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Couching
Surgical treatment of cataracts began with couching, described as early 800BC by Sushruta in India (Figure 1). A needle was passed through the sclera or cornea to push the white lens downward or backwards into the vitreous cavity. Patients were able to see forms and figures afterwards. In the middle ages, couchers travelled from town to town and using a common sewing needle would couch cataracts in the village square. Complication rates were obviously high and a couching procedure was considered a success if the patient was able to ambulate without assistance.
Extracapsular cataract extraction
Cataract surgery then advanced to extraction of the cataract rather than simply displacing it by couching (Jacques Daviel 1696-1762, Albrecht von Graefe 1828-1870). As the procedure was performed most safely after the cortex had liquefied, surgery was delayed until the cataract was 'ripe'. This initial technique did not gain wide acceptance due to the significant risks of endophthalmitis, incomplete cortex removal, chronic inflammation, capsular opacification and pupil block glaucoma.
Intracapsular cataract extraction (ICCE)
Due to the problems of extracapsular extraction, the technique evolved to removing the entire lens from the eye. Lysis of the zonular fibres was a problem and use of the cryoprobe in 1961 and subsequently chemical disillusion with the enzyme alpha-chymotrypsin improved the safety of ICCE to make it a very successful procedure, with published results of 85 per cent of patients achieving a best corrected visual acuity of 6/9 or better. Over 5 per cent of patients, however, were rendered blind due to complications such as infection, haemorrhage, retinal detachment or cystoid macular oedema. Furthermore, these patients required aphakic spectacles with their inherent problems.
Modern extracapsular cataract extraction (ECCE)
By preserving the posterior lens capsule, the risk of vitreous loss and therefore many of the potentially blinding complications may be reduced. With the growing use of the operating microscope for increased magnification, this technique therefore evolved alongside better ways to remove residual cortical material. This technique continued to be the procedure of choice during the 1980s and early 1990s.
Sutureless extracapsular (SECCE)
Despite all the modern advances in cataract surgery, our greatest challenge is still the large volume of cataract blindness in developing countries. Millions of people in the developing nations with reversible blindness due to cataracts continue to go untreated and modern phacoemulsification technology is too expensive to both purchase and maintain in these areas. Furthermore, the more advanced cataracts seen in these populations makes phacoemulsification difficult and expensive to run, with a higher risk of complications.
For these patients a high volume, low cost, low technology procedure that can deal with advanced cataracts but avoids the problems related to sutures and has a low complication rate is the paradigm.
Small incision or sutureless extracapsular cataract extraction (SECCE) has emerged as the procedure of choice for the developing world. The entire nucleus followed by the cortex is removed through a 6-8mm self-sealing sclerocorneal tunnel (Figure 2) and a single-piece rigid polymethylmethacrylate (PMMA) posterior chamber intraocular lens implant is then inserted into the capsular bag.
By alternating between two parallel operating tables, a single surgeon is able to perform over 15 cases per hour (Figure 3). Despite the high proportion of advanced and mature cataracts, the operative complication rate is low with vitreous loss occurring in less than 1 per cent of cases. Visual outcomes are also excellent with approximately 80 per cent of patients seeing 6/18 or better uncorrected in contrast to 90 per cent of these patients seeing 5/60 or worse pre-operatively.
Principles of modern phacoemulsification surgery
The current principles of cataract surgery are based on phacoemulsification cataract extraction through small incisions. Foldable intraocular lens implants are standard and virtually all surgery is now carried out under local anaesthesia, the majority being topical anaesthesia and as a day case procedure.
Day case surgery
For routine uncomplicated cataract surgery, discharge on the same day is now the norm. Adequate provision of transport is required as well as a friend or relative to escort the patient on the day of surgery. Patients who live on their own usually do not require to be accompanied overnight.
