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P. Hamrah, M. H. Dastjerdi, A. Chan, M. R. Dana, D. Pavan-Langston; Comparison of Corneal Nerve Alterations and Corneal Sensitivity in Herpes Simplex Keratitis With in vivo Confocal Microscopy. Invest. Ophthalmol. Vis. Sci. 2007;48(13):755.
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Neurotrophic keratopathy is thought to result from loss of corneal sensation due to denervation with most cases caused by herpes simplex keratitis (HSK). The purpose of this study is to correlate the degree of corneal denervation and morphology in HSK with corneal sensation.
We performed a prospective study in patients with acute (n=7) or chronic HSK (n=13). The corneal sensation was measured in both the affected and contralateral eyes, as well as in normal (n = 10) subjects with a Cochet-Bonnet aesthesiometer. HSK patients were grouped into normal (sensation >5.5 cm), as well as mild (>2.5 cm to ≤5.5cm) and severe (≤2.5 cm) loss of corneal sensation. Central corneae of normal subjects, eyes with HSV and their contralateral eyes were imaged with confocal microscopy (Confoscan 4). Two masked observers reviewed the in-vivo confocal images in regards to corneal nerve morphology of the subbasal plexus, including the total number of nerves, number of main nerve trunks, branching pattern, total length of nerves per image, tortuosity, nerve interconnections and the presence or absence of dendritiform cells.
The confocal scans revealed a significant (p< 0.05) decrease in total nerve count, length, branching and nerve interconnections in HSK eyes with normal sensation and even more marked decrease with loss of sensation. Tortuosity was slightly increased in HSV. Surprisingly, scans of contralateral eyes also revealed a decrease of total nerve length and number, as well as main nerve trunks to the level of the diseased eyes for eyes with normal or mild decrease in sensation, but did not further decrease to the level of severely desensitized eyes. In acute versus chronic HSK, the nerve length, number and interconnections dramatically decreased within days of HSV infection. Dendritiform cells, presumably Langerhans cells, were very superficial in the epithelium and variably increased in HSK.
Confocal microscopy reveals that the loss of the subbasal nerve plexus, starting immediately after the acute HSV infection, correlates highly with the loss of corneal sensation in HSK. Surprisingly however, the contralateral unaffected eyes also present with a loss of subbasal nerve plexus as compared with normal subjects.
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