Naturally occurring vitreous chamber-based myopia in the Labrador retriever.
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PURPOSE: To investigate whether myopia is present in a breed of domestic dog, the Labrador retriever, and how the ocular components are related to refractive error in this breed. METHODS: Cycloplegic refractive error was measured in 75 Labrador retrievers by retinoscopy. Corneal and crystalline lens radii of curvature were measured in the right eyes of 57 of these dogs using a video-based keratophakometer, with axial ocular dimensions measured using A-scan ultrasonography. RESULTS: Of the 75 dogs tested, 11 (14.7%) were myopic by at least -0.50 D in one eye, and 6 (8.0%) were myopic in both eyes (full range of refractive errors, +3.50 D to -5.00 D). Of the 57 dogs with ocular component measurements, seven (12.3%) were myopic by at least -0.50 D in the right eye. There was a significant negative correlation between refractive error and vitreous chamber depth (Spearman r = -0.42; P < 0.001). Myopic eyes had an elongated vitreous chamber depth (10.87+/-0.34 mm for myopic dogs, 10.02+/-0.40 mm for nonmyopic dogs; P < 0.0001, Kruskal-Wallis test). There was also a significant quadratic association between lens thickness and vitreous chamber depth (P < 0.005; R2 = 0. 11), indicating that thinner lenses occurred at both shorter and longer vitreous chamber depths. CONCLUSIONS: Myopia in the Labrador retriever is analogous to human myopia in that it is caused by an elongated vitreous chamber. Thinner crystalline lenses found at longer vitreous chamber depths may be analogous to lens thinning documented in human ocular development. The Labrador retriever warrants investigation as a potential model of myopia that is naturally occurring rather than experimentally induced. (+info)
A new video pachometer.
(50/5105)
PURPOSE: Many studies of the cornea would benefit from a simple, objective method to measure corneal thickness. In this study, a new optical pachometer based on video and computer technology was designed and tested. METHODS: The slit beam of a photographic slit lamp was monitored with a video camera through one half of the biomicroscope. When the slit was properly aligned with the cornea, the operator triggered a flash, and one video frame that included the flash was captured. A custom software package detected epithelial and endothelial edges. Corneal thickness was calculated from the median corneal image width and image widths from similar measurements of contact lenses with known thicknesses. Corneal thickness was measured in 25 subjects by using this new instrument and was compared to thickness measured by using a conventional Haag-Streit pachometer. RESULTS: Corneal thickness in the 25 subjects measured on the new instrument was 512+/-20 microm and 515-/+21 microm in the right and left eyes, respectively (mean+/-SD). Thickness of the same corneas measured on the Haag-Streit pachometer was 530+/-22 microm and 534+/-20 microm in right and left eyes, respectively. The average SD of 10 consecutive measurements was 6.6 microm and 6.7 microm on the video and Haag-Streit pachometers, respectively (n = 50 corneas). CONCLUSIONS: The video pachometer provides a fast, objective means of measuring corneal thickness. It is simple to use and provides precision equal to that of the Haag-Streit pachometer. (+info)
Contact lens-induced infection--a new model of Candida albicans keratitis.
(51/5105)
PURPOSE: A model of experimental keratomycosis was established that mimics human disease in which the only fungi present are those that are actively growing within the cornea. METHODS: Dutch-belted rabbits received a subconjunctival injection of triamcinolone acetonide to one eye. One day later the epithelium was removed from the central cornea and a standardized inoculum of Candida albicans blastoconidia was placed on the corneal surface and covered with a contact lens. The lids were closed with a lateral tarsorrhaphy. After 24 hours, the lid sutures and contact lens were removed. Five days later the animals were killed, and their corneas were subjected to separate isolate recovery and histology studies. A group of similarly infected rabbits without corticosteroid injection served as controls. RESULTS: Both groups developed invasive corneal disease. Although isolate recovery was not significantly different from corticosteroid-treated rabbits compared with controls, fungal biomass was increased. Hyphal invasion was limited to the anterior cornea in control eyes, but penetrated deep stroma in most of the corticosteroid-treated rabbits. CONCLUSIONS: Invasive corneal disease can be established with a surface inoculum. Corticosteroid administration increased corneal penetration of hyphae. Quantitative isolate recovery is not a reliable measure of the fungal load within the cornea. (+info)
Intraocular lenses in children: changes in axial length, corneal curvature, and refraction.