Local anaesthesia
Over 90 per cent of cataract operations in the UK are performed under local anaesthesia. The two most popular methods are sub-Tenon's anaesthesia. and topical anaesthesia by way of drops only to anaesthetise the eye. Sub-Tenon's anaesthesia is delivered using a blunt-tipped cannula delivered directly to the sub-Tenon's space following dissection through the conjunctiva and Tenon's capsule in the region of the inferonasal conjunctival fornix (Figure 4). This provides excellent retrobulbar anaesthesia yet minimises the risk of a penetrating globe injury (a well known risk following traditional peribulbar or retrobulbar injections). Patient satisfaction is high using this technique, even compared to topical anaesthesia. Topical anaesthesia is administered before surgery and can be complemented by intravenous sedation and also intracameral anaesthesia by way of unpreserved local anaesthetic injection into the anterior chamber at the time of surgery, if required. It is observed that without intracameral anaesthesia, although surgery is surprisingly painfree, patients often experience an ache at times, particularly if a change in anterior chamber depth occurs suddenly during surgery.
Small incision
Incision size in cataract surgery continues to reduce, alongside developments in surgical technology both of phacoemulsification and lens implant design. Incisions no longer require to be sutured and are now typically 3mm in size and self- sealing by way of a 2-plane construction and internal tamponade by intraocular fluid pressure. Small incision surgery has also resulted in a decline in wound rupture following blunt injury typically seen in ECCE wounds. Furthermore, based on studies examining the pressure required to rupture a cadaveric globe, it is remarkable that the eye will rupture at its weakest point, namely the insertion of the recti, rather than at the site of the phaco wound.
Small incisions are considered to be astigmatically neutral and contribute to rapid visual rehabilitation following surgery. The need to avoid bending or straining following small incision cataract surgery is less essential.
Site of incision
Small incisions or phacoemulsification cataract surgery may be clear corneal (at the corneal limbus (Figure 5) or sclerocorneal (a scleral tunnel is constructed, beginning 2mm posterior to the limbus and entering the anterior chamber approximately 1.5mm anterior to the limbus).
It is believed that scleral tunnel incisions induce less astigmatic change in comparison to clear corneal. However, the potential for wound-related complications is a little greater, in particular, hyphaema, delayed filtering blebs and early discomfort.
The site of incision also varies between being placed between the superior limbus and temporally. Temporal incisions are often used to overcome a prominent brow. However, there are other advantages of using a temporal incision. The temporal site is furthest from the visual axis, therefore providing more space to manoeuvre during surgery. As corneal incisions tend to relax the corneal curvature along that particular meridian, temporal incisions therefore help in facilitating postoperative 'with the rule' astigmatism following surgery, an advantage for elderly patients. To this purpose, many surgeons routinely aim to place incisions 'on-axis', along the steepest meridian.
Corneal sutures
Placement of sutures is nowadays a rare occurrence during routine phacoemulsification cataract surgery. Sutures are indicated if the incision is unlikely to seal completely, thereby increasing the risk of aqueous leak and hypotony, or of tear flow into the anterior chamber, with the risk of microbial contamination. Such a scenario may arise if the tunnel is of inadequate length or too wide (usually greater than 4mm). A corneal burn may also cause sufficient contraction to prevent self-sealing and require suture placement. Other indications for suture placement include: persistent iris prolapse, poor patient compliance and risk of self-injury postoperatively and sometimes following complicated cataract surgery, for example, vitreous loss. Nylon sutures are used due to its strength, elasticity, monofilament properties and slow reabsorption with minimal inflammation (Figure 6). Sutures are generally removed at six weeks postoperatively. They may be allowed to remain, if for example, concern exists over the integrity of the wound or removal may result in an undesirable change in refractive astigmatism. Nylon sutures gradually dissolve over 18 months and patients remain asymptomatic.
Viscoelastic
The development of viscoelastic technology stands alongside the introduction of the operating microscope in improving the safety and results of modern cataract surgery. A viscous clear biocompatible gel, for example sodium hyaluronate, is used to inflate the anterior chamber to allow capsulorrhexis. Viscoelastic is also injected following lens removal into the anterior chamber and the capsular bag to allow safe intraocular lens implantation. Viscoelastic materials possess a unique ability, based on their chemical structure to protect the corneal endothelium from mechanical trauma and maintain an intraocular space in the anterior chamber. They also can be used to directly manipulate intraocular structures while preventing mechanical damage to tissue and avoiding adhesions postoperatively. Substances currently used include sodium hyaluronate (Healon), chondroitin sulphate, (Viscoat) and hydroxypropylmethylcellulose (HPMC).
