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Biomedical subjects

R A Thoft

Publications and source records attributed to R A Thoft.

At least 37 records · Page 2Linked to original sources
PubMed1990

Indications for keratoepithelioplasty.

Thirteen patients with ocular surface failure were treated by keratoepithelioplasty using allografts of corneal limbal epithelial cells from donor eyes. The ocular surface was stabilized with long-term healing of persistent epithelial defects in five of eight eyes followed up for 4 to 19 months. The procedure was performed on an additional 5 patients with superficial keratopathies. Three of those five procedures resulted in a stable and clear optical surface. These results suggest that epithelial transplantation may be a useful option in the care of chronic ocular surface failure unresponsive to conventional medical management.

Adult↗
PubMed1990

Healing of excimer laser ablated monkey corneas. An immunohistochemical evaluation.

The healing response of the cornea following excimer laser anterior keratomileusis (a 4-mm-diameter ablation to a depth of 11, 23, or 46 microns) was analyzed immunohistochemically in adult rhesus monkeys. The ablated surface had reepithelialized and the synthesis of type VII collagen (a major component of anchoring fibrils) was evident by 7 days; the reestablishment of a nearly continuous anchoring fibril zone was evident after 12 weeks. Stromal fibroblasts, activated in response to wounding, expressed a fetal antigen for approximately 6 weeks. Although fibronectin and type VII collagen were present only transiently in the regenerating subepithelial stromal matrix in the subepithelial regions, some other alterations, including the presence of type III collagen, increased levels of keratan sulfates, and discontinuities in the anchoring fibril zone were evident even 18 months after wounding. The depths of the regenerated stroma, which were estimated from the depths of remnant staining for type VII collagen in the stromal matrix, generally, but not always, corresponded to the depths of the calculated ablation.

Animals↗
PubMed1990

Perforating eye injury in Allegheny County, Pennsylvania.

From 1980 through 1986, acute perforating eye injury (ICD codes 871.0-871.9) was diagnosed in 345 residents of Allegheny County, Pennsylvania. The mean incidence rate was 3.49 per 100,000 person years. There was no significant change in incidence over the seven-year period. The largest number of injuries occurred among individuals working with tools, of which 47 percent were occupational. Males had a 6.5-fold risk of injury relative to females. Blacks had a risk of 2.2 times that of Whites, mainly due to an excess of assaultive injuries. Individuals who had had recent ocular surgery accounted for 4.6 percent of cases overall, and for 31.6 percent of cases in those over age 60.

Adolescent↗
PubMed1990

Survival of Acanthamoeba in contact lens rinse solutions.

Acanthamoeba may cause a severe keratitis in contact lens wearers. Since most sterilization techniques require rinsing the lenses prior to insertion, contaminated solutions represent a potential vector for transmission of Acanthamoeba. The ability of rinse solutions to sustain an inoculum of Acanthamoeba polyphaga was investigated. A. polyphaga was exposed to 0.1% benzalkonium chloride, 0.001% thimerosal/0.1% edetate disodium, 0.1% edetate disodium, saline, tap water, and distilled water. The status of the organism was evaluated with direct microscopic counts and cultures to confirm viability. Incubation with 0.1% edetate disodium, saline, tap water, and distilled water resulted in the maintenance of reduced populations of viable organisms for 7 days. Benzalkonium chloride preserved saline and solutions containing thimerosal with edetate rendered the Acanthamoeba nonviable.

Acanthamoeba↗
PubMed1990

Antibasement membrane antibody-mediated experimental conjunctivitis.

