Grain growth resistance and increased hardness of bulk nanocrystalline fcc cobalt prepared by a bottom-up approach

Bulk nanocrystalline cobalt was prepared from reducing flame-spray-derived cobalt nanopowders exclusively in the face-centred cubic (fcc) modification. Compacts of approximately 60% density were obtained from uniaxial compression at room temperature and showed a strong resistance towards grain growth upon subsequent sintering to 90% relative density. The nanocrystalline structure remained stable well above 1000 degrees C and resulted in a pore-rich metal with about 10(15) nanovoids cm(-3). These sintered compacts displayed an up to three times higher bulk hardness if compared to conventional cobalt and local ductility as evidenced from scanning electron microscopy and nanoindentation. The strong grain-growth resistance and consequent increase in material hardness are discussed in respect of the presence of nanovoids, twin boundaries and material contamination.

Large-scale production of carbon-coated copper nanoparticles for sensor applications

Copper nanoparticles with a mean carbon coating of about 1 nm were continuously produced at up to 10 g h(-1) using a modified flame spray synthesis unit under highly reducing conditions. Raman spectroscopy and solid state (13)C magic angle spinning nuclear magnetic resonance spectroscopy revealed that the thin carbon layer consisted of a sp(2)-hybridized carbon modification in the form of graphene stacks. The carbon layer protected the copper nanoparticles from oxidation in air. Bulk pills of pressed carbon/copper nanoparticles displayed a highly pressure- and temperature-dependent electrical conductivity with sensitivity at least comparable to commercial materials. These properties suggest the use of thin carbon/copper nanocomposites as novel, low-cost sensor materials and offer a metal-based alternative to the currently used brittle oxidic spinels or perovskites.

The safety and efficacy of combined phacoemulsification and trabeculectomy with releasable sutures

AIM

To evaluate the combined phacoemulsification with acrylic intraocular lens implantation and trabeculectomy with releasable sutures, without the use of antimetabolites, performed by one surgeon.

METHODS

A retrospective analysis was performed on 251 eyes of 198 patients after a combined phaco/trabeculectomy procedure, followed up for an average of 16 months for vision, intraocular pressure (IOP), and number of glaucoma medications. Cox proportional hazard regression analysis provided measures of relative risk (RR) or hazards ratios and 95% confidence intervals (CIs) associated with the occurrence of several conditions or complications of surgery.

RESULTS

Mean preoperative variables were best corrected vision, 0.6 (SD 0.4) logMAR (20/80 Snellen); IOP, 18.7 (4.9) mm Hg; and number of glaucoma medications, 1.7 (0.8). Mean postoperative results were best corrected vision, 0.2 (0.4) logMAR (20/32 Snellen); IOP, 15.1 (3.2) mm Hg; and number of glaucoma medications, 0.3 (0.6). Postoperatively, the mean decreases from baseline were 19.2% for IOP and 84.1% for number of glaucoma medications; 85% of eyes required fewer glaucoma medications and 78% of eyes were medication free, with IOP control. There were no significant operative or postoperative complications.

CONCLUSION

Combined phacoemulsification and trabeculectomy with releasable sutures, in the absence of antimetabolites, is a safe, effective, and stable alternative for patients with cataracts and glaucoma.

A new donor cornea harvesting technique for posterior lamellar keratoplasty

AIMS

To describe a technique for posterior lamellar keratoplasty donor preparation.

METHODS

In an experimental study eight human donor research corneas were mounted onto an artificial anterior chamber and deep stromal pockets dissected. Four corneas were mounted in the standard endothelial side down orientation and dissected using standard instruments (group 1). Another four corneas were mounted endothelial side up and dissected using a flat spatula (group 2). Trephined lamellar graft thickness was assessed by ultrasound pachymetry. The grafts were also analysed using vital staining of the endothelium and standard histological preparation.

RESULTS

Achieved posterior graft thickness was 118 (SD 32) microm (group 1) and 92 (23) microm (group 2) (p=0.324). Percentage of devitalised endothelial cells was 0.86% (1.48%) (group 1) and 3.9% (2.9%) (group 2) (p=0.185). The dissections using both harvesting techniques remained in plane and were smooth.

CONCLUSIONS

A blunt spatula and endothelium side up orientation on an artificial anterior chamber can be used to create posterior lamellar dissections without compromising endothelial cell number or planarity when compared to standard endothelium side down harvest.

Microarray analysis of gene expression in human donor corneas

OBJECTIVES

To use microarray analysis to identify genes expressed in human donor corneas and to create a preliminary, comprehensive database of human corneal gene expression.

