A new method of detecting changes in corneal health in response to toxic insults (original) (raw)
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Fibril density reduction in keratoconic corneas
Journal of The Royal Society Interface, 2021
This study aims to estimate the reduction in collagen fibril density within the central 6 mm radius of keratoconic corneas through the processing of microstructure and videokeratography data. Collagen fibril distribution maps and topography maps were obtained for seven keratoconic and six healthy corneas, and topographic features were assessed to detect and calculate the area of the cone in each keratoconic eye. The reduction in collagen fibril density within the cone area was estimated with reference to the same region in the characteristic collagen fibril maps of healthy corneas. Together with minimum thickness and mean central corneal refractive power, the cone area was correlated with the reduction in the cone collagen fibrils. For the corneas considered, the mean area of keratoconic cones was 3.30 ± 1.90 mm 2 . Compared with healthy corneas, fibril density in the cones of keratoconic corneas was lower by as much as 35%, and the mean reduction was 17 ± 10%. A linear approximatio...
Investigative Opthalmology & Visual Science, 2003
The size and organization of stromal collagen fibrils influence the biomechanical and optical properties of the cornea and hence its function. How fibrillar structure varies with position across the cornea has not been fully characterized. The present study was designed to quantify the collagen fibril spacing and diameter across the normal human cornea and to relate this to the properties of the tissue. METHODS. Small-angle x-ray diffraction was used to map in detail the variation in fibril spacing and fibril diameter along orthogonal medial-lateral and inferior-superior meridians of five normal human corneoscleral discs. RESULTS. Mean fibril diameters remained constant across all corneas up to the limbus, whereupon a sharp increase was observed. However, mean fibril spacing across the central 4 ϫ 3 mm (prepupillary) cornea measured 5% to 7% lower than in the peripheral cornea. CONCLUSIONS. Collagen fibrils in the prepupillary cornea appear to be more closely packed than in the peripheral cornea. Anisotropy in fibril packing across the cornea has potential implications for the transparency and refractive index of the tissue. Biomechanically, it is possible that the higher packing density of stress-bearing collagen fibrils in the prepupillary cornea is necessary for maintaining corneal strength, and hence curvature, in a region of reduced tissue thickness. By inference, these results could have important implications for the development of corneal models for refractive surgery.
Quantification of Collagen Organization in the Peripheral Human Cornea at Micron-Scale Resolution
Biophysical Journal, 2011
The collagen microstructure of the peripheral cornea is important in stabilizing corneal curvature and refractive status. However, the manner in which the predominantly orthogonal collagen fibrils of the central cornea integrate with the circumferential limbal collagen is unknown. We used microfocus wide-angle x-ray scattering to quantify the relative proportion and orientation of collagen fibrils over the human corneolimbal interface at intervals of 50 mm. Orthogonal fibrils changed direction 1-1.5 mm before the limbus to integrate with the circumferential limbal fibrils. Outside the central 6 mm, additional preferentially aligned collagen was found to reinforce the cornea and limbus. The manner of integration and degree of reinforcement varied significantly depending on the direction along which the limbus was approached. We also employed small-angle x-ray scattering to measure the average collagen fibril diameter from central cornea to limbus at 0.5 mm intervals. Fibril diameter was constant across the central 6 mm. More peripherally, fibril diameter increased, indicative of a merging of corneal and scleral collagen. The point of increase varied with direction, consistent with a scheme in which the oblique corneal periphery is reinforced by chords of scleral collagen. The results have implications for the cornea's biomechanical response to ocular surgeries involving peripheral incision.
