What landmarks are seen in the anterior chamber angle?

The structures noted in anterior-to-posterior sequence are as follows (numbered list corresponds to numbers in Fig. 16-1 ):

• 1.
  

  Schwalbe’s line: The peripheral or posterior termination of the Descemet’s membrane, seen clinically as the apex or termination of the corneal light wedge. May be visible inferiorly as the most anterior nonwavy pigmented line.

  
  
• 2.
  

  Anterior, nonpigmented, trabecular meshwork (TM): Clear whitish band.

  
  
• 3.
  

  Posterior, pigmented, TM: Variably pigmented band of homogeneous width. Usually most pigmented inferiorly ( Fig. 16-2 ).

  
  

  
  

  
  

  

  
  

  
  

  Inferior quadrant of heavily pigmented open angle.

  
  
  
  
• 4.
  

  Schlemm’s canal: Variably visible light gray band at the level of the posterior TM. Elevated episcleral venous pressure or pressure from the edge of the goniolens will cause blood to reflux, making it appear as a faint red band.

  
  
• 5.
  

  Scleral spur: Narrow, white band of sclera invaginating between the TM and the ciliary body. Marks the insertion site of the longitudinal muscle fibers of the ciliary body to the sclera.

  
  
• 6.
  

  Ciliary body (CB) band: Pigmented band marking the anterior face of the ciliary body. Variably, iris processes may be seen as lacy projections crossing this band. By definition, iris processes do not cross the scleral spur. Projections that cross the scleral spur to the TM are peripheral anterior synechiae (PAS) and may be focal, pillar-like, or broad sheets.

  
  
• 7.
  

  Iris

Diagram of anterior chamber anatomy.

Why is a goniolens necessary to visualize the anterior chamber angle?

Light from the anterior chamber (AC) angle undergoes total internal reflection at the cornea (tear)–air interface, preventing direct visualization. A goniolens changes the refractive index at the interface, enabling visualization.

What are the different kinds of gonioscopy? How do they differ?

• •
  

  A Koeppe contact lens is used for direct gonioscopy. This technique is cumbersome, requiring the patient to be supine. A clear, viscous liquid such as methylcellulose is used as a coupling medium. By using a direct viewing system such as a binocular microscope, the anterior chamber angle is visualized.

  
  
• •
  

  Indirect gonioscopy uses a mirrored contact lens. The Goldmann three-mirror lens vaults the central cornea and requires a viscous coupling liquid. The Zeiss ( Fig. 16-3 ), Posner, or Sussman four- or six-mirror lenses directly contact the cornea and thus do not require a coupling agent beyond the patient’s normal tear film. These can be used at the slip lamp.

  
  

  
  

  
  

  

  
  

  
  

  Zeiss goniolens.

  
  

Which goniolens is preferred by most glaucoma specialists and why?

The Zeiss, Posner, and Sussman lenses are preferred by a majority of glaucoma specialists for the following reasons:

• •
  

  Speed and ease of use (they do not require a viscous coupling liquid and, because of their four or six mirrors, they do not need to be rotated to see all 360 degrees of the angle).

  
  
• •
  

  The ability to perform indentation gonioscopy and the absence of a suction effect on the eye. Indentation cannot be performed with the Goldmann lens because of its larger diameter. The suction effect of the Goldmann lens can sometimes artificially widen narrow angles. These two qualities can be critically important when evaluating eyes with narrow angles.

  
  
• •
  

  Elimination of the transient degradation of corneal clarity that is a consequence of the viscous liquid and Goldmann lens manipulation, which can make subsequent fundus examination difficult.

  
  

  Warning: When first mastering gonioscopy, the Zeiss lens can be more difficult than the Goldmann lens. In inexperienced hands, excessive indentation can easily occur, which will make the angle appear wider than it really is. Zeiss gonioscopy demands a light touch. One way to make sure you are not pressing is for the contact to be so light that you occasionally lose part of the contact meniscus. If you see any corneal striae or if your view is not crystal clear, you are probably indenting.

How is gonioscopy performed?

• 1.
  

  Topical anesthesia is essential for patient comfort and cooperation.

  
  
• 2.
  

  Rest your elbow on the slit lamp platform and your ring and/or small fingers on the side bar or on the patient’s cheek to help stabilize your hand.

  
  
• 3.
  

  Examination can be facilitated by asking the patient to stare straight ahead with the fellow eye without blinking.

  
  
• 4.
  

  To facilitate viewing a particular quadrant of the angle with indirect gonioscopy, either tilt the mirror toward the quadrant or have the patient look toward that mirror. For example, when viewing the superior angle, either tilt the inferior mirror upward, toward the superior angle, or have the patient look down slightly, toward the inferior mirror.

  
  
• 5.
  

  The superior–inferior relationships in the nasal and temporal mirrors and the nasal–temporal (right–left) relationships in the superior and inferior mirrors are preserved, not inverted as in indirect ophthalmoscopy. For example, when viewing the superior angle through the inferior mirror, an area of PAS seen at five o’clock in the mirror is actually at one o’clock, not eleven o’clock.