METHODS

A complementary DNA (cDNA) library was constructed from transplant-quality, human donor corneas. Biotin-labeled RNA was transcribed from the cDNA library and hybridized in duplicate to microarrays containing approximately 5600 human genes. Results were analyzed using a gene database of the National Institutes of Health, Bethesda, Md. Reverse transcriptase polymerase chain reaction analysis was performed to confirm corneal expression of genes identified by microarray analysis.

RESULTS

Duplicate microarrays identified the expression of 1200 genes in human donor corneas. Chromosomal loci had been assigned to 1025 (85%) of these genes. A preliminary database of human corneal gene expression was compiled. A Web site containing these genes was created. Six collagen genes were identified that had not previously been localized within the cornea. Five apoptosis-related genes were identified, 4 of which had not previously been localized within the cornea. Three genes previously shown to cause corneal diseases were identified. Reverse transcriptase polymerase chain reaction analysis of genes identified by microarray analysis confirmed the corneal expression of 2 apoptosis-related genes and 1 collagen gene.

CONCLUSIONS

Microarray analysis of healthy human donor corneas has produced a preliminary, comprehensive database of corneal gene expression. Large-scale analysis of gene expression has the potential to generate large amounts of data, which should be made readily accessible to the scientific community. The Internet offers many potential advantages as a medium for the maintenance of these large data sets.

CLINICAL RELEVANCE

Identification of structural, apoptosis-related, and disease-causing genes within the cornea by microarrays may increase the understanding of normal and abnormal corneal function with likely relevance to corneal diseases and transplants.

The role of apoptosis in the pathogenesis of Fuchs endothelial dystrophy of the cornea

OBJECTIVE

To investigate the potential role of apoptosis in the pathogenesis of Fuchs endothelial dystrophy of the cornea.

METHODS

Twenty-one corneal buttons from patients with Fuchs dystrophy and 15 control corneas were studied. Apoptosis was assessed by the in situ end-labeling of double-stranded DNA breaks, and by immunohistochemical characterization of cellular markers associated with apoptosis (Fas, FasL, Bcl-2, and Bax). Expression of Bcl-2 and Bax mRNA in the corneal stroma and endothelium was separately analyzed by a semiquantitative reverse transcriptase polymerase chain reaction. Furthermore, cultivated keratocytes generated from diseased corneal buttons and donor rims were exposed to camptothecin, an apoptotic inducer, for 6 and 24 hours. They were then examined for protein and messenger RNA (mRNA) expression of apoptotic regulatory molecules.

RESULTS

DNA fragmentation was seen in the epithelium, stroma, and endothelium in 6 of 7 corneas with Fuchs dystrophy. A statistically significant difference was identified in the expression of Bax and its mRNA in the stroma, but not in the endothelium of Fuchs dystrophy corneas. Following exposure to camptothecin, keratocytes from patients with Fuchs dystrophy responded with an increased level of Bax and a low level of Bcl-2. This trend was distinctively different from the response of normal keratocytes.

CONCLUSIONS

The evidence in this study points to a disease-related disturbance in the regulation of apoptosis in Fuchs dystrophy. Our findings suggest that excessive apoptosis may be an important mechanism in the pathogenesis of Fuchs dystrophy.

Spontaneous corneal perforation in a patient with unusual unilateral pellucid marginal degeneration

A 56-year-old man presented with acute loss of vision and tearing in his left eye. Slitlamp examination demonstrated peripheral corneal edema extending between the 2 and 6 o'clock positions as well as a perforation located inferiorly. The right eye was unremarkable. An emergent crescentic lamellar keratoplasty was performed. The patch graft remained clear during the 30-month follow-up, and visual acuity improved significantly. No changes occurred in the right eye. This case represents an unusual, unilateral corneal ectatic disorder, most likely pellucid marginal degeneration.

Cataract surgery by phacoemulsification in adults with retinopathy of prematurity

PURPOSE

To report the preoperative, operative, and postoperative factors associated with phacoemulsification cataract surgery in adults with retinopathy of prematurity.

METHODS

Records of patients with retinopathy of prematurity who underwent phacoemulsification at The Wilmer Institute between January 1990 and January 2000 were retrospectively searched. Seventeen adults (9 women, 8 men) with retinopathy of prematurity were identified who had undergone phacoemulsification for visually significant cataract or phacomorphic glaucoma and who had at least 6 months of postoperative follow-up.

