substantia propria, and loss of goblet cells. Only in the responsive cases were these changes generalized. Prominent Bitot's spots represented massive accumulations of Gram-positive bacilli and keratin debris. Responsive cases improved histologically within seven days of treatment, and goblet cells began to return within two weeks. These results support our previous suggestions that there is little basis for attempting to differentiate, clinically, between the two types of lesions and that at least some nonresponsive lesions represent a persistent metaplastic change induced during a prior episode of vitamin A deficiency.

Adolescent↗
PubMed1981

Aspergillus keratitis with intraocular invasion.

A healthy 48-year-old man developed Aspergillus keratitis following mild corneal trauma. Intensive medical therapy, initially empirical, then guided by in vitro sensitivity testing, as well as attempts at surgical excision of the infection, were ultimately unsuccessful. The poor therapeutic response may have been due to fungal penetration of the deep corneal stromal before treatment was initiated. The clinical and histologic features of A keratitis are described and related to fungal keratitis in general. The strengths and limitations of laboratory diagnostic aids are discussed. Fungal keratitis may follow a disarmingly mild early clinical course, but requires prompt, aggressive therapy if serious complications are to be avoided.

Aspergillosis↗