The possible role of tear fluid thyroxine in keratoconus development.

The normal thyroxine level in tears was found to be two orders of magnitude lower than in serum. In thyroxine function tests, keratoconus patients were found to be hypothyreotic, euthyreotic or hyperthyreotic. However, independently of their thyroid function, the tear thyroxine levels of keratoconus patients were 2-50 times higher than that of subjects free of ocular pathology. Tear thyroxine levels were higher during the progression of keratoconus and declined once corneal curvature reached a new steady value.