Limbus

• Limbus


  Transitional zone between the transparent cornea and the opaque sclera
• Limbus


  • Particularly important for drainage of aqueous humour, obstruction of which leads to glaucoma
• Clinical assessment of the drainage angle

  1. Van Herick's test

  2. Pen-torch test

  3. Gonioscopy
• Van Herick's test

  Ratio of corneal thickness (C) : gap (G) between back of cornea and front of iris
• Ratio ≥ 0.5


  Angle open
• Ratio < 0.5


  Angle closure possible
• Eclipse method (pen-torch shadow method)


  Assessment of drainage angle, more shadow (eclipse) occurs for shallow drainage angles
• Gonioscopy


  Cannot view drainage angle directly due to total internal reflection (TIR), gonioscopic lens (G) used, placed on cornea (C)
• Angle open if

  Trabecular meshwork (TM) seen
• Angle closure if

  Trabecular meshwork obscured
• Angle-closure glaucoma if


  No structures seen
• Optometrists should be able to explain glaucoma treatments, involving the use of drugs or surgery, to their patients
• Limbus


  Transitional zone between the transparent cornea and the opaque sclera
• Limbus


  • Particularly important for drainage of aqueous humour, obstruction of which leads to glaucoma
• Clinical assessment of the drainage angle

  1. Van Herick's test

  2. Pen-torch test

  3. Gonioscopy
• Van Herick's test

  Ratio of corneal thickness (C) : gap (G) between back of cornea and front of iris
• Ratio ≥ 0.5


  Angle open
• Ratio < 0.5


  Angle closure possible
• Eclipse method (pen-torch shadow method)


  Assessment of drainage angle, more shadow (eclipse) occurs for shallow drainage angles
• Gonioscopy


  Cannot view drainage angle directly due to total internal reflection (TIR), gonioscopic lens (G) used, placed on cornea (C)
• Angle open if

  Trabecular meshwork (TM) seen
• Angle closure if

  Trabecular meshwork obscured
• Angle-closure glaucoma if


  No structures seen
• Optometrists should be able to explain glaucoma treatments, involving the use of drugs or surgery, to their patients