How can I determine which patients may have narrow angles and need gonioscopy?

The van Herick technique uses a thin slit beam focused at the limbus to approximate angle depth by comparing the peripheral AC depth to corneal thickness. Grade I has a peripheral AC depth less than one-quarter of the corneal thickness; grade II is one-quarter of the corneal thickness; grade III is one-half of the thickness; and grade IV is one corneal thickness or more. Patients who are grade I or II certainly have narrow angles and should have gonioscopy. This technique, however, should never replace gonioscopy in eyes with clear media as part of a glaucoma evaluation. It falsely gives the appearance of an open angle in some eyes with plateau iris or anterior rotation of the ciliary body (see classification below).

What are the different gonioscopic anterior chamber angle classification systems?

Table 16-1 summarizes the Scheie system, which is rarely used, and the Schaffer system, which is the most commonly used.

The Spaeth system, however, is the most descriptive. The first element is a capital letter (A to E), for the level of iris insertion:

• •
  

  A = Anterior to TM

  
  
• •
  

  B = Behind the Schwalbe’s line, or at the TM

  
  
• •
  

  C = At scleral spur

  
  
• •
  

  D = Deep angle, CB band visible

  
  
• •
  

  E = Extremely deep

If during indentation gonioscopy, the true iris insertion is noted to be more posterior than originally apparent, the original impression is put in parentheses, followed by the true iris insertion outside parentheses.

The second element is a number that denotes the iridocorneal angle width in degrees at the level of the trabecular meshwork, usually from 5 to 45 degrees.

The third element is a lower-case letter describing the peripheral iris configuration:

• •
  

  f = Flat

  
  
• •
  

  b = Bowed or convex

  
  
• •
  

  c = Concave

  
  
• •
  

  p = Plateau configuration

In addition, the pigmentation of the posterior TM is graded on a scale of 0 (none) to 4 (maximal). For example, (A)C10b, 2+PTM refers to an appositionally closed 10-degree angle that, with indentation, opened to the scleral spur and revealed moderate pigmentation of the posterior TM.

How do I know if I can safely dilate a patient, with or without a slit lamp?

If no slit lamp is available, use a penlight and shine it from the temporal side perpendicular to the central visual axis. In an eye with a normal or “safe” anterior chamber depth, the entire nasal half of the iris will be illuminated as well as the temporal half. In an eye with a shallow or questionable anterior chamber depth, none or only part of the nasal half of the iris will be illuminated. This technique does not hold true in eyes with plateau iris.

If a slit lamp is available, angles that are less than or equal to 15 degrees are at risk for closure and probably should not be dilated. An eye with a 20 degree angle should be watched closely, as it may narrow further with time, and should be reevaluated with tonometry and gonioscopy after dilation. An exception to these general guidelines is plateau iris (discussed later), in which the angle may be wider than 20 degrees and still at risk for closure. Thus, the peripheral iris configuration is also very important.

What are other methods of evaluating anterior chamber angles besides gonioscopy?

There are several imaging devices that can display the anterior chamber angles. Ultrasound biomicroscopy (UBM) uses ultrasound to visualize the angles. The ultrasound waves are not blocked (absorbed) by the iris pigmented epithelium. Therefore, it has the advantage of visualizing the ciliary body. UBM is particularly useful to identify a plateau iris configuration. Anterior-segment optical coherence tomography (OCT) uses a diode laser to obtain anterior segment imaging. Limbus-to-limbus images are possible in a single scan with the Visante OCT. OCTs designed for retinal imaging can perform anterior segment imaging if used with adaptive lenses. However, because the diode laser can be blocked by the iris pigmented epithelium (especially in dark irises), OCT cannot visualize the CB as clearly as UBM in individuals with dark irises. In addition to UBM and OCT, Scheimpflug cameras (Pentacam) use a specific optical principle to image angles. Classification of angles by UBM and OCT is different from that by gonioscopy. Gonioscopy is still the gold standard of angle classification. Gonioscopy also gives valuable information such as pigmentation or presence of abnormal vessels that cannot be demonstrated by imaging devices.

How is angle closure classified?

• I.
  

  By clinical presentation

  
  
  
  
  • A.
    

    Acute

    
    
  • B.
    

    Subacute or intermittent

    
    
  • C.
    

    Chronic

  
  
  
  
• II.
  

  By mechanism

  
  
  
  
  • A.
    

    Posterior pushing mechanism

    
    
    
    
    • 1.
      

      Pupillary block (can occur in phakic, pseudophakic, or aphakic eyes)

      
      
      
      
      • a.
        

        Relative Idiopathic (i.e., primary angle closure) Miotic induced

        
        
      • b.
        

        Absolute or true: By posterior synechiae from any inflammatory etiology

      
      
      
      
    • 2.
      

