Which condition is characterized by lack of crystalline lens?

Aphakia is a condition characterized by the absence of the crystalline lens in the eye. This condition can occur due to surgical removal of the lens, often because of cataracts, or it can arise as a result of congenital factors. The crystalline lens plays a crucial role in focusing light onto the retina, and its absence can lead to significant visual impairment, affecting a person's ability to see clearly at various distances.

In contrast, myopia, presbyopia, and hyperopia describe refractive errors related to how light is focused in the eye but do not involve the absence of the crystalline lens. Myopia refers to nearsightedness, where close objects are seen clearly while distant objects appear blurry. Presbyopia is an age-related condition that affects the ability to focus on near objects due to the hardening of the lens, which reduces its flexibility. Hyperopia, or farsightedness, occurs when distant objects can be seen more clearly than close ones, often due to the eyeball being too short or the lens being too weak to focus light properly. Each of these conditions involves the lens but does not entail its absence as seen in aphakia.