Oncology nurses: masters in the art of caring

Thalidomide, when administered orally, is an inhibitor of angiogenesis in the basic fibroblast growth factor (bFGF)-induced rabbit cornea micropocket assay. We now show in the mouse that thalidomide given intraperitoneally but not orally significantly inhibits bFGF-induced and vascular endothelial growth factor (VEGF)-induced corneal neovascularization. We further demonstrate that this inhibition is independent from thalidomide's ability to suppress tumor necrosis factor-alpha (TNF-alpha) production. Experiments examining thalidomide's enantiomers reveal-that the S(-)-enantiomer has the strongest antiangiogenic activity in VEGF-induced and bFGF-induced corneal neovascularization. Structure activity studies suggest that thalidomide's anti-angiogenic activity is related to the open ring metabolites resulting from hydrolysis. Together these data support a correlation between thalidomide's antiangiogenic and teratogenic activities.     

Thalidomide inhibits corneal angiogenesis induced by vascular endothelial growth factor

BACKGROUND: Ocular diseases caused by neovascularization are among the leading causes of blindness. No specific pharmacological treatment is available. Among potential drugs, thalidomide deserves special interest since a wide body of clinical experience exists. However, its antiangiogenic effect is controversial. We therefore investigated the effect of thalidomide on corneal angiogenesis induced by vascular endothelial growth factor (VEGF), which has a special role among angiogenic growth factors. METHODS: Corneal neovascularization was induced in NZW rabbits by an intrastromal pellet loaded with 500 or 750 ng VEGF. Animals received two daily feedings of 200 mg/kg thalidomide. RESULTS: Significant inhibition of corneal angiogenesis (P < 0.0001) was caused by the teratogenic dose of thalidomide after the 5th day of treatment and persisted for more than 16 days. No obvious side effects were recorded. CONCLUSIONS: Thalidomide has a significant antiangiogenic effect against VEGF-induced neovasclar growth. Together with earlier findings this observation indicates that the drug inhibits two angiogenic pathways which are mediated through integrin adhesion molecules.     

Corneal neovascularization induced by xenografts or chemical cautery. Inhibition by cyclosporin A

PURPOSE: Neovascularization of the cornea occurs in numerous pathologic states causing decreased visual acuity and blindness and is a major complication of corneal allotransplantation. The purpose of this study was to investigate the effect of topical and systemic cyclosporin A (CsA) on corneal angiogenesis induced by xenotransplantation or by chemical cauterization. The subcutaneous disc angiogenesis system (DAS) also was used to study the effects of CsA on angiogenesis in a nonocular site. METHODS: Corneal angiogenesis was provoked by either xenotransplantation or chemical cautery. Rats from experiments using both of these models were subdivided into four treatment groups. Topical treatment was administered by using 4% CsA eye drops or vehicle (castor oil) four times daily for 10 days. Systemic therapy consisted of daily (5 mg/kg per day) subcutaneous injections of CsA or vehicle. In the DAS experiments, rats received CsA or vehicle systemically or intradisc. The amount of neovascularization was quantitated by digital image analysis in corneal flat preparations and sections of discs. RESULTS: Rats that received xenografts or cautery manifested less corneal neovascularization than did control animals after topical of subcutaneous CsA treatment. CsA also enhanced the survival of corneal xenografts. A difference between CsA and vehicle-treated animals in the DAS experiments was not detected. CONCLUSIONS: CsA effectively retards the growth of new vessels in the cornea after xenotransplantation or chemical cauterization and prolongs xenograft survival. However, CsA does not suppress angiogenesis in all systems, because it was ineffective in blocking vessel growth in the subcutaneous DAS.     

