Complications of cataract surgery - Wiley Online Library

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Complications of cataract surgery

Clin Exp Optom 2010; 93: 6: 379–389 Elsie Chan FRANZCO Omar A R Mahroo MB BChir PhD David J Spalton FRCS FRCP FRCOphth Ophthalmology, St Thomas’ Hospital, London, UK E-mail: [email protected]

Submitted: 28 March 2010 Revised: 10 June 2010 Accepted for publication: 25 June 2010

DOI:10.1111/j.1444-0938.2010.00516.x Modern cataract surgery is safe in more than 95 per cent of patients. In the small number of cases where a serious complication occurs, the most common is an intra-operative posterior capsular rupture. This can lead to vitreous loss or a dropped nucleus and can increase the risk of post-operative cystoid macular oedema or retinal detachment. Postoperatively, posterior capsular opacification is the most common complication and can be readily treated with a YAG capsulotomy. The most devastating complication is endophthalmitis, the rate of which is now significantly decreased through the use of intracameral antibiotics. As a clinician, the most important step is to assess the patient pre-operatively to predict higher risk individuals and to counsel them appropriately. In these patients, various pre- or intra-operative management steps can be taken in addition to routine phacoemulsification to optimise their visual outcome.

Key words: capsular rupture, cataract surgery, complications, phacoemulsification

Cataract surgery is now the most common surgical procedure performed in the Western world. Since the conversion from extracapsular extraction to phacoemulsification, the outcomes of cataract surgery have improved greatly, with the risk of complications falling. The only national survey of cataract surgery outcomes in the United Kingdom found that for 55,567 cases reported, there were no complications in more than 95 per cent of cases. Ninety-one per cent of patients with no ocular comorbidities achieved a post-operative visual acuity of 6/12 or better, with 45.9 per cent of all eyes achieving 6/6 or better.1 Despite ongoing advances in cataract surgical technology, a small number of complications will always exist. This article outlines some of the more common intra-

operative and post-operative complications and the management options that are available. The article draws on our experience from our own clinical practice, discussions with colleagues, and data presented at international conferences and from electronic literature searches performed on the PubMed database (accessed March 2010) focusing on the various topics discussed. PRE-OPERATIVE CONSIDERATIONS One of the most important steps in cataract surgery is to anticipate cases that are considered higher risk and to both inform the patient and plan in advance, if any changes in technique or additional equipment are required. For example, a patient with pseu-

© 2010 The Authors Clinical and Experimental Optometry © 2010 Optometrists Association Australia

doexfoliation syndrome and associated phacodonesis may require a capsular tension ring insertion at the time of surgery. A patient who is unable to lie still may require a general anaesthetic. Such steps are important to avoid excess anxiety and disappointment for both the surgeon and patient, if any complication were to occur, and to allow the most appropriate management at the time of surgery. In this way, we can provide the patient with the best possible surgical outcome. INTRA-OPERATIVE COMPLICATIONS

Posterior capsular rupture The most common intra-operative complication is rupture of the posterior lens

Clinical and Experimental Optometry 93.6 November 2010

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Complications of cataract surgery Chan, Mahroo and Spalton

capsule. This is a potentially serious complication due to the associated risk of a dropped nucleus, vitreous loss leading to retinal detachment and cystoid macular oedema and difficulties with placement of the intraocular lens. Generally, rates vary usually between less than one per cent to 4.1 per cent in most institutions.2 The UK Cataract National Database of cataract surgery performed by all grades of surgeons reported a posterior capsular rupture rate of 1.92 per cent.1 From this database, risk factors that were identified as increasing the risk of posterior capsular rupture were increased age (adjusted odds ratio [AOR]: 2.37 for those older than 90 years), male gender (AOR: 1.28), the presence of glaucoma (AOR: 1.3), diabetic retinopathy (AOR: 1.63), dense cataracts (AOR: 2.99), pseudoexfoliation/ phacodonesis (AOR: 2.92), presence of vitreous opacities (AOR: 2.46), small pupil size (AOR: 1.45), axial lengths of greater than 26.0 mm (AOR: 1.47), use of the systemic medication doxazosin (AOR: 1.51), inability to lie flat (AOR: 1.27), and junior surgeons performing the surgery (AOR: 3.73 for Senior house officers).3 Narendran and colleagues3 have attempted to quantify the cumulative risk of multiple risk factors to help predict the probability of an intra-operative complication. The causes of rupture of the posterior capsule usually involve touch of surgical instruments and can be caused at any stage of the procedure. Capsular block from excessive hydrodissection can cause a capsular rupture even prior to phacoemulsification. Other more common causes of capsular rupture are touch from the phacoemulsification probe or second instruments during the phacoemulsification of the lens or from irrigation/aspiration instruments during cortical cleanup. Touch from instruments may also cause an anterior rhexis tear, which can then extend posteriorly to create a posterior capsular tear. More rare causes of posterior capsular rupture include trauma during intraocular lens insertion and puncture from loose cannulas during hydration of wounds or intracameral injections at the conclusion of surgery. There is hardly a stage of surgery

