A Shallow Anterior Chamber
Modern phacoemulsification cataract removal is usually a controlled event that, with experience and good equipment, progresses smoothly. One risk factor for an increased complication rate in cataract extraction is a shallow anterior chamber.1
Although in itself, this is not usually an insurmountable problem, when extreme, it can make access to the cataract very difficult and may necessitate a change in approach (ie, adaptability) to achieve a successful outcome.
INITIAL ASSESSMENT
In the clinic, it is important to estimate the anterior chamber depth as part of the general ophthalmological work-up. This will not only anticipate potential surgical problems, but also guide the examiner to look for other pathologies. For example, evidence of previous raised intraocular pressure, dislocated crystalline lens (Figure 1), or microphthalmia may be found.
Biometric evaluation of the eye also gives valuable information regarding anterior chamber depth and its relationship to the overall dimensions of the eye. During surgery, access into the anterior chamber may be difficult, purely because of its limited depth. Additionally, there is a difference in the anatomical relationship of the iris root and peripheral cornea, meaning that iris prolapse is more likely to occur intraoperatively. Maneuvers such as filling the anterior chamber with viscoelastic or hydrodissection of the nucleus—which in a normal eye would be straightforward—may be accompanied by a sudden rise in pressure of the globe and iris prolapse through the wound.
A difference in approach is needed with these eyes to allow the surgeon to maintain control of events, limit tissue damage and postoperative inflammation, and avoid more serious intraoperative complications. Using Smith's2 method to assess anterior chamber depth at the slit-lamp is useful. More accurate methods are available, including optical methods employing an additional device that is attached to the slit-lamp. Whatever method is used, the central anterior chamber depth is usually calculated. This predicts the space, which may be available in the center of the anterior chamber; it only informs about the peripheral chamber in a relative way. Any patient with a biometric measurement of less than 22 mm axial length should be regarded as a potentially difficult case.
TIPS AND TRICKS TO APPLY
Below is a list of tips to remember when operating on a patient with a shallow anterior chamber. These suggestions, although not exhaustive, provide some measure of control when removing cataractous lenses in eyes with shallow anterior chambers.
• Make sure the patient is able to fully cooperate during the operation. The ability to lie in a suitable position is important.
• General anesthesia should be considered if sufficient cooperation in positioning cannot be ensured.
• Large volumes of local anesthetic are best avoided, as increased intraorbital pressure may exacerbate an already difficult access.
• Consider an approach from the temporal aspect of the cornea if there is a prominent brow or a small deep-set globe.
• It is helpful to perform the sideport incision first. Then, partially fill the anterior chamber with viscoelastic through this incision. The blade used to make this wound is kept as parallel to the iris as possible, and it may be necessary to insert viscoelastic through the sideport incision before it is completed. This allows entry of the blade far enough into the anterior chamber without injuring the relatively forward bowed iris.
• Performing the capsulorhexis through the sideport with a cystotome is often helpful, because the anterior chamber is more easily maintained. Bending a 27-gauge needle at the time of surgery may be beneficial, as some preformed cystotomes are too anteriorly curved and make performing the rhexis in a shallow chamber more difficult.
• Once the anterior chamber is partially filled with viscoelastic, the main wound may be fashioned. Using a corneal tunnel, leave a 1-mm gap from the limbus, and keep the tunnel short. A stepped wound should be used to ensure watertightness, as iris prolapse will easily occur if a forward-sloping nonstepped wound is fashioned.
• When performing hydrodissection, small volumes of fluid, gently injected, are best. Forcible injection or large boluses of fluid will rapidly increase intraocular pressure (especially if the fluid is below the level of the iris plane), and the iris will be forcibly prolapsed through the wound (Figure 2).
• A small bleb of viscoelastic may be placed just inside the wound before the phaco probe is inserted; the probe is inserted with reflux on. This ensures a forward-projecting stream of fluid from the probe, as it enters the eye and helps maintain the chamber. If ordinary flow through the sideports of the infusion sleeve is utilized, then the phaco needle tip is inserted 1 mm to 2 mm into the eye before infusion enters the wound.
• A flatter trajectory of the phaco needle is required, but accepting that any of the usual techniques for nucleus removal can be employed.
• I/A is probably most easily accomplished using a bimanual technique, separating the irrigation from the aspiration. A second sideport may be made on the opposite side of the main wound, thus not entering the main (most unstable) wound at all during this stage.
• IOL implantation is relatively straightforward, as after removal of the cataract, there is more room in the anterior chamber. The capsular bag may be somewhat floppy at this stage, and care must be taken not to catch it in the last stages of lens removal when it can be very mobile.
Larry Benjamin, DO, FRCS, FRCOphth, is in the Department of Ophthalmology at Stoke Mandeville Hospital, in Aylesbury, UK. He did not provide financial disclosure information. Dr. Benjamin is a member of the CRST Europe Editorial Board. He may be reached at larry.benjamin@btopenworld.com.
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