In ocular cicatricial pemphigoid, the binding of circulating antibodies to conjunctiva is believed to initiate an antibody-mediated cytotoxic response that results in inflammation and tissue damage. To develop a model of antibody-mediated conjunctival inflammation, we examined the effect on conjunctiva of local or systemic administration of a murine monoclonal antibody against basement membrane of stratified squamous epithelium. Neonatal rabbits were given either a single subconjunctival or intraperitoneal injection of the antibody. Eyes were graded clinically for inflammation and conjunctival biopsies were performed. After subconjunctival injection, clinical and histologic inflammation as well as murine antibody and rabbit complement binding to conjunctival basement membrane were detected. With systemic administration there was post-injection clinical inflammation, and conjunctival basement membrane-bound murine antibody was detected. There was no difference observed in conjunctival mitotic rate or goblet cell frequency between treatment groups and controls, following either route of administration. We have created, therefore, a model for antibody-mediated conjunctivitis in rabbits by local or systemic administration of a monoclonal antibody against a component of stratified squamous epithelial basement membrane.

Analysis of Variance↗
PubMed1989

Hyperproliferation of conjunctival fibroblasts from patients with cicatricial pemphigoid.

The characteristic conjunctival scarring in cicatricial pemphigoid is a consequence of subepithelial fibrosis. The fibroblast is the cellular element responsible for fibrosis. To increase the understanding of the pathogenesis of abnormal fibrosis in cicatricial pemphigoid, the growth characteristics of conjunctival fibroblasts, from untreated patients with cicatricial pemphigoid (n = 9) and normal controls (n = 6), were studied in tissue culture. The latent period until fibroblast outgrowth began from the conjunctival explant was determined, as were the plating efficiency and doubling time of cells from first-passage cultures. Outgrowths of fibroblasts from patients with cicatricial pemphigoid appeared significantly sooner than from controls, 8.1 +/- 3.8 vs 19.3 +/- 6.4 (mean +/- SD) days. While there was no significant difference in the plating efficiency between fibroblasts from cicatricial pemphigoid (mean +/- SD, 116.4% +/- 44.6%) and those from controls (71.0% +/- 39.4%), the doubling time was significantly faster for cicatricial pemphigoid than for controls, 26.5 +/- 8.5 vs 50.7 +/- 7.8 hours. Thus, conjunctival fibroblasts from patients with cicatricial pemphigoid are hyperproliferative in tissue culture when compared with normal controls. Therefore, scarring, which characterizes cicatricial pemphigoid, may be due, in part, to excessive fibroblast proliferation.

Aged↗
PubMed1989

The multipotential cells of the limbus.

Ample evidence exists that there is a centripetal movement of cells from the periphery of the cornea toward the centre. While conjunctival cells have the capacity to transdifferentiate into corneal epithelial cells, the limbal region appears to act as a barrier between the conjunctival and corneal epithelia, even after large epithelial defects are created. The existence of limbal stem cells is suggested by the apparent role of the limbus in acting as a source of peripheral corneal cells. While specific staining of limbal cells has been reported in the rabbit, there is no positive identification of such stem cells in the human. However, in the human there is negative staining for both a keratin cytoskeleton antigen and a cell surface antigen in the limbal epithelial zone. Efforts positively to identify human limbal stem cells continue, as do efforts to culture and transplant such cells.

Animals↗
PubMed1989

The role of the limbus in ocular surface maintenance and repair.

Since Claes Dohlman's original treatise on the corneal epithelium, a great deal has been learned about the biology of that layer. Its maintenance depends in part on centripetal movement of cells from the periphery toward the center. To some degree the supply of these peripheral cells appears to be dependent on the proliferation of cells at the limbus, from so-called 'stem cells'. Studies of stem cell replication and differentiation of their progeny will lead undoubtedly to new insights into the the mechanisms responsible for many of the chronic abnormalities of the central corneal surface.

Cell Differentiation↗
PubMed1989

Unique parameters in the healing of linear partial thickness penetrating corneal incisions in rabbit: immunohistochemical evaluation.