Inhibitory effects of plasminogen fragment on experimentally induced neovascularization of rat corneas

BACKGROUND: Corneal neovascularization plays an important role in the pathogenesis of a number of corneal disorders. Recently a polypeptide was demonstrated, generated by the primary tumor, that inhibited angiogenesis and growth in metastases. This polypeptide is similar to a 38-kDa plasminogen fragment. METHODS: We surgically implanted into rat corneal stroma a slow-release ethylene-vinyl-acetate (EVA) copolymer pellet containing basic fibroblast growth factor (bFGF) to induce corneal neovascularization. Then we applied aqueous solution containing plasminogen fragment to the rat cornea in order to observe the degree of inhibition of angiogenesis. RESULTS: In the eyes of control rats, neovascularization from the limbus to the pellet occurred, graded 4+ in all five animals. In plasminogen fragment-treated rats, there was virtually complete inhibition of the neovascular response to the pellet. Of five treated rats, three showed no neovascularization and two demonstrated grade 1+ neovascularization. The difference in the degree of neovascularization between control and plasminogen fragment treatment was statistically significant (P < 0.05). CONCLUSION: Our studies provide the first direct evidence that rat corneal neovascularization is inhibited by instillation of plasminogen fragment. This agent may prove useful in the treatment of corneal angiogenic disorder.     

Oxygen consumption and ATPase activity in the corneal epithelium of rabbits with alloxan induced hyperglycemia

PURPOSE: To more fully investigate the effect of hyperglycemia on the aerobic metabolism of the corneal epithelium. METHODS: Corneal epithelial oxygen uptake rates and adenosine triphosphatase (ATPase) activities were measured in alloxan-induced diabetic and control rabbits over a 10 week period. RESULTS: A transient reduction in epithelial oxygen uptake rate was seen at week 1. A chronic 14% reduction in oxygen consumption occurred after 6 weeks of hyperglycemia. Epithelial ouabain-sensitive ATPase activity was unaffected by 10 weeks of hyperglycemia. Epithelial ouabain-insensitive ATPase activity decreased 14% after 10 weeks of hyperglycemia. CONCLUSIONS: Ten weeks of hyperglycemia in the alloxan induced diabetic rabbit was associated with a 14% decrease in corneal oxygen uptake, a 14% decrease in corneal epithelial ouabain-insensitive ATPase activity and no change in corneal epithelial ouabain-sensitive ATPase activity. The Crabtree effect may help explain some of the clinical signs seen in the diabetic cornea as well as explaining why diabetic patients can wear contact lenses with minimal clinical problems.     

Effect of a topically applied neutralizing antibody against vascular endothelial growth factor on corneal allograft rejection of rat

BACKGROUND: Studies in corneal transplant rejection remain important because acute immunologic rejection continues to be the leading cause of human corneal transplant failure. As the permeability of vessels and the neovascularization induce cells infiltration into the graft, we considered the possibility that vascular endothelial growth factor (VEGF), a potent permeability-increasing factor and angiogenesis-mediating factor, could participate in the immune response. METHODS: As the established corneal transplant model for rejection, the corneal transplant between Lewis and Fisher rats has been reported. First, we evaluated VEGF production in the graft by immunohistochemical method in the animal model. Next, we tried to neutralize the effect of VEGF by topical administration of anti-VEGF antibody. We administered anti-VEGF antibody as eye drops for 10 days just after the transplantation of the established animal corneal transplant model. RESULTS: VEGF was strongly produced from the infiltrative cells into the graft. Anti-VEGF antibody significantly suppressed the acute rejection compared with saline or rabbit IgG. CONCLUSIONS: The inhibition of VEGF by topically applied neutralizing antibody is a new potential therapeutic strategy for the treatment of corneal transplantation.     

Borreliosis--Lyme disease--a growing clinical problem

Neovascularization on the center of rabbit cornea was induced by 5N.NaOH alkali burns. We studied the change in localization of acidic fibroblast growth factor (a-FGF) and basic fibroblast growth factor (b-FGF) through corneal neovascularization with immunohistochemistry, using eyes which we enucleated on the 3rd, 7th, and 14th day. Moreover, by co-cultivation of rabbit corneal stromal cells and adrenal cortical vascular endothelium of bovine, a capillary-like code was induced, in which we also studied the localization of a-FGF and b-FGF on the 3rd, 7th, and 14th day. On the 14th day after the alkali burn we recognized intrastromal neovascularization and positive staining of a-FGF and b-FGF around it. Strong staining of a-FGF was observed in goblet cells through the experimental period. In control eyes we recognized positive reaction of a-FGF in corneal and conjunctival epithelium. In co-cultured cells, we recognized positive staining of both a-FGF and b-FGF around the capillary-like code which was induced among the corneal stromal cells.     

