Biomedical subjects
Publications and source records attributed to K R Kenyon.
A most unusual complication of penetrating keratoplasty is the rapid thermal denaturation of a human donor cornea upon accidental exposure to temperature of 50 degrees to 60 degrees C, the result of inadequate cooling of a Teflon trephine block following autoclave sterilization.
Of 76 members of a large pedigree with familial aniridia, 61% of the 38 affected patients had visual acuity of 6/9 (20/30) or better and only 5% had acuity of 6/60 (20/200) or worse. Cataracts were present in 18% of affected patients; glaucoma in 13%; and strabismus in 34%. Sixteen percent of affected patients had strabismic amblyopia. No patient had nystagmus or corneal pannus. The good visual acuity in this family, as compared to that in others, indicates that the absence of iris tissue alone cannot account for the severe visual problems usually associated with aniridia.
A 62-year-old white woman with hypertensive diabetes had central retinal artery occlusion of her right eye. Serial electroretinographic (ERG) studies demonstrated reversible changes in the scotopic components but permanent reduction of the photopic b-wave. Serial simultaneous fluorescein and indocyanine green angiographic studies demonstrated a perfusion defect in the choroid involving part of the macula which subsided after reopening the retinal circulation. Differential hypoxic susceptibility of the ERG photopic and scotopic b-waves was demonstrated, and changes in the patient's retinal tissue oxygenation were postulated on the basis of retinal and choroidal angiographic studies performed during and after central retinal artery occlusion to account for the observed changes in serial ERGS.
A 57-year-old black man had François-Neetens speckled dystrophy of the cornea and orbital phycomycosis. Examination of family members confirmed an auto-somal-dominant pattern of inheritance. Light and electron microscopic study of the cornea of a blind eye disclosed that the corneal opacities were represented by swollen, vacuolated keratocytes filled with histochemically demonstrable acid mucopolysaccharide and complex lipids. Thus, this dystrophy may represent a dominantly inherited metabolic disorder confined to the cornea.
To determine the effects of thermokeratoplasty (TKP) on the basement membrane complexes of the corneal epithelium, transmission electron microscopy was performed on the corneal buttons of five patients with failed TKP and on two normal corneas and five corneas with keratoconus that were immediately treated by TKP (acute TKP). The consistent findings of thermal dissolution of basement membrane after acute TKP and persistent defects of basement membrane complexes many months after therapeutic thermokeratoplasty were significant. Given the potentially damaging effects of thermokeratoplasty on the epithelial basement membrane, faulty epithelial adhesion should be anticipated after thermokeratoplasty and should be treated aggressively, possibly with careful prophylactic use of bandage hydrophilic contact lenses.
Electron microscopic study of an epiretinal membrane obtained from a 69-year-old black woman during pars plana vitreoretinal surgery with vitreous hemorrhage complicating a retinal vein obstruction revealed extensive proliferations of fibrous astrocytes that had secreted fibrillar and basement-membrane collagens. Hemosiderin-containing macrophages were also found. Neovascular elements were present and appeared identical to normal retinal capillaries.
Thermal cauterization of the corneas of nine rhesus monkeys was performed by multiple thermokeratophore applications at temperatures of 90 degrees or 120 degrees C. Significant clinical observations included the resteepening of corneal curvature, delayed epithelial healing, stromal haze or scarring, and peripheral neovascularization. Reestablishment of tight adhesion of the regenerated epithelium to Bowman's layer required approximately 6 weeks. By transmission and scanning electron microscopy, the original basement membrane seemed relatively intact immediately following cauterization but disappeared within 1 week. The regeneration of new basement membrane complexes began at 1 week with the appearance of short discontinuous segments of basement material with hemidesmosomes and similarly required approximately 6 weeks for complete restoration.
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A 45-year-old woman with juvenile-onset diabetes had persistent corneal edema after a pars plana vitrectomy and lensectomy procedure. Phase contrast and electron microscopic observation of the patient's cornea revealed extreme attenuation of the endothelial cell layer and abnormal collagenous and basement membrane material interposed between Descemet's membrane and the endothelium. Endothelial fibrous proliferations in this case were consistent with the development of ultrastructurally identical fibrous proliferations in many other situations involving dysfunction of the corneal endothelium.
Multiple early untreated lesions of angiomatosis retinae in the peripheral retina and optic disk were discovered after death in both eyes of a patient with von Hippel-Lindau disease. Each of the four peripheral angiomas was studied by a different technique: routine light microscopy of serial histologic sections, electron microscopy, flat mount and trypsin digestion, and frozen section with special stains for lipid. The large capillaries comprising the core of each angioma displayed normal endothelium, basement membrane, and pericytes. Thus, capillary hemangioma of the retina is a more correct histopathologic designation for the von Hippel angioma than terms such as hemangioblastoma or hemangioendothelioma. Interstitial cells separating the vascular channels of the angioma were identified as astrocytes that contain large lipid-filled cacuoles. Serial histologic sections demonstrated that both retinal and choroidal vessels communicate with vascular channels of the juxtapapillary capillary hemangiomas.
