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THE FUNCTION OF PECTEN OCULI. CONUS PAPILLARIS IN REPTILES AND ITS ANALOGUE PECTEN OCULI IN BIRDS EVOLVED IN TANDEM WITH INCREASING URIC ACID IN SERUM

Amund Ringvold

The aim of this work is to identify the function of conus papillaris (CP) in reptiles and its analogue pecten oculi (PO) in birds. The study is based exclusively on information available in literature.

Currently the two apparently incompatible hypotheses at the forefront are: PO provides nutrition to the retina, or, alternatively, PO regulates intraocular pH to counter anaerobic retinal metabolism.

The present survey demonstrates that the development of CP occurred while reptiles evolved from aquatic to terrestrial life, and nitrogen waste excretion in urine changed from being predominantly ammoniotelic to mainly uricotelic during the same period of evolution. Accordingly, a correlation in time exists between the development of CP and the gradual alteration in protein catabolism. Furthermore, both the serum uric acid (UA) and the vascular permeability of PO increased during this period. Assuming that the retina is nourished through trans-vitrial diffusion from PO, a consequence could be that the heavily soluble UA leaks into the vitreous body compromising light transparency of the eye media.

Conclusion/new hypothesis: The ocular impact of increasing serum UA is minimized through three documented mechanisms: the well-known removal of UA via the trabecular meshwork, along with the here established selective blood-ocular barrier to UA, and the improved UA solubility through intraocular alkalization by PO's carbonic anhydrase.