Inhibition of corneal inflammation by the topical use of Ras farnesyltransferase inhibitors: selective inhibition of macrophage localization

PURPOSE: Ras farnesyltransferase inhibitors are known to block the membrane translocalization of oncogenic Ras protein. They inhibit the cytoplasmic mitogen-activated protein kinase signaling cascade related to Ras protein. Thus far, Ras farnesyltransferase inhibitors have been exclusively regarded with the anticancer drugs. The object of this study was to elucidate the role of Ras farnesyltransferase inhibitors on the corneal opacity induced by an inflammatory stimulus. METHODS: We used a cauterization-induced corneal inflammation model. The central corneas of BALB/c mice were cauterized with silver nitrate (1 mm in diameter). Ras farnesyltransferase inhibitors, either manumycin or gliotoxin eye drops (each drug dissolved in balanced salt solution [BSS] at concentrations of 1 mM), were topically delivered to the cauterized cornea every 8 hours; BSS eye drops were used as a control. Clinical signs such as corneal edema, opacity, and corneal neovascularization, which are major causes of visual disturbance, were then examined 96 hours after the cauterization. The corneal edema and opacity were clinically scored under a stereoscopic microscope. The corneal neovascularization was evaluated by the length of the blood vessels from the limbus and the sum of extension central angle of vascularized limbus. Furthermore, the corneas were examined histologically, and the phenotypes of the cornea-infiltrating cells were analyzed by flow cytometry. RESULTS: The control corneas showed prominent edema, neovascularization, and opacity. Histologic analysis revealed corneal epithelial and endothelial cell loss and a large amount of inflammatory cell infiltration into the corneal stroma. Flow cytometric analysis revealed that most of the infiltrating cells were neutrophils and macrophages. In contrast, the degree of corneal edema, neovascularization, and opacity was significantly less in the manumycin- or gliotoxin-treated corneas than in the control corneas. Histologically, the manumycin- and gliotoxin-treated corneas showed minimum edema and good epithelialization. Flow cytometric analysis showed corneal infiltration of macrophages to be selectively and clearly inhibited. Neither manumycin nor gliotoxin produced any side effects in the noncauterized normal cornea either clinically or histologically. CONCLUSIONS: Ras proteins play an important role in cauterization-induced corneal inflammation and the opacity it induces. Ras farnesyltransferase inhibitors thus have a great potential for improving the treatment of corneal opacity induced by a corneal inflammatory stimulus.     

The effect of hypertonic ointments on corneal alkali burns

Alkali-burned rabbit corneas were treated with 40% glucose or 5% sodium chloride ophthalmic ointments 3 times daily for 6 weeks and examined clinically and histologically. Treatment with hypertonic ointment as compared to untreated controls demonstrated decreased corneal neovascularization and ulceration. The possible nutritional advantage of hypertonic glucose did not prove beneficial compared to hypertonic sodium chloride.     

Alkali burn-induced synthesis of inflammatory eicosanoids in rabbit corneal epithelium

