voluminous regional anesthetic injection, a Valsalva maneuver, or coughing. The position of the head relative to the body, and how massive that body is, will affect the ocular intravascular pressure.

On the other side of the equation is the IOP. In a closed eye, homeostasis is usually maintained unless the IOP drops below 5 mm Hg. However, the relationship between the two pressures, the IOP and the ocular intravascular pressure, over time is also a factor. An eye that is accustomed to a higher IOP that suddenly falls to 0 mm Hg is less likely to tolerate that change than an eye with a chronic very low IOP. So if there is a precipitous drop in IOP from a very high level and the intravascular pressure remains constant, an effusion becomes more likely. Think of a long-standing glaucoma patient who has filtering surgery. If the IOP is very low for several days, a suprachoroidal effusion is quite common (most are not clinically significant, but present nevertheless).

In the setting of cataract surgery, the two pressures can be thought of simplistically; the choroidal intravascular pressure is “posterior” and the IOP is “anterior.” In this force equation, the anterior pressure must be in balance with the posterior pressure. If the anterior pressure drops suddenly to zero, there is nothing to hold back the posterior pressure, except the blood vessel wall (quite weak in the choriocapillaris), the retina, the gravitational pressure of the vitreous, and the zonulocapsular diaphragm.

The duration of decreased IOP is an important additional risk factor in developing AISH. In our study7 of AISH, patients undergoing phacoemulsification developed their intraocular positive pressure later in the procedure (Fig. 8–5). Those having extra-

capular cataract extraction (ECCE) (9.0- to 10.0-mm incision) developed positive pressure soon after nucleus delivery in most cases. This phenomenon is presumably related to the greater time duration of relative maintenance of near-normal anterior pressure with phacoemulsification than with large-incision extracapsular surgery. Surgeons performing penetrating keratoplasty and glaucoma filtering procedures confirm that the duration of hypotony correlates with the onset of positive pressure.

From a pressure differential point of view, the worst-case scenario consists of an obese patient with a bull neck laying with his head lower than his body, who also has a blood pressure of 210/120 in his ophthalmic arteries and has had an IOP of 40 mm Hg for years. His peribulbar block has been too voluminous, impairing venous outflow. He further complicates the pressure differential by coughing, accentuating this Valsalva nightmare. And you have to perform large incision cataract surgery on his only seeing eye!

Now consider the factors affecting the barrier between the posterior and anterior pressures.

CHOROIDAL VASCULAR FRAGILITY

The innermost layer of the choroid is the choriocapillaris, made up of large, fenestrated capillaries without an elastic lamina. The lumina are large enough to allow red blood cells to pass easily through into the expandable choroidal space. Sattler’s layer of medium-sized vessels is found between the choriocapillaris and the outermost Haller’s layer of large

vessels. Two long posterior and 20 short posterior ciliary arteries must pierce the sclera to enter the choroid. Four vortex veins drain the blood from the choroid.

Anything that makes the thin choroidal vessel weaker, more prone to leakage and rupture, will make an AISH more likely. The aging process, senescence, makes the vascular wall more brittle. Years of hypertension may contribute; diabetes certainly can lead to greater vascular leakage. A history of carotid occlusive disease or coronary artery disease suggests that the choroidal vessels are also affected by the arteriosclerotic process.

With fluctuation of the IOP, there is distortion of the soft tissues of the eye. In some cases, there is actual deformation of the globe, as in nucleus expression ECCE. These factors create a shearing force in the choroidal vascular space. This shear contributes to the likelihood of vascular leakage into the suprachoroidal space. Scleral rigidity in the senescent eye may contribute to the shearing force between the choroidal vessels and a less pliable scleral wall.

Anticoagulation with aspirin or warfarin would theoretically increase the likelihood that once a suprachoroidal hemorrhage occurred, it would be more likely to proceed rapidly.

Speaker et al8 performed a case-control study of risk factors in 68 cases of what they called “suprachoroidal expulsive hemorrhage” from the 35,459 patients having intraocular surgery at their institution between 1981 and 1986. It is not clear what percentage of these cases had only sudden intraoperative hardening of the eye and not prolapse of intraocular contents because both groups met the patient inclusion criteria. We may conclude that these 68 cases covered the AISH spectrum, and not just the rarer, true expulsive hemorrhages. The authors found that the statistically significant risk factors were a history of glaucoma, axial length greater than 25.8 mm, elevated IOP greater than 18, generalized atherosclerosis, and intraoperative tachycardia greater than 85 beats/minute (Table 8–1). They suggested an interesting correlation between an increased risk of AISH with increased intraoperative sympathetic tone and a decreased risk

TABLE 8–1 A CASE-CONTROL STUDY OF RISK

FACTORS FOR INTRAOPERATIVE SUPRACHOROIDAL

EXPULSIVE HEMORRHAGE

Glaucoma

Increased axial length >25.8 mm

Elevated IOP >18

Elevated intraop pulse >85 bpm

Generalized atherosclerosis

From Speaker et al.8

CHAPTER 8 POSITIVE PRESSURE • 69

with antihypertensives that block sympathetic outflow from the central nervous system.

