Figure 1 of Varma, Mol Vis 2010; 16:2626-2633.

Figure 1. Intraocular penetration of Caffeine in aqueous and lens. Twenty microliters of the caffeine eye drop preparation labeled with 14C1-caffeine was instilled in the eyes of anesthetized rats. Samples of aqueous were prepared as described in the text and their radioactivity determined by liquid scintillation counting. The concentrations of the caffeine were then calculated with reference to the specific activity of caffeine in the eye drop. The results are described as Means of four aqueous and four lens samples. The standard deviation at each point was less than 0.35 mM.