Retrobulbar injection

In-depth discussions of the anatomy of the eye and adnexa have been adequately covered elsewhere in the pharmaceutical literature [13-17] and in recent texts on ocular anatomy. Here a brief overview is presented of the critical anatomical features that influence the nature and administration of ophthalmic preparations. In this discussion, consideration will be given primarily to drugs applied topically, that is, onto the cornea or conjunctiva or into the palpebral fornices. Increasingly, drugs are being developed for administration by parenteral-type dosage forms subconjunctivally, into the anterior and posterior chambers, the vitreous chamber, Tenon s capsule, or by retrobulbar injection. 

Several topically applied local anesthetics are routinely used by the eye care specialist in certain routine diagnostic procedures and for various relatively simple surgical procedures such as insertion of punctal plugs and surgical vision correction. The first of these to be used was cocaine, in concentrations ranging from 1 to 4% [30]. More modern local anesthetics, however, such as tetracaine hydrochloride and proparacaine hydrochloride, have replaced cocaine as drugs of choice in these procedures. For surgical procedures of a more complex nature, lidocaine hydrochloride and similar local anesthetics as retrobulbar injections have been used [31]. 

Very few injectable dosage forms have been specifically developed and approved by FDA for intraocular use. However, the ophthalmologist uses available parenteral dosage forms to deliver antiinfectives, corti-costerioids, and anesthetic products to achieve higher therapeutic concentrations intraocularly than can ordinarily be achieved by topical or systemic administration. These unapproved or off-label uses have developed over time as part of the physician s practice of medicine. However, these drugs are usually administered by subconjunctival or retrobulbar injection and rarely are they injected directly in the eye [301]. 

In a study in Rhesus monkeys, retrobulbar administration of local anesthetics resulted in a low incidence of muscle fiber lesions in the extraocular muscles closest to the site of injection. Most lesions resulted in the degeneration and regeneration of muscle fibers on the surface of the muscles, but occasionally a massive internal lesion was seen. 

When higher concentrations of drugs, particularly corticosteroids and antibiotics, are required in the eye than can be delivered by topical administration, local injections into the periocular tissues can be considered. Periocnlar drug delivery includes subconjunctival, snb-Tenon s, retrobulbar, and peribulbar administration. 

Figure 3-17 Relative positions of periocular injections. A, Subconjunctival B, sub-Tenon s C, retrobulbar.

Compared with the retrobulbar technique, peribulbar anesthesia provides similar anesthesia and akinesia for both anterior segment and vitreoretinal surgical procedures, but some patients may have inadequate akinesia and require additional injections. In addition, the onset time of blockade is not as rapid as with retrobulbar injection. Nevertheless, peribulbar anesthesia reduces the potential for inadvertent globe penetration, retrobulbar hemorrhage, and direct optic nerve injury. Although serious problems with retrobulbar and peribulbar injections are uncommon, numerous complications have been reported (Box 3-3). 

Periocular steroids can be administered by subconjimcti-val, sub-Tenon s capsule, or retrobulbar injection. A topical anesthetic often is instilled before the steroid is injected. This route of administration can be effective during surgical procedures, as a supplement to topical and systemic steroids in cases of severe inflammation, and in patients not compliant with the prescribed regimen. 

A cluster of 25 cases of transient or permanent diplopia occurred after 13 retrobulbar blocks, 10 peribulbar blocks, and two unknown techniques, possibly related to the non-availability of hyaluronidase, highhghting the likely importance of hyaluronidase in preventing anesthetic-related myopathy in the extraocular muscles (290). Other reports of 21 cases of persistent postoperative diplopia following the peribulbar technique (291) and 4 cases foUowing the retrobulbar technique during the period of non-availabihty of hyaluronidase support this theory (292). Bupivacaine and lidocaine may be contraindicated for peribulbar or retrobulbar injections without hyaluronidase. 

A retrobulbar injection in a 45-year-old woman with high myopia was complicated by globe perforation with vitreous and submacular hemorrhage (304). 

Complications from retrobulbar block can arise from accidental scleral perforation and intraocular injection of local anesthetic. 

