Occlusion break surge: gravity-based systems. The schematic depicts (A) the anterior chamber and (B) IOP. During unobstructed flow, aspiration and infusion are balanced to maintain a stable anterior chamber (A1) and IOP (B1). When the phaco tip becomes occluded with nuclear material, fluid flow is blocked (A2) and IOP increases (B2). With occlusion break, vacuum stored in aspiration tubing during occlusion (ie, no flow) can cause a sudden increase in aspiration rate (A3) and lead to a drop in IOP (B3). Infusion during unobstructed flow after occlusion break leads to recovery of the anterior chamber (A4) and IOP (B4). IOP = intraoperative pressure.