Cornea

The initial contact point for a light ray is the tear film, which covers the eye's surface to maintain moisture. Glands around the eyelids generate tears and a specialized oil, blending to form this film that coats the cornea—the eye's typically transparent outer layer. Insufficient tear production, known as dry eyes, can lead to vision impairment, redness, or discomfort. Beyond the cornea lies the anterior chamber, filled with clear aqueous fluid akin to water, regulating eye pressure. Disruptions in aqueous production or drainage may elevate eye pressure, potentially leading to glaucoma.

Iris

Located within the anterior chamber is the iris, determining one's eye color. Functioning akin to a camera's diaphragm, it expands and contracts the pupil to regulate the amount of light entering the eye.



Lens

The crystalline lens plays a crucial role in directing light onto the retina. It adjusts its shape slightly to enable focusing between objects at varying distances. However, with aging, the lens loses flexibility and the ability to adjust, resulting in presbyopia. Individuals with presbyopia typically require reading glasses or multifocal lenses. Over time, the lens may lose its clarity, turning yellowish or cloudy—a condition known as cataract—which compromises image quality on the retina. When a cataract significantly affects vision, it can be surgically replaced with a clear artificial lens implant.

Vitreous

Continuing our exploration of the eye, we encounter the vitreous—a clear, gel-like substance filling the eye's interior. Initially firmly connected to the retina, situated behind it, the vitreous gradually adopts a more watery consistency with age and may detach from the retina. This process can lead to the formation of small clumps or strands within the vitreous, causing shadows perceived as "floaters." While often harmless, floaters can occasionally signal underlying issues like retinal tear or detachment, warranting a comprehensive eye examination for proper evaluation.

Retina

Lastly, light reaches the retina, a thin tissue lining the innermost eye wall. Similar to camera film, the retina detects incoming light rays, converting them into electrical/chemical signals transmitted via the optic nerve to the brain. The peripheral retina governs side vision, while the macula, situated in the central area, facilitates precise central and color vision. At the macula's center lies the fovea, densely packed with special cone cells, granting it 20/20 vision capability. Diseases impacting the macula, like macular degeneration, lead to diminished central, straight-ahead vision.

Retinal Layers

Similar to layers of film, the retina consists of multiple layers, each with distinct functions. Light first encounters the nerve fiber layer, where nerve cells extend from various retina parts to the optic nerve. Beneath this layer lies the majority of retinal blood vessels, responsible for nourishing the inner retina. The outermost layer, the photoreceptor layer, comprises cones (for fine/color vision) and rods (for low-light vision), converting light into nerve signals. A human retina typically contains around 120 million rods and six million cones, with most cones concentrated in the macula. These photoreceptor cells rest atop the retinal pigment epithelium (RPE), maintaining their health and function. Beneath the RPE lies the retina's second set of blood vessels within the choroid layer, nourishing the photoreceptors through the RPE and choroidal blood vessels.

Optic Nerve

The optic nerve conveys information from the retinas to the brain, where it is interpreted as visual images. Comprising approximately one million nerve fibers, this nerve enters the eye's back, creating the "blind spot" devoid of rods or cones. Typically, this blind spot goes unnoticed due to its off-center position and the eye's swift movements, enabling the brain to compensate for the lack of information. However, in glaucoma, elevated intraocular pressure can lead to nerve damage.