Olho

Olho is the organ of vision in humans and many animals. It detects light, forms images, and relays information to the brain to enable sight. In humans, the eye is protected by the orbit and surrounded by accessory structures that keep the surface moist and clean.

Anatomy and components: The eye comprises external structures (eyelids, eyelashes, conjunctiva) and a globe with three layers. The outer fibrous layer includes the sclera and cornea, the latter allowing light to enter. The middle vascular or uveal layer consists of the iris, pupil, ciliary body, and choroid, which supply blood to the retina. The inner neural layer is the retina, containing photoreceptors (rods for dim light and motion, cones for color and detail). The lens, held by the ciliary apparatus, focuses light onto the retina. The anterior segment contains the aqueous humor; the posterior segment contains the vitreous humor. The optic nerve conducts visual signals from the retina to the brain, where processing occurs in the visual cortex.

Function and visual pathway: Light passes through the cornea and lens, is focused on the retina, and is translated into neural signals by photoreceptors. These signals travel via retinal neurons to the optic nerve, synapse at the thalamus, and reach the visual cortex for perception and interpretation.

Development and variation: The eye develops from embryonic tissues, with the retina arising from neural ectoderm and the lens from surface ectoderm. While the basic plan is conserved, eyes vary across species in size, shape, and acuity.

Common conditions and care: Refractive errors (myopia, hyperopia, astigmatism), cataracts, glaucoma, age-related macular degeneration, and conjunctivitis are among common issues. Regular ophthalmologic evaluation, protective eyewear, and good tear film maintenance support eye health.