How Light Affects Biological Systems

Our pupil’s ability to change size is an essential physiological response that adjusts the amount of light hitting the retina to optimize vision and protect the retina. Pupils constrict in response to brightness, whereas they dilate in response to dark conditions (known as the pupillary light response or reflex). In contrast, these responses are related; they are considered to be driven by different neural pathways (Mathôt, 2018).

^{Figure 3. The Eye and the Brain, source: VectorMine/Shutterstock}