Cataract is defined as the loss of transparency of the natural lens of the eye, usually due to the ageing process. It can also be found in younger people secondary to congenital, drug induced, inflammatory or trauma aetiologies. Age related cataract is the most common type and causes gradual progressive loss of vision leading to blindness. Cataract is the greatest cause of blindness worldwide; approximately 20 million people are thought to be blind from cataracts (Foster 1999). In the UK 30% of people over the age of 65 have a significant cataract in one or both eyes, increasing to 71% in people over the age of 85 (Reidy 1998). It is estimated that 2.4 million people over the age of 65 in England and Wales have visually impairing cataracts (Reidy 1998; Minassian 2000). In addition it is estimated that a further 225,000 cases of visually impairing cataracts are expected each year (Minassian 2000). The only recognized treatment available for cataracts is surgery.

In the UK the recognized current best technique for cataract removal is the extracapsular technique of phacoemulsification with the implant of an intraocular lens (RCO 2004). In a national survey phacoemulsification was the method of surgery used in 77% of patients treated in the UK (Desai 1999a). In the USA 89% of cataracts are removed by phacoemulsification (Leaming 1999). The superiority of phacoemulsification over other extracapsular techniques is well established (Minassian 2001). In 2002, 270,000 phacoemulsification procedures were performed in England and Wales (RCO 2004) making it the commonest elective surgical procedure performed in the UK (RCO 2004).

Anaesthesia for cataract surgery
An ideal anaesthetic should provide pain free surgery with minimal systemic or local complications. It should be cost effective and facilitate the surgical procedure (RCO 2004). The options for anaesthesia are: general anaesthesia (Moffat 1995), local anaesthesia (Hamilton 1988) or anaesthesia free (Pandey 2001), although this is still to find acceptance by surgeons or patients due to the pain caused from the operation. Local anaesthesia can consist of periocular blocks (sub‐Tenon, peribulbar and retrobulbar), subconjunctival injection or topical with or without the addition of intracameral local anaesthesia (RCO 2004).

There has been a dramatic change of anaesthetic practice for ophthalmic surgery in the last decade. The use of local anaesthesia has risen from 20% in 1991 (Hodgkins 1992) to 86% in 1997 (Desai 1999b). Maximum health economic benefit is achieved if cataract surgery is delivered on a day care basis using local anaesthesia.

The severe risks with traditional sharp needle blocks (peribulbar and retrobulbar blocks) of globe perforation (Duker 1991), optic nerve damage (Pautler 1986), respiratory arrest (Wittpenn 1986) and even brainstem anaesthesia (Gomez 1997) have been well documented. This led to the introduction of two new techniques of anaesthesia for cataract surgery; topical anaesthesia (Fichman 1992), a needle free procedure and sub‐Tenon block (Stevens 1992), a blunt cannula procedure. Both of these have gone on to become standard for cataract surgery in the United Kingdom.

In a review of local anaesthetic techniques for cataract surgery (Friedman 2001), sub‐Tenon's anaesthesia appears to be as effective in pain control during surgery as sharp needle techniques and to be less painful on administration. This review (Friedman 2001) was limited though as they only included one trial using sub‐Tenon block and it is now dated.

The advantages of topical anaesthesia over sub‐Tenon block are time saved in administration, shorter duration of action, allowing the patient to rapidly regain sight after surgery (Kershner 1993) and less pain during the administration of anaesthesia (Friedman 2001) but there is evidence that patients report more pain intraoperatively under topical anaesthesia (Fukasaku 1994; Friedman 2001). Patients have also been shown to be less satisfied with topical anaesthesia compared with a sub‐Tenon block (Ruschen 2005) for cataract surgery. Although there is some work suggesting advantages to both techniques, there has been no recent systematic attempt to compare both techniques for all relevant outcomes.

Anaesthetic procedures

Sub‐Tenon block
A drop of local anaesthetic is placed on the eyeball to numb the front of the eye. The patient is then asked to look up and out. The conjunctiva of the eye is held with blunt forceps and a small incision is made in it with curved scissors. A small blunt sub‐Tenon's cannula is passed through this hole round towards the back of the eye, alongside the globe, and local anaesthetic is injected behind the eye, within the deep lining of the eyeball, in the sub‐Tenons space.

Topical anaesthesia
Local anaesthetic (in drop or gel form) is placed on the surface of the eye. This may be supplemented by the injection of local anaesthetic to the front chamber of the eye, intraoperatively, with a blunt needle through the operative incision (intracameral).

Rationale for a systematic review
There are published data comparing topical anaesthesia with sub‐Tenon block for cataract surgery but there remains discussion over which is the optimal technique. We are conducting this review to collate results of the different trials and to summarize the best available evidence for topical anaesthesia and sub‐Tenon block for cataract surgery. This will help guide patients, cataract surgeons, anaesthetists and healthcare managers in the choice of anaesthetic technique for surgery.

Glossary of terms
Phacoemulsification: modern, small incision, suture‐less cataract surgery
Peribulbar block: sharp needle technique with anaesthetic administered outside the orbital muscle cone at the back of the eye
Retrobulbar block: sharp needle technique with anaesthetic administered inside the orbital muscle cone at the back of the eye
Conjunctiva: the membrane lining the front of the eyeball
Subconjunctival block: anaesthetic administered under the membrane lining the eyeball