Decompression, or sudden drop in IOP, is thought to be the inciting event for malignant glaucoma. It is usually accompanied by anterior chamber shallowing. During surgery, decompression may occur during incision creation, while moving instruments in and out of the eye particularly larger ones like hand-pieces for phacoemulsification (phaco) or irrigation-aspiration, when creating openings for glaucoma filtration surgery or during wound closure if tissue apposition is insufficient. Following surgery, decompression can occur due to wound leak or excessive filtration from glaucoma surgery.

Reduced IOP from decompression may result in choroidal expansion as increased blood volume rushes into the potential vascular space. The choroid covers a large surface area and a small increase in its thickness can add significant volume to the intraocular contents pushing other structures anteriorly. Normally, aqueous outflow either via trans-scleral drainage or anteriorly through the trabecular meshwork would compensate for this event. However, this may not occur in the susceptible eye due to a combination of factors. These include a reduced ability for fluid to transmit through vitreous due to poor conductivity, limited lens-iris channel area for anterior migration of aqueous, and reduced trans-scleral outflow due to thicker sclera. In eyes with these characteristics, a decompression event may result in anterior lens-iris movement and significant anterior chamber shallowing [4].

Risk factors for malignant glaucoma include shallow anterior chamber and shorter axial length. These conditions are more common in female hyperopes [5, 6].

The risk of malignant glaucoma may be reduced, though not eliminated, by avoiding decompression during surgery.

During cataract surgery, when withdrawing the phaco hand piece after lens removal or when withdrawing the irrigation-aspiration hand piece after cortex or viscoelastic removal, the anterior chamber often shallows, signaling decompression. To avoid this, one can inject balanced salt solution (BSS) or viscoelastic through the paracentesis to maintain the anterior chamber pressure. The choice between BSS or viscoelastic would depend on the next step planned in surgery. Typically, the authors would inject BSS following phacoemulsification to prepare for cortex removal, viscoelastic following cortex removal to prepare for lens insertion, and BSS after viscoelastic removal to prepare for wound hydration. To reduce tremor, the surgeon can depress the plunger using the index finger while holding the syringe between the thumb and middle finger, rather than the traditional method of depressing the plunger with one’s thumb. This technique takes practice and one can do so on routine cases so that the skill is honed for use when needed.

During filtration surgery, decompression can occur when creating an ostium as well as during closure. Viscoelastic can be used in the anterior chamber during ostium creation to avoid shallowing. As well, during closure of a trabeculectomy flap, periods of excessive aqueous egress can occur resulting in anterior chamber shallowing. With the microscope centered on the flap and the surgeon’s attention focused on suturing, this may go unnoticed. By periodically checking the anterior chamber status during this step, one can inject BSS or viscoelastic to help avoid excessive shallowing and decompression. Similarly, during tube shunt entry and manipulations, care in avoiding excessive anterior chamber shallowing may help reduce the risk of subsequent malignant glaucoma.

Definitive treatment for malignant glaucoma aims to restore the normal relationship between the anterior and posterior segments by establishing a unicameral eye. This can be achieved through a stepwise approach which begins with less invasive approaches and reserves more invasive strategies only for cases that do not resolve with earlier steps (Fig. 15.2).

Medical management consists of cycloplegics to help pull the lens-iris diaphragm posteriorly and aqueous suppressants to reduce intraocular volume as well as control pressure. Although traditionally this has been reported to be successful in up to 50 % of patients [7], more recent reports suggest this number may be as low as 10–14 % [8, 9]. Furthermore, since medical management does not address the underlying anatomic issue, cycloplegia often cannot be discontinued [2], suggesting a role for medications to help control but not necessarily cure malignant glaucoma.