readministration of anesthetic injections, with the potential additional complications as noted above.

ANATOMIC CONSIDERATIONS

The incidence of ocular penetration is significantly higher in eyes that have axial lengths greater than 26 mm as determined by ultrasonic biometry. This increased incidence is most likely due to the increased incidence of staphylomata or previous scleral buckle in this population. In fact Duker et al40 estimate the incidence at 1 in 140 cases in such eyes. The increased susceptibility of staphylomatous eyes is most likely due to less predictability of the relationship of the equator to the overall axial length of the globe. Whereas nonstaphylomatous eyes have a predictable anterior-posterior shape and the location of the equator can be projected, in eyes with staphylomata these proportions are distorted. In the latter, there is an elongated anterior-posterior dimension that is not entirely predictable,41 even when compared to nonpathologic myopic eyes42 (Fig. 1–1). Because a misjudgment of even 1 or 2 mm can lead to globe penetration, it is the charge of the person giving the block to review the patient’s chart and recognize the axial length of the eye prior to administering the injection43 (Fig. 1–5).

Similarly, deep-set eyes with small, tight orbits are at risk for injury44 due primarily to the unexpectedly posterior position of the equator with respect to the lateral orbital rim, as well as to the difficulty in manipulating the needle in the insufficient space between the orbital rim and the globe (Fig. 1–6).

PATIENT MOVEMENT

Patient cooperation is essential for successful regional anesthesia outcomes. Nowhere is this more true than in orbital regional anesthesia. Critical structures within the orbit are in close proximity to one another. Any unanticipated movement may result in ocular perforation. As pointed out earlier, it is essential to obtain sedation appropriate to the patient’s clinical status. This usually indicates administration of a light, anxiolytic dose of sedative without obtundation in conjunction with a skillfully performed, “painless” anesthetic block. For example, this has been described by Hustead,45 who uses a subconjunctival injection of dilute anesthetic before the retrobulbar anesthetic injection. I believe that sedation resulting in complete obtundation of patients can be hazardous because in such patients sudden, unexpected, and unpredictable movements occur. Other causes of unpredictable movement are psychi-

A

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B

FIGURE 1–5 Anatomic variations in axial length. (A) Normal eye. The expected anteroposterior (AP) dimensions are evident. (B) Myopic eye. The proportions are normal but the larger AP diameter shifts the equator slightly posteriorally. (C) Staphylomatous eye. The AP dimension is unpredictable. The potential for ocular perforation is increased.

atric or behavioral disorders, mental retardation; neurologic movement disorders; unwanted environmental stimuli, such as loud noise or power failure; and uncomfortable or unstable patient positioning. Finally, pain itself may cause the patient to move suddenly. Therefore, appropriate sedation in a quiet, comfortable room with proper patient head support and power backup should be provided during this critical step in cataract surgery.

Many times, unfortunately, there are no known specific predisposing factors leading to perforation. In rare instances, well-trained, experienced practitioners working on quiet, cooperative patients will experience globe perforation. Therefore, the occurrence of a perforation is certainly not prima facie evidence of negligence or malpractice.44

DIAGNOSIS OF PERFORATION

The occurrence of ocular penetration is often not apparent to the operator. Sometimes, due to the limited volume of the globe, resistance to injection is appreciated at the time of injection. Bullock et al46 reported a case of inadvertent globe penetration in which a sufficient volume of fluid was injected into the vitreous cavity that it caused the eye to explode, extruding the ocular contents into the subconjunctival space. The investigators subsequently determined that 3600 mm Hg pressure (from about 2 cc of injectate) was required to cause explosion in eye-bank eyes. However, in cases of complete perforation in which the needle enters and then exits from the posterior pole, injection may occur without resistance. Indeed, the presence of a “perfect block” with total globe akinesia and anesthesia may result precisely due to the posterior orbital location of the injection. Conversely, globe hypotony may be observed if the

needle penetration or perforation occurred without injection into the globe.

Severe pain may sometimes herald an ocular perforation; however, this may vary according to the type of needle used (sharp vs. dull), the type and amount of sedation, and the pain tolerances of the patient.44

A popping sensation may be felt as the needle penetrates the globe. However, because this is sometimes felt by the practitioner during normal blocks when piercing a connective tissue septum, its significance may not be readily appreciated. This popping sensation can also be elicited from perforation of a blood vessel, the optic nerve sheath, or an extraocular muscle.

Intraoperatively, the surgeon may be aware of a diminished red reflex in such patients. Postperforation, in the preponderance of cases, a vitreous hemorrhage, retinal detachment, or retinal tear is seen in a majority of cases. Occasionally, the presence of these complications may not be appreciated until the postoperative visit, sometimes even weeks later.

TREATMENT

Treatment initially requires early recognition of the problem. The cataract surgery should be canceled until the eye can be stabilized. In cases of intraocular injection, significant intraocular pressure elevation may trigger closure of the central retinal artery. In such cases, immediate consideration should be given to performing a vitreous tap or even pars plana vitrectomy to lower the intraocular pressure. For less severe pressure elevation mannitol may be used to create an osmotic deturgescence of the vitreous cavity. Vitreous hemorrhage and/or detachment require the intervention of a retina specialist employing the usual treatment protocols for repair.