PURPOSE: Alkali burning of the rabbit cornea is a well-established model for the study of anterior surface inflammation, neovascularization, and wound-healing processes. 12-hydroxyeicosanoids have been implicated as mediators of such responses. 12(S)-hydroxyeicosatetraenoic acid (12[S]-HETE) is a lipoxygenase-derived arachidonate metabolite and 12(R)-hydroxyeicosatetraenoic acid (12[R]-HETE) is formed by a cytochrome P450 monooxygenase; both give rise to the potent angiogenic factor 12(R)-hydroxyeicosatrienoic acid (12[R]-HETrE). In this study, the authors correlate the pattern of their synthesis in the corneal epithelium with the inflammatory response after alkali injury. METHODS: New Zealand albino rabbits were anesthetized and alkali burns created with 10-mm filter paper discs (1 N NaOH for 2 minutes). Corneas were then rinsed; 1 to 7 days later, corneal epithelium was scraped and used to assess 14C-arachidonic acid conversion to 12-HETE and 12-HETrE enantiomers in the presence of NADPH by chiral high-pressure liquid chromatography. The inflammatory response secondary to the alkali burn was quantified through area measurements of reepithelialization and neovascularization. RESULTS: Alkali burn induced a time-dependent production of corneal epithelial 12-HETE and 12-HETrE. A marked increase in 12-HETE and 12-HETrE synthesis was evident at day 2 (from 22 +/- 7 to 139 +/- 22 ng/hour) after injury, increasing to 800 +/- 68 ng/hour at day 7. Chiral analysis revealed a time-dependent synthesis of the R and S enantiomers of 12-HETE (24% R, 76% S) and 12-HETrE (72% R, 28% S). Total arachidonate metabolism, as well as the formation of 12(R)-HETrE, correlated with the area of neovascularization (P < 0.01 and P < 0.02, respectively). CONCLUSIONS: The results demonstrate that surviving and regenerating epithelium has an increased capacity of synthesizing 12(S)-HETE and 12(R)-HETE and that maximal production of 12(R)-HETrE, a known direct and indirect angiogenic factor, coincides with neovascularization in this model. Thus, the lipoxygenase and cytochrome P450-dependent activities increased in a time-dependent manner, indicating the potential involvement of both pathways in the inflammatory response to alkali burn. The formation of significant quantities of 12(R)-HETE and 12(R)-HETrE is a novel finding in this alkali injury model.     

Effects of topically applied antioxidants in experimentally provoked polymorphous light eruption

BACKGROUND: Polymorphous light eruption (PLE) is the most common photodermatosis, with a prevalence of 10-20% in Western European countries and in the USA. Only few preventive measures for PLE exist, while its etiology and pathogenesis are still elusive. Recent theories on pathogenesis discuss the possible influence of oxidative stress. OBJECTIVE: The presented randomized, placebo-controlled, double-blind study examines for the first time the protective effect of 3 different topically applied antioxidative preparations in experimentally photo-induced PLE. METHOD: 30 patients with a history of PLE underwent photoprovocation after having had applied 3 different formulations with antioxidants and one formulation with the vehicle only to the extensor surface of their upper arms, representing the individual site of predilection, twice daily for 1 week prior to and during the consecutive week of photoprovocation. The antioxidants used were combinations of different concentrations of alpha-glycosylrutin, ferulic acid and tocopheryl acetate. RESULTS: Evaluation after the 4th photoprovocation revealed that the development and severity of PLE and concomitant pruritus were significantly reduced by the application of distinct combinations of antioxidants. CONCLUSION: The results offer a new insight into possible pathomechanisms of PLE and suggest a new approach for preventive and therapeutic measures.     

Interleukin 1 receptor antagonist suppresses allosensitization in corneal transplantation

OBJECTIVE: To delineate the mechanisms by which topical interleukin 1 receptor antagonist (IL-1RA) treatment promotes orthotopic corneal allograft survival. METHODS: Corneal buttons were prepared from eyes of C57BL/6 mice and placed orthotopically in normal or neovascularized (high-risk) eyes of BALB/c mouse recipients. Topical IL-1RA (or vehicle alone) was applied to grafts 3 times daily until the grafted eyes were enucleated. Corneal specimens were evaluated for content of Langerhans cells. A week after enucleation, 1 group of recipients was tested for allospecific delayed-type hypersensitivity elicited by intrapinnae injections of donor splenocytes. In companion experiments, a second group of mice that underwent transplantation, IL-1RA treatment, and enucleation was challenged with orthotopic skin grafts from B10.D2 donor mice (sharing minor H antigens with C57BL/6 mice) to determine whether the second group of mice could reject grafts bearing corneal donor minor H alloantigens in an accelerated fashion. RESULTS: Mice whose orthotopic corneal allografts were treated topically with IL-1RA acquired neither donor-specific delayed-type hypersensitivity (P<.001) nor the capacity to reject orthotopic donor-type skin allografts in an accelerated manner (P<.05), whereas controls treated with vehicle alone developed delayed-type hypersensitivity and rejected B10.D2 grafts in an accelerated manner. Moreover, IL-1RA-treated grafts placed in both high-risk (P = .01) and normal-risk (P = .004) eyes displayed significantly reduced levels of infiltrating Langerhans cells compared with vehicle-treated controls. CONCLUSIONS: Topical IL-1RA promotes corneal allograft survival in large part by preventing activity of recipient Langerhans cells, and thereby preventing these cells from inducing systemic allosensitization. These data suggest that IL-1 plays a key role in promoting allosensitization when corneal allografts are placed orthotopically. ClINICAL RELEVANCE: Suppression of allosensitization by topical IL-1RA may prove a clinically useful method for enhancing corneal transplant survival.     

