Final answer:
A posterior lenticonus is an eye condition in which the back part of the lens protrudes in a conical shape, potentially causing vision issues. It is unrelated to the spinal terms provided.
Step-by-step explanation:
A posterior lenticonus is an eye condition and not related to the posterior longitudinal ligament or the lumbar curve. This condition involves a conical protrusion of the back part of the lens inside the eye, which can cause visual problems. It is a rare type of cataract that can be present at birth (congenital) or develop later. Unfortunately, the information provided about the posterior longitudinal ligament and lumbar curve does not relate to the posterior lenticonus as these terms refer to the spine, not the eye. A correct answer would detail the eye condition - where the normally round shape of the lens is altered, sometimes leading to vision impairment.