Studies on corneal polysaccharides. V. Changes in corneal glycosaminoglycans in transient stromal edema

Corneal Optical Densitometry in the Evaluation of 2-Year Graft Function Following Endothelial Keratoplasty

This study aimed to assess clinical application of the Scheimpflug corneal tomography for objective evaluation of corneal optical density in eyes undergoing Descemet's stripping endothelial keratoplasty (DSEK). In this prospective study, 39 pseudophakic eyes with bullous keratopathy were enrolled. All eyes underwent primary DSEK. Ophthalmic examination included best corrected visual acuity (BCVA) measurement, biomicroscopy, Scheimpflug tomography, pachymetry, and endothelial cell count. All measurements were taken preoperatively and within a 2-year follow-up period. Gradual BCVA improvement was observed in all patients. After two years, the mean and median BCVA values were 0.18 logMAR. A decrease in central corneal thickness was noted only during the first 3 months postoperatively and was followed by a gradual increase. Corneal densitometry decreased constantly and most significantly in the first 3 months postoperatively. The consecutive decrease in endothelial cell count of the transplanted cornea was most significant during the first 6 months postoperatively. Six months postoperatively, the strongest correlation (Spearman's r = -0.41) with BCVA was found for densitometry. This tendency was maintained throughout the entire follow-up period. Corneal densitometry is applicable for objective monitoring of early and late outcomes of endothelial keratoplasty, showing a higher correlation with visual acuity than pachymetry and endothelial cell density.

Recipient corneal thickness and visual outcome after Descemet's stripping automated endothelial keratoplasty

BACKGROUND

Descemet's stripping automated endothelial keratoplasty (DSAEK) is widely performed for endothelial failure. Unfortunately, the visual outcome is often mediocre and the underlying cause unclear. This study examines whether corneal light scatter and recipient corneal thickness (RCT) influence the visual outcome after DSAEK.

METHODS

Patients attending clinical control after DSAEK were recruited during 4 months. In total, 125 eyes from 93 patients were enrolled. Postoperative time averaged 20±13 months. Data from previous controls were also reviewed. Examinations included corrected distance visual acuity (CDVA), Pentacam and anterior-segment OCT. From OCT and Pentacam data, RCT and lamellar graft thickness (LGT) were determined. Corneal densitometry was estimated from Pentacam images.

RESULTS

6 months after DSAEK, RCT measured 482±27 μm. After 3 years, RCT was significantly higher, measuring 505±23 μm. Pentacam and OCT showed similar variations in RCT. Also, in paired observations, from patients with previous controls, RCT increased significantly. Concurrently, corneal densitometry decreased and CDVA improved from 0.30±0.13 logMAR by 6 months to 0.17±0.08 logMAR by 4 years. No changes in LGT were observed. Changes in RCT, densitometry and CDVA were significantly correlated.

CONCLUSIONS

The study suggests that changes in RCT and corneal densitometry are important for the visual outcome after DSAEK.

Stromal edema in klf4 conditional null mouse cornea is associated with altered collagen fibril organization and reduced proteoglycans

PURPOSE

Klf4, one of the highly expressed transcription factors in the mouse cornea, plays an important role in maturation and maintenance of the ocular surface. In this study, the structure and proteoglycan composition of the Klf4 conditional null (Klf4CN) corneal stroma was investigated, to further characterize the previously reported Klf4CN stromal edema.

METHODS

Collagen fibril spacing and diameter were calculated from scattering intensity profiles from small angle synchrotron x-ray scattering patterns obtained across the cornea along a vertical meridian at 0.5-mm intervals. Collagen fibril organization and proteoglycans were visualized by electron microscopy (EM), with or without the cationic dye cuprolinic blue. Proteoglycans and glycosaminoglycans were further analyzed by fluorophore-assisted carbohydrate electrophoresis (FACE) and immunoblot analysis. Q-RT-PCR was used to measure the transcript levels.

RESULTS

In the central cornea, the average collagen interfibrillar Bragg spacing increased from 44.5 nm (SD +/-1.8) in wild-type to 66.5 nm (SD +/-2.3) in Klf4CN, as measured by x-ray scattering and confirmed by EM. Mean collagen fibril diameter increased from 32 nm (SD +/-0.4) in wild-type to 42.3 nm (SD +/-4.8) in Klf4CN corneal stroma. Downregulation of proteoglycans detected by EM in the Klf4CN stroma was confirmed by FACE and immunoblot analysis. Q-RT-PCR showed that, whereas the Klf4CN corneal proteoglycan transcript levels remained unchanged, matrix metalloproteinase (MMP) transcript levels were significantly upregulated.

CONCLUSIONS

The Klf4CN corneal stromal edema is characterized by increased collagen interfibrillar spacing and increased diameter of individual fibrils. The stroma also exhibits reduced interfibrillar proteoglycans throughout, which is possibly caused by increased expression of MMPs.

A morphological study of the rabbit corneal assay

We present a morphological study of the rabbit corneal assay. The effects of corneal pockets filled with methylcellulosis carriers with and without basic fibroblast growth factor (bFGF) were studied 4, 7, 11, 14 and 21 days following surgery. In the controls, strongly vacuolated keratocytes are present at the borders and especially at the bottom of the pocket. A large number of such cells can also be found in the region between the pocket and the epithelium. These cells obviously undergo necrosis. A few vacuolated keratocytes with poorly structured cytoplasm can even be found in the stroma between the pocket and the limbus. There are also changes in the epithelium. It is thinner than normal and the cells are longitudinally oriented. Construction of the pocket sometimes results in a fissure extending a variable distance from the bottom of the pocket to the limbus. Basic FGF induced blood-vessel growth from the limbus into the cornea. At least until day 7 this is accompanied by high vulnerability of the vessels, and changes in the pattern and structure of the extracellular matrix. Neutrophilic granulocytes, monocytes and a few mast cells migrate in front of the vessels. As in the controls, vacuolated and necrotic keratocytes are present within the stroma. From day 11 onward, many more vessels can be found in front of than behind the pocket, often located adjacent to vacuolated keratocytes. We suggest that an angiogenic substance placed in the corneal pocket is not the only angiogenic stimulus in the test, but acts together with many stimuli caused by the surgical manipulations.

