Primary Angle-Closure (PAC)

• Synechial or appositional closure of the anterior chamber angle secondary to multiple mechanisms resulting in raised intraocular pressure (IOP) & structural changes in the eyes but w/o glaucomatous optic neuropathy
  
  • Iridotrabecular contact (ITC) is the hallmark of PAC & the most commonly identified sign which indicates that treatment is required
  • Defined by at least 180 degrees of ITC together w/ an elevated IOP or peripheral anterior synechiae (PAS) or both

Mechanisms of Primary Angle-Closure Glaucoma

• 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 approx 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 & coming into contact w/ the trabecular meshwork &/or peripheral cornea
• Obstruction at the Level of Iris &/or Ciliary Body (“Plateau Iris”)
  
  • Results from variations in iris & ciliary body anatomy that brings the peripheral iris into contact w/ the trabecular meshwork
  • Ciliary processes that are anteriorly positioned cause typical “iris plateau configuration” in which the iris plane is flat & the anterior chamber is not shallow axially
  • Characterized by a more anterior iris insertion, a thicker iris & a more anterior ciliary body position 
• Other less frequent mechanisms include anomalies at the lens level, eg thicker, more anteriorly placed lens, & 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 & 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-fold; 1st-degree relatives are at higher risk)
  • Older age
  • Female
  • Asian or Inuit descent

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