The anterior segment is the front third of the eye

Human eye

The human eye is an organ which reacts to light for several purposes. As a conscious sense organ, the eye allows vision. Rod and cone cells in the retina allow conscious light perception and vision including color differentiation and the perception of depth...

 that includes the structures in front of the vitreous humour

Vitreous humour

The vitreous humour or vitreous humor is the clear gel that fills the space between the lens and the retina of the eyeball of humans and other vertebrates...

: the cornea

Cornea

The cornea is the transparent front part of the eye that covers the iris, pupil, and anterior chamber. Together with the lens, the cornea refracts light, with the cornea accounting for approximately two-thirds of the eye's total optical power. In humans, the refractive power of the cornea is...

, iris

Iris (anatomy)

The iris is a thin, circular structure in the eye, responsible for controlling the diameter and size of the pupils and thus the amount of light reaching the retina. "Eye color" is the color of the iris, which can be green, blue, or brown. In some cases it can be hazel , grey, violet, or even pink...

, ciliary body

Ciliary body

The ciliary body is the circumferential tissue inside the eye composed of the ciliary muscle and ciliary processes. It is triangular in horizontal section and is coated by a double layer, the ciliary epithelium. This epithelium produces the aqueous humor. The inner layer is transparent and covers...

, and lens

Lens (anatomy)

The crystalline lens is a transparent, biconvex structure in the eye that, along with the cornea, helps to refract light to be focused on the retina. The lens, by changing shape, functions to change the focal distance of the eye so that it can focus on objects at various distances, thus allowing a...

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Within the anterior segment are two fluid-filled spaces:

• the anterior chamber
  Anterior chamber
  The anterior chamber is the fluid-filled space inside the eye between the iris and the cornea's innermost surface, the endothelium. Aqueous humor is the fluid that fills the anterior chamber. Hyphema and glaucoma are two main pathologies in this area. In hyphema, blood fills the anterior chamber...
  
   between the posterior surface of the cornea (i.e. the corneal endothelium
  Corneal endothelium
  The corneal endothelium is a single layer of cells on the inner surface of the cornea. It faces the chamber formed between the cornea and the iris....
  
  ) and the iris.
• the posterior chamber
  Posterior chamber
  The posterior chamber should not be confused with vitreous chamber. The posterior chamber is a narrow chink behind the peripheral part of the iris of the lens, and in front of the suspensory ligament of the lens and the ciliary processes. The Posterior Chamber consists of small space directly...
  
   between the iris and the front face of the vitreous.

Aqueous humor fills these spaces within the anterior segment and provides nutrients to the surrounding structures.

Some ophthalmologists and optometrists specialize in the treatment and management of anterior segment disorders and diseases.