Alteration of the stromal architecture and depletion of keratan sulphate proteoglycans in oedematous human corneas: histological, immunochemical and X-ray diffraction evidence

The structure and content of the extracellular stromal matrix of several oedematous human corneas was investigated using electron microscopy, X-ray diffraction and biochemical techniques. Electron microscopy revealed the presence of wavy lamellae and various sized collagen-free 'lakes' within the stroma of the oedematous corneas, with their posterior sections containing by far the largest 'lakes'. The existence of 'lakes' was supported by the equatorial X-ray diffraction evidence. Staining the oedematous corneas with Cuprolinic blue prior to electron microscopical and meridional X-ray diffraction studies demonstrated a loss of stromal proteoglycans normally associated with collagen. Immunochemical evidence demonstrated reduced levels of antigenic keratan sulphate in the oedematous corneas while biochemical techniques revealed constant chondroitin sulphate levels in the same corneas.

Tolerance of human corneal endothelium to glycerol

As an initial step in the development of a method for corneal cryopreservation by vitrification, we attempted to establish the maximum concentration of glycerol to which human corneal endothelium could be exposed at 4 degrees C for 15 min without damage. Damage was defined as an increase in mean endothelial cell size or the inability to maintain corneal thickness for 1 week after exposure to glycerol. Using a system for long-term corneal perfusion, we perfused 24 paired human corneas with glycerol at 4 degrees C. The concentration of glycerol increased at a rate of 20% (w/v) (2.2 M) per hour until the desired maximum concentration was reached for that cornea, stabilized for 15 min, and then decreased at the same rate. The corneas were then perfused at 37 degrees C with Dulbecco's medium at a rate of 5 microliters/min under 18 mm Hg intracameral pressure for 7 days with daily measurements of corneal thickness. Endothelial morphology was examined by specular microscopy and by scanning electron microscopy. After 7 days of perfusion at 37 degrees C, there was a statistically significant direct relationship between the maximum concentration of glycerol to which the experimental eyes had been exposed and the increase in mean endothelial cell size. The mean endothelial cell size increased in corneas exposed to glycerol concentrations of 40, 50, and 60% (w/v), but did not differ significantly from baseline measurements in the corneas exposed to 30% glycerol or less. Thus, there was no detectable damage to human corneas exposed to 30% (w/v) (3.3 M) glycerol in this system. Tolerance of higher concentrations may be achieved by changes in the rates of addition and removal of glycerol or in the composition of the perfusate.

Organ culture of rabbit cornea: morphological analyses

Tissues maintained in vitro often undergo changes in the pattern of protein synthesis that result in the deposition of macromolecules quantitatively or qualitatively unrelated to those normally synthesized. In these preliminary studies, we modified published techniques to maintain adult and neonate rabbit corneas in vitro for 24 to 48 h. Measurements of corneal wet weight, and histologic and ultrastructural analyses were made to determine the success of maintaining rabbit corneas in culture. The results show that rabbit corneas can maintain normal corneal hydration and tissue structure for at least 48 h when incubated in Coon's modification of Ham's F12, 5% fetal or newborn calf serum, 2 mM glutamine, and 2% chondroitin sulfate or 2% 50 kDa dextran sulfate at 37 degrees C in a 5% CO2/air atmosphere. In addition, we confirmed previous observations that corneal explants must have a 1 to 2 mm rim of limbal sclera, and the organ placed in the culture dish with the epithelial side down to guard against damage and insure endothelial functioning. Normal ultrastructure of neonate rabbit cornea is also maintained when organ-cultured with these procedures. Moreover, neonate corneas continue to synthesize collagen in culture.

Corneal superficial unwettable defect. I. Clinical and histopathological study

In 11 patients, the clinical, histological and histochemical picture of an unusual corneal affection termed "corneal superficial unwettable defect", is reported. It develops during the healing of various corneal lesions. Clinically, it is described as a defect of the epithelium with a denuded and changed Bowman's membrane, the surface of which repells tears and cannot be stained with fluorescein. In the histological picture, the changed Bowman's membrane has fibrillar or foamy appearence. It stains strongly with colloidal iron and alcian blue, but PAS and toluidine blue reactions are weak. Histochemical reactions for neutral fats are strongly positive, but those for phospholipids are negative. The results of extractions speak for the presence of some lipid component, which is neither neutral fat nor phospholipid. Hence it is supposed that there may be some waxes-ointment bases, reacting with the pathologically changed Bowman's membrane. The possible mechanisms injuring or influencing the Bowman's membrane are also discussed.

The hydration of proteoglycans of bovine cornea

The water sorptive and retentive capacities of three corneal proteoglycans with different keratan sulfate/chondroitin-4-sulfate compositions were investigated. The calcium salt of a predominantly keratan sulfate containing proteoglycan had hydration properties similar to that of calcium keratan sulfate. The proteoglycan containing predominantly calcium chondroitin-4-sulfate side chains sorbed water to a greater extent than pure calcium chondroitin-4-sulfate but its retentive power was somewhat less. The proteoglycan containing about twice as much keratan sulfate as chondroitin-4-sulfate, on a dissaccharidic molar basis and had hydration properties which were closer to the behavior of chondroitin-4-sulfate than keratan sulfate. The results are discussed in terms of structure and polymer interaction in the proteoglycan matrices.