These factors may explain why we found in our prospective series of patients that AISH was more likely in senescent eyes (those with very brunescent nuclear cataracts, not necessarily in those patients who were older), which required ECCE rather than phacoemulsification,7 and why we found AISH more likely in those with significant vascular disease, especially those requiring systemic anticoagulation. It is not possible to discern which are the preeminent factors. Is it senescence, the larger incision ECCE (with more hypotony and choroidal shear), the history of vascular disease, or the anticoagulation?

INCIDENCE OF AISH

The reported incidence of AISH during cataract surgery has varied significantly, from 3.1% with intracapsular cataract extraction (ICCE) to 0.03% with phacoemulsification.9,10 Some of this variation can be ascribed to the definition employed; some investigators included limited suprachoroidal effusions while others studied only complete expulsive hemorrhages. Some have been very careful observers and included limited suprachoroidal effusions, whereas others may not have counted them. We also see a clear reduction in the incidence of AISH over time as our cataract surgical techniques have improved, decreasing both the incision size and the intraoperative time.

Although the number of operations is low, Bukelman et al9 reported a decrease in their incidence after they moved from ICCE in 521 cases (3.1%) to ECCE in 368 cases (2.2%). The next step in our surgical evolution and its relation to AISH was best evaluated by Eriksson et al.10 They examined the records of 37,565 cases from 1990 to 1996; 14,352 had undergone ECCE and 23,213 had phacoemulsification. The incidence of AISH had dropped in a highly statistically significant manner from 0.13% with ECCE to 0.03% with phacoemulsification (p = 0.0003).

Davison’s11 experience details this evolutionary phenomenon with different phacoemulsification techniques. In his original study of AISH from 1986, he encountered an incidence of 0.81% with iris plane emulsification. By 1993, using a capsular bag phacoemulsification technique that reduced the amplitude of intraocular pressure swings, his incidence had dropped to 0.06%.12 I have also seen this happen in my practice. By seeking to maintain an extremely watertight incision and reduce intracameral pressure fluctuations as much as possible, my incidence has dropped from 0.45% of all phacoemulsification cases to 0.08%.

PREVENTIVE MEASURES

All of these risk factors are additive; that is, the patient with all five of the risk factors is more likely to develop AISH than the patient with one. The surgeon must think about prevention in susceptible patients and be prepared to deal with an AISH in these cases.

Do phacoemulsification! The studies cited above demonstrate a lower incidence of AISH with phacoemulsification than any other cataract extraction technique. By employing the small, self-sealing incision, the surgeon accomplishes several goals: the intracameral pressure is more stable, the globe is not mechanically distorted, and the eye can be quickly closed if a choroidal effusion arise. It is very important to decrease the fluctuation of IOP during cataract extraction. A steady, somewhat elevated “anterior pressure” can be maintained with an elevated infusion bottle, a watertight incision, and the use of viscoelastic when an infusion instrument is not in the anterior chamber. Blumenthal et al13 have demonstrated a decreased incidence of AISH in eyes in which they used an anterior chamber maintainer.

In patients with glaucoma or ocular hypertension, try to get the IOP as controlled as possible before surgery. This may require carbonic anhydrase inhibitors in addition to topical agents. The goal is to prevent a great, sudden fall in IOP when the anterior chamber is entered. Remember that the duration as well as the degree of hypotony are risk factors. If a larger incision must be employed, it should be closed, with the anterior chamber maintained as much of the time as possible. Preplaced sutures are essential in eyes with AISH risk factors requiring larger incision surgery. In an eye with a 4+ brunescent nucleus in which I must perform ECCE, I will place three interrupted 9-0 nylon sutures after creating a posterior scleral shelved incision, but before entering the anterior chamber.

Control the blood pressure and heart rate before surgery. We instruct our patients to take all of their normal medications the day of their eye surgery. We routinely give benzodiazepam to anxious patients before surgery. In patients with uncontrolled hypertension or preoperative tachycardia, we will give intravenous labetalol to block both and receptors. This medication is very effective at decreasing the overall sympathetic tone of the patient.

INTRAOPERATIVE DIAGNOSIS

The most important factor in achieving a successful resolution of AISH is the rapidity with which the surgeon recognizes the event. The diagnosis must be

made at the earliest possible moment so the surgeon can perform the most efficacious treatment. If recognized early, the result will be a completely normal eye; if the warning signs are ignored, an expulsive hemorrhage may eventuate in evisceration. The difference between these two outcomes may be due to a diagnostic delay of only 1 to 2 minutes. That is as long as it takes for an eye to go from positive pressure to expulsive hemorrhage.