The healing of penetrating nonperforating linear corneal incisions in rabbit was analysed immunohistochemically. Regeneration of the basement membrane (BM) zone was evaluated by analysing the following components using monoclonal antibodies (MAbs): 1) an antigen designated AgHEBM1 (a 66k Mr polypeptide), 2) type VII collagen which is associated with anchoring fibrils and 3) an antigen designated Ag63/D7 which is associated with the lamina densa and anchoring plaques. Concomitant activity in the regenerating stroma was evaluated by analysing the distribution of 1) fibronectin, 2) keratan sulfate and 3) a fetal antigen, designated AgM12, (an intermediate filament associated protein with a Mr of 130k). Synthesis of the BM zone components was not evident at day 2 postwounding but was seen at day 7, only at the deepest aspects of the wounds. Re-establishment of a continuous BM zone was evident by day 60. The stromal regeneration had started by day 7, at the deepest aspect of the wounds, as judged from the distribution of stromal antigens including the fetal antigen AgM12. The number of activated cells (cells expressing AgM12) had decreased significantly by day 30 and diminished by day 60. Between day 30 and day 180 the thickness of the regenerated tissues had not increased significantly although the stroma had not yet reached its normal thickness. Even after six months, the epithelial plug persisted and the concentration of the sulfated epitopes of keratan sulfates in the regenerated stromal matrix were less than in the surrounding nonwounded regions. The cessation of expression of AgM12, by the cells in regenerating stroma, coincided with the relative decrease in extracellular matrix syntheses. The return of the stromal cells to the quiescent state also coincided with re-establishment of a continuous BM zone between the epithelium and the stroma in the regenerated tissue. These observations suggested that the synthesis, assembly and remodeling of stromal and epithelial extracellular matrices during the healing of penetrating corneal wounds may be influenced by the interactions between activated stromal cells and epithelial cells.

Animals↗
PubMed1988

Diamond burring and surgical keratectomy. Morphologic comparison in the rabbit.

We compared the effects of diamond burring keratectomy (DBK) and surgical superficial lamellar keratectomy (SLK) on the rabbit corneal epithelial healing rate and corneal morphology 1, 4, 7, and 14 days after wounding. Epithelial defects healed significantly more slowly following 10-mm-diameter SLK than following DBK. Restoration of normal epithelial morphology occurred within two weeks in the DBK corneas. During the same interval, SLK corneas showed poor transition of basal to superficial cell morphology. Four days after surgery, the DBK corneas all exhibited marked keratocyte depletion in the anterior stroma but fibrocytes uniformly repopulated this area by 14 days after wounding. Conversely, the SLK corneas all had a hypercellular band of fibrocytes in the anterior stroma by four days following surgery and continued to increase in cellularity through 14 days after wounding. These data indicate that DBK is the preferred procedure for creation of a recipient bed for epithelial lenticles in keratoepithelioplasty and conjunctival transplantation.

Animals↗
PubMed1988

Rapid diagnostic test for ocular adenovirus.

A new, direct, enzyme immunoassay test (Adenoclone, Cambridge BioScience, Hopkinton, MA) was evaluated for the rapid diagnosis of ocular adenovirus infections. In 36 culture-proven cases of adenovirus ocular infection, direct Adenoclone testing of conjunctival swabs was positive in 24 of 31 patients (77%) tested within 1 week of onset of symptoms, and in one of five patients (20%) who presented after 1 week (P less than 0.02). Overall sensitivity was 69%, whereas specificity was 100%. The authors conclude that a positive Adenoclone test is reliable in the rapid diagnosis of early adenovirus ocular infections.

Adenoviridae Infections↗
PubMed1988

Comparison of limbal and peripheral human corneal epithelium in tissue culture.

