Fung-Rong Hu

The cornea in young myopic adults.

AIMS To further understand the effect of refractive error on the corneal dimensions and function. METHODS Corneal curvature, corneal thickness, and axial length measurements were performed, as well as specular microscopy and fluorophotometry, on patients with various refractive statuses. 216 subjects, mean age 22.2 (SD 4.2) years, were examined. Patients with previous contact lens wear history, external eye diseases, as well as previous ocular surgeries, were excluded. RESULTS The corneas were flatter in eyes with longer axial length (r = −0.22, p = 0.003). Eyes with more myopic spherical equivalent had longer axial length (r = −0.90, p <0.001) as well as less corneal endothelial density (r = 0.20, p = 0.037). Corneal endothelial density decreased in eyes with longer axial length (r = 0.24, p = 0.019); however, it correlated neither with corneal thickness (r= −0.06, p = 0.59) nor with corneal curvature (r = −0.07, p = 0.52). The corneas had a mean corneal thickness of 533 (SD 29) μm and were thinner in more myopic eyes (r = 0.16, p = 0.021). The corneas tended to be thinner in eyes with longer axial length. However, the correlation did not reach statistical significance (r = −0.11, p = 0.14). Besides, there was no significant correlation between the corneal thickness and the corneal curvature (r = −0.13, p = 0.093) and the endothelial permeability (r = 0.042, p = 0.69). The corneas with higher endothelial density had larger corneal transfer coefficient (r = 0.26, p = 0.024) and higher permeability to fluorescein molecules (r = 0.28, p = 0.014). Nevertheless, the corneal endothelial permeability did not correlate significantly with either the axial length (r = −0.18, p = 0.11) or the degree of myopia (r = 0.12, p = 0.26). CONCLUSION Changes in the anterior segments as the eyeball elongates in myopia progression included flatter corneal curvature, decreased corneal thickness, as well as decreased endothelial density. These factors should be considered in refractive surgery.

Quality of vision after laser in situ keratomileusis Influence of dioptric correction and pupil size on visual function

Purpose: To determine the influence of pupil size and the amount of ablation on visual performance and on the patients perception of glare or halo after laser in situ keratomileusis (LASIK). Setting: Department of Ophthalmology, National Taiwan University Hospital, Taipei, Taiwan. Methods: This study included a random cross‐section of 50 eyes of 32 patients with “uniform” topography at least 6 months after LASIK and 51 eyes of 28 patients who had normal corneas. Each LASIK patient completed a survey rating adverse effects such as symptoms of night glare and halo. Pupil diameter and best spectacle‐corrected visual acuity (BSCVA) were measured under photopic and scotopic conditions. Contrast sensitivity was measured with an MCT 8000 (Vistech Consultants, Inc.) under daytime and nighttime and with night glare conditions. A Technomed C‐scan (Technomed Technology) was performed, and the potential corneal visual acuity (PCVA) was calculated after the settings for the pupil size were changed to the values measured under bright‐light or dim‐light conditions. Results: No significant difference was found between the post‐LASIK and normal cornea groups in photopic or scotopic BSCVA (P>.05). In cases of moderate myopia, the post‐LASIK group had decreased PCVA and contrast sensitivity (P<.05). In cases of high myopia, the post‐LASIK group had decreased contrast sensitivity at spatial frequencies of 1.5 cycles per degree (cpd) under daytime conditions and 3 cpd under nighttime conditions (P<.05). Glare or halo symptoms did not correlate with scotopic BSCVA, PCVA, or nighttime contrast sensitivity with or without glare (P>.05). Pupil size was not significantly correlated with glare or halo symptoms, BSCVA, or contrast sensitivity under scotopic or photopic conditions (P>.05). In moderate myopia, the amount of attempted correction of the spherical equivalent (SE) was correlated with halo symptoms (P<.05; adjusted r2 = 0.17). In high myopia, the amount of attempted astigmatism correction was correlated with the development of glare symptoms (P<.05; adjusted r2 = 0.16). Conclusions: There was a decrease in contrast sensitivity in post‐LASIK eyes. The amount of attempted correction of the SE or astigmatism was correlated with the development of glare and halo symptoms. Pupil size was not significantly correlated with glare or halo symptoms, BSCVA, or contrast sensitivity in post‐LASIK patients with “uniform” topography who had scotopic pupils not larger than 7.0 mm.

