Primary Angle-Closure (PAC)

• Synechial or appositional closure of the anterior chamber angle secondary to multiple mechanisms resulting in raised intraocular pressure (IOP) and structural changes in the eyes but without glaucomatous optic neuropathy
  
  • Iridotrabecular contact (ITC) is the hallmark of PAC and the most commonly identified sign which indicates that treatment is required
  • Defined by at least 180 degrees of ITC together with an elevated IOP or peripheral anterior synechiae (PAS) or both, without optic neuropathy

Mechanisms of Primary Angle-Closure

• Mechanisms responsible for angle closure are defined in terms of anatomic location of obstruction to aqueous flow
• Important to determine the mechanism involved since initial management is directed at the underlying disease
• Pupillary Block Mechanism
  
  • Accounts for approximately 75% of cases of primary angle-closure
  • Aqueous flow from the posterior chamber through the pupil to the anterior chamber is blocked, resulting in the peripheral iris bowing forward and coming into contact with the trabecular meshwork and/or peripheral cornea
• Obstruction at the Level of Iris and/or Ciliary Body (“Plateau Iris”)
  
  • Results from variations in iris and ciliary body anatomy that brings the peripheral iris into contact with the trabecular meshwork
  • Ciliary processes that are anteriorly positioned cause typical “iris plateau configuration” in which the iris plane is flat and the anterior chamber is not shallow axially
  • Characterized by a more anterior iris insertion, a thicker iris and a more anterior ciliary body position 
• Other less frequent mechanisms include anomalies at the lens level, eg thicker, more anteriorly placed lens, and posterior to the lens (aqueous misdirection syndrome), eg forward movement of the lens iris diaphragm results in intraocular pressure (IOP) elevation

• Most angle closures are asymptomatic until advanced
  
  • Specificity and sensitivity of symptoms for identifying angle closure are very poor, although symptoms such as redness, pain, halos, blurring of vision may help identify significant angle closure

• Demographic risk factors
  
  • Family history of angle closure (increases glaucoma risk 5- to 8-fold; first-degree relatives are at higher risk)
  • Older age
  • Female
  • Asian or Inuit descent

• Ocular risk factors
  
  • Increasing intraocular pressure 
  • Hyperopia
  • Shallow central anterior chamber depth
  • Shallow peripheral anterior chamber depth
  • Steep corneal curvature
  • Short axial length
  • Thick crystalline lens