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L.J. Muller, E. Pels, Staff Cornea Bank; Distribution of Stromal and Subbasal Nerves in Fresh Human Corneas . Invest. Ophthalmol. Vis. Sci. 2005;46(13):877.
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Purpose: Based on light and electron microscopic observations and in vivo confocal microscopy we have published a scheme for the sub–basal nerve plexus in human corneas (Müller et al. EER, 2003). This scheme is still incomplete because the orientation of the nerves in the periphery, especially in the 6 and 12 o’clock regions, is unknown. Furthermore, it was recently demonstrated that in LASIK patients an eye with a nasal hinge shows less dry eye symptoms than its fellow eye with a superior hinge (Donnenfeld, Ophthalmology 2003). This urged us to perform a refined study on the orientation of both stromal and sub–basal nerves. Methods: Nine fresh corneas (2 marked in the orbit), post–mortem time 11–24 hrs, were stained with gold chloride. Five of these corneas were divided into 11 pieces which were analyzed separately. To avoid loss of tissue the pieces were cut manually into 3–5 parallel sections from epithelium to endothelium. One cornea was divided into an anterior and a posterior part before staining. Results: At 6 and 12 o’clock large deep stromal nerves have essentially a vertical orientation whereas nasal and temporal (2,3,4 and 8,9,10 hrs) large nerves have essentially a horizontal orientation. The latter keep their orientation in the mid–anterior stroma and their number seems to exceed that of the vertical oriented nerves. The large nerves (<font face="symbol">Æ</font> 40–60 µm) run obliquely towards the stromal surface and bifurcate into medium (<font face="symbol">Æ</font> 10–20 µm) and subsequently into small nerves (<font face="symbol">Æ</font> 2.5–6 µm). In the apex only few small stromal nerves are present, indicating that most of the stromal nerves pass Bowman’s layer in the mid–periphery to form the plexus of sub–basal nerves (SBN). These SBN run parallel to Bowman’s layer over 1–4 mm in a vertical direction in the apex, in a vertical or a horizontal direction in the mid–periphery and are absent near the limbus. However, below the limbal epithelium there is a plexus of curved nerves, which was sofar found only at the nasal side. Conclusions: The density and preferred horizontal orientation of the stromal nerves might be as important or even more important as the orientation of the subbasal nerves to explain the hinge related dry eye symptoms. However, a possible role of the sub–epithelial limbal nerves cannot be excluded.
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