Roger W. Beuerman

Interface inflammation after laser in situ keratomileusis: Sands of the Sahara syndrome

Purpose: To determine the source of the interface debris that causes the interface inflammation known as “sands of the Sahara” after laser in situ keratomileusis (LASIK). Setting: Department of Ophthalmology, LSU Eye Center, Louisiana State University Medical Center School of Medicine, New Orleans, USA. Methods: A microkeratome (Automated Corneal Shaper) was used to make a LASIK flap in 8 eyes of 4 rabbits. In 4 eyes, the blade was used directly from the sterile pack; in the contralateral 4 eyes, the blade was cleaned prior to use. In vivo confocal microscopy of the corneas was performed 1 day after surgery. An unused, cleaned blade and an unused, uncleaned blade, as well as blades used in the rabbit eyes, were examined by scanning electron microscopy. Methods: Confocal microscopy revealed numerous fragments of debris surrounded by inflammatory cells in the LASIK flap interfaces created by blades taken directly from the sterile package. Interfaces created by the cleaned blades showed only rare, scattered bits of debris. Scanning electron microscopy of the unused blades showed debris on the uncleaned blade removed directly from the sterile package. Conclusion: Post‐LASIK interface inflammation may be caused by debris on the microkeratome blade, although other sources are possible. The interface debris and inflammation can be reduced or eliminated by cleaning the microkeratome blade before use.

Ultrastructure of the human cornea

The transparent nature of the cornea and its importance in the visual pathway as the major refracting lens of the eye have intrigued workers in many different disciplines and their studies have added immeasurably to the understanding of the cornea in health and disease. Reviews of the structure of the cornea date back to the earliest days of electron microscopy (Hogan et al., 1971; Klyce and Beuerman, 1988; Kuwabara, 1978; Rouiller et al., 1954), yet, due to changing insights into corneal structure provided by cell biology, as well as new clinical developments, current ultrastructural reviews of the cornea have new relevance in both basic science and clinical ophthalmic research.

A Unified Theory of the Role of the Ocular Surface in Dry Eye

It is our belief that the pathology of dry eye occurs when systemic androgen levels fall below the threshold necessary for support of secretory function and generation of an anti-inflammatory environment (Fig. 3). When this occurs, both the lacrimal gland and the ocular surface become irritated and inflamed, and they secrete cytokines that interfere with the normal neural connections that drive the tearing reflex. This leaves the lacrimal gland in an isolated condition, perhaps exacerbating atrophic alterations of the glandular tissue. These changes allow for antigen presentation at the surface of the lacrimal acinar cells and increase lymphocytic infiltration of the gland. A similar series of events may be occurring on the ocular surface. From this hypothesis we conclude: 1. The ocular surface, lacrimal gland, and interconnecting innervation act as an integrated servo-mechanism. 2. Once the lacrimal gland loses its androgen support, it is subject to immune/neurally mediated dysfunction. 3. The ocular surface is an appropriate target for dry eye therapeutics.

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.

Clinical Article Accumulation of PN1 and PN3 Sodium Channels in Painful Human Neuroma-Evidence from Immunocytochemistry

Summary.Summary. Background: The axolemmal distribution and density of voltage-gated sodium channels largely determines the electrical excitability of sprouting neurites. Recent evidence suggests that accumulation of sodium channels at injured axonal tips may be responsible for ectopic axonal hyperexcitability and the resulting abnormal sensory phenomena of pain and paresthesias. For future improvement in pain management it is necessary to identify structurally significant generators of autorhythmicity. A first step in this regard will be to determine the predominant types of sodium channels in injured axons. The opportunity to test human specimens from painful and non-painful neuroma is of great value. Methods: We employed immunocytochemical methods to investigate if two types of highly specific voltage-gated sodium channel subtypes could be detected in sections of human neuroma. Findings: Both subtypes of sodium channels PN1 and PN3 accumulated abnormally in human neuromas. The immunoreactive pattern was more pronounced in painful neuromas. This is in contrast to previous reports that focused either on PN1 or PN3 as main generators of hyperexcitability induced pain. Interpretation: Both, PN1 and PN3 seem to be involved in hyperexcitability induced pain. It can be expected that a variety of other highly specific voltage gated sodium channel subtypes will be detected in regenerating peripheral nerve in the near future, which contribute to the development of neuropathic pain states. Thus, in order to therapeutically control hyperexcitability induced neuropathic pain, it might be worthwhile to develop pharmaceuticals that can selectively block different sodium channel subtypes and subunits. A review of the role of sodium channels in neuropathic pain is implemented in the discussion.

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.

