Light hits cells in your retinas and they send coded signals back to the brain which then help create visuals you perceive.

Eyes resemble cameras in that they consist of two parts. At its front lies a clear structure called the cornea; behind that lies an opaque circle known as the pupil.

The Cornea

The cornea is the transparent dome that encases and admits light into your eye. Composed of transparent, nonvascular tissue called squamous epithelium, its five layers include: squamous epithelium, Bowman’s membrane, stroma, Descemet’s membrane and endothelium. Due to its incredible thin and flexible nature, allowing rapid swelling but prompt returning back to its normal size without significant swelling afterwards; additionally it features unmyelinated nerve endings which make it highly sensitive to light sensitivity allowing sharp object focus while contributing to great vision overall for most individuals.

Focusing power is provided by a crystalline lens located directly behind the cornea. Made up of dense, non-rigid proteinaceous material, most refractive errors — nearsightedness, farsightedness and astigmatism — result from less-than-optimal curvature or symmetry of this lens; as a result it should be periodically replaced to maintain good vision.

Behind the crystalline lens lies a gelatinous mass known as vitreous humor that occupies two-thirds of the volume of an eyeball (globe). Consisting primarily of water (99%), vitreous humor nourishes both cornea and lens via blood circulation.

Eyes are protected from foreign bodies by an opaque mucous membrane called the sclera and lined internally by a transparent mucous membrane called conjunctiva, divided into palpebral (eyelid) and bulbar divisions. When an eye becomes irritated, blood vessels in its conjunctiva become dilatational which produces brick-red color to give hyperemia; the conjunctiva also features non-movable folds to protect it against foreign bodies; however infections of its iris/ciliary body such as keratitis may close off these folds completely creating opaque pink color in its surroundings.

The Pupil

Once light has traveled through the cornea, it enters an opaque circular opening called the pupil. Pupil size can be actively controlled using two sets of smooth muscles that open and close in response to brainstem signals; they help maintain an optimal amount of light entering the retina–too much may damage it while too little makes seeing difficult.

Dilator and sphincter muscles control pupil size. They react to signals sent from both the parasympathetic nervous system (with its major center being in the dorsal midbrain) and melanopsin-containing ganglion cells that provide color vision as well as objects in our environment that contain hues or brightness levels that differ significantly between individuals.

To see things at a distance, the lens must first be flattened; this is accomplished using circularly arranged ciliary muscles which expand and contract the lens. Once flattened, light can then focus onto the retina – a thin layer of light-sensitive cells which convert electrical impulses to nerve impulses – before traveling along its course into the brain where an image of what was seen can be processed by it.

A thin film of fluid surrounding the retina serves to cushion it from mechanical impacts while providing a clear image by dispersing light rays that hit its surface.

The eye is an astoundingly complex optical device. The cornea and lens bend incoming light to focus it onto the retina, where photosensitive cells (rods and cones) detect objects’ colors before sending neural impulses back to the brain for visual processing. Pupil control regulates how much light enters each pupil while cornea, lens, retina combine together to produce sharp images of scenes or objects viewed through them. Furthermore, adaptability means it can adjust to various lighting conditions while distinguishing different light sources at various wavelengths.

The Lens

The lens is a biconvex anatomic structure of the eye that transmits and focuses light onto a sharp image on the retina at the back of the eye. This organ is controlled by muscles, with a gradient refractive index for dynamic light focusing at different distances. Furthermore, crystallin proteins make this organ highly refractive allowing most light through.

Lenses are flexible enough to enable various degrees of focusing, and accommodating is the process by which these adjustments occur. Accommodating can cause constricting of pupil which allows an eye to switch between seeing objects at various distances.

As people age, their ability to accommodate their eyes decreases; this condition is known as presbyopia. Early stage presbyopia causes stress on both ciliary muscle and lens; when this happens unevenly or evenly it results in myopia or astigmatism depending on whether these meridians (from front to back).

Focusing of light occurs through the lens’s refractive index gradient, created by different concentrations of alpha-crystallins in lens epithelial cells. These proteins play an integral part in maintaining transparency as well as transport, cell signaling and survival processes within our bodies.

The lens is protected by a basement membrane called the lens capsule that is produced by lens epithelial cells. The inner surface of this capsule is coated with an oily substance known as hyaluronan which helps the lens maintain flexibility and lubricity. A series of thin ligaments called suspensory ligaments – also referred to as zonules of Zinn – connect the lens capsule at one end with the ciliary body while at its other end connect to an active muscle called the sphincter muscle within ciliary body – contracts when contracts while relaxes when contracted and larger when relaxed.

The Retina

The retina is a light-sensitive layer of nervous tissue lining the inner back surface of an eyeball that converts images cast upon it by cornea, pupil, lens and optic nerve into impulses which travel back to the brain for perceptual awareness. In effect, your eye serves as a camera: its aperture controls how much light reaches cornea and lens (the photographic objective), with optic nerve transmitting images directly to visual cortex of brain; while numerous cell structures that make up retina serve their primary function.

By the time light reaches our retinas, approximately 90% has already been scattered or lost. 10% of light passes through a layer in the retina known as the outer limiting membrane, which appears like an oddity under an electron microscope – it actually comprises numerous occluding junctions which seal off photosensitive cells known as rods and cones from their remaining part of each cell. After passing through the outer limiting membrane, subsequent layers include: (a) photoreceptor layer with photosensitive outer segments of rods and cones (photoreceptors); (b) outer nuclear layer which contains rods and cone cell bodies (rods and cones); (c) inner plexiform layer which contains synapses between axons of rods/cones and dendrites/neuron intermediate neurons; and (d) inner ganglion cell layer which contains cell bodies of ganglion cells that form optic nerve fibres (Photoreceptor layer);

An area of the retina (known as the inner retinal vascular tunic) that is relatively insensitive to light is also important; this area serves other functions. The innermost vascular tunic contains dense meshwork of blood vessels which provide our eyes with blood; as well as helping maintain adhesion between retina and vitreous humor.

Vitreous humor, a thin and clear gelatinous substance found between the lens and retina in an eyeball, contributes to eye stability by providing support and helping focus light onto retina.