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L.J. Muller, P. Rama, U. Merlin, A. de Wolf, G.F. J. M. Vrensen; In advanced stages of keratoconus the complex plywood arrangement of the anterior stroma is only slightly affected . Invest. Ophthalmol. Vis. Sci. 2004;45(13):3824.
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Purpose: The most anterior stroma (100–120 µm) of healthy human corneas is characterized by a complex plywood arrangement of interwoven collagen lamellae. This makes it resistant to swelling after treatment with water. Keratoconus (KC) corneas are known to display disruptions in the anterior lamellae and the question addressed was whether these corneas are still able to withstand the same swelling pressure. In a preliminary study, large stromal nerve fibers appeared to be more obvious in KC corneas. We elaborated on this item whether it is a general characteristic. Methods: Of 9 corneal buttons in advanced stages of KC (age 25–43 yrs), 3 were treated for one day with water (KC+) and 6 served as controls (KC–). They were routinely processed for light and electron microscopy and compared to 12 donor buttons treated with water (C+) and 10 fresh buttons obtained from melanoma patients (C–). The epithelium and anterior stroma of central and central–peripheral samples were studied in serial frontal (∼1 µm) and ultrathin sections and the thickness was measured in cross–sections. Results:The swelling of KC+ buttons (4 times) is considerably more pronounced than that of C+ buttons (2–3 times). Although the borderline at 100 –120 µm in KC+ buttons is not as straight as in C+ buttons, the most anterior stroma is slightly affected. Only at the location of breaks in Bowman’s layer the stroma is disrupted in KC+ buttons, indicating that a great part of the swelling resistant stroma is still present in advanced stages of KC. KC– buttons have lost their curvature as reflected in the disappearance of concentric circles of stroma, Bowman’s Layer and epithelium in frontal sections. In contrast, KC+ corneas regain their curvature and exhibit the same concentric circles as seen in C– corneas. The thick and long stromal nerves were obvious in all KC– corneas studied. In addition, in 3 buttons dendritic cells were seen in the near vicinity of the few remaining large subbasal nerves. Conclusions: The complex interwoven plywood structure of the most anterior stroma is only slightly affected in advanced stages of KC. Although these corneas are certainly more vulnerable than healthy controls, they still have a tensile strength sufficient to overcome complete ectasia. Stromal nerves have either increased in density or they are easier observed in frontal views due to changes in corneal curvature.
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