Is there a higher concentration of K+ in the tear film or in blood plasma?

The correct understanding revolves around the composition of the tear film and blood plasma. Potassium ions (K+) are present in higher concentrations in the tear film compared to blood plasma.

This higher concentration in the tear film serves several important physiological roles, including regulation of osmotic pressure and maintenance of corneal hydration. The cornea is avascular, relying on tears for nutrient supply, and elevated K+ levels contribute to the biochemical environment necessary for corneal health and function.

In contrast, while blood plasma does contain K+, its concentration is generally lower than that in the tears. This discrepancy highlights the specific adaptations of the ocular surface, suggesting that the tear film is tailored to meet the unique nutritional and functional needs of the eye.

Thus, recognizing the physiological roles of K+ within the tear film—specifically in maintaining ocular surface health—clarifies why the tear film exhibits a higher concentration of K+ than blood plasma.