Be suspicious of patients and eyes exhibiting the risk factors mentioned above. During surgery, be constantly cognizant of the anterior chamber depth. If it seems to shallow progressively, check first for mechanical/external factors. If none are present, then evaluate the fluid inflow and outflow. Make sure the fluid leaving the eye through the incision or paracentesis is not excessive. This might require a suture to create a watertight system. If outflow is not a problem, check the inflow to see if the infusion tubing is kinked or the sleeve is too compressed within the incision (Table 8–2). Is the BSS bottle empty? If this quick checklist fails to uncover the problem, remove the infusion instrument from the eye and look for subtle signs of fluid misdirection.

This is an appropriate time to place a cellulose sponge or Q-tip over the incision to both seal the opening and qualitatively assess the IOP. Positive posterior pressure causes a convex posterior capsule, a shallow anterior chamber, and, eventually, iris prolapse. Applying several minutes of Q-tip pressure over the incision will gradually soften the eye if fluid misdirection is the problem; it may become even harder if an AISH is in progress. Don’t waste time before applying Q-tip pressure! If a suprachoroidal effusion is occurring, the first step in effective management has taken place.

MANAGEMENT OF AISH

If the eye has become rock hard, an AISH is in progress. The patient may also complain of pain despite adequate anesthesia; there is a rich supply of ciliary nerves throughout the choroid. There is no need to waste time on other diagnostic tests at this juncture. The surgeon should immediately close the incision, with sutures if necessary, and apply significant di-

TABLE 8–2 POSITIVE PRESSURE CHECKLIST

Anterior chamber depth

External factors

Fluid inflow/outflow

Fluid misdirection Apply Q-tip pressure

rect Q-tip pressure over the incision to the globe (Fig. 8–2). Some surgeons even use their gloved finger. This external, anterior pressure will increase the IOP and tamponade the effusion or hemorrhage, thus limiting its extent. It is very important to limit the effusion or small hemorrhage to avoid stretching and rupturing the larger choroidal vessels in the suprachoroidal space. By maintaining the uveal anatomy, the tangential shearing force of the effusion is limited, preventing hemorrhage. This event occurs along a logarithmic time line; things move slowly at first, but eruptively fast toward the end.

The suture material should have good tensile strength and be easily handled; 8-0 nylon is a good suture. If the eye remains hard after 5 to 10 minutes of Q-tip pressure, place a sterile gauze over the closed eyelids and then place the Honan balloon over the eye (Fig. 8–6). The balloon can be inflated to 50 mm Hg and the eye checked every 10 to 15 minutes. The surgeon may choose to confirm the diagnosis of AISH by performing indirect ophthalmoscopy or scleral transillumination at this point.

There is no doubt that the retinal circulation is threatened during episodes of AISH; however, applying significant anterior pressure is necessary to prevent an expulsive hemorrhage. This is the price we pay to save the eye. Hayreh and Weingeist14 have shown that retinal ischemia is tolerated for 90 to 100 minutes with good recovery of visual evoked responses and retinal morphology; ischemia beyond this time results in irreparable retinal damage. They state, “The retinal tolerance time to acute ischaemia is almost identical whether the ischaemia is produced by clamping the central retinal artery alone or by raising the intraocular pressure to above the level of the arterial blood pressure (with arrest of both the

CHAPTER 8 POSITIVE PRESSURE • 71

retinal and choroidal circulations).” The additional benefit of controlling the AISH by raising the IOP is that it does slow or stop the choroidal circulation, aiding in the arrest of a choroidal hemorrhage.

Note that performing a sclerotomy is not recommended because it is counterproductive. The goal is to achieve tamponade rapidly; a sclerotomy takes precious moments and prevents tamponade by creating another opening through which blood may flow. Maumenee and Schwartz15 also recommended simply suturing the corneal incision and not creating a sclerotomy: “Drainage of the choroid through a transscleral puncture is not necessary.” Lakhanpal16 has demonstrated experimentally in the rabbit eye that “immediate sclerotomy during the acute formation . . . resulted in further increase in the suprachoroidal hemorrhage, with marked extension of the hemorrhage into the retina and vitreous.”

Under no circumstances should the wound be opened in an attempt to perform an ECCE. The large wound and immediate anterior segment hypotony will lead to immediate expulsive hemorrhage and loss of the eye.

The surgeon may also choose to treat the inevitable postoperative pressure elevation by beginning systemic therapy at this time. We give one or two ampules of intravenous mannitol and 500 mg of acetazolamide. We also give 100 mg of intravenous (IV) hydrocortisone in an attempt to reduce vascular permeability and ocular inflammation.

If the patient is having cataract surgery under topical anesthesia, the pain may require a peribulbar injection and systemic sedation. Once the incision is sutured, a regional anesthetic block is administered and the Honan balloon is applied. In the setting of an AISH, this may seem counterintuitive, as it adds