Eye

The eye (oculus) is an organ of vision, which is a complex optical system. The eyeball has an almost spherical shape with a diameter of about 24 mm and a mass of 7–8 g. Through vision, a person receives up to 80% of information about the world around him.

Eye shells

The eyeball consists of three membranes:

Fibrous (external):

• Sclera - dense white shell, frame of the eye (5/6 surface)
• Cornea - transparent front part (1/6), provides 2/3 of the refractive power of the eye

Vascular (medium):

• Iris - a colored diaphragm with a pupil in the center
• Ciliary body - produces intraocular fluid, contains the muscle of accommodation
• Choroid - vascular network that supplies the retina

Retina (internal) is a neural tissue containing photoreceptors.

Optical media

Light passes through 4 transparent media:

1. Cornea - refractive power ~43 diopters
2. Aqueous humor of the anterior chamber
3. Lens - biological lens (~19 diopters), can change curvature (accommodation)
4. Vitreous is a gel-like mass that fills 2/3 of the volume of the eye.

The total refractive power of the eye is about 60 diopters.

Retina

The retina contains 130 million photoreceptors of two types:

• Rods (~120 million) - black and white vision, works in low light
• Cones (~7 million) - color vision, three types (red, green, blue)

The macula (macula) is the center of the retina with the maximum concentration of cones. In its center is the fovea (hole), which provides the greatest visual acuity.

Blind spot is where the optic nerve exits; there are no photoreceptors.

Pupil and accommodation

Pupil is a hole in the iris, the diameter of which is adjustable from 2 to 8 mm. In the dark it expands (mydriasis), in the light it contracts (miosis).

Accommodation is the ability of the eye to focus at different distances due to changes in the curvature of the lens. With age, the lens loses elasticity - presbyopia (age-related farsightedness) develops.

Refractive errors

• Myopia (myopia) - the eye is elongated, the focus is in front of the retina
• Hypermetropia (farsightedness) - the eye is shortened, the focus is behind the retina
• Astigmatism - uneven curvature of the cornea

Knowledge of the anatomy of the eye is necessary for ophthalmologists to perform operations - from laser correction to lens replacement for cataracts.

In the Humio app, a 3D model of the eye is available - examine the membranes, lens, retina and optic nerve layer by layer, rotating the model in any direction.