Safer ocular anaesthesia

Local anaesthesia for eye surgery is usually safe, but serious complications may sometimes occur. Sharp-needle blocks (retrobulbar or peribulbar) can potentially cause blindness or even death. Sub-Tenon's blocks, using a blunt-ended cannula, appear to be much safer. However, they can also cause serious complications. Sharp-needle techniques (retrobulbar and peribulbar injections) These appear to have the highest likelihood of serious complications. Blindness may occur if the needle pierces the globe or optic nerve. If the local anaesthetic is inadvertently injected inside the optic nerve sheath, it may track back to the brainstem and cause brainstem anaesthesia. The patient may stop breathing and lose consciousness, and this may be accompanied by fitting (epileptic seizures) and unstable blood pressure. Death is likely to occur if these complications are not managed properly. If the needle pierces an artery, this may cause a tense haematoma (retrobulbar haemorrhage): if not managed properly, this could cause globe ischaemia and blindness. Adrenaline (epinephrine) in the anaesthetic mixture could cause vasospasm, and this has been implicated as a cause for 'wipe-out' syndrome: post-operative blindness with no obvious cause. Sub-Tenon's Sub-Tenon's blocks are thought to be much safer than sharp-needle blocks. However, all of the above complications could still occur. If a long metal cannula is used, this might perforate the optic nerve sheath or the arteries at the back of the globe. If these arteries are damaged, blindness appears more likely to occur from ischaemia, rather than due to pressure from a haematoma. The sub-Tenon's technique requires some dissection of the conjunctiva and Tenon's capsule in order to reach the sub-Tenon's space. If there is a lot of scar tissue (e.g. from previous surgery, injury, traditional medicines, etc.) this may result in an inadvertent globe perforation. The sub-Tenon's dissection also provides a possible route for bacteria to enter, with the potential for an orbital infection. Minimal anaesthesia (topical, intra-cameral, sub-conjunctival) With minimal anaesthesia techniques, these risks are largely avoided, but these techniques have other potential problems. Retrobulbar, peribulbar and sub-Tenon's local anaesthesia will temporarily paralyse the extra-ocular muscles, providing good operating conditions with an immobile eye. By contrast, topical, intra-cameral and sub-conjunctival local anaesthesia result in a potentially 'mobile' eye, and this might lead to challenges for the surgeon and possibly complications and a poor outcome. Many surgeons believe that these techniques are unsuitable for surgery on the 'open eye' (e.g conventional sutured large incision extra-capsular cataract extraction), because …