at which a posterior capsular rupture cannot occur. Some types of cataract are also known to have a higher risk of posterior capsular defects. Congenital posterior polar cataracts have a high incidence of an inherent capsular defect at the site of the lens opacity and therefore, patients must be appropriately counselled and many surgeons perform hydrodelineation to form a cleavage plate between the epinucleus and nucleus rather than hydrodissection between the cortex and capsule to remove the lens.4 Patients who have had a vitrectomy also face a higher risk either due to a capsular defect, if lens touch from the vitrector was the cause of the post-operative cataract, or because of a floppy, less stable posterior capsule during phacoemulsification due to the loss of stabilisation from the absence of the vitreous face. This is discussed in more detail below. The challenges faced by the surgeon following a posterior capsular rupture vary depending on the stage at which it has occurred. Generally, a rupture that occurs earlier in the case is much more problematic than one that occurs after the lens and cortex have already been removed. An early rupture causes difficulties that may necessitate either enlargement of the corneal/limbal wound to facilitate lens removal, to prevent subsequent dropped nuclear fragments, if not the whole lens, into the vitreous cavity, which would then require a vitrectomy. The actual incidence of dropped nuclei is low, at around 0.18 per cent.1 Despite the psychological trauma of a second operation to both patient and surgeon, 56 per cent of patients will still have a final post-operative vision of better than 6/12.5 The timing of vitrectomy and lensectomy should usually be within three weeks post-operatively and will depend on factors such as corneal clarity, degree of intraocular inflammation and intraocular pressure. Early vitrectomy improves visual results, with a decreased risk of glaucoma, cystoid macular oedema and retinal detachment.6 If the cataract has been removed in entirety prior to capsular rupture, disruption of the vitreous face leads to the presence of vitreous in the anterior chamber.


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Without adequate anterior vitrectomy, vitreous strands can lead to destabilisation of the IOL, a peaked pupil, vitreous through the surgical wound, chronic uveitis and subsequent post-operative risk of retinal tears and detachment, cystoid macular oedema and endophthalmitis. Visualisation of the vitreous can be improved with the use of triamcinolone injected into the anterior chamber to aid its removal.7 The decision about the position of IOL placement depends on the size of the posterior capsular defect. If it is a small focal defect, the lens can still be placed carefully in the bag, made safer if a posterior capsulorrhexis is performed.8 If there is any doubt and definitely in all cases of a large defect, the IOL needs to be placed in the sulcus. While no optimal IOL exists for sulcus placement in such a situation, the currently available three-piece foldable lenses suffice. Prolapsing the optic of the IOL through the anterior rhexis (optic capture) can help centration and reduce problems such as iris chafing and pigment dispersion from the square edge of the optic (Figure 1).9 Post-operatively, the patient’s peripheral retina should be checked carefully for tears or breaks that may have occurred from vitreous traction during surgery. Managed correctly, the visual outcome of patients who suffer a posterior capsular rupture is still very good, with over 90 per cent of patients having an improvement in their vision from pre-operative levels.2

Zonular dehiscence The rate of zonular dehiscence reported in the UK National Cataract Database was 0.46 per cent.1 Careful history-taking and examination of the lens are important preoperatively to assess for lens stability and the presence of weak zonules. Ruptured zonules occur most commonly in the setting of ocular trauma or in pseudoexfoliation syndrome. In Marfan’s syndrome, the zonules are often stretched rather than ruptured, although the consequence is the same. In such cases, it is important to look for the presence of vitreous in the anterior chamber and counsel the patient appropriately regarding the risks associated with surgery. © 2010 The Authors