Micron, 2005
Aim: To assess the impact of measurements of different numbers of small collagen fibrils at different final magnification values on the resultant mean values for fibril diameter (FD). Methods: Very high magnification (33,000!) electron micrographs were taken of the posterior-central zone of the corneal stroma from young adult rabbits (2 kg), printed at 46,000 or 50,000!, scanned at 400 d.p.i. and 35 mm slides prepared. These were projected to give final magnifications between 150,000! and 450,000!. An overlay of fibril outlines was prepared from the projected images and the fibril diameters (FD's) measured to within 0.5 mm. Results: On the overlays, at different projection magnifications, the average FD's ranged from 4 to 13.5 mm to allow measures to be made at a real resolution of between 3.5 and 1 nm. Using a fixed sized region of interest (ROI) on the overlays, the average values of FD's ranged between 24.9 and 31.7 nm, and could vary (for any particular micrograph) by up to 3.6 nm according to the number of FD's measured (nZ 34-384/ROI). Using a fixed number of FD measures (nZ100) at different projection magnifications yielded average FD values from different corneas of between 25.1 and 35.2 nm, which could vary by up to 4.3 nm depending on the magnification used. Conclusions: The results indicate that different average values for measures of fibril diameter of small collagen fibrils can easily be obtained according to the final magnification used and the number of fibrils measured, and that the overall averages can depend on whether the data sets are averaged or pooled. These aspects of the morphometry of small collagen fibrils therefore need to be carefully specified.
Comparative study of fibrillar collagen arrangement in the corneas of primates and other mammals
The Anatomical …, 2007
This study is a comparative study of the relationship between corneal structure, morphology, and function in a range of mammalian species. Xray scattering patterns were gathered at regular spatial intervals over the excised cornea (and in most cases also the scleral rim) of humans, marmosets, horses, cows, pigs, rabbits, and mice. All patterns were analyzed to produce quantitative information regarding the predominant orientation of fibrillar collagen throughout the tissue. The predominant direction of corneal collagen varies between mammals. This variation is not related to the size, shape, or thickness of the cornea or the frequency with which the animal blinks. A relationship does, however, appear to exist between corneal collagen arrangement and visual acuity. An excess of collagen directed toward one or both sets of opposing rectus muscles is a feature of animals that have an intermediate to high level of visual acuity. There is a significant variation in the arrangement of corneal collagen between different mammalian species. This finding may be related to differences in the frequency of action and the forces generated by the various extraocular muscles during eye movement and image fixation. Anat Rec, 290:1542Rec, 290: -1550Rec, 290: , 2007Rec, 290: . 2007 Wiley-Liss, Inc.
The Effect of Collagen Shields on Rabbit Corneal Reepithelialization After Chemical Debridement
We evaluated the effect of precarved collagen lenses on the kinetics of epithelial wound healing in an experimental model of corneal erosions. After induction of anesthesia, central corneal erosions of 5-mm diameter were created in New Zealand white rabbits using n-heptanol. Animals were randomly assigned either to the treatment group or to one of three control groups. Each animal in the treatment group received a precarved collagen shield made from porcine sclera. Immediately after creation of the corneal epithelial defects, topical fluorescein sodium was applied, and the corneas were photographed. Similar follow-up examinations were conducted at 5, 24, 30, 48, 72, and 96 hr after defect creation. Epithelial defect areas were calculated by projecting the photographic slides onto a computerized digitizing pad. Reepithelialization kinetics were compared for the four treatment groups. When initial wound size was taken into account, no significant difference between mean reepithelialization rates was noted. These results indicate that collagen lenses do not adversely affect the speed of corneal reepithelialization, and may, because of their documented biodegradibility and drug delivery capability , be useful in the clinical management of corneal epithelial erosions. Invest Ophthalmol Vis Sci 31:1294-1300,1990
Anterior and posterior corneal stroma elasticity after corneal collagen crosslinking treatment
Experimental Eye Research, 2013