Tumor necrosis factor-alpha and interleukin-1 induce activation of MAP kinase and SAP kinase in human neuroma fibroblasts.

Two cytokines, tumor necrosis factor-alpha (TNF-alpha) and interleukin-1 (IL-1), which are released by macrophages during the early inflammatory phase of nerve injury, are known to induce activation of mitogen-activated protein kinase (MAPK) and stress-activated protein kinase (SAPK), which locate at different signal transduction pathways and are involved in cell cycle G0/G1 transition and cellular proliferation in human fibroblasts. Activation of these two protein kinases by the cytokines may stimulate fibroblast proliferation in damaged nerves and thereby play a role in the formation of a neuroma, a disorganized mass of tissue that interferes with neural regeneration and repair. To investigate the possibility that this mechanism is operative in neuroma formation, we used cultured, serum-starved fibroblasts from surgically removed human neuromas stimulated with TNF-alpha and/or IL-1 alpha and IL-1 beta, and measured the activation of MAPK and SAPK using myelin basic protein (MBP) and human c-Jun (1-169) glutathione S-agarose transferase (GST) fusion protein as substrates. For comparison, neuroma fibroblast cultures were also stimulated with phorbol 12-myristate 13-acetate (PMA) and platelet-derived growth factor-AB (PDGF-AB), a potent activator for MAPK. TNF-alpha and both forms of IL-1 produced a rapid activation of MAPK, with a peak at 15 min for TNF-alpha stimulation, and a peak at 30 min for IL-1 stimulation. TNF-alpha combined with either IL-1 alpha or IL-1 beta produced a synergistic effect on the activation of MAPK. The increases in MAPK induced by TNF-alpha and IL-1 were similar to the increases induced by PMA and PDGF-AB. To confirm the presence of MAPK, immunoprecipitation and immunoblotting were carried out on experimental and control lysates. TNF-alpha and IL-1 also increased activation of SAPK, but to a lesser extent than MAPK. PMA and PDGF-AB were also much less effective in stimulating activation of SAPK. Our findings indicate that TNF-alpha and IL-1 activate parallel signal transduction pathways in human neuroma fibroblasts, and that they are relatively stronger activators of MAPK than of SAPK. Previous studies have convincingly demonstrated that MAPK and SAPK are involved in human fibroblast proliferation. The results of our study suggest that TNF-alpha and IL-1 may play a role in frustrating functional nerve regeneration after injury by stimulating these two kinases, which, in turn, leads to fibroblast proliferation and formation of neuromas.

Assessment of the long-term corneal response to hydrogel intrastromal lenses implanted in monkey eyes for up to five years.

ABSTRACT The biocompatibility of hydrogel intracorneal lenses (ICLs) implanted in monkey eyes was evaluated for periods ranging up to five years. Seventy‐three plus or minus powered ICLs made of Lidofilcon A (68% water) or Lidofilcon B (79% water) were implanted following lamellar dissection with a microkeratome. Ten sham surgical procedures were performed without ICL implantation as controls. Eyes were followed for up to five years by slitlamp biomicroscopy and specular microscopy. Light and transmission electron microscopic evaluations of enucleated eyes were performed at various intervals. Minimal tissue reaction was noted; both hydrogel materials appeared to be equally well tolerated. Failures usually occurred as a result of microkeratome problems encountered during surgery. Histopathological changes to the cornea included epithelial thinning anterior to the thickest portion of the ICL, fibroblastic activity along the ICL‐stromal interface, and deposition of an amorphous extracellular material adjacent to the ICL. These observations did not appear to be clinically significant as the eyes were quiet by slitlamp examination. Removal of three ICLs eight to ten months prior to enucleation restored the normal histological characteristics of the cornea. The endothelial cell density of ICL‐implanted eyes decreased by 4.3% (n =17) six months after surgery but remained stable thereafter. The variation in endothelial cell area and percentage of hexagonal cells did not change over 50 months. The results appear to demonstrate that high water content synthetic ICLs can be well tolerated in the monkey cornea for up to five years.

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.

Neurogenic Inflammation: A First Line of Defense for the Ocular Surface

Neurogenic inflammation and innate immunity may work together to protect mucosal surfaces, including the ocular surface. When the eye is exposed to pathogens, chemical irritants, or mechanical disruption, neurogenic inflammation is produced through release of neuromodulators, such as substance P and calcitonin gene-related peptide. This leads to the breakdown of the blood-tissue barrier, edema, and release of polymorphonuclear leukocytes into the tears, thus allowing intervention of systemic immunity. Neurogenic mechanisms may have a significant role in the onset and chronicity of ocular surface inflammation in conditions such as dry eye.