Retroviral vector-mediated gene transfer into keratocytes in vitro and in vivo

PURPOSE: To determine the potential of somatic gene transfer as a technique for modulating corneal wound healing after superficial keratectomy. METHODS: The transduction of human and rabbit keratocytes with beta-galactosidase and herpes simplex virus thymidine kinase genes was performed. In vitro, human and rabbit keratocytes were transduced with retroviral vectors bearing beta-galactosidase or HStk (herpes simplex virus thymidine kinase) genes. In vivo, rabbit keratocytes were transduced by topical application of vector supernatant after a superficial keratectomy. In vitro and in vivo, expression of the beta-galactosidase gene was examined with histochemical staining. In vitro, ganciclovir cytotoxicity in HStk gene-transduced keratocytes and bystander effect in co-cultures of HStk(+) and HStk(-) keratocytes were measured by determining the degree of confluency of cells in 6-well plates after 10 days of incubation. Corneal haze in rabbits was measured after transduction with Hstk and subsequent treatment with topical ganciclovir. RESULTS: In vitro, both human and rabbit keratocytes were transduced successfully with both beta-galactosidase and HStk genes. Transduction efficiency was greater with human (22%) than with rabbit (16%) cells, and both HStk-transduced cell lines showed dose-dependent ganciclovir cytotoxicity and a significant bystander effect. In vivo, expression of beta-galactosidase within vimentin-positive corneal stromal cells confirmed transduction of keratocytes in the rabbit after superficial stromal keratectomy with an efficiency of 25% to 40%. Postoperative application of topical ganciclovir reduced corneal stromal haze in rabbits. CONCLUSIONS: The ability to genetically transduce stromal keratocytes provides a new strategy for understanding the important cellular and molecular events that influence corneal wound healing, thus offering a potential approach to decrease or prevent corneal haze and scarring after superficial keratectomy.     

FK-506 delays corneal graft rejection in a model of corneal xenotransplantation

FK-506 is a relatively new immunosuppressant similar in action to cyclosporine A, but is much more potent. Its primary action is against T lymphocytes, the major cellular component in corneal allograft rejection. The purpose of this study was the evaluation of the ability of topical and systemic FK-506 in preventing corneal xenograft rejection in an experimental animal model. Cross-species xenotransplants were used as the most vigorous stimulus to induce corneal rejection. Corneas derived from Hartley guinea pigs were transplanted into the left eyes of 32 male Lewis rats. Topical treatment was administered by using FK-506 0.3 mg/ml in a cyclodextrin suspension or vehicle (cyclodextrin suspension) four times per day. For systemic treatment, 0.5 mg/kg/day of FK-506 or vehicle (saline) was administered intraperitoneally. Treatments were started 60 minutes after surgery and continued for 21 days. The grafts underwent a double-masked examination, and a score was given for clarity, edema, and vascularization. The animals were sacrificed 21 days after transplantation. The control groups had allograft rejection after 6.75 +/- 0.31 (topical vehicle) and after 7.37 +/- 0.32 (systemic vehicle) days. The FK-506-treated groups showed allograft rejection after 14 +/- 0.88 (topical FK-506) or after 16.25 +/- 1.23 (systemic FK-506) days. In addition, FK-506-treated rats manifested less corneal neovascularization than control animals. We conclude that systemic or topical FK-506 is effective in prolonging xenograft survival in the rat keratoplasty model.     