Subconjunctival Injection of Bevacizumab (Avastin) on Corneal Neovascularization in Different Rabbit Models of Corneal Angiogenesis

PURPOSE Bevacizumab is a potent recombinant humanized monoclonal antibody directed against vascular endothelial growth factor (VEGF). The purpose of this study was to evaluate the therapeutic effect of subconjunctival injection of bevacizumab on corneal neovascularization (NV) in different rabbit models. METHODS Several rabbit models of corneal NV were used, including (1) a corneal micropocket assay with VEGF pellet, (2) a corneal micropocket assay with basic fibroblast growth factor (b-FGF) pellets, (3) mechanical limbal injury-induced corneal NV, and (4) an alkali-induced model of corneal NV. Subconjunctival injections of bevacizumab (0.25-2.5 mg) were applied twice per week for 2 to 8 weeks. Digital photographs of the cornea were analyzed to determine the length of corneal NV and the area of cornea covered by NV as a percentage of the total corneal area. Immunohistochemical staining with anti-human IgG antibody labeled with Cy3 was used to determine the detection of intracorneal distribution of bevacizumab after injection. RESULTS Subconjunctival injection of bevacizumab caused significant inhibition of corneal NV formation as measured by length or surface area in all animal models (P<0.05). No significant ocular complications were found. Staining of bevacizumab was found in the corneal stroma for 3 to at least 14 days in the different rabbit models. CONCLUSIONS Subconjunctival injection of bevacizumab is effective in inhibiting corneal NV in several rabbit models. Bevacizumab may diffuse into the corneal stroma and persist for a few days after injection. It may be useful in preventing corneal NV in the acute phase of various kinds of corneal inflammation.

Netrin-1 Simultaneously Suppresses Corneal Inflammation and Neovascularization

PURPOSE To investigate the effect of netrin-1 on alkali burn-induced corneal inflammation and neovascularization. METHODS The expression of netrin-1 and its receptors UNC5A, UNC5B, UNC5C, UNC5D, adenosine 2b receptor (A2BAR), deleted in colorectal cancer (DCC), and neogenin in normal and alkali-burned rat cornea were determined by RT-PCR and/or Western blot analysis, or immunostaining. Topical netrin-1 protein was applied to treat rat corneal alkali-burn injury for 14 consecutive days, started right after the injury or 10 days postinjury. Corneal inflammation and neovascularization were observed under slit lamp microscope. The apoptosis of corneal cells was determined by terminal deoxynucleotidyl transferase-mediated nick end labeling assay. Corneal inflammatory cell infiltration was evaluated by immunostaining of anti-PMN and anti-ED1 antibodies. The expression of epidermal growth factor (EGF), vascular epidermal growth factor (VEGF), and pigment epithelium-derived factor (PEDF) in rat cornea was determined by Western blot analysis. RESULTS Netrin-1 and its receptor UNC5B were expressed in normal rat corneal epithelium and stromal cells, and their expression decreased after corneal alkali burn. Exogenous netrin-1 administered on rat ocular surfaces resolved alkali burn-induced corneal inflammation, and also suppressed corneal neovascularization. Furthermore, netrin-1 could reverse neovascularization in alkali-burned cornea. The authors found that netrin-1 executed the functions through various mechanisms, including upregulating EGF expression, accelerating epithelial wound healing, inhibiting neutrophil and macrophage infiltration, reducing corneal cell apoptosis, and restoring the equilibrium of VEGF and PEDF in the wounded cornea. CONCLUSIONS Netrin-1 could dampen inflammation, inhibit, and reverse neovascularization in alkali-burned cornea.

Overnight orthokeratology-associated microbial keratitis.

