Human Eye Anatomy, Myopia, and Hyperopia: Vision Explained
Eye Anatomy
The human eye, the organ of vision, is an optical system producing images on the retina. This inner eye surface, light-sensitive and roughly spherical (about 25 mm in diameter), displays real, inverted images. Key parts include:
- Sclera: The external, white, opaque, and resistant membrane. In front, it becomes the transparent cornea.
- Cornea: The transparent front part of the eye, allowing light entry.
- Choroid: A membrane lining the eye’s interior (except the cornea), absorbing light.
- Aqueous Humor: A transparent liquid (n=1.34) behind the cornea, retained by the lens.
- Lens: An elastic, transparent, gelatinous body acting as a converging lens. Its curvature, and thus power, is adjusted by ciliary muscles.
- Vitreous Humor: A gel-like, transparent liquid (n=1.34) filling most of the eyeball.
- Pupil: A variable-diameter opening in the iris, regulating light entry.
- Iris: The pigmented part giving the eye color, controlling pupil size.
- Retina: A thin layer (about 0.5 mm) of light-sensitive nerve cells (cones and rods) lining the choroid.
- Macula (Fovea): A small, central retinal area (about 0.25 mm) with maximum cone concentration, providing sharpest vision.
- Optic Nerve: Connects the retina to the brain, transmitting visual information.
- Blind Spot: The area where the optic nerve exits, lacking photoreceptor cells.
Myopia (Nearsightedness)
Myopia results from excessive convergence of the eye’s optical system. The image focus, at rest, falls before the retina. Causes include excessive lens or corneal convergence, or an elongated eyeball. Distant objects appear blurry, while near objects are clear. Correction involves diverging lenses, which cause the image to focus on the retina.
Hyperopia (Farsightedness)
Hyperopia is characterized by insufficient convergence of the eye’s optical system. The image focus, at rest, falls behind the retina. Causes are opposite to myopia, such as reduced lens or corneal convergence, or a shortened eyeball. Distant objects may be clear with accommodation, but near objects appear blurry. Correction involves converging lenses, which cause the image to focus on the retina.