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Fiona Stapleton, Cecilia Chao, Isabelle Jalbert, Preeji Sudharman Mandathara, Sailesh Kolanu, Mark D P Willcox, Maria Markoulli, Jingjing You, Juno Kim, Edward Lum, Blanka Golebiowski; Relationships between central corneal nerve parameters and tear neuropeptides. Invest. Ophthalmol. Vis. Sci. 201657(12):.
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© ARVO (1962-2015); The Authors (2016-present)
Tear neuropeptide levels are likely to be relevant in the maintenance of normal corneal nerve morphology and function. This study evaluated associations between central corneal nerve parameters using in vivo confocal microscopy and the most abundant tear neuropeptides, Substance P (SP) and Calcitonin Gene Related Peptide (CGRP) in humans.
Participants (n=189) aged 16-76 years, included normal (n=97), post-LASIK (n=20), keratoconic (n=28), allergic (n=22), itchy eyes (n=13) and diabetic (n=9) subjects. One eye of each subject underwent imaging of the central corneal subbasal nerve plexus using an in vivo laser scanning confocal microscope. Nerve fibre density (NFD), nerve fibre interconnections (NFI), average nerve fibre width (NFW) and nerve fibre tortuosity gradings (NFT) were evaluated. Tears were collected and levels of SP and CGRP were measured using commercially available ELISAs. Associations between tear neuropeptides and central nerve fibre parameters were evaluated using Pearson or Spearman correlation tests as appropriate, and partial correlations were used to control for age and contact lens use. Within the normal group, the effects of age and contact lens wear were evaluated using a grouped t-test.
After controlling for age, tear CGRP levels were associated with nerve fibre tortuosity grade, (r=0.56, p<0.001). There were no other associations between tear neuropeptides and nerve fibre parameters. Neither contact lens wear nor age consistently affected tear SP or CGRP or nerve fibre parameters. There was a strong association between tear SP and CGRP levels in normals (r=0.81, p<0.001), however this relationship became less robust when data for the post-LASIK and keratoconus groups were added to the model.
Tear neuropeptide levels appear consistent with age and were unaffected by contact lens wear. Of all the nerve morphology variables, nerve fibre tortuosity was significantly associated with tear CGRP in all subjects. Higher nerve tortuosity and tear CGRP levels were observed in post-LASIK and keratoconic subjects, which may be consistent with nerve remodelling or reinnervation in these groups. Tear SP and CGRP appear to be strongly associated in a normal ocular surface although this relationship appears to be disrupted in certain diseases affecting corneal nerves.
This is an abstract that was submitted for the 2016 ARVO Annual Meeting, held in Seattle, Wash., May 1-5, 2016.
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