Clinical and Experimental Optometry © 2010 Optometrists Association Australia


Figure 1. Retroillumination photograph showing optic capture of the intraocular lens through the anterior rhexis following a posterior capsular tear Capsulorrhexis can be difficult in patients with zonular dehiscence. Depending on the degree of instability, iris hooks may be required to support the anterior capsule.10 A capsular tension ring can also be inserted. These are designed to sit at the equator of the lens within the capsule to provide support by spreading the tension on the zonules. They are particularly useful in cases of focal zonular loss of less than 180 degrees. In the event of greater than 180 degree loss, techniques such as using a sutured Cionni ring, while technically challenging, can lead to excellent surgical results. The Cionni ring is similar to a capsular tension ring but is modified with the addition of one or two eyelets, through which a suture can be placed to stabilise the ring to the sclera.11 Alternatively, a capsular tension ring segment (Ahmed segment) can be placed in the bag rather than a full 360-degree ring. Again, it needs to be sutured to the sclera. If such a ring or segment is not available, the IOL may be decentred or be unstable in either the bag or sulcus and an anterior chamber lens may need to be inserted.

In many cases zonular dehiscence is not noted pre-operatively or may have occurred as the result of surgical trauma. Such cases may be the result of inherent zonular weakness, such as pseudoexfoliation syndrome, trauma or in very elderly patients. Surgical trauma may be caused by excessive traction on zonules such as during lens rotation or unintentional direct vacuum/aspiration of the peripheral capsule from the phacoemulsification probe or irrigation/aspiration probes. In these cases, the management is the same as previously described and depends on the extent of dehiscence and stage at which it occurred. In the event that the posterior capsule is not intact, a capsular tension ring is contraindicated. Any vitreous that has prolapsed through into the anterior chamber must of course be recognised and removed by anterior vitrectomy. After stabilisation of the capsule and removal of any vitreous, the IOL can often be safely placed in the bag.

Suprachoroidal haemorrhage Suprachoroidal haemorrhage is very rare with small incision cataract surgery with an


incidence around 0.04 per cent.12 It occurs as the result of sudden rupture of bridging vessels in the suprachoroidal space and with larger incision cataract surgery and can have devastating consequences with a sudden intraocular pressure rise leading to expulsion of ocular contents through the surgical wound. Risk factors for a suprachoroidal haemorrhage include older age, high intraocular pressure, a history of systemic cardiovascular disease, systemic hypertension and complicated cataract surgery.13 When it occurs, it is recognised by sudden shallowing of the anterior chamber and iris prolapse associated with progressive loss of the red reflex and raised intraocular pressure. Wounds should be sutured immediately and intraocular pressure lowered with systemic acetazolamide or mannitol. Experienced surgeons may drain the blood via sclera flaps. The visual outcome has been reported to be 40 per cent patients achieving 6/12 or better, with another 40 per cent less than 6/60.12 It is worth mentioning at this point that there is no evidence of any increased risk of any significant intraocular bleeding as the result of systemic anticoagulant use in routine cataract surgery.14 POST-OPERATIVE COMPLICATIONS

Posterior capsular opacification Posterior capsular opacification (PCO) is the most common post-operative complication of cataract surgery. Residual lens epithelial cells are inevitably left at surgery in the equatorial capsular bag. Migration of lens epithelial cells to the posterior capsule can cause increasing opacity impairing the vision of the patient, with a fall in visual acuity and contrast sensitivity15,16 (Figure 2). Risk factors include younger age, uveitis and ocular inflammation or diseases such as retinitis pigmentosa. A considerable volume of clinical research shows that a square IOL edge inhibits lens epithelial cell migration to the posterior capsule.17–19 In the event of the development of postoperative posterior capsular opacification, the treatment is a capsulotomy using an


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IOP secondary to post-operative steroid eye-drops. The rise in IOP in the latter group will settle after discontinuation of topical steroids but those in the former group will often require anti-glaucoma medication or even surgery in more extreme cases.