Angiogenesis in rheumatoid arthritis: pathogenic and clinical significance

In summary, angiogenesis, the formation of new blood vessels, is important in leukocyte extravasation and thus the pathogenesis of RA. The outcome of neovascularization highly depends on the imbalance between angiogenic and angiostatic mediators produced in the rheumatoid synovium. Therefore, angiogenesis research is important for the understanding of the pathogenesis of inflammatory arthritis. In addition, existing and potential angiostatic drugs may be useful for future therapy of RA.     

The occlusal theory further complicated

The aim of the study is to identify nitric oxide synthase (NOS) in the rabbit cornea and further investigate the physiological role of nitric oxide in the rabbit cornea. For histological identification, an immunohistochemical technique using anti-NOS monoclonal antibodies was employed. For the physiological study, we measured the corneal thickness in vivo as an indicator of corneal edema by ultrasonic pachymetry. The measurements were repeated before and after ipsilateral injections of N(G)-nitro-L-arginine methyl ester (L-NAME) or N(G)-nitro-D-arginine methyl ester (D-NAME) or 6-anilino-5,8-quinolinedione (LY-83583) with contralateral injection of vehicle (balanced salt solution) into the anterior chamber of the rabbit. We also monitored intraocular pressure (IOP) by pneumatonometry. Endothelial NOS (eNOS) immunoreactivity was demonstrated both in the corneal epithelium and the endothelium. The corneal thickness significantly increased after L-NAME or LY-83583 without significant rise of IOP, whereas no change was detected after vehicle or D-NAME. These results suggest that NO is spontaneously produced in the corneal endothelium and the NO/cyclic GMP pathway is involved in maintainance of corneal thickness.     

Human T- and B-cell reactivity to the 16kDa alpha-crystallin protein of Mycobacterium tuberculosis

PURPOSE: To determine whether inflammatory corneal neovascularization (CNV) is associated with interleukin-1 (IL-1) activity and if so, to assess the efficacy of topical interleukin-1 receptor antagonist (IL-1ra) to suppress CNV. METHODS: Inflammatory CNV was induced on day 0 by placement of paracentral intrastromal sutures in BALB/c murine eyes. Quantification of IL-1alpha and -beta cytokine levels was done by a sandwich enzyme-linked immunosorbent assay (ELISA) on the supernatants of incubated corneas excised at specified time points after induction of CNV (n = 6 per time point studied). To study suppression of CNV by IL-1ra, animals were divided into treatment subgroups that received topical 20 mg/ml of IL-1ra mixed in 0.2% sodium hyaluronate (n = 28) or placebo (vehicle) alone (n = 22) 3 times daily during days 0-35. Other groups of animals received placebo for 1 (n = 10) or 2 (n = 14) weeks before being switched and retained on IL-1ra. Neovascularization was assessed biomicroscopically and graded by using a standardized scheme. RESULTS: Induction of CNV stimulus was associated with a significant surge in the expression of both IL-1alpha (p < 0.001) and IL-1beta (p < 0.001) as early as 2 h after the stimulus, which peaked at 24 h, before decreasing substantially in the case of IL-1beta and returning to basal levels by day 7. Topical application of IL-1ra led to a significant suppression of CNV for the duration of therapy only if initiated early after induction of the neovascular stimulus. Initiation of therapy 1 week after CNV induction was associated only with a transient suppression in the angiogenic response. CONCLUSION: Our data strongly implicate IL-1 as a critical mediator in the early phase of CNV and suggest that IL-1ra can be an effective modality in suppressing CNV if initiated sufficiently early after the inflammatory neovascular stimulus.     

Confocal microscopic characterization of wound repair after photorefractive keratectomy