RESULTS

Cataract extraction by phacoemulsification was performed on 20 eyes. Follow-up ranged from 6 to 103 months (mean, 32 months). A posterior chamber intraocular lens was placed in 18 eyes; two eyes were left aphakic for refractive reasons. Zonular weakness was noted in two eyes in which the intraocular lens was suture fixated to the sclera. Concomitant trabeculectomy was performed in one eye. Visual acuity improved in 18 of 20 eyes and remained unchanged in two eyes. Postoperatively, visual acuity was worse than 5/200 in two eyes, 5/200 to worse than 20/100 in five eyes, 20/100 to 20/50 in five eyes, and 20/40 or better in eight eyes. One eye developed a rhegmatogenous retinal detachment 1 month after cataract surgery; the retina was successfully reattached.

CONCLUSIONS

Although cataract extraction in eyes with regressed retinopathy of prematurity may present challenges, such as high myopia, monocularity, glaucoma, and previous ocular surgery, phacoemulsification in this series proved to be relatively safe as well as visually rehabilitating. The surgeon should be aware of the special considerations in this population, alert to potential zonular weakness intraoperatively, and careful of increased postoperative risks, including retinal detachment.

Management of flap striae

There have been no comprehensive investigations of striae after LASIK. The ophthalmic literature has few reports, and no one consistent therapy has been recommended. Striae are relatively uncommon; nevertheless, refractive surgeons need a systematic approach in prevention and therapy for striae. Careful flap handling and positioning can prevent many striae. Early recognition is very important and makes treatment significantly more likely to eliminate or reduce the striae. If the striae are identified within 24 hours, lifting and refloating will likely result in resolution of the striae. If the striae are more imbedded and have been present longer, additional techniques, such as those discussed, are helpful. New techniques will likely be developed because of an increase in lamellar procedures and an increase in the occurrence of striae.

The role of apoptosis in the early corneal wound healing after excimer laser keratectomy in the rat

BACKGROUND

The potential role of apoptosis in corneal wound healing after excimer laser keratectomy was investigated in a rat model.

METHODS

Lewis rats underwent laser keratectomy using a 193-nm excimer laser. The central corneas were ablated in three depths: group A, epithelium; group B, superficial stroma; group C, deep stroma. Eyes were collected at 1, 12, 24, and 36 h and 1 week. Cellular markers associated with apoptosis--Fas, Fas ligand (FasL), Bcl-2, and Bax were examined by immunohistochemistry. Keratocyte depletion and endothelial changes were evaluated histologically. In situ end labeling of double-stranded DNA breaks was used to demonstrate apoptosis in corneal sections.

RESULTS

Keratocyte depletion was observed in 6 (50%) of 12 rats (total from groups A, B, and C) at 12 h, 11 (73%) of 15 at 24 h, 3 (20%) of 15 at 36 h, and 2 (15%) of 13 at 1 week after laser surgery. Corneal endothelial edema was observed in the ablation zone. Expression of Fas, FasL, Bcl-2, and Bax in corneal cells showed dynamics similar to that of keratocyte depletion and endothelial changes. There was less expression of apoptotic molecules in newly generated epithelial cells and more in endothelial cells of the stromal ablation groups.

CONCLUSIONS

Excimer laser keratectomy triggered apoptosis of corneal keratocytes and endothelial cells. More endothelial edema was observed in the stromal ablation than in the epithelial ablation group. The expression of apoptotic molecules coincided with the period of keratocyte depletion and regeneration and of endothelial recovery, suggesting that apoptosis is a dynamic part of corneal wound healing and remodeling after excimer laser keratectomy.

Surgical management of recurrent iris stromal cyst

PURPOSE

To report the clinical history and surgical management of recurrent congenital iris stromal cyst.

METHOD

Case report. Argon laser endophotocoagulation and cryotherapy were used to treat a recurrent iris stromal cyst in an 18-month-old boy.

RESULTS

At 43 months of follow-up, there was no recurrence or evidence of epithelial ingrowth.

CONCLUSION

Treatment with argon laser endophotocoagulation and cryotherapy resulted in complete resolution of a recurrent congenital iris cyst.

Herpes simplex virus DNA identification from aqueous fluid in Fuchs heterochromic iridocyclitis

PURPOSE

To report the presence of herpes simplex virus DNA in the aqueous humor of an eye with Fuchs heterochromic iridocyclitis.

METHODS

In an eye with a clinical diagnosis of Fuchs heterochromic iridocyclitis, samples of aqueous humor and anterior capsule of the lens were obtained during cataract surgery. Polymerase chain reaction was performed on the samples to detect the presence of viral DNA including herpes simplex virus, varicella-zoster virus, and cytomegalovirus. Serologic analysis was also performed for antiviral immunoglobulins.

