Wei Jia Liu

University Hospital Southampton, Southampton, United Kingdom

Introduction

Ocular hypotony is classically defined as an intraocular pressure (IOP) below 6.5 mmHg (statistical definition) or as an IOP low enough to result in visual loss (clinical definition) (1). Persistent hypotony can result in hypotony maculopathy, a condition first described by Dellaporta in 1954, which is characterised by chorioretinal folds, retinal vascular tortuosity, and optic disc oedema (2). Recognition of hypotony maculopathy is key, as this can be sight-threatening and timely intervention may prevent permanent visual loss.

Causes and pathophysiology

The causes of ocular hypotony and subsequent maculopathy are vast. Mechanistically, causes can be broadly divided based on two underlying pathophysiological categories: excessive aqueous humour outflow and reduced aqueous humour production.

1. Increased aqueous humour outflow

This is most commonly encountered in postoperative settings but may also arise following trauma or due to inflammatory processes. Causes include (1, 2):

• Excessive filtration following glaucoma surgery
• Leaking filtering blebs
• Surgical wound leaks
• Cyclodialysis clefts, creating a direct communication with the suprachoroidal space
• Scleral perforation
• Ocular inflammation e.g., uveitis (can enhance uveoscleral outflow)

2. Decreased aqueous humour production

Alternatively, hypotony may result from impaired aqueous humour secretion due to ciliary body dysfunction, inflammation, or reduced perfusion. Contributing factors include (1, 2):

• Toxic effects of antimetabolites such as mitomycin C on the ciliary body
• Ciliochoroidal detachment
• Iridocyclitis causing inflammatory ciliary shutdown
• Ocular inflammation e.g., uveitis
• Retinal detachment with secondary ciliary body dysfunction
• Systemic conditions such as severe dehydration
• Myotonic dystrophy
• Vascular occlusive disease leading to ciliary body hypoperfusion (e.g., central retinal artery occlusion)

Among all causes, glaucoma filtration surgery remains the most frequently implicated, with reported incidences of postoperative hypotony maculopathy reaching up to 18% (2).

Risk factors (3)

Several patient and surgical factors increase susceptibility to hypotony maculopathy, including:

• Myopia
• Male sex
• Younger patients
• Use of antifibrotic agents, particularly mitomycin C and 5-fluorouracil (leading to reduced scarring and increased risk of overfiltration)

Clinical features

Symptoms

Patients may present with reduced central visual acuity, blurry vision, and metamorphopsia, although some may be asymptomatic.

Signs

Clinical examination typically reveals a low IOP, often below 6.5 mmHg, accompanied by painless visual decline and a hyperopic shift in refraction due to posterior scleral flattening. Fundoscopic examination demonstrates characteristic findings, including optic disc oedema and chorioretinal folds within the posterior pole, frequently radiating from the fovea. Retinal vessels may appear tortuous with venous congestion. Less commonly, cystoid macular oedema or serous retinal detachment has been reported (4).

Investigations and diagnosis

Diagnosis is guided by the patient’s history and clinical examination findings, with further investigations, such as imaging, providing supportive evidence.

Optical coherence tomography (OCT)

OCT plays an important role in the diagnosis and follow-up of hypotony-related maculopathy. OCT may demonstrate retinal and choroidal folds, as well as macular oedema (4, 5).

Fundus fluorescein angiography (FFA)

FFA can highlight chorioretinal folds and assist in distinguishing choroidal from retinal involvement. Typical findings include alternating bands of hyperfluorescence and hypofluorescence corresponding to the crests and troughs of choroidal folds (2).

Indocyanine green (ICG) angiography

ICG angiography may identify cases not evident on FFA, demonstrating multiple hypofluorescent streaks in the posterior pole (6).

B-Scan ultrasonography

B-scan ultrasonography is useful when media opacity limits fundus visualisation. It may reveal associated choroidal or retinal detachments, as well as thickening of the posterior sclera and choroid (2).

Management and prevention

Treatment strategies are directed toward correcting the underlying cause of hypotony. Early recognition and prompt normalisation of IOP are essential, as prolonged hypotony can result in irreversible damage to the optic nerve and macula.

Following glaucoma filtration surgery, hypotony most commonly arises from bleb leakage or excessive filtration. Conservative management of bleb leaks includes topical antibiotics, aqueous humour suppressants (to reduce flow through the leak and aid closure), and the use of bandage contact lenses to promote epithelial healing (2). Management options for over-filtering blebs include compression sutures, application of trichloroacetic acid, using laser or cautery, or surgical bleb revision (2).

Surgical intervention is often required in traumatic cases, such as scleral rupture or retinal detachment. In refractory cases with persistent chorioretinal folds, pars plana vitrectomy has been described. Peeling of the internal limiting membrane may reduce tractional forces from subclinical fibrocellular proliferation and facilitate anatomical recovery (7).

Prevention

Identification of high-risk patients is crucial prior to glaucoma-filtering procedures. Preoperative counselling should emphasise the risk of hypotony maculopathy in susceptible individuals.

Intraoperative and postoperative strategies to minimise hypotony include the use of safety-valve incisions, meticulous scleral flap construction with adequate suturing, and gradual suture removal to avoid abrupt drops in IOP (8). Antimetabolites should be applied cautiously, ensuring minimal contact with conjunctival edges to reduce the risk of conjunctival thinning and subsequent bleb leaks (1). Nonpenetrating glaucoma surgeries, such as canaloplasty and deep sclerectomy, were developed in part to reduce complications associated with traditional filtering procedures, including hypotony and its sequelae (2).

References

1. Thomas M, Vajaranant TS, Aref AA. Hypotony maculopathy: clinical presentation and therapeutic methods. Ophthalmol Ther. 2015;4(1):79–88.
2. Costa VP, Arcieri ES. Hypotony maculopathy. Acta Ophthalmol Scand. 2007;85(6):586–597.
3. Fannin LA, Schiffman JC, Budenz DL. Risk factors for hypotony maculopathy. Ophthalmology. 2003;110(6):1185–1191.
4. Kokame GT, de Leon MD, Tanji T. Serous retinal detachment and cystoid macular edema in hypotony maculopathy. Am J Ophthalmol. 2001;131:384–386.
5. Budenz DL, Schwartz K, Gedde SJ. Occult hypotony maculopathy diagnosed with optical coherence tomography. Arch Ophthalmol. 2005;123:113–114.
6. Masaoka N, Sawada K, Komatsu T, Fukushima A, Ueno H. Indocyanine green angiographic findings in 3 patients with traumatic hypotony maculopathy. Jpn J Ophthalmol. 2000;44:283–289.
7. Benson S, Barton K, Gregor Z. Vitrectomy for a persisting macular fold in a case of resolved hypotony maculopathy. Am J Ophthalmol. 2004;138(3):487–489.
8. Suñer IJ, Greenfield DS, Miller MP, Nicolela MT, Palmberg PF. Hypotony maculopathy after filtering surgery with mitomycin C: incidence and treatment. Ophthalmology. 1997;104:207–214.