PURPOSE: Development of postoperative corneal haze and regression of refractive effect are unfavorable clinical complications of excimer laser photorefractive keratectomy (PRK). Although exact mechanisms remain to be elucidated, these outcomes have been attributed to post-PRK corneal wound healing. The purpose of this study was to evaluate corneal wound repair quantitatively after PRK in a rabbit model using a newly developed in vivo technique, termed confocal microscopy through focusing (CMTF). METHODS: Twelve rabbit corneas received a monocular, 6-mm diameter, 9.0-diopter PRK myopic correction. Animals were evaluated sequentially up to 6 months after surgery by in vivo CMTF, which uses an image-intensity depth profile to measure epithelial and stromal thickness and uses corneal light reflectivity as an objective estimate of corneal haze. At differing temporal intervals, in vivo morphology was correlated with ex vivo histology using fluorescence microscopy. RESULTS: One week after PRK, an acellular layer of 86 +/- 24 microns was found anteriorly in the remaining stroma, which demonstrated surgically induced keratocyte death. Underlying keratocytes became activated and migrated toward the wound bed; repopulation was completed within 3 weeks. One week after PRK, there was a significant increase (P < 0.001) in light reflections detected from the photoablated stromal surface (1745 +/- 262 U) and from the underlying activated fibroblasts (713 +/- 607 U). Corneal reflectivity peaked at 3 weeks (4648 +/- 1263 U) and decreased linearly to 889 +/- 700 U by 6 months after the PRK; this corresponded to a reflectivity six times greater than the level seen in unoperated corneas. Two weeks after PRK, initial corneal edema had resolved, revealing an actual ablation depth (maximal stromal thinning) of 118 +/- 8 microns. Starting at 2 weeks after surgery, the stroma underwent gradual rethickening that reached 98% of the preoperative thickness at 6 months after PRK; at that time, only 6% of the initial photoablation depth persisted. By contrast, the central corneal epithelium showed no significant postoperative hyperplasia. CONCLUSIONS: Rabbit corneas treated by PRK showed a remarkable stromal wound-healing response that ultimately led to the restoration of the original stromal thickness by 6 months after surgery, demonstrating complete regression of the initial photoablative effect. Additionally, corneal wound healing was associated with increased light reflections from both the photoablated stromal surface and the activated wound-healing keratocytes underlying this area. Based on these findings, the authors hypothesize that the development of clinically observed corneal haze in PRK patients may be related, in part, to activation of corneal keratocytes and to putative changes in the extracellular matrix.     

Cyclic nucleotide phosphodiesterases: diversity, classification, structure and function

PURPOSE: The effects of anti-inflammatory non-steroidal therapy combined with free-radical scavengers were studied and compared to corticosteroid use in the treatment of experimental corneal injury. METHOD: Eighty New Zealand albino rabbits were used in this study. A corneal alkali burn was induced by applying 1-N NaOH filter paper on the central axis of the right cornea for 30 s. Animals were distributed into five treatment groups: group 1 (control group) was only given gentamicin; group 2 was treated with 0.5% dimethylthiourea (DMU); group 3 received 1% dexamethasone; group 4 was given combined 0.5% DMU and 1% indomethacin; group 5 was treated with 0.5% DMU and 0.1% diclofenac sodium. One 50-microliter drop of gentamicin was instilled every 12 h, whereas the other drugs were instilled every 6 h (50 microliters). All groups received the same antibiotic treatment as the control group. The animals were killed on the 5th day. Inflammatory index, area and perimeter of the wounded corneal zone, and corneal transparency were evaluated. RESULTS: No significant differences in the inflammatory index were found between the treatment groups and the control group after 72 h. Significant differences (p < 0.001) were observed at 24 h in groups 3-5 when compared with the control group. Planimetry showed significant differences in group 4 when compared with the other groups (p < 0.05). Corneal transparency study showed statistically significantly better values in groups 4 and 5, when compared with the other groups, including group 3 (p < 0.05). CONCLUSIONS: The use of 0.5% DMU combined with 1% indomethacin can be considered an alternative to corticosteroid treatment in our experimental chemical corneal injury.     

The topographic distribution of the first sites of diabetic retinal neovascularization

PURPOSE: To examine the topographic distribution of the origin of diabetic retinal neovascularization. METHODS: The eyes of 3,121 patients with background diabetic retinopathy were investigated. These patients were volunteers in systemic medical therapy experiments. Color stereo photographs were obtained annually. The first retinal neovascularization sites were identified and the distances from the optic nerve measured. RESULTS: In 1 year, neovascularization originated in 282 eyes. The superotemporal quadrant, at 6 mm from the optic disk, was the most frequent initial site. CONCLUSIONS: The first retinal neovascularization sites cluster around specific anatomic foci. This information should influence retinopathy monitoring protocols.