Radial intrastromal lines in Acanthamoeba keratitis. Case report.
Explore the source record for details and available documents.
Acanthamoeba↗
Biomedical subjects
R W Beuerman
Publications and source records attributed to R W Beuerman.
Neural activity from the acutely infected HSV-1 rabbit cornea.
Herpes simplex virus type 1 (HSV-1) infections of the human cornea are often accompanied by abnormal sensations. In this study, a combination of physiological and structural methods was used to examine the innervation of the corneas of rabbits with HSV-1 lesions of varying severity. Degeneration of the plexiform neural layer adjacent to dendritic lesions and surrounding normal neurology provided a basis for the limited physiological changes. Extensive degeneration of the corneal innervation at all levels occurred within the anesthetic area of the geographic lesion. Abnormal physiological activity characterized by hyperexcitability and loss of stimulus specificity were included in the physiological profile. Collateral sprouts seen in the geographic lesion were suggested as an anatomical substrate for the abnormal neural activity. Thus, the neural changes could be associated with the severity of HSV-1 lesions.
Action Potentials↗
Corneal nerves contain intra-axonal HSV-1 after virus reactivation by epinephrine iontophoresis.
Experimental ocular models of herpes simplex virus type 1 (HSV-1) reactivation have been used to monitor viral shedding in the tear film and the appearance of corneal epithelial lesions, but the temporal correlation between reactivation and the presence of viral particles in the corneal nerves has not been made. Two New Zealand white rabbits were inoculated with 20 microliters of HSV-1 McKrae strain (5.0 x 10(6) PFU/ml) in each eye. Beginning on postinfection day 82, ocular iontophoresis (0.8 mAmps for 8 min) of 0.01% epinephrine was done once a day for 3 consecutive days to induce reactivation. Ten limbal nerves from four corneas processed for transmission electron microscopy contained 883 unmyelinated and 40 myelinated axons. Seven nerves were positive for virus. Viral particles were found only in unmyelinated axons, and in low frequency (24/883). Virus was not found in Schwann cells, perineurium, or adjacent stroma nor were virus particles seen exiting axons. No enveloped virions were found. Axons from six nerves of four control corneas from rabbits with latent, but not reactivated, HSV-1 did not contain virus particles. Induction by corneal iontophoresis of epinephrine suggests that HSV-1 is translocated from the ganglion to the cornea through axonal transport mechanisms. For the first time, evidence of anterograde, intra-axonal transport of HSV-1 particles in response to epinephrine reactivation is demonstrated.
Animals↗
Stimulation of neurite growth by epithelial implants into corneal stroma.
The neuronotrophic action of various ocular tissues to stimulate the ectopic formation of preterminal and terminal neural structures was tested in vivo. Pockets within the collagenous corneal parenchyma were implanted with pieces of epithelium, collagen with and without basal lamina, or conjunctival epithelium. After 3-4 weeks, corneas stained by the gold chloride procedure showed axon terminals within the epithelial cyst and plexiform arrangements at the periphery. In contrast, neither conjunctival epithelium nor collagen showed the ability to stimulate neural growth.
Animals↗
Interface opacities in epikeratophakia.
Although small, peripheral, cystic, or putty-gray infiltrates were observed along the suture tracks in 20 of 100 pediatric patients after epikeratophakia at Louisiana State University Medical Center, New Orleans, they progressed to clinically significant opacities in only three. In one, the interface material was curetted and the lenticule was reattached. The removed material was identified histologically as epithelial cells in varying states of degeneration. In a second case, the graft became hazy and the opacity involved most of the interface. The lenticule was removed, and epikeratophakia was again performed. On the posterior surface of the removed lenticule was a multilayered epithelium that had infiltrated into adjacent stromal lamellae. In the third case, a clear cyst resolved without intervention over a five-year period. These cases illustrate the importance of meticulous removal of all surface epithelium and the necessity for copious irrigation of epithelial debris intraoperatively. Epithelial ingrowth should not be confused with bacterial infection. Such opacities can be treated by curettage or aspiration of the invading material or removal of the epikeratophakia lenticule if spontaneous resolution does not occur.
Aphakia↗
Epithelial wound closure in the rabbit cornea. A biphasic process.
The rapid and complete repair of the corneal epithelium following ocular surgery or trauma is essential for the maintenance of normal visual acuity. In this study the authors examined epithelial wound healing in the rabbit after cells were mechanically removed leaving the basal lamina intact. The decrease in wound area (mm2/hr) was neither linear nor amenable to simple kinetic analysis. However, analysis of the data in terms of the decrease in wound radius (mm/hr) revealed a biphasic process consisting of an initial latent phase with no epithelial movement (5.5 +/- .3 hr), followed by a linear healing phase. The rate of epithelial movement in the linear healing phase was 64 +/- 2 microns/hr. Neither the latent phase nor the rate of epithelial migration during the healing phase was affected by variations in initial wound size. Ultrastructural studies demonstrated that during the latent phase there was an increased desquamation of surface cells as well as cellular and subcellular reorganization of the basal cells. At the end of the latent phase, the leading edge of the wound was composed of a single cell layer. The onset of epithelial migration coincided with the first ultrastructural observation of typical ruffled membranes and filopodia. This work demonstrates that the analysis of the decrease in wound radius provides a straightforward and accurate means to assess the kinetics and therapeutic modulation of epithelial wound healing.