The main disadvantage of using viscoelastic is the significant elevation of intraocular pressure seen postoperatively if any is retained and not completely removed during surgery. It is presumed that this is the result of large molecules of viscoelastic creating mechanical resistance in the trabecular meshwork. The pressure-spike typically resolves within 72 hours.
Capsulorrhexis
During tradition extracapsular cataract extraction (ECCE) the anterior capsule was opened using a series of stab incisions lined in a circular manner to form a large 'can-opener' capsulotomy. However, due to the increased manipulation of the nucleus within the capsule during phacoemulsification, any point of weakness in the capsulotomy would easily result in a radial tear extending to the equator and even beyond, to involve the posterior capsule.
In the mid 1980s, a continuous circular capsular tear was developed known as the 'capsulorrhexis' so that no point of weakness would exist in the anterior capsular opening. The stress distribution at the edge of the capsulorrhexis is uniform and therefore low at any point, thereby providing a strong capsulorrhexis edge, resistant to tearing (Figure 7).
Hydrodissection
Following capsulorrhexis, a gentle injection of balanced saline solution (fluid with physiological pH, osmolarity and mineral content) is placed between the lens capsule and cortex to separate the lens from the capsule and mobilise the lens prior to phacoemulsification. A typical wave of fluid is seen passing behind and across the lens within the view of the operating microscope, confirming that this has been completed (Figure 8).
Phacoemulsification
In 1967, Kelman described a single-instrument technique for cataract removal using an ultrasound probe within which lies a piezoelectric crystal to convert electrical energy into vibrating shock wave energy. In a manner similar to a hammerdrill the hard nucleus is liquefied.
A number of strategies for phacoemulsification techniques exist to break the lens up within the capsular bag. 'Divide and conquer 'and 'phaco-chop' are among the most popular techniques currently used. The term 'divide and conquer' was coined to describe techniques whereby the nucleus is systematically divided and then fragmented rather than randomly emulsified (Figure 9). 'Phaco-chop', a technique introduced by Nagahara in 1993 is based on the principle of splitting wood to fracture the nucleus using a chopping instrument to split the nucleus once impaled by the phacoemulsification tip (Figure 10). The main advantage of the 'chop' technique minimises the amount of phacoemulsification time and energy used thereby minimising corneal endothelium loss. A disadvantage to this technique is the greater care that is required to prevent anterior capsule tear when inserting the chopper at the edge of the nucleus.
Laser cataract surgery
It is a common misperception among patients that cataract surgery is performed using a laser. Lasers such as the erbium:YAG laser have shown promise as a new emerging technique for lens nucleus removal. Studies show that the laser energy dissipated by an internal probe is localised with possibly less heat emission in comparison to traditional ultrasonic phacoemulsification techniques. There also seems to be very little difference in outcomes when compared to conventional surgery techniques. However, laser is considered less effective particularly when dealing with dense cataracts and do not have any obvious benefit with regards to reducing corneal endothelial loss. The main use for laser in cataract surgery therefore remains for posterior capsulotomy as a treatment for postoperative posterior capsule opacification.
Micro-incision phacoemulsi-fication cataract surgery
Corneal incision size continues to increase such that an emerging technique known as 'bi-manual phacoemulsification' has emerged. Surgery is performed through incisions less than 2mm in size. The main purpose for reducing the incision size is to reduce surgically induced astigmatism and wound-related complications. The traditional coaxial phacoemulsification probe is split so that the irrigation and aspiration components are separated and are carried out through two micro-incisions. The theoretical benefits of separating these components through two micro-incisions are to stabilise the anterior chamber and improve fluidics during surgery. This may be of particular benefit in young patients in whom a stable anterior chamber may minimise shifts of the vitreous and therefore help reduce the risk of retinal tears. Although outcomes of micro-incision bi-manual surgery have been reported, studies comparing micro-incision and coaxial phacoemulsification suggest that total phacoemulsification time can be further lowered and also surgically-induced astigmatism can be reduced using bi-manual techniques. However, at present, the wound then needs to be enlarged in order to insert the most currently available intraocular lens implants. The next step is therefore to develop injectable intraocular lens implants that can be inserted through smaller incisions than currently possible.
Intraocular lens implantation
The use of the rigid PMMA intraocular lenses has now been largely superseded by foldable IOLs made of silicone, acrylics or hydrogels. Foldable IOLs allow 6mm diameter optics to be inserted through 3.2mm incisions (Figures 11 and 12). These can now also be injected by way of injectable devices.