Corneal decompensation

Figure 2. Opacification of the posterior capsule

Nd:YAG laser, if it is visually significant. We consider posterior capsular opacification to be visually significant if there is a subjective and objective decrease in vision consistent with the degree of posterior capsular opacification noted on slitlamp examination. Rates of YAG capsulotomies in pseudophakes up to 20.4 per cent are reported.20 The procedure is simple, with excellent outcomes in immediately improving the patient’s vision. Reported risks of YAG capsulotomy include shortterm intraocular pressure rise, subluxation of the IOL and increased risk of cystoid macula oedema.21 Thus, most people prefer not to perform YAG capsulotomies earlier than three months postoperatively. An increased risk of retinal tears and detachment is more controversial. The risk is probably higher in young patients and high myopes who already have a generally higher risk of retinal detachment than the normal population.22 While the exact mechanism of how a YAG capsulotomy may be related to a retinal tear or hole is uncertain, it possibly involves disruption to the vitreous.21 A hole or tear may be caused by anterior vitreous detachment during phacoemulsification, followed by a forward displacement of the vitreous as the result of the capsulotomy.22

Raised intraocular pressure Eyes undergoing cataract surgery have been shown to have a transient postoperative rise in intraocular pressure (IOP). This can be exacerbated if the viscoelastic materials used during surgery are incompletely aspirated from the eye and different agents have been shown to confer different risks of raised IOP.23 Higher molecular weight viscoelastics have been shown to result in a higher rise in post-operative IOP. This can be avoided by administering oral acetazolamide or topical pressure-lowering agents in the immediate and early post-operative period.24 Practice varies in different departments: a survey conducted in the UK showed that one-third of surgeons routinely used a pressure-lowering agent, and in most cases this was oral acetazolamide.25 Some surgeons are more likely to use such agents in patients in whom IOP control is more critical, such as those with advanced glaucoma, as it has been suggested that glaucoma patients may be more likely to develop a rise in IOP.26 Other causes of ocular hypertension after cataract surgery include pigment dispersion secondary to sulcus placement of the intraocular lens, particularly if a single-piece acrylic lens is used,9 and also steroid responders who develop raised


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There is a degree of corneal endothelial cell loss after cataract surgery of around five to eight per cent. Risk factors include a shorter axial length and longer phacoemulsification time.27,28 Corneal decompensation following cataract surgery is more common in those patients with preexisting endothelial cell dysfunction, such as in Fuchs’ endothelial dystrophy, where the remaining endothelial cell function post-operatively may not be sufficient to keep the cornea clear, thus causing decompensation, oedema and corneal thickening. To try to avoid this situation, it is important to avoid excessive phacoemulsification power during cataract surgery and to use a combination of a dispersive viscoelastic (for example, Viscoat, Alcon Laboratories) during surgery to coat and thus protect the endothelium and a cohesive viscoelastic (for example, Healon, Abbott Medical Optics), coined the ‘soft shell technique’.29,30 In the event that the cornea does not clear post-operatively, a corneal graft (endothelial graft) may be necessary to improve the patient’s vision. Pseudophakic bullous keratopathy is currently the second most common indication for corneal graft surgery in the UK. Thus, in patients who have Fuch’s endothelial dystrophy, the timing of cataract surgery needs to be carefully balanced based on the state of the endothelium, the corneal thickness and the degree of cataract. Early surgery is preferred, as a dense cataract will require much higher phacoemulsification power and consequent increased endothelial cell loss.

Cystoid macular oedema Cystoid macular oedema (CMO) can cause a reduction in vision after cataract surgery and in this context, is also termed Irvine-Gass syndrome. Intraretinal fluid accumulates in the outer plexiform and © 2010 The Authors



Figure 3. Ocular coherence tomographic image of cystoid macular oedema; this patient later had intravitreal triamcinolone

inner nuclear layers forming cystic spaces. Cystoid macular oedema typically presents as a reduction in visual acuity (usually down to 6/18 or 6/24), possibly with distortion a few weeks after surgery. It occurs after about two per cent of uncomplicated procedures, although asymptomatic cystoid macular oedema demonstrable on fluorescein angiography may have a much higher incidence.31 Pre-operative risk factors include diabetes, uveitis, previous retinal vein occlusion, epitretinal membrane, use of topical prostaglandin analogues and cystoid macular oedema following fellow eye surgery.32 Studies have shown that use of peri-operative topical non-steroidal anti-inflammatory (NSAID) medication in addition to, or even instead of, routine topical steroid drops, can lower the incidence of pseudophakic angiographic cystoid macular oedema,33,34 however their use is not routine in most departments and some express concern with using multiple drops and the risks of drop toxicity. Some ophthalmologists add topical NSAIDs post-operatively for patients deemed to be more at risk of macular oedema, such as those with diabetic retinopathy but no consensus exists in terms of their use. Intra-operative com-