RESULTS

Herpes simplex virus DNA was identified in the aqueous humor but not in the anterior capsule. Serum immunoglobulin G was positive for herpes simplex virus, varicella-zoster virus, and cytomegalovirus.

CONCLUSIONS

The presence of herpes simplex virus DNA in the aqueous humor of an eye with Fuchs heterochromic iridocyclitis suggests that herpes simplex virus infection may play a role in the pathogenesis of Fuchs heterochromic iridocyclitis.

Phototherapeutic keratectomy for superficial corneal fibrosis after radial keratotomy

We report on 4 patients who developed superficial corneal fibrosis after radial keratotomy. All 4 were treated successfully with manual debridement of the epithelium and manual excision of the fibrous scar, followed by phototherapeutic keratectomy.

Cytokine-induced calgranulin C expression in keratocytes

The authors have identified a corneal stromal protein (CO-Ag) that may be involved in the pathogenesis of Mooren's ulcer. The CO-Ag cDNA sequence is identical to that of human neutrophil calgranulin C (CaGC). This study sought to demonstrate expression of the CaGC gene in the human cornea and in corneal keratocytes after cytokine stimulation. In situ hybridization and immunohistochemistry were used to localize CaGC mRNA and protein in normal and diseased human corneas, including a specimen with Mooren's ulcer. Cultured bovine keratocytes were stimulated with IL-1 alpha or TNF-alpha, and reverse transcription polymerase chain reaction (RT-PCR) was performed to amplify CaGC cDNA from cytokine-stimulated keratocytes and unstimulated controls. Southern blotting verified the specificity of the RT-PCR amplification products. In situ hybridization detected human CaGC mRNA in the stroma of corneas with Fuchs' dystrophy, postinfection corneas, and a cornea with Mooren's ulcer. In cultured bovine keratocytes, peak levels of CaGC mRNA were reached 6 h after cytokine stimulation. Southern blots with an oligonucleotide probe specific for CaGC detected the RT-PCR products of expected sizes (273 bp) and confirmed that the amplified CO-Ag sequence was identical to that of CaGC. These studies are the first to demonstrate the presence of CaGC in the human cornea and the ability of stromal keratocytes to produce CaGC (CO-Ag). The up-regulation of CaGC gene expression by corneal keratocytes due to proinflammatory cytokines from trauma or inflammation may induce autoimmunity that ultimately results in Mooren's ulceration.

Inflammatory response in the early stages of wound healing after excimer laser keratectomy

OBJECTIVE

To evaluate the inflammatory response and its potential role in the early stages of corneal wound healing after excimer laser keratectomy.

MATERIALS AND METHODS

Lewis rats underwent excimer keratectomy using a 193-nm excimer laser. The central corneas were ablated in 3 depths: group A, epithelium; group B, superficial stroma; or group C, deep stroma. Eyes were harvested 1, 12, 24, and 36 hours, and 1 week after the rats were killed. Immunohistochemistry was used to test frozen sections with monoclonal antibodies of various inflammatory cellular markers.

RESULTS

Reepithelialization was observed at 12 hours in group A, and at 24 hours in groups B and C. Regenerated epithelium covered the denuded corneal surface in groups B and C after 1 week. The expression of major histocompatibility complex II antigen was detected in infiltrating cells, corneal epithelial cells, and endothelial cells 1 hour after surgery. Only a few macrophages and Langerhans cells were in the limbus at baseline. Macrophages migrated from the limbus to the corneal ablation zone and increased 2-fold after 36 hours in all 3 groups compared with baseline. Occasional lymphocytic infiltration was identified after 25 to 36 hours.

CONCLUSION

Macrophages play an active role in the wound healing after laser keratectomy and may contribute to transient corneal haze.

Defensin gene expression in the cornea

PURPOSE

To determine whether defensin genes are expressed in human corneas and bovine corneal keratocytes.

METHODS

In situ hybridization and immunohistochemistry were used to localize defensin mRNA and protein in normal and diseased human corneas. Cultured bovine keratocytes were stimulated with IL-1alpha or TNFalpha to determine whether defensin mRNA production occurred. Reverse transcription polymerase chain reaction (RT-PCR) was performed to amplify defensin cDNA from cytokine-induced keratocytes, and Southern blots were used to verify the specificity of RT-PCR amplification products.

RESULTS

Defensin mRNA and protein were not detected in normal human corneal stroma, but were readily detectable in the corneal stroma in cases of rejected transplants and postinfectious keratitis. IL-1alpha was a potent inducer of defensin gene expression in keratocytes, which began 12 h after challenge and peaked at 18 to 24 h. TNFalpha weakly induced defensin mRNA in keratocytes at about 18 h. Southern blots of the RT-PCR products probed with an oligonucleotide complementary to internal sequences of defensin demonstrated the appropriately sized products (198 bp) specific for defensin.

