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Ocular System

Primary angle closure glaucoma (PACG)

Acute ocular hypertension disease that may lead to irreversible damage to the optic nerve and other ocular tissues

Acute ocular hypertension disease that may lead to irreversible damage to the optic nerve and other ocular tissues

  • Ophthalmic emergency

Clinical definitions:

Based on objective findings, this classification is widely used in the classification of subjects in research
  • Primary Angle Closure Suspect (PACS): Eye in which appositional contact between the peripheral iris and posterior trabecular meshwork is present or considered possible, in the absence of elevated intraocular pressure (IOP), peripheral anterior synechiae (PAS), disc or Visual Field (VF) changes.
  • Primary Angle Closure (PAC): PACS with statistically raised IOP and/ or primary PAS, without disc or VF changes
  • Primary Angle Closure Glaucoma (PACG): PAC with glaucomatous optic neuropathy and corresponding VF loss.

Etiology

Ocular risk factors:

PCAG is caused by disorders of the iris, the lens, and retrolenticular structures.
  • Crowded anterior segment in a small eye
  • Shallow central anterior chamber depth
  • Thicker and more anteriorly positioned lens
  • Short axial length of the eye

Risk factors:

  • Female sex
  • Older age
  • Asian ethnicity (eg, Chinese)

Pathophysiology

Primary closed-angle glaucoma is characterized by apposition of the peripheral iris against the trabecular meshwork resulting in obstruction of aqueous outflow by closure of an already narrow angle of the anterior chamber.

Aqueous Humor Drainage Pathways of Healthy and Glaucomatous Eyes | Weinreb, R. N., Aung, T., & Medeiros, F. A. (2014). The pathophysiology and treatment of glaucoma: a review. JAMA, 311(18), 1901–1911. https://doi.org/10.1001/jama.2014.3192

Typical features of PACG eye:

  • Shallow anterior chamber
  • Increased thickness of the lens
  • Hyperopic refractive error
  • Short axial length

Presentation

  • Sudden onset of severe unilateral eye pain or a headache
  • Associated with blurred vision, rainbow-colored halos around bright lights
  • Nausea and vomiting

Vogt’s triad:

Seen in postcongestive glaucoma and in treated cases of acute congestive glaucoma
  1. Glaucomflecken: Anterior subcapsular lenticular opacity
  2. Patches of iris atrophy
  3. Slightly dilated non reacting pupil (due to sphincter atrophy)

Diagnosis

Ophthalmoscopic examination:

  • Hazy cornea (due to very high IOP)
  • Pupil mid-dilated and vertically oval
  • Pupil poorly reactive to light
  • Classically, the eye is rock hard

Gonioscopy:

Simple, handheld, mirrored instrument is placed on the patient’s eye, followed by examination of the angle using a slit-lamp biomicroscope
Gonioscopic Imaging and Optical Coherence Tomographic Imaging of Open-Angle and Closed-Angle: A lens with a prism is placed on the eye during gonioscopy, a process during which the examiner is able to examine the angle configuration and assess for the presence of angle closure. A, The arrowhead points to the lack of contact between the iris and angle. Image on the right shows the anterior segment captured by optical coherence tomography. The arrowheads point to visible trabecular meshwork. B, The angle is closed with the trabecular meshwork not visible due to apposition of the iris to the angle. In the right image, the arrowheads indicate apposition of the iris to the angle wall; the anterior chamber is shallow and the iris has a slightly convex configuration. This is more noticeable in the region of the iris on the right. | Weinreb, R. N., Aung, T., & Medeiros, F. A. (2014). The pathophysiology and treatment of glaucoma: a review. JAMA, 311(18), 1901–1911. https://doi.org/10.1001/jama.2014.3192

Shaffer system:

Describes the degree to which the anterior chamber angle (ACA) is open
Modified from a figure by T.Tarrant. | Gonioscopy Simulation
Anterior chamber angle (ACA) grading system as described by Shaffer. | Evaluation of Nasal and Temporal Anterior Chamber Angle with Four Different Techniques – Scientific Figure on ResearchGate. Available from: https://www.researchgate.net/figure/ACA-grading-system-as-described-by-Shaffer_tbl2_276494875 [accessed 19 Nov, 2020]

Ultrasound biomicroscopy:

Ultrasound biomicroscopy image demonstrating plateau iris configuration | See, J. L., Aquino, M. C., Aduan, J., & Chew, P. T. (2011). Management of angle closure glaucoma. Indian journal of ophthalmology, 59 Suppl(Suppl1), S82–S87. https://doi.org/10.4103/0301-4738.73690

Management

Acute primary angle-closure is an ocular emergency and requires immediate management to avoid blindness. The aims of the treatment are to achieve rapid pressure control with topical and systemic medications to limit optic nerve damage.

Immediate management:

  • IV Acetazolamide f/b oral taper (carbonic anhydrase): Reduces aqueous humour production
  • IV Mannitol
  • First-line antiglaucoma medications

Laser peripheral iridotomy:

Eliminate pupillary block and widen the angles by reducing the pressure differential between the anterior and posterior chambers
Closed-Angle Glaucoma Treatment by Laser Peripheral Iridotomy: C, Arrowhead points to the full-thickness hole in the iris. | Weinreb, R. N., Aung, T., & Medeiros, F. A. (2014). The pathophysiology and treatment of glaucoma: a review. JAMA, 311(18), 1901–1911. https://doi.org/10.1001/jama.2014.3192

Laser iridoplasty:

By applying surface photocoagulation burns in the iris, tissue contraction results in pulling of the peripheral iris away from the trabecular meshwork, thereby opening the anterior chamber angle.

Surgical iridectomy:

If iridotomy is unsuccessful or difficult to perform because of a cloudy cornea
  • Prophylactic iridotomy should be carried out for the fellow eye, which is at high risk of acute angle closure.

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