A shallow anterior chamber is a condition in which the anterior chamber depth (ACD), the space between the corneal endothelium and the iris/lens anterior surface, is shallower than normal. Generally, a central anterior chamber depth < 2.5 mm is considered a guideline, but in elderly hyperopic eyes with a short axial length, it may be relatively shallow even within the normal range.
In primary angle-closure disease (PACD), characteristic anatomical structures such as a shallow anterior chamber, short axial length, and a relatively thick lens positioned anteriorly are observed. A shallow anterior chamber is not a disease in itself but appears as a clinical sign of various conditions, including angle-closure disease. It is often managed as a continuum from PACS to PAC to PACG.
Approximately 0.7% of people aged 40 and older worldwide have primary angle-closure glaucoma (PACG), with an estimated 20.2 million patients, of whom about 15.5 million are Asian 2). With aging, the lens thickens and shifts forward, and the anterior chamber naturally tends to become shallower.
| Risk factors | Details |
|---|---|
| Sex and age | More common in elderly women |
| Refraction and eye shape | Hyperopia, short axial length, small corneal diameter, lens thickening |
| Family history | First-degree family history of angle-closure glaucoma |
| Race | Higher prevalence in Asians (Chinese, Japanese) and Inuit2) |
| Medications | Anticholinergics, mydriatics, tricyclic antidepressants, SSRIs, nasal decongestants |
| Precipitating factors | Prolonged head-down posture, nocturnal physiologic mydriasis |
In the shallow anterior chamber stage (PACS), most patients are asymptomatic and immediate treatment is not always necessary. However, prophylactic laser iridotomy (LI) has been reported to reduce the risk of developing PAC by 47% at 6 years and 70% at 14 years2). Progression from PACS to PAC/acute attack is relatively rare, occurring in about 4% at 6 years and 12% at 14 years. However, it is important to decide on a management plan in consultation with an ophthalmologist, considering factors such as family history, frequency of mydriatic use, and difficulty in accessing medical care.
Symptoms of shallow anterior chamber are broadly classified into acute and chronic types depending on the cause and course.
In acute primary angle closure (APAC) attacks, a rapid and severe elevation of intraocular pressure to 40–80 mmHg occurs, requiring emergency ophthalmic management.
Subjective symptoms:
Objective findings:
Chronic shallow anterior chamber is often asymptomatic and may go unnoticed until moderate intraocular pressure elevation of 20–30 mmHg or visual field changes are detected. Slit-lamp microscopy reveals a shallow peripheral anterior chamber, and screening is performed using the van Herick method and gonioscopy.
This may indicate an acute angle-closure glaucoma attack. If severe unilateral eye pain, headache, nausea, along with decreased vision, blurred vision, and colored halos appear simultaneously, immediate ophthalmic emergency care should be sought. Intraocular pressure can rapidly rise to 40–80 mmHg, and irreversible optic nerve damage can occur within hours without treatment. Self-medication with over-the-counter drugs is dangerous; prompt ophthalmic intervention (eye drops, intravenous medication, laser treatment) is necessary.
The causes of shallow anterior chamber are broadly divided into five categories.
① Anatomical/Physiological
Mechanism: Shallow anterior chamber due to structural features of the anterior segment
Short axial length (hyperopia): The eyeball is small, and the anterior chamber is congenitally shallow.
Age-related lens enlargement: The lens thickens and moves forward, making the anterior chamber shallow.
Congenitally narrow anterior segment: Shallow anterior chamber associated with microphthalmos or microcornea.
② Pupillary Block
Mechanism: Blockage of aqueous humor flow from the posterior chamber to the anterior chamber leads to forward bulging of the iris.
Relative pupillary block: Contact between the posterior iris surface and the anterior lens surface → increased posterior chamber pressure → trabecular meshwork obstruction.
Includes acute/chronic primary angle closure glaucoma (APACG/CACG), plateau iris, and lens-induced glaucoma 1).
③Ciliary body and choroidal disorders
Mechanism: Secondary shallow anterior chamber due to forward displacement of posterior ocular tissues.
Malignant glaucoma: Anterior rotation of the ciliary body or abnormal aqueous flow into the vitreous cavity → forward displacement of the vitreous → circumferential shallow anterior chamber.
