Intraoperative Shallow or Flat Anterior Chamber
During extracapsular cataract extraction (ECCE) or phacoemulsification, the anterior chamber may become shallow because of inadequate infusion, leakage through an oversized incision, external pressure on the globe, “positive vitreous pressure,” fluid misdirection syndrome, suprachoroidal effusion, or suprachoroidal hemorrhage. If the reason for loss of normal chamber depth is not apparent, the surgeon first reduces aspiration, then raises the infusion bottle height, and checks the incision. If the incision is too large, the surgeon may partially suture it in order to keep the chamber formed. External pressure on the globe can be relieved by readjusting the surgical drapes or the eyelid speculum. “Positive vitreous pressure,” or forward displacement of the lens–iris diaphragm, occurs more commonly in patients who are obese or who have thick necks, in patients with pulmonary disease such as chronic obstructive pulmonary disease (COPD), and in patients experiencing a level of anxiety or discomfort that may lead them to squeeze their eyelids or perform a Valsalva maneuver. Placing obese patients in a reverse Trendelenburg position may alleviate the pressure. Intravenous mannitol can be used to reduce the vitreous volume and deepen the anterior chamber in selected cases.
If the reason for the loss of anterior chamber depth or the elevated IOP is unknown, it is important to check the red reflex to evaluate for the possibility of a suprachoroidal hemorrhage or effusion. In these situations, the eye typically becomes very firm, and the patient becomes agitated and reports experiencing pain. The surgeon should immediately close the incisions and confirm the diagnosis by examining the fundus with an indirect ophthalmoscope or fundus lens. If the hemorrhage or effusion is significant, the operation should be postponed until the pressure has decreased. (See the section Suprachoroidal Effusion or Hemorrhage, later in this chapter, and BCSC Section 12, Retina and Vitreous.)
In posterior fluid misdirection syndrome, irrigation fluid infused into the anterior chamber may be misdirected into the vitreous cavity through intact zonular fibers or through a zonular or capsular tear, causing an increase in the vitreous volume with subsequent forward displacement of the lens and shallowing of the anterior chamber. The fluid may accumulate in the retrolental space or dissect posteriorly along the vitreoretinal interface. If gentle posterior pressure on the lens or reinflation of the capsular bag with OVD does not alleviate the fluid accumulation, an intravenous infusion of mannitol and waiting at least 20 minutes may allow the anterior chamber to deepen. If suprachoroidal effusion or hemorrhage has been ruled out, the surgeon can insert a 20- to 23-gauge needle through the pars plana into the vitreous by direct visualization, gently aspirate fluid vitreous, and deepen the anterior chamber with irrigation fluid or OVD. Alternatively, vitreous aspiration may be performed with a cutting/aspirating pars plana vitrectomy tip inserted through a sclerotomy 3.5 mm behind the limbus, combined with infusion of balanced salt solution or injection of additional OVD into the anterior chamber.
A shallow or flat anterior chamber can also occur postoperatively; see Chapter 11 for further discussion.
Excerpted from BCSC 2020-2021 series: Section 11 - Lens and Cataract. For more information and to purchase the entire series, please visit https://www.aao.org/bcsc.