Primary and secondary
angle-closure glaucoma

Patients with anatomically narrow angles and primary and secondary chronic angle-closure glaucoma are usually asymptomatic. Those with advanced glaucoma complain of blurry vision and visual field defects.

Patients with acute angle closure present with sudden eye pain, conjunctival redness, and corneal oedema. The intraocular pressure is mostly between 40 and 80 mmHg. Those patients describe halos around lights and may even have transient vision loss. They often develop symptoms of nausea and vomiting.

Patients may have subacute or intermittent angle closure. They represent with milder symptoms like some blurring of the vision or halos with mild to moderate eye pain, brow ache, or headache. Symptoms are often resolved if patients go to sleep or go into a lit room.

Intraocular pressure measurement

The gold standard for IOP measurement is Goldmann Applanation Tonometry (GAT). Fluorescein dye is placed on the patient’s eye to highlight the tear film. A split-image prism divides the image of the tear meniscus into a superior and an inferior arc. The intraocular pressure is taken when these arcs are aligned such that their inner margins touch.(15)

Errors that may cause false IOP reading: Central corneal thickness, excessive or insufficient fluorescein in the tear film affecting the thickness of the overlapping arcs, high astigmatism, irregular or scarred cornea, pressure from a finger on the eyelid while taking the measurement, and breath holding or Valsalva manoeuvre by the patient during measurement.

Another option is rebound tonometry (iCare devices use this technique). It has a good agreement with Goldman and Tono-Pen readings. A 1.8mm diameter plastic ball on a stainless steel wire is held in place by an electromagnetic field in a battery-powered handheld device. A spring moves the wire and ball forward rapidly when a button is pushed. When the ball hits the cornea, the ball and wire decelerate; the deceleration is more rapid if the IOP is high and slower if the IOP is low. The speed of deceleration is measured and converted by the device into IOP. No anaesthetic is necessary. Central corneal thickness also affects the accuracy of IOP measurement.(15) Air Puff Tonometer, Ocular Response Analyser (ORA),  Tono-Pen, and Schiøtz  are other options to measure IOP. 

Central corneal thickness measurement

Central corneal thickness (CCT) is one of the biomechanical attributes of the cornea. Thick corneas may give false positive high IOPs, whilst thin corneas may give false average IOPs. Standard corneal thickness is considered between 540 and 560 microns. CCT may be helpful in baseline risk profiling, but despite existing IOP correction algorithms, the European Glaucoma Society suggests avoiding them.(28)

Anterior chamber angle examination

There are a few methods to examine the anterior angle: Gonioscopy on a slit lamp, ultrasound biomicroscopy, or anterior OCT.

Gonioscopy is essential to diagnose narrow or closed angles and should be performed on the initial visit. Various classification systems have been described to assess the extent of an open angle. The ideal way to perform gonioscopy is in a dark room using a small rectangle of light only as bright as necessary to view the angle structures, as light can open an appositionally closed angle in about one-third of cases. Dynamic or compression or indentation gonioscopy is essential to differentiate appositional and synechial closures. Gentle pressure on the cornea with the goniolens pushes back the iris and reveals whether the angle can be opened further; if not, synechial closure is present.(3) This manoeuvre can also help break acute attacks by forcing fluid into the periphery and opening areas of appositional closure.

Different classification systems are used to classify whether the anterior angle is closed or opened. Shaffer classification system describes the degree to which the angle is open rather than the degree to which it is closed (compared to the Scheie’s system). The Shaffer system approximates the angle at which the iris inserts relative to the trabecular meshwork.

Remember that it is difficult to perform gonioscopy in patients with acute angle-closure attacks.

Table 1: Schaffer classification system(16)

It is important to do a thorough eye examination and look for potential causes of narrow-angle, like new vessels of the angle, cells, and keratic precipitates (KPs) in the anterior chamber, posterior synechiae, posterior segment masses, thick cataract, and anterior chamber depth.

Slit lamp examination/colour fundus photography is helpful in examining people with suspected glaucoma. The following features should be considered in patients with suspected glaucoma(18):

• High cup: disc ratio
• Cup: disc ratio asymmetry between eyes (usually considered significant if greater than 0.2)
• Vertical elongation of cup
• Focal neuro-retinal rim thinning or notching
• Vessel bayoneting
• Beta-zone peripapillary atrophy (occurs as a result of atrophy of the RPE and choriocapillaris)
• Disc haemorrhage

Optical coherence tomography – it is part of routine imaging in glaucoma patients. It analyses RNFL and optic nerve heads in patients with a chronic type of glaucoma.

Visual fields test – automated threshold perimetry is used to diagnose early signs of visual field defects and to monitor progression. The defects involved in POAG are:

Patients suspected of having angle-closure glaucoma presenting at optometry practices should be referred to ophthalmology by specific guidelines set by the local healthcare system.

Surgery

Peripheral laser iridotomy is a surgical procedure that may have a preventative effect in preventing pupillary block. Therefore, patients with narrow angles should be regularly monitored.

Management of acute angle-closure attack

The role of medical therapy in acute angle-closure attacks is to lower IOP, reduce pain, and clear corneal oedema in preparation for iridotomy:

Topical medical therapy

Always check for potential contraindications of using the below drugs: 

• Beta-blockers
• Selective alpha agonists
• Carbonic anhydrase inhibitors
• Miotics (e.g., pilocarpine 2%) may help break an early angle-closure attack but may be ineffective if the iris is already ischemic. Likewise, high-concentration miotics (e.g., pilocarpine 4%) should be avoided because of the potential for forward displacement iris-lens diaphragm.
• Hyperosmolar agent (e.g. 5% sodium chloride) – assists in clearing corneal oedema
• Prednisolone 1% – decreases inflammation.

Systemic medical therapy includes oral or intravenous carbonic anhydrase inhibitors and osmotic agents (i.e., intravenous mannitol). 

An experienced eye care specialist should do paracentesis. Be aware that it is only performed in cases with very high IOPs to buy time for medications to start working.

Laser iridotomy, including the contralateral eye, should be done as quickly as possible.