Choroidal hemorrhage, choroidal detachment, and intraocular tumors (choroidal elevation).
④Postoperative and traumatic causes
Mechanism: Shallow anterior chamber due to low intraocular pressure, wound leakage, or tissue damage
Overfiltration after filtering surgery (hypotony), inadequate watertightness of corneal incision, postoperative choroidal detachment, after ocular trauma.
After filtering surgery in eyes with chronic angle-closure, the risk of shallow anterior chamber, choroidal detachment, and malignant glaucoma is particularly high.
⑤ Inflammatory
Mechanism: Anterior displacement of posterior ocular tissues due to edema and inflammation
Harada disease (Vogt-Koyanagi-Harada disease): Angle closure caused by choroidal and ciliary body edema. Bilateral, with systemic symptoms (headache, tinnitus, skin manifestations).
Secondary glaucoma associated with uveitis may also present with a shallow anterior chamber.
Multiple mechanisms are involved in the development of angle-closure glaucoma1).
Secondary angle closure can be caused by intumescent cataract, lens dislocation, topiramate or sulfonamide drugs (inducing ciliary body edema), scleral buckle surgery, and panretinal photocoagulation2).
Drugs with mydriatic effects or those that induce ciliary body edema are dangerous. These include anticholinergics (butylscopolamine, scopolamine, antihistamines, antipsychotics), sympathomimetics (nasal decongestants), tricyclic antidepressants, SSRIs, topiramate, and sulfonamide drugs2)3). Mydriasis triggers attacks because pupillary block is maximal at mid-dilation (4–6 mm). If shallow anterior chamber or angle closure is noted, it is important to consult an ophthalmologist before using these medications.
Diagnosis of shallow anterior chamber and angle closure requires a combination of several examinations.
This is a non-contact screening examination using only a slit-lamp microscope. The patient’s eye is kept in primary gaze, and a thin slit beam is directed at the temporal corneal limbus at a 60-degree oblique angle. The peripheral anterior chamber depth (ACD) is evaluated as a ratio to the peripheral corneal thickness (CT). It does not require a gonioscope or special equipment and is widely used for screening angle closure.
| Grade | ACD/CT Ratio | Likelihood of Angle Closure |
|---|---|---|
| 4 | ≥ 1 | Almost none |
| 3 | 1/4 to less than 1 | Low |
| 2 | = 1/4 | Possible (indication for detailed examination) |
| 1 | < 1/4 | High |
| 0 | 0 (contact) | Occluded |
Grade 2 or lower (ACD/CT ≤ 1/4) indicates possible angle closure, and gonioscopy should be performed. However, in plateau iris, the central anterior chamber is relatively deep, so it may be missed on screening, requiring caution.
Gonioscopy is the clinical standard for angle evaluation. It is performed in a dark room using a thin slit beam, taking care to avoid illuminating the pupil, and evaluating all four quadrants.
It can scan all four quadrants simultaneously without contact. It can be performed by a technician and is suitable for dynamic evaluation of angle changes under both dark and light conditions.
Quantitative evaluation indices (all still under development) 2):
Although there may be discrepancies with gonioscopy, it is useful for tracking changes over time 2). It cannot assess color information, neovascularization, or angle nodules, and does not replace gonioscopy.
It is the only examination method that can evaluate the ciliary body and the posterior surface of the iris. It is essential for diagnosing plateau iris and malignant glaucoma.
Characteristic UBM findings of plateau iris:
Plateau iris is thought to be involved in about one-third of cases where ITC persists after LI2). It is superior to AS-OCT in identifying plateau iris2).
| Stage | ITC ≥ 180° | IOP elevation or PAS | Glaucomatous optic neuropathy (GON) |
|---|---|---|---|
| PACS (Primary Angle Closure Suspect) | Present | Absent | Absent |
| PAC (Primary Angle Closure) | Present | Present | Absent |
| PACG (Primary Angle Closure Glaucoma) | Present | Present | Present |
ITC: iridotrabecular contact. Assessed by gonioscopy or AS-OCT 2).
