Updated: 8/25/2022

Eye Anatomy

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  • The structures of the eye
    • cornea
      • a transparent structure that allows light to enter the eye
    • pupil
    • iris
      • covered by the conjunctiva, a transparent mucous membrane
        • remember that the conjunctiva lines the inside of the eyelids as well, up to the limbus
        • clinical correlate
          • conjunctivitis
            • which describes inflammation of the conjunctiva
    • lens
    • sclera
    • limbus 
      • which is the border of the cornea and sclera
    • medial and lateral canthus
  • Light enters the eye through the cornea and lens which results in
    • an image (inverted and reversed) being formed in the retina
      • the area on the retina with the highest visual acuity is the fovea, which is surrounded by the macula
      • medial (nasal) to the fovea is the optic disc, which  
        • is where axons exit forming the optic nerve (cranial nerve II)
          • note that the optic nerve does not have photoreceptors over it, resulting in a small blind spot
      • photoreceptors
        • there are two classes
          • rods
            • provides vision in a low-level light environment
            • does not detect color
            • Retinitis pigmentosa is an inherited disorder characterized by degradation of rod photoreceptors. It presents with progressively deteriorating night vision and peripheral vision 
          • cones
            • highly represented in the fovea
            • detect color
  • choroid
    • is a vascular layer of the eye
  • ciliary body
    • is found between the choroid and the iris and is composed of the
    • ciliary muscle
      • which is controlled by the parasympathetic fibers in the oculomotor nerve in order to
        • contract, resulting in miosis
    • ciliary processes    
      • which have zonular fibers extending from this structure to the lens forming the suspensory ligament
  • Lens
    • transparent biconvex disc behind the pupil that provides additional refractive power. Is composed of:
      • lens capsule
      • subcapsular epithelium
      • lens fibers
    • disease processes that affect the lens include
      • cataracts - opacifiction of the crystalline lens
      • ectopia lentis - lens dislocation
      • presbyopia - decreased elasticity of the lens leading to impaired accomodation 
  • Anterior chamber
    • describes the area behind (posterior) to the cornea and infront (anterior) to the iris
  • Posterior chamber
    • describes the area posterior to the iris and anterior chamber
  • Aqueous humor pathway
    • the ciliary body produces aqueous humor into the posterior chamber which
      • flows through the space between the lens and iris into the
        • anterior chamber and finally drains into the
          • trabecular meshwork and then canal of Schlemm
          • uveoscleral pathway
  • Blood supply
    • an arterial source is from the ophthalmic artery 
      • the short posterior, long posterior, and anterior ciliary arteries
      • central retinal artery which
        • supplies the optic nerve
      • occlusion presents as painless, acute loss of vision in the affected eye 
    • venous drainage is from
      • the vorticose veins
      • central retinal veins

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