To perform a safe cataract surgery and to keep the patient comfortable and pain-free, we need to give a sufficient level of anesthesia. For beginning surgeons, giving a retrobulbar injection of anesthetic is a good way to achieve both anesthesia and akinesia.
For experienced cataract surgeons, using a combination of topical anesthesia and intra-cameral anesthesia tends to work the best. I favor topical tetracaine eye drops combined with preservative-free dilute (1% or less) lidocaine given in the anterior chamber. For a resident who is starting to learn cataract surgery, a higher level of anesthesia such as a retrobulbar block should be given.
The agents used are typically lidocaine 1% (Xylocaine), bupivicaine 0.75%(Marcaine), or a combination of the two. The lidocaine tends to start working faster and lasts for a shorter period of time compared to the bupivicaine which can last for many hours more. The anesthetic is drawn into a 5 or 10 cc syringe and an Atkinson retrobulbar needle is used. This needle is 25 gauge but has less of a bevel and is not as sharp as a traditional 25g needle. The idea is that it may be less likely to inadvertently penetrate the globe.
The injection should start at the infero-lateral quadrant with care taken to avoid the lateral rectus, inferior rectus, and inferior oblique muscles. Avoid puncturing the eyelid skin close to the lid margin since there are often vessels here which tend to bleed.
The needle needs to go through the skin and then the orbital septum (the first pop that is felt), then through the orbit and into the muscle cone (the second pop that is felt), with the tip finally entering the intra-conal space. At this point, pull back slightly on the plunger to confirm that the needle is not in a vessel. Then inject about 3 or 4 cc of anesthetic into the muscle cone. Avoid injecting a large volume of anesthetic due to the limited volume of the orbit (about 30 ccc in most adults). A huge volume of injection (8 to 10 cc) will cause pressure behind the globe and this will cause difficulties during cataract surgery.
A helpful technique is to use the fingertip or the cap of the needle to depress the lower eyelid and expose the inferior equator of the globe which creating a gap by pushing the globe to the side. Once the equator is seen, it is a straight and short path for the needle to enter the intra-conal space.
As the anesthetic liquid is injected, the globe will come forwards and become a bit proptotic. After the injection is complete, the globe can be massaged to disperse the anesthetic bolus, reduce the retro-bulbar pressure, and resolve the proptosis. This can be confirmed by checking the globe’s resistance to retropulsion, which should be about the same as the untouched other eye once the anesthetic bolus is spread evenly.
Click below to learn the technique for doing a retro-bulbar anesthetic block: