Many studies have been done as to the differences in how vision works between nocturnal and diurnal animals. There are differences at both the anatomical and physiological levels:

Physilogical Differences
Acetylcholine (ACh) is an integral part of both the central and peripheral nervous systems. A study was performed in order to analyze the concentration of ACh in the corneal epithelium (where generally the highest concentration of ACh is found) of various nocturnal and diurnal mammals. The data from this study of various diurnal and nocturnal mamlian species is shown below (Tables 1-A and 1-B):

Table 1-A

Diurnal Species	Corneal Epithelium (ng/mg wet weight)	Sample Size
Roe Deer	66.0 (44 - 88)	6
Cattle	45.8 (34 - 58)	6
Wildcat	33.5 (30 -37)	2

Table 1-B

Nocturnal Species	Corneal Epithelium (ng/mg wet weight)	Sample Size
Lynx (10 years/5 mo.)	nd./nd.	2/4
House Cat	nd.	12

-Tables 1-A and 1-B show the Acetylcholine in the Corneal Epithelium of diurnal and nocturnal species. ACh values are means, nd. stands for "not detected". As shown, all diurnal species pooled contained varying levels of ACh in their corneal epithelium, whereas nocturnal species had undetectable levels. (Tables adapted from Ringvold et al., 2005)

Chromatograms of the relative abundance of ACh in the Wildcat (diurnal feline) and the lynx (nocturnal feline) are also shown to help better visualize the difference in ACh levels between diurnal and nocturnal felines (Figure 1):

Figure 1


Figure 1 - Chromatogram for Cheetah and Lynx. I.S. stands for International standard (acetyl-B-methylcholine). As shown from this chromatographic comparison, the diurnal cheetah showed levels of acetylcholine in the corneal epithelium, whereas there was no detectable ammounts of actylcholine in the corneal epithelium of the nocturnal lynx (Figure adapted from Ringvold et al., 2005).

Conclusion:
The results showed that ACh was present in significant amounts in the corneal epithelium of every diurnal mammal tested. By contrast, no ACh was detected in any of the nocturnal mammals tested (Ringvold et al., 2005). These results helped to show that there are significant physiological differences between nocturnal and diurnal mammalian vision. The feline was a perfect specimen to study because the different nocturnal and diurnal species of cat helped prove the results to be even more significant by cutting out variables such as comparing very different mamalian species. This study has helped to bring up new questions regarding vision and ACh that may need to be investigated in the future to learn more about the physiological aspects of vision.

Questions or Comments? Please e-mail me at mirogers@davidson.edu