(52/5105)
AIM: To assess changes in axial length, corneal curvature, and refraction in paediatric pseudophakia. METHODS: 35 eyes of 24 patients with congenital or developmental lens opacities underwent extracapsular cataract extraction and posterior chamber intraocular lens implantation. Serial measurements were made of axial length, corneal curvature, objective refraction, and visual acuity. RESULTS: For patients with congenital cataracts (onset < 1 year age) the mean age at surgery was 24 weeks. Over the mean follow up period of 2.7 years, the mean increase in axial length of 3.41 mm was not significantly different from the value of an expected mean growth of 3.44 mm (paired t test, p = 0.97) after correction for gestational age. In the developmental cataract group (onset > 1 year of age) the mean age at surgery was 6.4 years with a mean follow up of 2.86 years. This group showed a mean growth in axial length of 0.36 mm that was not significantly different from an expected value of 0.47 mm (paired t test, p = 0.63). The mean preoperative keratometry was 47.78 D in the congenital group and 44.35 D in the developmental group. At final follow up the mean keratometry in the congenital group was 46.15 D and in the developmental group it was 43.63 D. In eyes followed for at least 2 years, there was an observed myopic shift by 24 months postoperatively of 3.26 D in the congenital cases (n = 10) and 0.96 D in the developmental cases (n = 18). CONCLUSION: The pattern of axial elongation and corneal flattening was similar in the congenital and developmental groups to that observed in normal eyes. No significant retardation or acceleration of axial growth was found in the eyes implanted with IOLs compared with normal eyes. A myopic shift was seen particularly in eyes operated on at 4-8 weeks of age and it is recommended that these eyes are made 6 D hypermetropic initially with the residual refractive error being corrected with spectacles. (+info)
The bovine mimecan gene. Molecular cloning and characterization of two major RNA transcripts generated by alternative use of two splice acceptor sites in the third exon.
(53/5105)
Mimecan is a proteoglycan expressed by many connective tissues. It was originally isolated in a truncated form as a bone-associated glycoprotein, osteoglycin, and was considered an osteoinductive factor. Recently, we demonstrated that the full-length translation product of the cDNA encoding mimecan is a corneal keratan sulfate proteoglycan present in other tissues without keratan sulfate chains. We also described multiple mimecan mRNA transcripts generated by differential splicing and alternative polyadenylation. In this study, we isolated genomic clones and determined the genomic organization of the bovine mimecan gene. The gene is spread over >33 kilobases of continuous DNA sequence and contains eight exons. The newly discovered first exon, identified by 5'-rapid amplification of cDNA ends, consists of a 5'-untranslated region and is enriched in C+G nucleotides. Two transcription initiation sites starting at the first and at the second exons were determined by primer extension. Molecular characterization shows that alternatively spliced RNA isoforms are generated by the use of two distinct splice acceptor sites in the third exon situated 278 base pairs apart. We determined a partial genomic structure of the human mimecan gene and demonstrated two alternatively spliced RNA transcripts that are generated likewise. Despite the diversity of mimecan transcripts, the primary structure of the core protein is encoded from exons 3 to 8 and remains unchanged, indicating its functional importance. Using ribonuclease protection assay, we analyzed the patterns of spliced RNA expressed in cultured bovine keratocytes. We demonstrated that their expression is differentially modulated in a temporal manner by basic fibroblast growth factor. (+info)
Inhibition of fibroblast-like cell proliferation by interleukin-1 blockers, CK-119 and CK-122.
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AIM: To study potent and nontoxic agents to inhibit fibroblast proliferation. METHODS: Fibroblast-like corneal and conjunctival cells were cultured and inhibited by interleukin-1 (IL-1) blockers, dihydropyridazino-pyridazines CK-119 and CK-122. The cell growth and syntheses of DNA, RNA, and protein after IL-1 blocker incubation were determined. RESULTS: CK-119 and CK-122 inhibited cell growth of corneal fibroblast at 30 mg.L-1. DNA and RNA syntheses in corneal fibroblasts were markedly inhibited by CK-119 and CK-122 whereas protein synthesis was either unaffected or mostly enhanced at 30-100 mg.L-1 and 100-300 mg.L-1, respectively. Similar results were obtained in conjunctival cell cultures by CK-119 and CK-122 at 3-10 mg.L-1 and 30-100 mg.L-1, respectively. CONCLUSION: CK-119 and CK-122 are potent IL-1 blockers to inhibit cell growth of fibroblast-like corneal and conjunctival cells mainly through the inhibition of DNA and RNA syntheses but not protein synthesis. (+info)
Conditional expression of the ErbB2 oncogene elicits reversible hyperplasia in stratified epithelia and up-regulation of TGFalpha expression in transgenic mice.
