Mathematical modeling of photoreceptor metabolism

Photoreceptors are the sensory cells of the eye and have the most important role in vision. They convert light to electrical signals, which are sent to the brain via the optic nerve. Vision deterioration or blindness occur if the vitality of photoreceptors is compromised. To understand how to mitigate such pathological cases, it is essential to study the metabolism of photoreceptors, as this is the factor of greatest importance for photoreceptor vitality. We develop a mathematical model of nonlinear ordinary differential equations to describe metabolic dynamics in a single photoreceptor, focusing on key metabolites, such as glucose, pyruvate and lactate. Using bifurcation techniques, we find that the model has a bistable regime, biologically corresponding to a healthy versus a pathological state. We also conduct sensitivity analysis to determine which processes have the largest impact on the photoreceptor metabolic system. The results indicate that of greatest importance are the pathways linking photoreceptor metabolism with the metabolism of the retinal pigment epithelium, a cellular layer in the retina with which photoreceptors have a reciprocal resource relation.