Figure 4. Fluorescein angiogram of cystoid macular oedema (a different patient from that in Figure 3) demonstrating petaloid pattern of leakage around the fovea and leakage at the disc

plications including posterior capsular rupture with vitreous loss also increase the risk. The advent of optical coherence tomography (OCT) has allowed accurate, non-invasive assessment of macular morphology, and hence facilitates the diagnosis of cystoid macular oedema, which has the appearance of optically empty intraretinal spaces (Figure 3). Interestingly, OCT studies have shown that even in nonclinical cystoid macular oedema eyes, an asymptomatic increase in macular thickness can be shown at 12 weeks after surgery.35 Fluorescein angiography in cystoid macular oedema gives a classic ‘flower petal’ appearance as dye accumulates in cystic spaces in the outer plexiform layer, radiating from the foveal centre (Figure 4). The condition will usually resolve spontaneously and it has been shown that topical steroids and NSAIDS may hasten this resolution.32 If topical treatment fails, intravitreal steroids may be injected to bring about resolution. In some cases, a specific cause may be identified, such as vitreous traction. This may be the result of an intra-operative posterior capsular tear with vitreous loss with inadequate anterior


vitrectomy resulting in residual vitreous strands in the anterior chamber adhering to the corneal section. This may then be addressed by various means, including YAG laser treatment to vitreous strands that are in contact with the corneal incision or returning to the operating theatre for further anterior vitrectomy. In some cases, a pars plana vitrectomy may be of benefit. The overall prognosis is good, with more than 90 per cent of cases resolving over two years.36

Retinal detachment The risk of retinal detachment increases after cataract surgery. In most cases this is due to induction of a posterior vitreous detachment, probably induced or associated with loss of internal volume from removal of the cataractous lens and replacement with a thinner IOL. An increased risk persists for many years after surgery. A cumulative risk of about 0.9 per cent four years after surgery has been reported, with the risk increasing each year after surgery.37 One study reported that the increased risk persisted for at least six years and that the overall cumulative eight-year incidence of retinal detachment


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was increased by almost nine-fold in operated eyes.38 Reports have also shown that the risk is increased with certain pre-operative patient factors, so pre-operative discussion in these groups may be important. These include history of previous retinal detachment in the other eye (odds ratio: 12.3), long axial length (OR: 3.2 for eyes longer than 23 mm), male gender (OR: 2.2) and younger age.39 In high myopes, the cumulative risk may not reach a plateau until 10 years after cataract surgery.40 Young myopic patients who have not had a posterior vitreous detachment are particularly at risk and this needs to be borne in mind particularly in those patients having clear lens extraction to correct refractive error. Intra-operative events such as a posterior capsular tear and zonular dehiscence increase the risk, with reported odds ratios of 19.9 and 12.4, respectively.39 Dislocation of nuclear fragments into the vitreous increases the risk further.41 Careful examination should be performed when pseudophakic patients present with symptoms suggestive of a retinal tear or posterior vitreous detachment, as peripheral retinal breaks can often be difficult to visualise due to an impaired view from anterior or posterior capsular fibrosis or by the edge of the intraocular lens. We generally advise patients to seek rapid attention if they experience symptoms but there is no evidence to support repeated dilated fundal examinations annually after cataract surgery, though it is plausible that this could detect asymptomatic tears or early detachments.