Key points for differential diagnosis:
Anterior segment OCT (AS-OCT) is non-contact, can be performed by technicians, imposes less burden on patients, and is excellent for quantitative assessment and longitudinal follow-up. In contrast, gonioscopy allows observation of iris color, neovascularization, and angle nodules, and can differentiate appositional closure from PAS using compression. Currently, gonioscopy remains the gold standard for definitive diagnosis. A practical approach is to use AS-OCT for screening and then perform gonioscopy for detailed examination when abnormalities are found 2).
Treatment of shallow anterior chamber is selected based on the cause, stage, and urgency.
An acute attack is an ophthalmic emergency, and intraocular pressure should be lowered as quickly as possible.
| Drug | Dosage and Administration | Precautions |
|---|---|---|
| 20% Mannitol solution | 1.0–2.0 g/kg intravenously over 30–60 minutes | Contraindicated or use with caution in heart failure or renal impairment |
| Glycerol | 300–500 mL intravenously over 45–90 minutes | Monitor for hyperglycemia in diabetic patients |
| 1–2% Pilocarpine hydrochloride | Instill every 20–30 minutes (2–3 times per hour) | Ineffective when sphincter paralysis occurs due to high intraocular pressure. May worsen pupillary block by forward movement of the ciliary muscle 1) |
| Acetazolamide | 10 mg/kg IV or oral | Monitor for metabolic acidosis and electrolyte abnormalities |
| Corticosteroid eye drops | Usual concentration as appropriate | To reduce inflammation |
Note that when the iris sphincter is paralyzed due to high intraocular pressure, frequent administration of pilocarpine is ineffective and may worsen pupillary block by anterior movement of the ciliary muscle1).
This is chosen when drug therapy is insufficient or when rapid corneal clearing is needed.
This is the definitive treatment for relieving pupillary block and is rated as recommendation grade 1A in the 5th edition of the Glaucoma Practice Guidelines1).
Replacing the lens with an intraocular lens increases anterior chamber depth and fundamentally resolves pupillary block (recommendation grade 1A)1). In the acute phase, the risk of intraoperative complications is high, and an experienced surgeon is recommended (recommendation grade 1B)1).
If elevated intraocular pressure persists after LI relieves pupillary block, additional medical or surgical treatment for residual glaucoma is added1).
EAGLE trial (Lancet 2016): A multicenter RCT comparing early lens extraction (phaco-IOL) with LI for PAC (IOP ≥ 30 mmHg) and PACG (IOP ≥ 21 mmHg). At 3 years, the early lens extraction group had approximately 10 times better medication-free IOP control than the LI group, and QOL measures were significantly better4). Based on these results, lens reconstruction is recommended as first-line treatment for APAC patients1).
Aqueous outflow reconstruction procedures (goniosynechialysis, trabeculotomy, MIGS) are indicated for cases with extensive PAS1).
Replacing the aged lens (approximately 5 mm thick) with a thin intraocular lens (approximately 0.5–1 mm) increases anterior chamber depth by an average of 1–2 mm. Additionally, in eyes with angle closure, lens extraction causes the ciliary processes to move posteriorly, further widening the angle. This dual mechanism relieves pupillary block, normalizing anterior chamber depth and opening aqueous outflow pathways. The EAGLE study demonstrated in a large RCT that this effect significantly surpasses that of LI alone 4).
Relative pupillary block is the most common mechanism of angle-closure disease.
This is the pathophysiological basis for why mydriatics, anticholinergics, and dark environments at night can trigger acute attacks.
Plateau iris is a condition in which the iris root is bent forward due to anterior displacement of the ciliary processes.
Dynamic changes in the choroid may contribute to acute angle closure attacks. Imaging studies have reported a mechanism in which choroidal expansion during intraocular pressure elevation increases posterior pressure, pushing the lens-iris diaphragm forward and triggering angle closure 3). This is considered one of the reasons why acute attacks tend to occur at night (in darkness) and in a face-down position (choroidal congestion).
Cataract surgery replaces the thickened lens with a thin intraocular lens, which not only increases anterior chamber depth but also, in eyes with angle closure, causes the ciliary processes to move posteriorly after lens extraction, further widening the angle. This dual mechanism supports the high efficacy of early lens extraction demonstrated in the EAGLE trial4).