Purpose: This study was designed to report the clinical aspects, microbiologic findings, and treatment outcomes of overnight orthokeratology-associated microbial keratitis. Methods: Medical records of patients with overnight orthokeratology-associated microbial keratitis at National Taiwan University Hospital from August 2000 to October 2001were reviewed. The clinical and microbiologic characteristics and treatment outcomes were investigated. Results: Nine patients (in total 10 eyes) from aged 8 to 17 (mean, 12.3 ± 2.9) years were included in this study. Eight patients had a unilateral infection and one had a bilateral infection. The initial best corrected visual acuities ranged from hand motion to 20/20. The lesions were located at the central cornea in nine eyes (90%). Smears and cultures from corneal scrapings were obtained from all patients. Four eyes were culture-positive, which included nonfermentative Gram-negative bacillus, Pseudomonas aeruginosa and Acanthamoeba. Positive smears from another two eyes revealed Gram-negative bacilli and double-walled cyst. All patients were cured using antimicrobial medications with complete re-epithelization and disappearance of corneal infiltrates. Four eyes had a final best corrected visual acuity of 20/30 or worse after a mean follow-up of 9.4 months, including one eye that had visual acuity of hand motion only. Complications included corneal opacity in all eyes, glaucoma in one eye, and cataract in one eye. Conclusions: Overnight orthokeratology is an important risk factor of microbial keratitis, especially in school children. Acanthamoeba and Gram-negative bacilli, especially Pseudomonas aeruginosa, are the most common pathogens in our series. The risk of microbial keratitis after overnight orthokeratology should not be overlooked.

Comparison of the Bacteriostatic Effects, Corneal Cytotoxicity, and the Ability to Seal Corneal Incisions among Three Different Tissue Adhesives

Purpose: To compare the bacteriostatic effects, corneal cytotoxicity, and ability to seal corneal incisions among fibrin glue and 2 commercially available cyanoacrylate derivatives: N-butyl cyanoacrylate and methoxypropyl cyanoacrylate. Methods: The bacteriostatic activities of these tissue glues were verified by measuring the zones of bacterial growth inhibition surrounding the adhesive droplets on agar plates inoculated with Staphylococcus aureus, Streptococcus pneumoniae, Pseudomonas aeruginosa, Escherichia coli, or Mycobacterium chelonae. Corneal cytotoxicity was tested by a direct contact method by using cultured bovine corneal epithelial cells, keratocytes, and corneal endothelial cells challenged with droplets of adhesives. Each of the cells was treated with droplets of adhesives. The ability to seal corneal incisions was verified by calculating the maximum intraocular pressure resistant to leakage of rabbit corneal stab wounds sealed with tissue adhesives. Results: Methoxypropyl cyanoacrylate and N-butyl cyanoacrylate showed bacteriostatic effects against S. aureus, S. pneumoniae, and M. chelonae but not P. aeruginosa and E. coli. In contrast, fibrin glue had no such effects against either Gram-positive or -negative bacteria (P < 0.01). Methoxypropyl cyanoacrylate showed the highest levels of corneal cytotoxicity, followed by N-butyl cyanoacrylate. Fibrin glue, however, showed minimal cytotoxicity (P < 0.01). Methoxypropyl cyanoacrylate and N-butyl cyanoacrylate also displayed a greater ability to seal corneal incisions than that of fibrin glue (P < 0.01). Conclusions: The bacteriostatic effects, corneal cytotoxicity, and ability to seal corneal incisions differed among the 3 compounds tested. These different properties should be considered when choosing tissue adhesives during corneal surgery.

Changes in corneal autofluorescence and corneal epithelial barrier function with aging.

Corneal epithelial permeability studies using fluorophotometers were performed on 90 eyes of 51 normal subjects. After recording the autofluorescence of the cornea (AFC) and of the lens (AFL), we applied 20 µl of 2% sodium fluorescein to the conjunctival sac. The corneal fluorescence 45 min later (F45), which paralleled the corneal epithelial permeability to fluorescein, was measured by fluorophotometer and analyzed. All parameters of the two eyes of each subject correlated well with each other. There was positive correlation between AFL and patient age and between AFC and patient age (r=0.78, p<0.001, and r=0.74, p<0.001, respectively). The F45 increased exponentially with advancing age ( r= 0.67, p<0.001). The strong correlation between AFC and AFL in each eye (r=0.79, p<0.001) indicated corresponding aging processes in both the cornea and the lens. The increase in epithelial permeability with age possibly represents a subclinical breakdown of barrier function, rendering the corneas more vulnerable to insults.