Endophthalmitis Endophthalmitis is one of the most feared complications of cataract surgery due to its devastating consequences. The most common risk factors are posterior capsular rupture, prolonged surgical time, wound leak and less experienced surgeons. Other factors that are more controversial include increased patient age, corneal incision site and wound configuration.42,43 The rates of endophthalmitis vary in retrospective audits. In the most useful study, the European Society of Cata-

ract and Refractive Surgery performed a prospective randomised controlled trial of antibiotics in endophthalmitis, with the incidence in the placebo group being 0.34 per cent.44 Endophthalmitis can present either acutely or as a chronic form. Acute cases occur within days of surgery and present with pain, redness, marked anterior chamber cells, hypopyon and vitritis, and are most commonly caused by grampositive organisms (93 per cent in total, 49 per cent of which are coagulase-negative staphylococci) and typically originate from the patient’s lid flora.45 Chronic cases can occur many weeks later and can present as persistent inflammation. Prompt diagnosis is vital with an anterior chamber tap and vitreous biopsy, with or without a core vitrectomy. Acute treatment consists of intravitreal antibiotics, usually ceftazidime and vancomycin and primary vitrectomy depending on the severity of the case. In chronic cases (more than six weeks after surgery), Proprioniobacterium acnes must be considered as a cause of chronic inflammation. A fluffy white posterior capsular plaque is classically seen, as it is thought that the organism sequesters between the capsule and IOL. Apart from intravitreal antibiotics (usually vancomycin) and vitrectomy, a capsulectomy with or without IOL extraction may be required.46,47 Taking appropriate measures to prevent endophthalmitis is crucial. Many different factors in cataract surgery have been investigated extensively for their role as a risk factor for endophthalmitis. Currently, the three most accepted methods of reducing the risk are to use an appropriate antiseptic solution (povodone-iodine), adequate draping of the surgical field to exclude the eyelashes and the use of intracameral antibiotics, such as cefuroxime at the conclusion of surgery. The European Society of Cataract and Refractive Surgeons (ESCRS) study demonstrated that a single dose of 1 mg in 0.1 mL of intracameral cefuroxime at the conclusion of surgery reduced the risk of endophthalmitis by a factor of almost five, from 0.34 down to 0.07 per cent.44 In countries where cefuroxime is not available, such as in Australia, intracameral cephazolin has been


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used as an alternative. Significant blepharitis should also be managed preoperatively as most organisms causing infection are derived from the patient’s own flora. Other methods for preventing endophthalmitis include the use of preoperative topical antibiotics. In the USA, the majority of surgeons use topical fourth generation fluoroquinolones (gatifloxacin or moxifloxacin) one to three days pre-operatively rather than intracameral antibiotics, with most surgeons citing concerns regarding the lack of commercially available antibiotic for intracameral use.48 There are several points to note: 1. No prospective randomised trial has been performed to prove the efficacy of pre-operative antibiotics. 2. Pre-operative topical antibiotics have not been proven to decrease the risk in a large case-controlled study of 205 cases of endophthalmitis in Western Australia.43 3. Fourth-generation fluoroquinolones are not yet available in Europe and Australia, although they are available in some Asian countries. Using other preoperative antibiotic drops, such as chloramphenicol is not routine practice in Australia at present.

Refractive surprise While choosing the target refraction for individual patients is beyond the scope of this article, in general, we choose emmetropia (-0.50 to 0.00 D) in both eyes for our patients. Other options include maintaining myopia in patients with preexisting myopia or monovision, where emmetropia in one eye is combined with a degree of myopia in the fellow eye to decrease spectacle dependence at distance and near. Biometry is most commonly performed by applanation A-scan, immersion A-scan or by optical coherence using the IOL Master (Carl Zeiss, Germany). The IOL Master is generally considered to be the most accurate and the gold standard but it cannot be used with very dense or mature cataracts or in patients with poor fixation. In contact lens wearers, soft lenses should be discontinued for 24 to 48 hours and rigid lenses discontinued up to two to © 2010 The Authors



