Understanding Eye Anatomy and Function

Aug 6, 2024

Anatomy of Eye

External Structures

  • Eyelids
    • Protect the eyeball
    • Open and close by voluntary or reflex action
    • Keep the surface of the eye and conjunctiva moist
  • Eyelashes
    • Short hair projecting from the border of the eyelid
    • Trap large airborne particles
  • Conjunctiva
    • Thin epithelium covering the surface of the eyeball
    • Secretes mucus to lubricate, clean, and maintain moisture

Internal Structures

  • Cornea
    • Transparent, curved layer
    • Bends light to converge at the lens
  • Aqueous Humor
    • Transparent, watery liquid in the anterior cavity
    • Medium for diffusion of oxygen and nutrients
    • Refracts light and maintains the shape of the eyeball
  • Iris
    • Pigmented with color
    • Contains radial and circular muscles to regulate light entering the eye
  • Pupil
    • Round hole at the center of the iris through which light enters
  • Lens
    • Soft, transparent, and elastic
    • Focuses light onto the retina
    • Held in place by suspensory ligaments
  • Ciliary Body
    • Muscle that contracts and relaxes
    • Adjusts the focus strength of the lens for near or distant objects
  • Vitreous Humor
    • Transparent, jelly-like substance at the rear of the eye
    • Refracts light and, along with aqueous humor, maintains the shape of the eyeball

Retina and Associated Structures

  • Retina
    • Light-sensitive layer of the eye
    • Contains photoreceptor cells (rods and cones)
    • Converts light energy to electrochemical signals
  • Optic Nerve
    • Transmits electrochemical signals to the brain
  • Blind Spot
    • Area where nerve fibers leave the eye
    • Lacks photoreceptor cells
  • Choroid
    • Middle layer on top of the retina
    • Contains black pigments to prevent internal refraction of light
  • Sclera
    • Tough, opaque, non-elastic outer layer
    • Helps maintain the shape of the eyeball
  • Eye Muscles
    • Hold the eye in place
  • Lachrymal Gland (Tear Gland)
    • Secretes tears

Types of Tears

  • Basal Tears
    • Always present in the eye
    • Lubricate and nourish the cornea
    • Contain natural antibiotics to prevent bacterial infections
  • Reflex Tears
    • Produced in response to external stimuli (e.g., dust, onion vapors)
    • Excess basal tears wash out irritants
  • Psychic Tears
    • Produced due to emotions
    • Contain more proteins and hormones acting as natural painkillers

Vision Process

  • Cells in the retina absorb light rays from objects
  • Vision fields of both eyes overlap to form stereoscopic, 3D vision
  • Brain translates information from both eyes to form an image