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J.R. Horne, J. Fulton, M. Gondo, J.P. Bergmanson; Anatomical Evidence for the Structural Reinforcement of the Stromal-Anterior Limiting Lamina Interface in the Human Cornea . Invest. Ophthalmol. Vis. Sci. 2003;44(13):885.
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Purpose: In ectatic corneal disease, a stromal weakening leads to an anterior protrusion of the cornea. The purpose of this study is to ultrastructurally characterize the anterior limiting lamina (ALL)/stromal interface with an emphasis towards identification of morphological evidence for tissue modifications and interactions suggestive of a structural function. This may explain inherent corneal strength and corneal ectasia in certain pathological conditions. Methods: Two eyebank-harvested corneas (C1&C2) , from two separate individuals, were preserved in 2% glutaraldehyde in 80mmol/L cacodylate buffer (pH 7.4, l20-340mOsm/kg) and prepared for transmission electron microscopy (TEM) according to an established protocol. Montages of micrographs, taken from central cornea and magnified to X10,204, were assembled for a panoramic view of the interface. The frequency and extent of lamellar projections into ALL and the ALL projections into stroma were assessed morphometrically using a Jeol 100C operating at 60KV. Results: ALL thickness was measured in 10 different places and was on average 8.16um and 8.20um for C1 and C2 respectively. Stromal lamellar projections into ALL were relatively infrequent and shallow, and in neither cornea did fibers project further than 1.1um (avg: C1 0.65um and C2 0.76um). Short fibrous projections from ALL into stroma were noted and were on average 0.94um for both corneas. Adjacent to the interface were, at intervals, areas of increased electron-density in the stromal matrix around apparently terminating lamellae. These electron-dense formations (EDF) measured 1.99um (C1) and 1.22um (C2) in diameter and were located within 1.96um of ALL. Conclusions: This study found only superficial and limited mingling between the two corneal layers. Stromal projections into ALL and ALL projections into stroma were on average less than 1um. It seems that many lamellae approaching the interface simply level off to run parallel to ALL and eventually terminate in one of the above mentioned EDF's. The previously, undocumented sub-ALL EDF's interacting with apparently terminal lamellae may have a function in facilitating adhesion between the two layers. Based on our observations, it appears that anterior stromal lamellae, when terminating in central cornea, do not form distinct and well developed insertions into ALL. Therefore, a contributing factor to corneal ectatic disease may be the loss of EDF's rather than central lamellar disinsertions.
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