CONCLUSIONS

This report demonstrates the presence of defensin in the human cornea and the capacity of corneal keratocytes to produce defensin mRNA in response to IL-1alpha and TNFalpha. Release of defensins by keratocytes in response to cytokines elaborated in corneal inflammation may contribute to the host defense response in microbial keratitis.

Cataracts. Lifting the clouds on an age-old problem

Cataracts are the most common treatable form of reduced vision in older adults. Although the incidence of cataracts is high after age 65, careful history taking and clinical examination are essential to establish the diagnosis. Cataract surgery is medically indicated when the view to the retina is obscured or lens-induced disorders place the eye at risk for further damage. However, even when patients have no specific associated medical problem, other than decreased visual acuity, cataract extraction offers an important means for maintaining independence and improving quality of life.

Refractive and keratometric results after the triple procedure: experience with early and late suture removal

OBJECTIVE

The objective of this study was to determine the outcome of early and late suture removal after the triple procedure (i.e., penetrating keratoplasty, cataract extraction, lens implant).

DESIGN AND PARTICIPANTS

The refractive and keratometric results of 106 eyes undergoing the triple procedure were reviewed. The target postoperative refractive error was -1 diopter (D).

RESULTS

Average length of follow-up was 40.3 months. Twenty eyes had sutures removed early (<18 months after surgery), 39 had sutures removed late (> or = 18 months after surgery), and 47 had sutures still intact at last follow-up. A best spectacle-corrected visual acuity of 20/40 or better was achieved in 90% of eyes with sutures removed early, 82.1% with sutures removed late, and 70.2% with sutures in place. For all eyes, the mean spherical equivalent at last follow-up was -2.50 D, with 75% of eyes falling between -4 and +2 D. The mean final refractive error was -3.40 +/- 3.53 D for eyes with sutures removed early and -1.79 +/- 3.99 D for eyes with sutures removed late. Eyes with sutures remaining had a mean final refractive error of -0.33 +/- 2.25 D. There was an overall decrease in refractive and keratometric astigmatism after both early and late suture removal with no significant difference between groups. However, there was a wide range of change with some eyes experiencing a decrease and others an increase in astigmatism. Mean postoperative K readings increased significantly for both groups after suture removal (final mean K, 47.00 D) but remained stable for eyes with sutures in.

CONCLUSION

The authors data suggest that the final refractive error and net change in refractive and keratometric astigmatism after the triple procedure are not dependent on the timing of suture removal.

Prospective, randomized vector analysis of astigmatism after three-, one-, and no-suture phacoemulsification

PURPOSE

To compare surgically induced astigmatism and visual outcomes after three-, one-, and no-suture phacoemulsification.

SETTING

Johns Hopkins Hospital, Baltimore, Maryland and Manhattan Eye, Ear, and Throat Hospital, New York, New York, USA.

METHODS

This prospective, randomized study followed 131 patients treated with phacoemulsification with a 5.5 mm self-sealing scleral tunnel and implantation of a 5.5 mm poly(methyl methacrylate) posterior chamber lens. Radial 10-0 nylon sutures were used in the three- and one-suture groups.

RESULTS

Mean astigmatism was greatest in the first postoperative week in all groups and stabilized after 8 weeks. The percentage of patients with with-the-rule (WTR) astigmatism increased from baseline in the one- and three-suture groups and decreased in the sutureless group. Mean uncorrected Snellen acuity was significantly better in the no- and one-suture groups than in the three-suture group at 1 week. There were no significant differences in uncorrected acuity at other times. No statistically significant differences in the surgically induced spherical equivalent were noted among the three groups during the 1 year follow-up. There was significantly less surgically induced keratometric astigmatism in the one-suture group at 4 (P = .03) and 8 (P = .007) weeks postoperatively. At all follow-ups, the sutureless group had the greatest proportion of patients, with significant ATR astigmatic shift (1 week, 17%; 4 weeks, 32%); and the lowest proportion of patients with significant WTR astigmatic shift (10% after 1 week). At 4 weeks, the percentage of patients with significant WTR shift in the one-suture group dropped to that in the sutureless group (10%); however, those in the one-suture group had less ATR astigmatic shift (16%).

CONCLUSION

Sutureless and one-suture surgery resulted in a low percentage of WTR induced astigmatism 4 weeks postoperatively. Compared with sutureless surgery, the one-suture surgery resulted in less ATR shift.