Which of the Purkinje images moves forward with accommodation?

Purkinje images are reflections of an object from the different surfaces of the eye's optical components, primarily the cornea and lens. In the context of accommodation—where the eye changes its focus from distant to near objects—it's important to understand how these reflections behave.

Purkinje image I is a reflection from the anterior surface of the cornea, while image II comes from the posterior surface of the cornea. Purkinje images III and IV are reflections from the anterior and posterior surfaces of the lens, respectively.

When the eye accommodates, the lens becomes more rounded to provide a greater refractive power needed for near vision. This process alters the position of the lens and affects how the Purkinje images move. Specifically, Purkinje image III, which reflects off the anterior surface of the lens, moves forward as the lens bulges during accommodation. This movement forward is a result of the lens's shape changing, leading to the image reflecting from its surface shifting position.

In summary, Purkinje image III is unique in that it moves forward with accommodation, reflecting the changes in lens curvature that occur to focus on nearby objects.