Ocular Anatomy

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Ocular Anatomy

• A Vision Teacher s Guide

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The Human Eye
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Eyelid

• In addition to tear spreading, the eyelid is
  primarily responsible for corneal nutrition
• Also provides protection to cornea
• Lashes offer additional protection

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Lacrimal System/Tear Film

• Lacrimal system is responsible for tear
  production and drainage
• Made up of 3 layers
• Created primarily by lacrimal apparatus and
  meibomian glands
• Lubricate the eyeball, provides oxygen/nutrition
  for cornea, has antibacterial properties and
  helps wash away debris
• Also have unique composition which keeps surface
  of cornea slick

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Lacrimal System
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Cornea

• Made up of 5 layers
• Specialized Transparent Tissue
• No blood vessels
• Primarily responsible for refracting light
• Does more of the job than the lens
• More nerve endings than anywhere else in the body
• Protection to the eye
• The only part of the eye that is transplanted
  from one person to another

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Aqueous humor

• Fills space between cornea and iris
• Continuously produced by ciliary body
• Flows into chamber through the pupil
• Drains from eye through trabecular meshwork to
  canal of schlemm
• Nourishes the cornea and lens
• Gives front of eyeball form and shape
• Anterior chamber is area between the cornea and
  the iris filled with aqueous
• Posterior chamber is the area behind the iris and
  in front of the lens filled with aqueous

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Limbus

• Juncture between the cornea and the sclera
• Nourishes peripheral corneaassists in corneal
  wound healing
• Pathway for aqueous outflow (contains trabecular
  meshwork and canal of schlemm)

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Conjunctiva

• Thin translucent mucous membrane starts at the
  limbus and covers the sclera and inner surface of
  the eyelid
• Has some responsibility of tear production
• Subject to infectionproblems from contact lens
  use
• Can be degraded by environmental conditions heat,
  wind, dust, etc.

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Sclera

• Whites of the eye
• Made up of 3 layers
• Tough, fibrous tissue site of extra-ocular
  muscle attachment
• Opaque...allows no light to enter
• Subject to inflammation

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Iris

• The colored part of the eyeunique to every
  individual like a fingerprint
• Color is dependent on the amount of pigment
• A diaphragm, the iris has tiny muscles that
  control the light levels in the eye
• Has 2 layers
• Pupil is located in the center of the iris
• pupil hole it is not an eye structure per se

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Lens

• Transparent, biconvex structure, held in place by
  ciliary zonules
• Composed of 6 layers
• Refracts light
• Nutrition comes from aqueous humorinsoluble
  deposits of proteins build up over time
  cataracts
• A clouding of the lens and capsule
• Live long enough and you WILL have some degree of
  cataract
• cataracts also caused by other agents

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Ciliary body

• Connects the choroid with the iris
• Has three parts including
• The ciliary muscle is ring shaped muscle that
  controls the shape of the lens (accommodation)
• The ciliary process is the attachment site for
  the zonules and produces the aqueous in the pars
  plicata
• The ciliary ring is attached to the choroid and
  is composed of the pars plana. The pars plana has
  no known function in the post-fetal eye thus this
  is a safe area through which surgical instruments
  may be inserted

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Zonules

• Attach the lens to the ciliary body
• May become broken or stretched causing the lens
  to move out-of-place

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Vitreous

• A thick, transparent gel like substance that
  fills the center of the eyeball, giving it form
  and shape
• A canal runs through the vitreous from optic disk
  to the lens. It is a developmental leftover from
  the hyaloid artery. Usually regresses but may
  persist and result in floaters
• May see reference to hyaloid membrane. This
  transparent tissue surrounds the vitreous and
  separates it from the retina
• Central retinal veins and arteries extend in
  bundles, exit and enter respectively through the
  optic nerve

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Choroid

• A brown vascular sheet lying between the sclera
  and the retina
• This is the blood supply for the retina

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Retina

• Most internal layer of eye, facing the vitreous
• Converts light energy into electrical energy
  which is then sent to the brain via the optic
  nerve
• Actually an extension of brain tissue
• Composed of 10 layerscontains photoreceptors
  cones, near center (responsible for seeing detail
  and color) and rods, in periphery (responsible
  for seeing in low light and seeing movement)
• Point of sharpest vision is in the fovea located
  in the center of the macula

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Ora Serrata

• A serrated juncture between the retina and
  ciliary body marking the transition between
  non-sensitive tissue and the retinal portion with
  many layers and specialized photoreceptor cells

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Intra-ocular muscles

• Purpose is to move eyes
• Maintain binocularity
• 6 muscles
• medial rectus (MR)moves the eye toward the nose
• lateral rectus (LR)moves the eye away from the
  nose
• superior rectus (SR)primarily moves the eye
  upward and secondarily rotates the top of the eye
  toward the nose
• inferior rectus (IR)primarily moves the eye
  downward and secondarily rotates the top of the
  eye away from the nose
• superior oblique (SO)primarily rotates the top
  of the eye toward the nose and secondarily moves
  the eye downward
• inferior oblique (IO)primarily rotates the top
  of the eye away from the nose and secondarily
  moves the eye upward

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Optic Nerve

• Purpose is for energy transmission to brain
• Subject to underdevelopment, damage, inflammation
  
• Contains over 1 million nerve fibersonce severed
  cannot be reconnectedno eye transplant
• Upon examination only the head can be seen by
  doctor. Should appear as yellowish pink, flat
  and with distinct margins
• The cup to disk ratio is evaluation as a measure
  of healthincrease in size of cup may indicate
  elevated pressure

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Optic Nerve Pathways/Visual Cortex

• Message is carried down the optic nerve through
  pathways to occipital cortex here vision becomes
  sight
• At the optic chiasm, the nasal nerve fibers
  cross temporal nerve fibers go straight back to
  cortex this arrangement impacts on visual fields
• Results in visual field losses can be predicted
  based on where damage is located on the optic
  nerve
• When damage is located anterior of the optic
  chiasm it is likely there will be a cortical
  component to the field loss

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