Hypotony

Hypotony refers to abnormally low intraocular pressure (IOP) in the eye. It is commonly defined as an IOP below the normal range, often less than 6 to 8 mmHg, though the exact threshold can vary by context. Hypotony may be acute or chronic and can affect vision and ocular structure.

Causes include decreased production of aqueous humor due to ciliary body dysfunction from inflammation, trauma, infection, or postoperative injury; and increased outflow through wound leaks or overfiltration after glaucoma surgery, such as trabeculectomy. Other contributors are choroidal effusions, hypotony from scleral or vitreous changes, and inflammatory conditions that suppress aqueous production. Wound leaks after incisional procedures are a common iatrogenic cause.

Signs and complications may include a shallow or flat anterior chamber, corneal edema, choroidal effusions or detachment, and hypotony maculopathy, which can produce visual distortion or reduced acuity. Chronic hypotony can lead to phthisis bulbi, in which the eye progressively atrophies.

Diagnosis relies on IOP measurement with tonometry and clinical examination of the anterior chamber depth. Imaging or ultrasound may be used if media opacity limits examination.

Management focuses on treating the underlying cause. This may involve repairing a wound leak, adjusting filtration in postoperative eyes, or employing conservative measures such as cycloplegic agents to deepen the anterior chamber and protect vision. Persistent or severe hypotony requiring intervention may necessitate surgical or interventional procedures. Prognosis varies with duration and severity of hypotony.