The purpose of this project was to assess anterior and posterior corneal stromal elasticity after corneal collagen cross linking (CXL) treatment in human cadaver eyes using Atomic Force Microscopy (AFM) through indentation. Twenty four human cadaver eyes (12 pairs) were included in this study and divided into 2 groups (6 pairs per group). In both groups, the left eye (OS) served as a control (no riboflavin or CXL treatment was performed) and the right eye (OD) underwent CXL treatment (30 min of riboflavin pretreatment followed by 30 min of exposure to 3 mW/cm 2 of ultraviolet light). In group 1, the anterior stroma was exposed by manual delamination of approximately 50 mm of the corneal stroma including Bowman's membrane. In group 2, the posterior stroma was exposed by delamination of the anterior 50% of the corneal stroma including Bowman's membrane. Delamination was performed after crosslinking treatment in the case of the treated eyes. In all eyes, the stromal elasticity was quantified using AFM through indentation. Young's modulus of elasticity for the anterior cornea (group 1) was 245.9 AE 209.1 kPa (range: 82.3e530.8 kPa) for the untreated control eyes, and 467.8 AE 373.2 kPa (range: 157.4e1126 kPa) for the CXL treated eyes. Young's modulus for the posterior cornea (group 2) was 100.2 AE 61.9 kPa (range: 28.1e162.6 kPa) for the untreated control eyes and 66.0 AE 31.8 kPa (range: 31.3e101.7 kPa) for the CXL treated eyes. Young's modulus of the anterior stroma significantly increased after CXL treatment (p ¼ 0.024), whereas the posterior stroma did not demonstrate a significant difference in Young's modulus after CXL treatment (p ¼ 0.170). The anterior stroma was stiffer than the posterior stroma for both the control and CXL treatment groups (p ¼ 0.077 and p ¼ 0.023, respectively). Our findings demonstrate that stiffness of the anterior corneal stroma after CXL treatment seems to increase significantly, while the posterior stroma does not seem to be affected by CXL.
Collagen ultrastructural changes during stromal wound healing in organ cultured bovine corneas
Experimental Eye Research, 2009
Corneal collagen ultrastructural changes occur during the healing process. The present study was designed to compare collagen ultrastructural changes after trephine wounding or flap creation. Bovine corneas were injured and maintained in organ culture for up to 4 weeks. Samples were removed from culture at 0, 1, 2, 3 and 4 weeks and snap frozen in liquid N 2 and x-ray scattering was used to measure changes in collagen interfibrillar spacing, intermolecular spacing and fibrillar diameter. Some samples were fixed in 10% Neutral Buffered Formalin solution and wax embedded for immunohistochemistry to monitor myofibroblast differentiation in corneal flaps. Swelling effects (i.e. changes in interfibrillar spacing) were more severe in trephined corneas than in those with stromal flaps. Collagen fibrillar diameter remained normal in the periphery of injured corneas, but increased significantly in areas within and around the wound in trephined samples and in the epithelial incision site in corneal flaps. Intermolecular spacing was unchanged in all samples. In the flaps, αSMA expression was only detected in an area adjacent to the epithelial plug, and cell numbers gradually increased during the culture. We conclude that stromal swelling is more rapid for trephine-wounded corneas than in stromal flaps, indicating that the intensity of the corneal healing response depends on the type of injury.
Ankara Üniversitesi Veteriner Fakültesi Dergisi
The aim of this study was to evaluate the effect of collagen shield on epithelial wound healing in rabbit eyes. Adult New Zealand Albino rabbits were used in the study. All surgical procedures were carried out under general anesthesia. Superficial keratectomies of 6 mm in diameter were created in 40 eyes of 20 rabbits and they were separated into 3 groups as the control (CN), medical treatment (CA) and collagen barrier (CB) groups. In the CN group, 6 rabbits received 0.9% NaCl drops. In the CA group, 7 rabbits received ciprofloxacin and acetylcysteine. In the CB group, a collagen shield was placed on corneal defect for 72 hours in 7 rabbits. Central corneal thickness was measured using an ultrasound pachymeter. Corneal thickness was determined before and at 72 and 96 hours after surgery. There was a significant increase (CA group: P<0.01, CB group: P<0.001) in corneal thickness at 72 hours. The wound size was evaluated immediately after the surgery, then at 72 and 96 hours. There was a significantly greater healing response in the collagen shield group (P<0.001) compared to the other groups. The earlier wound closure in the CB group may be due to protection and lubrication of the epithelial cells in the margins of the fresh wound. These findings suggest that the collagen shield may be useful when treating corneal surface conditions in which de-epithelialization is a component.