Peripheral human corneal epithelium grows better in tissue culture than central epithelium, but it is not known whether ocular limbal epithelium grows even better than does the peripheral corneal epithelium. In this work we compared the growth kinetics of limbal and peripheral human corneal epithelial cells in tissue culture. Four 1-2 mm2 explants, removed from the limbus or from peripheral cornea (1-2 mm inside the limbus) of eye bank eyes, were grown to confluence in primary culture. Cells were then passaged at 2 X 10(5) cells per dish. At intervals thereafter, the cells were counted in a hemocytometer to determine plating efficiency and growth curves. Mitotic activity was determined 4 days after passaging by labeling cultures with 3H-thymidine and counting aliquots using the hemocytometer and scintillation counter. In the primary cultures, limbal epithelium grew as small, uniformly polygonal cells. Peripheral corneal cells grew to a variety sizes. The 24 hr plating efficiency and doubling time of limbal epithelial cells were 47 +/- 8% and 80 +/- 14 hr, respectively, while those of peripheral corneal cells were 41 +/- 10% (P less than 0.1) and 131 +/- 25 hr (P less than 0.001). The mitotic activity of limbal cells was significantly higher than that of peripheral (2.9 +/- 1.2 vs. 0.8 +/- 0.6) (P less than 0.01). These results indicate that human ocular limbal epithelium grows better in culture than does peripheral human corneal epithelium.

Adult↗
PubMed1988

Response of ocular surface epithelium to corneal wounding in retinol-deficient rabbits.

The purpose of this study was to explore the nature and time course of the functional effects of early retinol deficiency on the ocular surface epithelium. To this end, the conjunctival epithelial healing rate, mitotic rate, and goblet cell frequency were determined following experimental ocular surface epithelial wounding in 15 rabbits sustained on a retinol-deficient diet and in 12 pair-fed controls. The animals were sacrificed at 2, 7, and 14 days after wound closure. The mean serum retinol level (+/- SEM) prior to wounding was 6.0 +/- 0.9 microgram/dl for the group fed the deficient diet. The mean serum and liver retinol levels for this group following defect closure were 4.0 +/- 0.5 micrograms/dl and 0 micrograms/g, respectively. These values are all significantly less than the analogous respective control values of 83.2 +/- 2.4 micrograms/dl, 77.6 +/- 2.3 micrograms/dl and 35.1 +/- 3.0 micrograms/g (P less than 0.001 for each pair, student t-test). In the retinol-deficient animals, the unwounded eyes had an abnormally high rate of conjunctival epithelial cell mitosis, the earliest ocular surface cellular abnormality detected. Hypermitosis of the unwounded corneal epithelium was also noted, though somewhat later than in the conjunctiva. Epithelial wound healing was delayed considerably in the retinol-deficient group, with only 33% of eyes in this group healed within the same time period as the controls (P less than 0.05, Chi-square). Normal numbers of goblet cells were noted in the conjunctiva of retinol-deficient animals, despite at least 5, and up to 8 weeks of profoundly depleted retinol stores.(ABSTRACT TRUNCATED AT 250 WORDS)

Animals↗
PubMed1988

An ultrastructural study of rabbit ocular surface transdifferentiation.

When debridement of the rabbit cornea is followed by re-epithelialization from the conjunctiva, a process of transdifferentiation of the endothelium occurs. Goblet cells appear peripherally 1 week after healing of the epithelial defect, are widespread at 2 weeks, and disappear centrally at 3 to 4 weeks. Six weeks after closure of the defect, the epithelium has reverted to the customary corneal appearance. The morphology of the regenerating epithelium was studied by light, transmission and scanning electron microscopy. The precursor cells for the goblet cells were identified in stage 1, before PAS-positive cells were present, as pairs of cells with dark cytoplasm and prominent Golgi. Subsequently, goblet cells were present in pairs, indicating that goblet cells are derived from non-goblet epithelial cells, and that they do not simply migrate onto the cornea. At the time of transdifferentiation, loss of goblet cells was shown to occur both by desquamation from the surface and by in situ cell death.

Animals↗
PubMed1987

Conjunctival goblet cells and mitotic rate in children with retinol deficiency and measles.

