Figure 5: Change in blur circle size following an increment in axial growth. The solid eye ball boundary indicates the original boundary of the sclera, the dashed boundary indicates the boundary after an increment in ocular growth. Dots on the boundaries indicate the positions of nodes in the retinal region of interest. For myopic defocus (focal plane located in front of the retina), incremental changes in growth result in increased blur circle size at nodes in the retinal region. For hyperopic defocus (focal plane located behind the retina), incremental changes in growth result in increased blur circle size. Based on the principles of the IRDT, hyperopic defocus will cause myopia due to excessive axial growth, while myopic defocus will cause relative hyperopia due to relatively reduced growth.