The authors added that retinal toxicity of the local anesthetic agent did not affect the visual outcome in this patient. Scleral perforation is a well-known complication of eye blocks for ophthalmic surgery. The incidence with retrobulbar techniques is 0.075% and with peribulbar blocks 0.0002%. When recognized, ocular perforation usually requires a vitreoretinal procedure and is associated with a poor visual outcome. Risk factors include an anxious or oversedated patient, long sharp needles, superior injection, incorrect angle of needle insertion, and myopic eyes. If the intraocular pressure is increased, paracentesis may acutely reduce it, preventing retinal and optic nerve ischemia and possible permanent visual loss. 

Possible techniques to reduce complications include avoiding Atkinson s position, the classical position for retrobulbar block (309), during injection, limiting the volume of solution injected, and the use of shorter needles (310,311). 

Peribulbar anesthesia is generally considered safer than retrobulbar anesthesia, with a lower incidence of adverse effects. It avoids deep penetration of the orbit and therefore inadvertent subarachnoid injection. It also seems to be safer with regard to the risk of bulb perforation (314). 

Lam DS, Tam BS, Chan WM, Bhende P. Combined cataract extraction and snbmacular blood clot evacuation for globe perforation cansed by retrobulbar injection. J Cataract Refract Surg 2000 26(7) 1089-91. 

Cowley M, Campochiaro PA, Newman SA, Fogle JA. Retinal vascular occlusion without retrobulbar or optic nerve sheath hemorrhage after retrobulbar injection of lidocaine. Ophthalmic Surg 1988 19(12) 859-61. 

Wadood AC, Dhillon B, Singh J. Inadvertent ocular perforation and intravitreal injection of an anesthetic agent during retrobulbar injection. J Cataract Refract Snrg 2002 28(3) 562-5. 

Retrobulbar injection probably offers little therapeutic advantage over the combined subconjunctival and parenteral routes. This route is recommended only for regional anesthesia of the orbit, particularly to supplement general anesthesia (Miller 1992). 

Periocular injections, subconjunctival, subtenons, and retrobulbar injection of drugs have been frequently investigated as a means to increase ocular availability. Subtenon injections of steroids, such as triamcinolone acetonide, are frequently used to control inflammatory conditions of the posterior segment such as cystoid macular edema, although this delivery route carries a risk of inadvertent intraocular injection (45). 

The ocular bioavailability from periocular injections is not well studied and the routes by which drugs penetrate the eye after such injections have never been satisfactorily elucidated. Levine and Aronson (46) used radiopaque media to demonstrate the diffusion of injected compounds from these sites in rabbits and found that subtenons and subconjunctival injections disperse and spread circumferentially around the eye but do not diffuse back to the orbit, while retrobulbar injections tend... 

Barza et al. (54) later reported that after subconjunctival injection of gentamicin, higher drug concentrations were found in ocular tissues from normal eyes than from inflamed, infected (Staphylococcus aureus endophthalmitis) eyes, despite the presumed reduction in blood-eye barrier in the inflamed eye. This result was not due to altered drainage into the tear film but may have been caused by increased ocular and orbital vascularity or decreased half-life within the eye (55). Similar results have been reported by Levine and Aronson (46) who found that inflammation caused a twofold decrease in ocular absorption of radiolabeled cortisol after retrobulbar injection although no such difference was seen following subconjunctival injection. Peak ocular concentrations were observed five minutes after administration. These authors also speculated that the difference in ocular absorption after retrobulbar injection was probably due to more rapid steroid removal from... 

Retrobulbar injections of radiolabeled methyl prednisolone acetate (insoluble) were found to produce elevated concentrations of steroid in the uvea, vitreous, and lens compared to IM injections on the squirrel monkey (56). This finding was not reproduced by Barry et al. (57), who also used radiolabeled methylprednisolone acetate, but failed to show a significant difference in either vitreal or uveal concentrations between treated and contralateral, untreated eyes after retrobulbar steroid injections in the albino rabbit. This apparent difference may have been due to interspecies variation or may be artifactual due to differences in tissue handling. 

Barry A, Rousseau A, Babineau LM. The penetration of steroids into the rabbit s vitreous, choroid and retinal following retrobulbar injections. Can J Ophthalmol 1969 4 395-399. 

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