To study the effect of retinol deficiency and measles on the conjunctival epithelium, we determined the epithelial mitotic rate (MR) and goblet cell frequency (GCF) in conjunctival biopsy specimens from preschool children in Hyderabad, India. We studied three groups of children: normal appearing, clinically retinol deficient (defined by the presence of superficial fine punctate keratitis), and clinically retinol deficient with measles. The last group was subdivided into those with low serum retinol levels (less than or equal to 20 micrograms/dL [less than or equal to mumol/L]) and those with normal serum retinol levels (greater than 20 micrograms/dL [greater than 0.70 mumol/L]). In the control group of seven normal-appearing children with a mean age of 4.6 years, the mean MR was 1.3% +/- 0.4%, and the mean GCF was 8.0% +/- 3.6% of the basal epithelial cells. In seven children with clinical retinol deficiency, the mean MR was 15.4% +/- 1.2%, and the mean GCF was 1.0% +/- 0.5%, values significantly different from normal ones. Among 11 children with clinical retinol deficiency, measles, and low serum retinol levels, the mean MR was 9.0% +/- 1.9%, and the mean GCF was 3.1% +/- 1.1%, values not statistically different from those in children with clinical retinol deficiency alone. Five children with clinical retinol deficiency, measles, and normal serum retinol levels had a mean MR of 10.2% +/- 3.7% and a mean GCF of 1.9% +/- 1.7%, values similar to those in the other disease groups. This indicates that retinol deficiency sufficient to cause clinical signs without subepithelial scarring or keratinization is associated with hyperproliferation of the conjunctiva whether or not there is a superimposed measles infection.

Biopsy↗
PubMed1987

Conjunctival epithelium in healing of corneal epithelial wounds.

The mitotic rate and goblet cell content of conjunctival epithelium following total or central corneal epithelial removal using n-heptanol was measured to determine how the conjunctival epithelium responds to injury and whether conjuctiva responds to central corneal epithelial loss. One day following a wound that removed corneal, limbal, and 1-2 mm of bulbar conjunctival epithelium, the mitotic rate of the remaining conjunctival epithelium was ten times normal (P less than 0.001), proving that the conjunctiva responds to injury by cellular proliferation. At 1 and 2 days following a limited 10 mm diameter central corneal wound, the mitotic rate of peri-limbal conjunctival epithelium was three to four times normal (P less than 0.01), and even following a 5 mm diameter central wound, it was three to four times normal on day 1 (P less than 0.05). Goblet cell frequency was a less reliable indicator of conjunctival response to corneal injury: it was decreased following the largest and smallest wounds but not affected by the 10 mm diameter wound. These studies demonstrate that conjunctival epithelium peripheral to the cornea is affected by small central corneal wounds, and may therefore play a role in corneal epithelium healing.

Animals↗
PubMed1987

Comparison of central and peripheral human corneal epithelium in tissue culture.

Past attempts to grow human corneal epithelium in culture had limited success, with confluence rarely attained. This work is to determine whether different areas of human corneal epithelium grow better in tissue culture. We compared the extent, the mitotic rates, and morphology of outgrowths and histology of explants from central and peripheral human corneas in culture. Explants, 2 mm in diameter, removed from eye bank eyes, were placed epithelial side up on a culture dish with modified SHEM tissue culture medium (Jumblatt et al, 1983). After 7 days, the tissues were fixed, stained and the area of outgrowths from explants measured using an image processor. For eight eyes from donors averaging 66 yr old, the average area of central outgrowths was 7.8 +/- 1.1 mm2, while that of peripheral outgrowths was 52.8 +/- 5.2 mm2 (P less than 0.001). The mitotic rate of outgrowths of central epithelium was significantly less than that of peripheral epithelium (1.1 +/- 0.5% vs 18.8 +/- 0.8%) (P less than 0.001). After 14 days, central outgrowths had not attained confluence and consisted of large cells. Peripheral outgrowths had attained confluence and consisted of small polygonal cells. Histology of explants showed that only one layer of epithelium remained on the stroma in central explants, but several layers were present on the peripheral explants. Thus, peripheral human corneal epithelium grows better in culture than does central human corneal epithelium.

Cornea↗