three weeks prior to performing biometry to stabilise the keratometric readings.49 Once the corneal curvature and axial length measurements are determined, several IOL formulae are available and each has its indications and some are better at predicting IOL power in excessively short or long eyes. The A-constants of lenses could also be modified from the manufacturer’s values based on each surgeon’s outcomes. With current IOL formulae and the use of the IOL master, the target refraction is achieved within one dioptre in 96 per cent cases.50 Biometry should always be inspected for any irregular results prior to surgery, such as asymmetry in axial lengths or keratometric values not reflected in refraction. Axial lengths outside of the range of 21.3 to 26.6 mm, keratometric values outside 41.0 to 47 D, astigmatism greater than 2.5 dioptres, axial length asymmetry of more than 0.7 mm and asymmetry of mean keratometric findings of greater than 0.90 dioptres have also been suggested as parameters to alert the surgeon to recheck values.51 In cases of a post-operative refractive surprise, the biometry should be carefully reconsidered prior to second eye surgery. One of the most common causes is an inaccurate axial length in cases where ultrasonic applanation is used instead of optical coherence because excess contact causes compression of the eye and thus a shorter axial length. Inaccurate axial lengths can also occur in high myopes in the presence of a staphyloma. Another increasingly common cause of inaccurate refractive outcomes is prior laser refractive surgery. Due to changes in the corneal curvature as the result of laser surgery, the keratometric findings obtained by the IOL master or manual keratometry are inaccurate as the current IOL formulae assume a relationship between the anterior and posterior curvatures of the cornea that no longer apply. Improved results can be obtained if the refraction and K values pre- and postLASIK are available or with new technology such as the Pentacam (Oculus) to measure corneal power and using specially developed formulae such as the BESSt formula.52

Other cases of patient dissatisfaction with refractive outcome may be patients with monovision. It is important to try to simulate monovision for patients prior to surgery. This may be in the form of contact lenses or trial lenses, either before surgery in either eye or after first eye surgery. Whether the dominant eye is corrected for distance or near may be less crucial.53 In patients who are unhappy with their post-operative refractive surprise, regardless of cause, surgical management options include IOL exchange, a piggyback IOL (a sulcus IOL placed in front of the existing IOL in the bag) or refractive laser surgery. COMPLICATIONS IN PATIENTS WITH OTHER OCULAR CO-MORBIDITIES Any ocular co-morbidity can increase the risk of a suboptimal post-operative visual result. The presence of diabetic retinopathy, age-related macular degeneration, glaucoma and uveitis can all influence outcome and it has also been suggested that cataract surgery itself may influence the progression of these conditions. The risk of complications is also increased in eyes that have had previous vitrectomy. Some of these co-morbidities are discussed in more detail below.

Diabetic retinopathy Several studies have shown that diabetic retinopathy and macular oedema worsen after cataract surgery, with the suggestion that cataract surgery itself accelerates progression, perhaps as a result of inflammatory mechanisms and haemodynamic changes. Some more recent studies have shown that there is no increase in risk of progression, suggesting that the risk is less with modern phacoemulsification techniques.54 In contrast, a recent cohort study concluded that cataract surgery could double the risk of progression of retinopathy,55 however, an important confounding factor is that the presence of a cataract itself may be a marker for worsening progression, hence the evidence is not clear.56 Thus, close follow-up with early post-


operative dilated fundal examinations is advisable for all diabetic patients, particularly if the status of the retinopathy or maculopathy was not assessable prior to cataract surgery due to the lens opacity. If these patients are examined late in the post-operative period, it can be difficult to determine whether the presence of macular oedema indicates pre-existing diabetic macular oedema or new pseudophakic cystoid macular oedema, for which the treatments differ. Laser photocoagulation is used to treat diabetic retinal changes: panretinal photocoagulation (PRP) for proliferative diabetic retinopathy and macular focal or grid laser for diabetic macular oedema. It is thought that macular laser treatment should be aggressive pre-operatively, where possible to optimise visual outcome. Panretinal photocoagulation is generally performed prior to surgery although a recent study interestingly suggested a possible benefit from undertaking panretinal photocoagulation after surgery.57 Visual outcome is poorer in eyes with more severe retinopathy or treatmentresistant macular oedema at the time of surgery and investigations are underway into whether the outcome in this group could be improved by combining cataract surgery with adjuvant treatments, such as injections of the steroid, triamcinolone, or the anti-VEGF agent, bevacizumab. Initial results have been reviewed and appear promising.56

Age-related macular degeneration Age-related macular degeneration (AMD) and cataracts often co-exist. Therefore, it is important to identify age-related macular degeneration prior to cataract surgery, as this will affect visual prognosis and the patient can then be appropriately counselled. There is also concern that cataract surgery may accelerate progression of AMD to more advanced forms, namely neovascular age-related macular degeneration or choroidal neovascularisation and geographic atrophy.58 Recent large studies including a report from the multi-centre Age-related Eye Diseases Study (AREDS), which included 8,050 eyes, have found no significant evidence to