      Lens induced

      
      
      
      
      • a.
        

        Phacomorphic (due to an intumescent cataractous lens or a swollen lens in a diabetic)

        
        
      • b.
        

        Lens subluxation

        
        
        
        
        • i.
          

          Trauma

          
          
        • ii.
          

          Pseudoexfoliation syndrome

          
          
        • iii.
          

          Hereditary/metabolic disorder (e.g., Marfan’s syndrome, homocystinuria)

        
        
        
        
      • c.
        

        Lens pushed forward

        
        
        
        
        • i.
          

          Aqueous misdirection syndrome (malignant or ciliary-block glaucoma)

          
          
        • ii.
          

          Mass (e.g., tumor, retinopathy of prematurity, persistent hyperplastic primary vitreous)

        
        

      
      
      
      
    • 3.
      

      Plateau iris

      
      
      
      
      • a.
        

        True plateau iris

        
        
      • b.
        

        Pseudoplateau—iris and ciliary body cysts

      
      
      
      
    • 4.
      

      Swelling/anterior rotation of the ciliary body (some overlap within this)

      
      
      
      
      • a.
        

        Inflammatory (e.g., scleritis, uveitis, after panretinal photocoagulation)

        
        
      • b.
        

        Congestive (e.g., after scleral buckling surgery, nanophthalmos)

        
        
      • c.
        

        Choroidal effusion—secondary to medications (e.g., topiramate), hypotony after trauma or surgery, uveal effusion, etc.

        
        
      • d.
        

        Suprachoroidal hemorrhage (SCH)—intraoperative or postoperative. Risk factors for SCH include previous intraocular pressure (IOP) elevation followed by hypotony, high myopia, advanced age, aphakia, previous vitrectomy, systemic hypertension or atherosclerotic vascular disease, and postoperative Valsalva maneuver

      
      

    
    
    
    
  • B.
    

    Anterior pulling mechanism—synechial angle closure

    
    
    
    
    • 1.
      

      Chronic appositional closure from any of the above

      
      
    • 2.
      

      Intraocular inflammation (uveitis)—forming synechial membrane

      
      
    • 3.
      

      Neovascular glaucoma

      
      
      
      
      • a.
        

        Central retinal vein occlusion (CRVO), accounts for one-third of cases

        
        
      • b.
        

        Diabetes mellitus, accounts for another one-third of cases

        
        
      • c.
        

        Carotid occlusive disease, comprises approximately 10% of cases

        
        
      • d.
        

        Miscellaneous (e.g., central retinal artery occlusion (CRAO), tumors, chronic retinal detachment)

      
      
      
      
    • 4.
      

      Iridocorneal endothelial syndrome

      
      
      
      
      • a.
        

        Progressive iris atrophy

        
        
      • b.
        

        Chandler’s syndrome

        
        
      • c.
        

        Cogan-Reese syndrome

      
      

    
    

  
  

What do the terms PACS, PAC, APAC, and PACG signify? How are they related to acute, subacute, and intermittent angle closure?

• 
  

  PACS stands for primary angle closure suspect

  
  
• 
  

  PAC stands for primary angle closure

  
  
• 
  

  PACG stands for primary angle closure glaucoma

  
  
• 
  

  APAC stands for acute primary angle closure

The terms refer to a new classification system of angle closure, which is currently used in most clinical and epidemiological studies. This system was developed by the International Society of Geographical and Epidemiological Ophthalmology between 1998 and 2005. PACS refers to patients with narrow angle on gonioscopy but without elevated IOP or presence of PAS. PAC refers to patients with narrow angle and elevated IOP or PAS. PACG refers to patients with narrow angle and glaucomatous optic neuropathy and/or visual field defects ( Table 16-2 ).

The purpose of this new classification system is to unify the definition of glaucoma. It reserves the term glaucoma for the presence of optic neuropathy. For example, a patient presenting with acute elevated IOP secondary to angle closure will be referred to as APAC instead of acute angle closure glaucoma, as the patient may not have developed (yet) glaucoma optic neuropathy at the episode of acute angle closure.

The new classification system relates to the traditional classification of angle-closure glaucoma to some degree. Acute angle-closure glaucoma is referred to as acute primary angle closure; chronic angle-closure glaucoma can be either PAC or PACG depending on the status of the optic nerve and visual field. Subacute or intermittent angle-closure glaucoma can be PACS, PAC, or PACG with self-limited symptoms. The status of the angle and optic nerve dictates the classification of angle closure instead of the patient’s symptomatology and probably has better prognostic value than the previous system.

The new classification intends to describe the natural history of angle closure. Anatomically narrow angles (i.e., PACS) are common; about 4 to 10% of the population above the age of 40 have some degree of narrow angle. Angles narrow with age as the lens thickens throughout life. Some (not all) PACS will progress to PAC and eventually to PACG. Some PACS will develop APAC. We are still trying to identify which subgroup of PACS will progress to PACG and evaluating effective preventive treatments.