Animals↗
K-Sol corneal preservation.
K-Sol, a new cornea preserving solution which contains no calf serum of foreign protein and is used for refrigerated storage of donor tissue, has storage procedures identical to those currently used for tissue preservation in McCarey-Kaufman medium. K-Sol can keep corneas alive and usable for penetrating keratoplasty for at least two weeks. The clinical results in a series of 17 patients indicated that tissue preserved in K-Sol for as long as two weeks, even when used by inexperienced surgeons in difficult or unfavorable cases requiring extensive anterior segment reconstruction, including reoperations or retained intraocular lenses, gave results virtually identical to those obtained with tissue preserved in McCarey-Kaufman medium for only two or three days.
Adult↗
Inflammation-induced stimulation of the synthesis of prostaglandins and lipoxygenase-reaction products in rabbit cornea.
The cyclooxygenase and lipoxygenase pathways that produce prostaglandins (PGs) and hydroxyeicosatetraenoic acids (HETEs) were studied in inflamed rabbit cornea. A cryogenic lesion was induced and five days later the epithelium, stroma and endothelium were isolated and incubated with [1-14C]arachidonic acid. After lesioning, the arachidonic acid metabolites, thromboxane B2, PGF2 alpha and 6-keto-PGF1 alpha exhibited the greatest increase in the stroma. Lipoxygenase products were formed in the three layers also, although 12-HETE predominated. The correlation between the synthesis of these compounds and corneal injury is discussed.
Animals↗
Threshold and signal detection measurements of the effect of soft contact lenses on corneal sensitivity.
Explore the source record for details and available documents.
Contact Lenses, Hydrophilic↗
Alteration of corneal epithelial ion transport by sympathectomy.
The cornea is dually innervated, receiving afferent nerves from the trigeminal ganglion and efferent nerves from the superior cervical ganglion. This study examines the specific effects of superior cervical ganglionectomy (SCGX) on the in vitro ion transport characteristics of the rabbit corneal epithelium. Two weeks after SCGX, epithelial Cl--dependent transport and total ionic conductance were increased in comparison to values obtained in paired control eyes. This increased transport level appeared to be independent of membrane receptor activity as demonstrated by lack of responsiveness to alpha-adrenergic, beta-adrenergic, serotonergic, dopaminergic, nicotinic cholinergic, or muscarinic cholinergic blockade. Nevertheless, SCGX produced a supersensitivity to epinephrine-stimulated transport as measured by the responsiveness of the ion transport current. Furthermore, SCGX abolished the responsiveness of the epithelium to serotonin. On the basis of these and earlier findings, the authors conclude that corneal sympathetic innervation influences membrane and receptor properties. Autonomic neurotrophic effects in the corneal epithelium include suppression of apical membrane Cl- permeability and of beta-adrenoreceptor sensitivity to biogenic amines. It is proposed that the corneal serotonergic receptors that activate Cl- transport lie on the sympathetic nerve terminals and stimulate this transport process by causing the neural release of a catecholamine.
Animals↗
Collateral sprouts are replaced by regenerating neurites in the wounded corneal epithelium.
Following various types of wounds and subsequent denervation, the reinnervation of the rabbit corneal epithelium was found to occur in two distinct phases that overlapped in time. In the first phase large numbers of collateral sprouts originated from the unmyelinated plexus at various distances proximal to the site of transection. Light and electron microscopic observations revealed that the sprouts began to degenerate about 7 days after wounding. Collateral sprouts were replaced by an equally numerous population of regenerating neurites extending from the transected stumps of the pre-terminal axons. We conclude that, in the wounded cornea, normal neurology is reconstituted by regenerating neurites, and not by collateral sprouts, which proliferate and then degenerate early in the healing process.
Animals↗
Responses of rabbit corneal nociceptors to mechanical and thermal stimulation.
We recorded 116 units from dissected strands of the long ciliary nerve of rabbit and tested them with punctate mechanical, cool, or warm stimulation. Seventy-two percent of the units responded only to mechanical stimulation, 17% responded only to cooling, and 11% were bimodal, responding to both warming and mechanical stimulation. Mechanical responses were rapidly adapting and decreased on successive stimulation at the same locus. Conduction velocities determined for 43 mechanical units were in the same low range of the A-delta group (mean = 2.71 m/s). Receptive fields for all classes of units found here overlapped and did not extend beyond the center of the cornea. Precise determination of field size for 20 mechanical units showed that most included 5 to 20% of the corneal surface and a few extended to about 40%. Activation of units responding to stimulation below the adapting temperature (33 degrees C) showed them to be sensitive to cooling steps of 0.5 degrees C. The average conduction velocity of five cold units was 0.94 m/s. Bimodal units were not active at 33 degrees C and responded to warming above 39 degrees C with an increased discharge frequency; however, the response did not include an initial high-frequency discharge as did that of the cool units.
