During accommodation, the zonule tension decreases when?

During accommodation, the ciliary muscle plays a crucial role in changing the shape of the lens to focus on near objects. When the ciliary muscle contracts, it reduces the tension on the zonules (the fibers connecting the ciliary body to the lens). This decrease in zonular tension allows the elastic lens to become more curved, thus increasing its power and enabling clear vision at closer distances.

Conversely, when the ciliary muscle relaxes, the zonule fibers become taut, increasing the tension on the lens and flattening it, which is necessary for distance vision. Therefore, the relationship between the ciliary muscle's state and zonular tension is fundamental to understanding how accommodation works.

The other options relate to different aspects of ocular function. For instance, an increase in lens curvature occurs as a result of decreased zonule tension caused by ciliary muscle contraction, not relaxation. Iris constriction, or miosis, is part of the pupilary response but does not directly affect zonule tension in the context of accommodation. The flattening of the corneal surface is related to overall ocular changes in response to various conditions but is not inherently connected to the mechanisms of accommodation related to zonule tension.