The corneas of three patients with keratoconus were examined by light and electron microscopy within approximately four months after onset of severe hydrops. The rupture and detachment of Descemet's membrane resulted in formation of extensive ledges. New endothelium completely resurfaced the exposed posterior stroma and the corresponding anterior aspect of the ledges. The endothelium also regenerated considerable basement membrane. In one case, clustered endothelium near the free end of the ledge appeared to have undergone fibrous metaplasia with secretion of extensive fibrillar and basement membrane material.
Corneal buttons from three patients with congenital central corneal leukoma (Peters' anomaly) were examined by light and electron microscopy. All cases exhibited a central absence of Bowman's membrane and iris synechiae to the periphery of the leukoma. In the first patient, extensive keratolenticular adhesion with retrocorneal fibrous tissue filling the central defect of endothelium and Descemet's membrane implicated late anterior displacement of the normally developed lens as the cause of secondary endothelial degeneration. In the second patient, attenuated endothelium and abnormally composed Descemet's membrane indicated primary dysgenesis of the endothelium. In the third patient, the extensive defect of posterior stroma with anterior stromal disorganization and endothelial metaplasia suggested dysgenesis of both the keratocytic and endothelial mesoderm. Thus, although no unified pathogenic mechanism was consistently applicable, either primary or secondary dysgenesis of the corneal mesoderm must be responsible.
Perifoveal capillary leakage of fluorescein was demonstrated in 60 per cent of 50 eyes when angiography was performed two weeks after cataract extraction. Repeat angiography six weeks postoperatively in 17 eyes demonstrated persistence of already established leakage in 11 of 12 eyes and no new leakage in five eyes previously negative. Cystoid macular oedema with visual acuity of less than 20/40 six weeks postoperatively occurred in five eyes (10 per cent). Eyes of patients with vascular disease and those patients of 60 years or older were found to have altered vascular permeability significantly more frequently. Inflammation was no more severe or prevalent in those patients who demonstrated leakage and no inflammation was clinically apparent in 10 of 11 eyes demonstrating dye leakage six weeks postoperatively. We conclude that the constitutional factors of age and vascular disease are of prime importance in causing altered vascular permeability in the early postoperative period after cataract extraction; factors causing sustained leakage with reduction of visual acuity were not demonstrated.
In summary, the histologic and ultrastructural pathology of the systemic mucopolysaccharidoses has been reviewed as they involve four aspects of the eye: 1) Conjunctival biopsy provides an excellent demonstration of the lysosomal storage lesion and may also afford diagnostic and therapeutic information. 2) Corneal clouding appears to be related to the degree of stromal acid mucopolysaccharide accumulation. 3) Retinal pigmentary degenerative changes are morphologically identical to those of other retinitis pigmentosa syndromes and may be the result of a primary disturbance of pigment epithelial function. 4) Optic nerve involvement may occur by several mechanisms, of which ophthalmologists should remain clinically aware in order to provide appropriate therapy.
The retrocorneal fibrous membrane in eight cases of the vitreous touch syndrome was characterized by homogeneous granular material, fine filaments arranged either singly or in bundles, multiple lamellae of basement membrane-like material, and banded figures of similar to 110 nm periodicity. Seven cases demonstrated an intact endothelial monolayer while only one showed cells in a markedly thickened fibrous layer. These findings support the pathogenic mechanism of endothelial fibrous metaplasia and secretory activity as the origin of the retrocorneal fibrous membrane in the vitreous touch syndrome.
Experimental and pathologic studies implicated the role of the epithelial basement membrane and its associated hemidesmosomes and anchoring fibrils in mediating tight adhesion between corneal epithelium and stroma. We evaluated the ultrastructural quality of basement membrane complexes in patients with Reis-Bücklers dystrophy, Cogan's microcystic dystrophy, and nontraumatic recurrent erosion who presented with clinically significant erosive symptoms. Despite the variable clinical and histopathologic appearances among these dystrophies, incompleteness of basement membrane complexes apparently was a common fault shared by these erosive disorders. Such basic incompetence at the basement membrane level can both provoke and sustain erosions, while the more individual pathologic manifestations of a given anterior dystrophy may be of less primary significance.
Fifty-seven penetrating keratoplasties were performed using human donor corneal material stored in modified Tissue Culture Medium 199 (TC-199). Fifty-six grafts were clear on the first postoperative day and remained clear for at least three weeks. During the follow-up period (average, 3.7 months), only four additional graft failures occurred. The reduced incidence of early graft edema is attributed to prolonged viability of corneal endothelium maintained in modified TC-199 medium prior to keratoplasty.
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