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The ErbB2 receptor tyrosine kinase (RTK) is expressed in basal cells of squamous epithelia and the outer root sheath of hair follicles. We previously showed that constitutive expression of activated ErbB2 directed to these sites in the skin by the keratin 14 (K14) promoter produces prominent hair follicle abnormalities and striking skin hyperplasia in transgenic mice. However, perinatal lethality precluded the establishment of a transgenic line for analysis of ErbB2 function in adult animals. To investigate the significance of ErbB2 signaling in epithelial tissues during and post development, we developed a K14-rtTA/TetRE-ErbB2 'Tet-On' bitransgenic mouse system. These mice were normal until the ErbB2 transgene was induced by exposure to doxycycline (Dox). Prenatal induction resulted in perinatal death. Postnatally, ErbB2 transgene expression was observed at 4 h after the initiation of Dox, and reached a plateau at 24 h. Skin hyperplasia followed after 2 days and these changes reverted to normal upon Dox withdrawal. In adults, as in the neonates, prolonged ErbB2 induction caused prominent skin and hair follicle hyperplasias. Severe hyperplasias in the cornea, eye lids, tongue and esophagus were also observed. ErbB2 transgene induction was accompanied by increased expression of TGFalpha, a ligand of epidermal growth factor receptor (EGFR), and to a lesser extent, EGFR, further enhancing RTK signal transduction. We conclude that ErbB2 plays important roles in both development and maintenance of hair follicles and diverse squamous epithelia and that this ligand-inducible and tissue-specific 'Tet-On' transgenic mouse system provides a means to study transgenes with perinatal toxicity. (+info)
Evaluation of corneal thickness and topography in normal eyes using the Orbscan corneal topography system.
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AIMS: To map the thickness, elevation (anterior and posterior corneal surface), and axial curvature of the cornea in normal eyes with the Orbscan corneal topography system. METHODS: 94 eyes of 51 normal subjects were investigated using the Orbscan corneal topography system. The anterior and posterior corneal elevation maps were classified into regular ridge, irregular ridge, incomplete ridge, island, and unclassified patterns, and the axial power maps were grouped into round, oval, symmetric bow tie, asymmetric bow tie, and irregular patterns. The pachymetry patterns were designated as round, oval, decentred round, and decentred oval. RESULTS: The thinnest point on the cornea was located at an average of 0.90 (SD 0. 51) mm from visual axis and had an average thickness of 0.55 (0.03) mm. In 69.57% of eyes, this point was located in the inferotemporal quadrant, followed by the superotemporal quadrant in 23.91%, the inferonasal quadrant in 4.35%, and the superonasal quadrant in 2.17%. Among the nine regions of the cornea evaluated (central, superotemporal, temporal, inferotemporal, inferior, inferonasal, nasal, superonasal, and superior) the central cornea had the lowest average thickness (0.56 (0.03) mm) and the superior cornea had the greatest average thickness (0.64 (0.03) mm). The mean simulated keratometry (SimK) was 44.24 (1.61)/43.31 (1.66) dioptres (D) and the mean astigmatism was 0.90 (0.41) D. Island (71.74%) was the most common elevation pattern observed in the anterior corneal surface, followed by incomplete ridge (19.57%), regular ridge (4.34%), irregular ridge (2.17%), and unclassified (2.17%). Island (32.61%) was the most common topographic pattern in the posterior corneal surface, following by regular ridge (30.43%), incomplete ridge (23. 91%), and irregular ridge (13.04%) patterns. Symmetric bow tie was the most common axial power pattern in the anterior cornea (39.13%), followed by oval (26.07%), asymmetric bow tie (23.91%), round (6. 52%), and irregular (4.53%) patterns. In the pachymetry maps, 47.83% of eyes had an oval pattern, and round, decentred oval, and decentred round were observed in 41.30%, 8.70%, and 2.18% of eyes, respectively. CONCLUSION: The information on regional corneal thickness, corneal elevation and axial corneal curvature obtained with the Orbscan corneal topography system from normal eyes provides a reference for comparison with diseased corneas. The Orbscan corneal topography system is a useful tool to evaluate both corneal topography and corneal thickness. (+info)