Complications during cataract surgery
Operative complications are an inevitable risk during cataract surgery and can occur at any stage during surgery. Each step during phacoemulsification relies on the success of the previous one. A poorly constructed wound could leak during surgery, resulting in an unstable anterior chamber and endothelial, iris or capsular injury. If the capsulorrhexis is too small, it may be damaged by the phaco probe. The tear may extend into the posterior capsule resulting in vitreous loss. Any error at any stage during surgery can have a cascading effect, magnifying the damage. Significant and well-recognised intraoperative complications are detailed below.
Complications during regional anaesthesia
Retrobulbar or intraorbital haemorrhage is a rare, sight-threatening complication that may occur immediately following retrobulbar or peribulbar anaesthesia. It is immediately recognised as acute proptosis, tenseness of the orbital contents and difficulty separating the eyelids. This may require an emergency lateral canthomy to release any orbital tightening and usually results in postponement of surgery.
Globe perforation as a complication of retrobulbar or peribulbar anaesthesia is well-documented. This is due to the use of a needle and may not be recognised at the time of administering anaesthesia. Such a complication may only be identified postoperatively if vision remains poor due to vitreous haemorrhage or an early retinal detachment. Eyes with staphylomata, or thin sclera due to high myopia may be at particular risk. Regional anaesthesia, including sub-Tenon's carries the risk of prolonged strabismus and diplopia. Vertical diplopia due to restriction of the inferior rectus muscle is thought to occur in approximately 0.5 per cent of cataract procedures and may require subsequent squint surgery. Conjunctival inclusion cysts are also known to occur at any conjunctival entry site.
Corneal complications during surgery
A tear in Descemet's membrane usually occurs if a blunt instrument has been inserted or when fluid is inadvertently injected between Descemet's membrane and the corneal stroma. It results in corneal stromal swelling and epithelial bullae in a localised area of the detachment, usually near the incision site. Small detachments may resolve spontaneously or be reattached with an injection of air into the anterior chamber for tamponade. Large detachments rarely may need suturing into place.
Corneal thermal burns may occur at the tunnel due to transfer of heat from the phaco probe, particularly if the wound is too tight or the probe is pressed against the corneal lip, thereby preventing adequate flow of irrigation along the probe. This can result in clouding of the cornea and contraction at this site and may result in wound leak as well as significant astigmatism postoperatively.
Capsule rupture during surgery
This serious complication, and one of the most significant, is estimated to occur in 1 per cent of phacoemulsification cataract procedures. It can occur at any one of four main stages during cataract surgery: At the time of hydrodissection, during phacoemulsification, removal of cortex or during insertion of the IOL. The principles of dealing with this complication include:
- Safely removing the remaining lens material
- Performing an anterior vitrectomy to carefully remove vitreous from the anterior chamber and the incision sites ? Preservation of remaining capsule to allow support for a posterior chamber IOL.
The visual results after capsule rupture are not as good as uncomplicated surgery. Studies suggest that approximately 85 per cent of patients subsequently achieve vision of 6/12 or better. Poor vision in the remaining 15 per cent is often due to cystoid macular oedema.
Choroidal haemorrhage or effusion
Choroidal haemorrhage or effusion occurs in approximately 0.1 per cent of cases and causes a forward shift of the iris-lens diaphragm, with prolapse of posterior structures and a change in the red reflex. Effusion may be a precursor to haemorrhage, although it may be difficult to differentiate the two. It is uncertain why this complication occurs but presumably is due to leakage or rupture of choroidal vasculature and is considered to occur more often in patients with underlying systemic vascular disease, hypertension, obesity, glaucoma or chronic ocular inflammation.
Rapid wound closure is required once this complication is recognised to prevent iris prolapse and expulsion of the lens, vitreous and blood (expulsive choroidal haemorrhage). Sclerostomies may also be performed using a blade or small trephine to drain blood posterior to the ora serrata.
This article is based on a chapter in Cataract by Raman Malhotra, a forthcoming book in the Elsevier Science Eye Essentials series.
Raman Malhotra is a consultant ophthalmic and oculoplastic surgeon at The Queen Victoria Hospital, East Grinstead, West Sussex