see also:

• ophthalmology

• these allow movements of the eye for gaze in various directions

• these protect the vulnerable cornea and help to prevent it drying out

• cornea
  • provides initial refraction of light along with the anterior chamber fluid
• anterior chamber
  • filled with aqueous humor
• iris and pupil
  • the iris gives the color to the eye - see eye color phenotypes and disease associations and allows for adjustment of the pupil size for different light brightness conditions
• intra-ocular muscles
  • pupillary muscles adjust pupillary size mainly to offset brightness issues but also as a signalling system as dilated eyes tend to make one more attractive to potential mates
    • Sphincter Pupillae (Pupillary Constrictor)
      • involuntary muscle controlled by the parasympathetic nervous system which constricts the pupil
      • constricting the pupil not only reduces the amount of light coming onto the retina but it also increases “depth of field” allowing a greater range of subject distances to be in focus - hence doctors use the “pin-hole” test to mimic this which helps assess visual acuity partly “correcting” any refractive errors of the eye
    • Dilator Pupillae (Pupillary Dilator)
      • involuntary muscle controlled by the sympathetic nervous system which dilates the pupil
    • see also mydriatics
  • ciliary muscles:
    • adjust focusing to provide accommodation
      • for near vision:
        • muscle contracts, moving the ciliary body inward, this releases tension on the suspensory ligaments (zonules of Zinn) attached to the lens which becomes thicker and more spherical, increasing its power to focus on close objects
      • for far vision:
        • muscle relaxes, which pulls the zonules tight which flattens the lens and decreases its refractive power, allowing focus on distant subjects
    • these also have an important role in maintaining intra-ocular pressures
      • when the muscle contracts, it pulls on the scleral spur, mechanically widening the spaces in the trabecular meshwork which increases the outflow of aqueous humor into Schlemm's canal, which helps lower eye pressure and prevents conditions like glaucoma.
• lens
  • provides further focusing of the light onto the retina
• posterior chamber
  • filled with vitreous humor

• the main visual sensory cells are rods (mainly monochromatic but more sensitive to light than cones) and cones (3 main types which detect colour)
• cones are most dense at the macula which is the central vision component of the retina
• the “blind spot” of the retina is optic disc where the optic nerve leaves the retina and there are no rods or cones to detect light in this region
• see also: color blindness / color vision deficiency

• optic nerve
• optic chiasma
• brainstem centres
• other processing centres
• visual cortex

• ciliary body
  • produces aqueous humor (AH), a clear fluid and helps maintain intraocular pressure (IOP) and nourishes avascular ocular tissues
• aqueous humor (AH)
  • AH exits the eye through two primary routes:
    • conventional outflow pathways
      • drains AH via the trabecular meshwork and Schlemm's canal and into episcleral veins
    • unconventional outflow pathways
      • involves drainage through the iris root, ciliary body, anterior choroid, and sclera, and orbit
      • includes connective tissue-filled spaces between ciliary muscle sheaths, extending through the supraciliary and suprachoroidal spaces to the macula and optic nerve head
      • via this pathway, AH and stromal proteins can exit the eye transsclerally, via the choroidal vasculature, and through recently identified ciliary body lymphatics which ¹⁾
• intra-ocular lymphatic pathways
  • drain to ipsilateral cervical lymph nodes
  • “uveolymphatic” pathway
    • discovered in 2009
    • lymphatic-related drainage pathway at the front of the eye
  • the posterior ocular lymphatic outflow, or POLO pathway
    • discovered in 2026²⁾
    • provides a route for fluid and waste to exit the eye via choroidal lymphatics and enter the body's lymphatic system