Genetic analysis of 14 families with Schnyder crystalline corneal dystrophy reveals clues to UBIAD1 protein function

Schnyder crystalline corneal dystrophy (SCCD) is a rare autosomal dominant disease characterized by progressive corneal opacification resulting from abnormal deposition of cholesterol and phospholipids. Recently, six different mutations on the UBIAD1 gene on chromosome 1p36 were found to result in SCCD. The purpose of this article is to further characterize the mutation spectrum of SCCD and identify structural and functional consequences for UBIAD1 protein activity. DNA sequencing was performed on samples from 36 individuals from 14 SCCD families. One affected individual was African American and SCCD has not been previously reported in this ethnic group. We identified UBIAD1 mutations in all 14 families which had 30 affected and 6 unaffected individuals. Eight different UBIAD1 mutations, 5 novel (L121F, D118G, and S171P in exon 1, G186R and D236E in exon 2) were identified. In four families with DNA samples from both affected and unaffected individuals, the D118G, G186R, T175I, and G177R mutations cosegregated with SCCD. In combination with our previous report, we have identified the genetic mutation in UBIAD1 in 20 unrelated families with 10 (including 5 reported here), having the N102S mutation. The results suggest that N102S may be a mutation hot spot because the affected families were unrelated including Caucasian and Asian individuals. There was no genotype phenotype correlation except for the T175I mutation which demonstrated prominent diffuse corneal haze, typically without corneal crystals. Protein analysis revealed structural and functional implications of SCCD mutations which may affect UBIAD1 function, ligand binding and interaction with binding partners, like apo E.

In-Vitro Effects of Dexamethasone on Cellular Proliferation, Apoptosis, and Na+-K+-ATPase Activity of Bovine Corneal Endothelial Cells

Purpose: To assess the in-vitro effects of dexamethasone (DEX) on the proliferation, apoptosis, and Na+-K+-ATPase activity of bovine corneal endothelial cells. Methods: Bovine corneal endothelial cells were cultured with DEX ranging from 10−10 to 10−3 M. The effect of DEX on the proliferation was analyzed by 3-(4,5-dimethylthiazol-2-yl)-5-(3-carboxy-methoxyphenyl)-2-(4-sulfophenyl)-2H-tetrazolium inner salt (MTS) assay. Apoptosis and necrosis were detected by staining with fluorescein-conjugated annexin V and propidium iodide, followed by flow cytometry. The effect of DEX on Na+-K+-ATPase activity was evaluated using non-isotopic methods. Results: DEX did not affect cellular proliferation or induce apoptosis/necrosis from 10−10 to 10−5 M. At 10−4 and 10−3 M, DEX significantly decreased proliferation and increased apoptosis and/or necrosis. DEX significantly increased the Na+-K+-ATPase activity from 10−8 to 10−6 M, with the maximal effect at 10−6 M (p < 0.01); this effect was inhibited by RU38486, an antiglucocorticoid molecule. Conclusions: Bovine corneal endothelial cells express glucocorticoid receptor (GR) mRNA and protein. DEX decreases cell proliferation and induces cellular apoptosis and/or necrosis at high concentrations. DEX also increases the Na+-K+-ATPase activity at certain concentrations.

The Effect of Topical Autologous Serum on Graft Re-epithelialization After Penetrating Keratoplasty

PURPOSE To analyze factors influencing corneal graft re-epithelialization after penetrating keratoplasty (PK) and evaluate the effect of topical autologous serum in promoting graft re-epithelialization. DESIGN Prospective interventional study. METHODS We analyzed 165 eyes of 165 patients who underwent PK between January 1, 2005 and December 31, 2007. Patients were divided into 2 groups according to routine use or non-use of postoperative 20% topical autologous serum. Postoperative slit-lamp examination after fluorescein staining was performed, and graft re-epithelialization time was recorded. Recipient/donor characteristics, surgical variables, and topical use of autologous serum were analyzed for their effects on post-PK graft re-epithelialization. Statistical analysis was performed by univariate and multivariate regression analysis using the ordinal logistic fit model to assess the potential risk factors influencing graft re-epithelialization after PK. RESULTS In univariate analysis, diabetes mellitus (DM), longer death-to-storage time and death-to-surgery time of the donor, and larger recipient size significantly delayed graft re-epithelialization (P < .05). Use of autologous serum significantly expedited graft re-epithelialization (P = .004). In multiple regression analysis, only DM in the recipient (odds ratio [OR] = 5.10, P < .001), postoperative use of autologous serum (OR = 0.54, P = .046), and larger graft size (OR = 4.44, P < .001) influenced graft re-epithelialization. The beneficial and healing effect of autologous serum is particularly significant in diabetic recipients and larger grafts. CONCLUSIONS Several factors may influence graft re-epithelialization after PK. Graft re-epithelialization time was longer in diabetic recipients and larger grafts. Use of autologous serum may be a beneficial strategy in these patients with potentially delayed epithelial healing.