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Anaesthesia techniques for cataract surgery
All cataract surgery at Metwest Eye Centre are performed under local anaesthesia. Despite the apparent simplicity of the techniques with minimal physiological disturbance to the patients, they will still need to be carefully prepared and screened for suitability for a particular technique.
Part of such preparation is a visit to their GP of LMO who will fill out a questionnaire regarding their general health. This important information assists their anaesthetist greatly in formulating their preoperative assessment as well as in managing their anaesthetic.
The suitability for a particular technique is largely determined by the surgeon's assessment in consultation with the anaesthetist, taking into account patient's general health status, specific condition (e.g. Parkinson's, claustrophobia, inability to lie flat on bed etc.), motivation, level of anxiety, command of English, medications (especially anticoagulants and anti-platelets agents), and of course eye condition. Before we discussed the specific local anaesthetic (L.A.) techniques, it cannot be stressed strongly enough how important sedation is as an adjunct to these techniques. Anxious patients will often feel significant discomfort or unpleasant sensation during any surgical procedure, even though the local anaesthetic is working perfectly and the operative area is completely numb. Sedation certainly "smoothes out the nerves" and makes the L.A. techniques works wonderfully. Modern short-acting sedative agents such as midazolam and propofol are generally employed for this purpose. They offer fairly accurate titrations to the desired level of sedation, and because of their short half lives, their effects are generally short-lived and patients are fully awake and "street-fit" at the conclusion of the surgery.
The two most common L.A. techniques for cataract surgery are:
1. Topical anaesthesia
This particular technique has only been made possible for cataract surgery since the advent of phaco-emulsification method of lens extraction. It simply involves instillation of local anaesthetic drops on the eye to anaesthetized the conjunctiva and then once the surgeon makes a stab incision into the anterior chamber, a further local anaesthetic dose is delivered into the anterior chamber to make the rest of the procedure painless.
For the technique to be successful, sedation is crucially needed to be at the appropriate level such that the patient is relaxed and yet awake enough for the surgeon to communicate with, and he/she needs to be appropriately educated about the procedure and relatively motivated, and possessed an acceptable level of command of English.
Without a doubt this technique is the safest option as it is devoid of the complications of regional blockade which can be relatively serious, and it enables the patient to experience the result almost immediately as the optic nerve is spared from local anaesthetics and also avoids them the necessity of wearing eye pads to protect the eye while the local anaesthetic block is wearing off.
2. Regional eye blockade.
This technique involves blocking the nerves that supply the eye, which requires administration of local anaesthetics close to those nerves. There are three main methods of injecting local anaesthetics around the eye depending on where the local anaesthetics is deposited :
- retrobulbar or intra-cone ( inside the imaginary cone formed by the six extra-ocular muscles which fanned out from their point of origins to their attachments on the eye)
- peribulbar or peri-cone ( outside the above mentioned cone )
- sub-tenon ( into the potential space under the tenon fascia of the globe )
Each of the above regional techniques has its own advantages and disadvantages, the choice is usually depending upon the anaesthetist's experience and familiarity, as well as certain patient's factors such as anticoagulation.
Unfortunately these techniques are associated with complications ranging from minor ones such as chemosis and subconjunctival haemorrhage to more major ones such as globe penetration, retrobulbar haemorrhage, and brainstem blockade by local anaesthetic. Even though these major complications are rare, they are real and can be devastating to both patient and anaesthetist alike. Because of these potential risks, topical anaesthesia is the preferred method if at all possible. Regional technique is reserved for those patients who are deemed to be unsuitable for topical method such as poor command of English, excessive anxiety, unmotivated patient, or simply refusal.