Afferent Pathways↗
Beta-adrenergic and serotonergic stimulation of rabbit corneal tissues and cultured cells.
The adult rabbit cornea synthesizes cyclic AMP in response to both serotonin and isoproterenol. The authors have examined the postnatal development of these pathways and attempted to localize the responsive cell type(s) by dissection, cell culture, and surgical denervation. Full thickness corneas of neonatal rabbits have beta-adrenergic responses similar to the adult but fail to respond to serotonin until the animals are 9-12 weeks old. When adult corneas are separated into epithelia, stromal, and endothelial layers, only the stromal layer synthesizes cyclic AMP in response to serotonin, whereas all layers respond to isoproterenol. When grown in tissue culture, keratocytes, epithelial, and endothelial cells are unresponsive to serotonin but respond to isoproterenol. Neither adrenergic nor sensory denervation abolishes the corneal adrenergic or serotonergic response pathways. These results indicate that the epithelial cells do not contain the serotonin stimulated, cyclic AMP-mediated pathway as originally postulated. The cell population that does contain this pathway is within the stroma and may be the Schwann cells.
Animals↗
Dopamine modulation of active ion transport in rabbit corneal epithelium.
The addition of micromolar quantities of dopamine stimulated ion transport in the isolated rabbit corneal epithelium. This response was blocked by pretreatment with the dopamine antagonist, haloperidol, and by the elimination of Cl- from the bathing solutions. The beta-adrenergic antagonist, timolol, was also a potent inhibitor of the epithelial response to dopamine. The presence of the serotonin antagonist, methysergide, or the dopamine beta-hydroxylase inhibitor, FLA-63, did not significantly alter the corneal response to dopamine. Following superior cervical ganglionectomy, the epithelial response to dopamine was abolished. These findings are consistent with the idea that Cl- secretion in the rabbit corneal epithelium can be modulated by preterminal dopamine receptors located on the sympathetic nerve fibers; therefore, dopamine stimulation appears to be a serial process mediated by the release of norepinephrine from sympathetic nerve terminals in the epithelium.
Animals↗
Corneal sensitivity after epikeratophakia.
Corneal sensitivity was tested in 60 eyes of 30 patients who underwent unilateral epikeratophakia for the correction of aphakia (20 patients) or keratoconus (10 patients). Postoperative recovery time ranged from 2 months to 21 months (mean: 10 months). Our results indicate a relative hypesthesia of the epikeratophakia lenticule when compared with the peripheral host cornea and contralateral control cornea. However, corneal sensitivity tested in 11 patients with more than 1 year follow-up was increased compared with the sensitivity of 19 patients whose postoperative recovery was less than 1 year. Histopathologic findings in two lenticules from a nonhuman primate demonstrated sparse epithelial axon terminals. Host corneal nerves appear to innervate the lenticules by intraepithelial extension and by penetration of the superficial keratectomy scar.
Animals↗
Neural remodeling following experimental surgery of the rabbit cornea.
Wounding of the cornea results in extensive damage to the innervation that must be repaired to restore its normal structure and function. Four types of experimental wounds were produced in the corneas of young albino rabbits: 180 degrees penetrating perilimbal incisions, 4-mm central circular keratectomies and keratotomies, and radial keratotomies. Following perilimbal incisions, the denervated half of the cornea was reinnervated primarily by regenerating nerves that penetrated the limbal scar tissue. New neural growth from the innervated portion of the cornea provided a minor contribution to the denervated area. The regenerative response of the nerves following nonpenetrating procedures was found to be a biphasic process. In the first phase, a short period of degeneration of all nerves within the area enclosed by the wound boundary overlapped in time with the appearance of long, large caliber, dense neurites that coursed perpendicularly to the wound margins. The neurites originated from the intact subepithelial plexus at some distance from the wound margins. The second phase was initiated by the degeneration of the wound-oriented neurites and the concomitant appearance of a second generation of neurites. These new neurites originated from the transected stumps of the regenerating subepithelial axons at or near the wound margins. The oblique disposition of the second wave of neurites was similar to that of basal leashes in normal corneas. Nonpenetrating wounding procedures exhibited similar neural remodeling principles. In both types of keratotomies, nerve endings terminated within the wound in enduring and densely packed neuroma-like arrangements, while in keratectomies, nerve endings continued to grow toward the center of the cornea.
Animals↗
Sensory denervation of the rabbit cornea affects epithelial properties.
Explore the source record for details and available documents.
Animals↗
Recovery of corneal sensation following hard contact lens wear and the implication for adaptation.
Recovery of corneal sensitivity was determined in hard contact lens wearers 2, 4, 6, 12, and 24 hr after removing the lenses. The extent of recovery was shown by the statistical similarity of the threshold values for the contact lens group and the thresholds of a group of subjects who had never worn contact lenses. Consideration of the time course of recovery and of the thermal modality of the stimulus suggest that the sensory decrement induced by contact lens wear cannot be attributed to simple adaptation.
Adaptation, Physiological↗