Refractive media of the eyeball

The refractive media of the eyeball is made up of structures that take part in focusing the ray of light onto the retina so the photoreceptors can detect it.

The eye has four refractive media structures: the cornea, lens, vitreous body, and aqueous humor.

The cornea is the part within the fibrous layer of the eyeball that makes up its frontal one-sixth. The cornea is a circular and transparent layer covering the pupil, iris, and anterior chamber.

The cornea is divided into five layers:

  • The stratified corneal epithelium
  • The Bowman's membrane
  • The corneal stroma
  • The Descemet's membrane
  • The corneal endothelium

The cornea is the main structure that is responsible for the refraction of light entering the eye. The refractive power happens on the anterior surface of the cornea. Here, the refractive index of the cornea is higher than that of the air. Maintenance of corneal transparency is essential to keep the cornea functioning.

The lens is located anterior to the vitreous body and posterior to the iris. The lens is a transparent structure. The lens has three parts: the elastic capsule, lens epithelium, and lens fibers. The elastic capsule surrounds the outer surface of the lens. The capsule works as a diffusion barrier. The lens epithelium lies deep into the capsule. The lens fibers make up most of the lens substance. With the help of the ciliary muscle, the stretch of the elastic capsule and convex of the lens changes leading to accommodation.

The vitreous body is found posterior to the lens. The vitreous body is the largest structure in the eyeball. The vitreous body does not contain blood vessels un nerve-ends. It is made of a gel-like substance called vitreous humor surrounded by a capsule. The vitreous body protects the lens and gives the eyeball a specific shape. The vitreous body is responsible for transmitting light. It supports the posterior surface of the lens.

The aqueous humor fills the eye chambers. It is produced by the ciliary processes. The aqueous humor firstly drains into the posterior chamber of the eyeball and then through the pupil into the anterior chamber. The aqueous humor supplies the lens and cornea with nutrients.