Lens-related glaucoma, aqueous misdirection and venous pressure

Find the mechanism before escalating drops

A high-pressure eye may require lens removal, relief of pupillary block, treatment of inflammation or investigation of an orbital vascular lesion. Secondary glaucoma therefore demands examination of chamber depth, lens position and maturity, inflammation, angle configuration and episcleral vessels. The same pressure reading can accompany an open angle obstructed by lens material or a closed angle pushed forward by an enlarged lens. Confusing these mechanisms delays definitive treatment.

Record symptoms, prior surgery, trauma and medications. Examine the fellow eye for its baseline anatomy. Gonioscopy, when feasible and safe, identifies closure, material or abnormal vessels. Anterior-segment optical coherence tomography and ultrasound biomicroscopy supplement rather than replace the clinical assessment. If the fundus cannot be seen, ultrasound may help identify a posterior mass or choroidal collection contributing to a shallow chamber.

Lens-induced mechanisms

Phacomorphic glaucoma arises when an intumescent lens crowds the anterior segment, often with a pupillary-block component. The chamber is shallow and the angle closes. Initial pressure reduction and control of inflammation make surgery safer; definitive management generally involves removing the causative cataract. An iridotomy may relieve a block component but cannot remove lens bulk.

Phacolytic glaucoma typically accompanies a hypermature lens with an apparently intact capsule. Leaked high-molecular-weight lens proteins and inflammatory material impair outflow in an open angle. Lens particles after capsule disruption can similarly obstruct the meshwork. Phacoantigenic inflammation is an immune response to exposed lens material, usually after surgery or trauma; raised pressure is one possible consequence. These entities should not all be labelled pupillary block.

A lens fragment in the anterior chamber after cataract surgery can cause localized corneal oedema and recurrent inflammation as well as pressure elevation. Search carefully beneath the iris and consider specialist removal. Do not manage indefinitely with additional pressure drops while leaving the source untreated. Exclude postoperative infection when pain, inflammation or vitreous involvement raises concern.

Aqueous misdirection

Aqueous misdirection, historically called malignant glaucoma, is associated with anterior displacement of the lens–iris diaphragm and a uniformly shallow central and peripheral anterior chamber. It may occur after glaucoma or other intraocular surgery and occasionally without surgery. A patent peripheral iridotomy helps distinguish it from ordinary pupillary block, although multiple mechanisms can coexist. Pressure is often high, but the diagnosis is anatomical and is not excluded by a particular pressure value.

Exclude suprachoroidal haemorrhage or effusion, wound leakage and a posterior mass. In a postoperative eye, ultrasound is especially useful when visibility is poor. A shallow chamber with a patent iridotomy should not lead reflexively to more pilocarpine: miotics can worsen forward displacement. Initial specialist treatment generally uses cycloplegia, aqueous suppression and, when appropriate, a hyperosmotic agent with systemic contraindications checked.

Pseudophakic eyes may be suitable for laser disruption of an accessible posterior capsule and anterior hyaloid pathway. Persistent cases may need vitrectomy with a patent communication across the iris, zonules, capsule and anterior hyaloid; removing central vitreous alone can leave the obstructing barrier. A phakic eye may require lens extraction as part of the operation. Follow chamber depth and pressure after intervention because recurrence can occur if the communication closes.

Raised episcleral venous pressure

Aqueous entering Schlemm canal ultimately drains into episcleral veins. Elevated downstream venous pressure can raise IOP despite an anatomically open angle. Dilated tortuous episcleral vessels, blood in Schlemm canal, proptosis, bruit, chemosis or motility disturbance should prompt investigation for a carotid–cavernous fistula or other orbital and systemic venous disorder. Do not interpret blood in the canal from gonioscopic pressure alone as diagnostic of a fistula.

Manage the underlying vascular or orbital cause with the relevant specialists. Pressure medication may be needed while this proceeds. Filtering surgery in a high-venous-pressure eye has additional risks, including choroidal effusion and haemorrhage, so operative planning requires the mechanism to be understood. An unexplained unilateral red eye with high pressure deserves more than an assumption of chronic conjunctivitis.

Comparing two urgent cases

An elderly patient with a swollen cataract, shallow peripheral chamber and closed angle has lens-related crowding. A recently operated patient with a patent iridotomy, uniformly flat chamber and no choroidal collection suggests misdirection. Both need urgent care, but their definitive anatomy differs. State the discriminating signs and the treatment that restores the relevant pathway rather than reciting a single drug sequence for both.

Sources: EGS aqueous misdirection guidance and EGS guidelines.