Glaucoma

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Glaucoma
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(No Transcript)
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• Intraocular pressure is determined by a balance
  between production and removal of aqueous humor
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• Aqueous is actively secreted into the posterior
  chamber by the ciliary process (non-pigmented
  epithelium), by a combination of active transport
  and ultrafiltration
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• Filtration As blood flows in the ciliary body's
  capillaries, it is coarsely filtered by the
  capillaries' endothelial cells. The resulting
  plasma is then refiltered by the pigmented and
  nonpigmented ciliary epithelial cells and is
  secreted into the posterior chamber 

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• Active transport occurring in the nonpigmented
  cilary epithelial cells induces small osmotic
  pressure gradients in between the cells. A higher
  concentration of solutes in the proximal part of
  the intercellular space generates a flow of
  water. The concentration diminishes from the
  proximal part to the distal part, releasing the
  liquid into the posterior chamber 
• It then passes through the pupil into the
  anterior chamber and leaves the eye predominantly
  through the conventional pathway

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Conventional Pathway

• Aqueous humor exits the eye through
  the trabecular meshwork into Schlemm's canal
• It flows through 2530 collector canals into the
  episcleral veins to reach the bloodstream 
• The greatest resistance to aqueous flow is
  provided by the trabecular meshwork, and this is
  where most of the aqueous outflow occurs
• Damage here raises the resistance and increases
  IOP in primary open angle glaucoma

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Uveoscleral Pathway

• A small proportion of the aqueous (4) drains
  across the ciliary body into the supra-choroidal
  space
• It is then absorbed into the venous circulation

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Intraocular Pressure

• Intraocular pressure is determined by a balance
  between production and removal of aqueous humor 
• Normal range 10 - 21 mmHg
• Hypotony is defined as intraocular pressure equal
  to or less than 5 mmHg which could indicate fluid
  leakage and deflation of the eyeball
• IOP decreases at night due to the slower
  production of aqueous humor
• Raised IOP causes mechanical damage to the axons
• Raised IOP also causes ischemia of the axons by
  reducing blood flow at the nerve head 

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Goldman Tonometer
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• against anesthesized cornea
• fluorescein is applied in the tear film
• 2 hemicircles are seen by the examiner
• force of contact is increased until the inner
  borders of the hemicircles just touch - endpoint
• the endpoint at which a fixed amount of the
  cornea is achieved

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Perimeter

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• accurate plotting of the visual field
• kinetic VF - patient indicates when he first sees
  a light of a specific size and brightness brought
  in from the periphery
• static VF - patient indicates when he first sees
  a stationary light of increasing brightness,
  presented anywhere in the visual field
• useful in chronic ocular and neurological
  conditions, to monitor changes in the visual field