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support this.59,60 Some cases of neovascular age-related macular degeneration are amenable to timely treatment with antiVEGF agents and therefore, accurate diagnosis is important, so that there is no delay in treatment. One report61 found a high incidence of neovascular age-related macular degeneration at one week after cataract surgery, suggesting that this was present pre-operatively, but was missed due to lens opacity. Therefore, close follow-up with a dilated fundal examination is advisable for age-related macular degeneration patients with a poor fundal view prior to cataract surgery. Also, a low threshold for performing fundus fluorescein angiography has been recommended to detect choroidal neovascularisation preoperatively particularly in patients with advanced age-related macular degeneration in the other eye.62

Glaucoma Cataract extraction alone has also been shown to lead to a long-term reduction in IOP in normotensive or ocular hypertensive eyes, perhaps by reducing the compression on the trabecular meshwork and canal of Schlemm by an enlarging lens.63 In patients with pre-existing glaucoma, there are several issues that need to be considered. For those with advanced glaucoma, the decision of whether to proceed with cataract surgery alone or a combined trabeculectomy and cataract extraction should be made according to the patient’s IOP control, tolerance to topical medications, degree of glaucomatous damage and degree of cataract. There is evidence that a combined procedure may be less successful than a trabeculectomy alone,64 whereas in those with previous trabeculectomy, cataract surgery may adversely affect the control of IOP post-operatively.65

Uveitis Patients with chronic uveitis are predisposed to cataract formation as a result both of the inflammation and its treatment with corticosteroids. The surgery can be technically difficult with a higher risk of intra-operative complications due to the presence of posterior synechiae, poorly dilated pupils and pupillary membranes.

Post-operatively, there is increased risk of reactivation of uveitis, capsular opacification, cystoid macular oedema and epiretinal membrane formation.66 The rates of post-operative inflammation may be lower with modern phacoemulsification techniques combined with a posterior chamber lens implant, compared to previous extracapsular extraction.67 Pre-operatively, cataract surgery is generally not contemplated until the eye is free from active uveitis. Frequently, this is achieved by the use of topical or oral corticosteroids or other anti-inflammatory therapies, while remaining vigilant of their possible short- and long-term side-effects, such as raised blood glucose in the case of systemic steroids. A lower rate of postoperative macular oedema, as measured by OCT, has been shown in patients with uveitis who were treated before surgery with oral steroids and in eyes in which the uveitis was controlled for more than three months pre-operatively.68 Intra-operatively, in some patients with significant posterior segment disease, phacoemulsification may be combined with intravitreal steroids or even a vitrectomy.69 Research is ongoing with respect to adjuvant anti-inflammatory agents that may be used at the time of surgery. In terms of intraocular lens type, silicone, acrylic and hydrogel lenses may be used but a possible advantage has been shown for acrylic lenses, which may cause less post-operative inflammation and posterior capsular opacification.70 Post-operatively, patients may require more intensive topical steroid or other immunomodulatory therapy for control of inflammation.

Vitrectomised eyes Pars plana vitrectomy involves removal of the vitreous via incisions at the pars plana. The vitreous may be replaced with gas or silicone oil and the procedure is performed for various vitreoretinal disorders including retinal detachment and nonclearing vitreous haemorrhage. Postvitrectomy cataract formation is common usually within one to two years. Vitrectomised eyes undergoing cataract surgery are at a higher risk of complications, partly as a result of changes due to the vitrec-


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tomy itself and partly due to the disorder which necessitated the vitrectomy.71 Calculation of intraocular lens power can be difficult as measurements of axial length are less reliable, for example, ultrasonic biometry will overestimate the axial length in eyes containing silicone oil. The error is smaller with optical coherence biometry and can be limited by appropriate change to the biometric settings. Intra-operatively, the anterior capsule may be rigid following prolonged exposure to silicone oil. The posterior capsule may have been inadvertently touched during the vitrectomy and the incidence of posterior capsular plaques and posterior capsular tears may be more common. Hydrodissection needs to be performed carefully to avoid rupturing the posterior capsule. Loss of vitreous support and possible zonular weakening can mean the anterior chamber fluctuates during surgery, increasing the risk of a posterior capsular tear and zonular dehiscence. Lowering the irrigation rate intraoperatively can help counter an excessively deep anterior chamber. Zonular instability may account for the higher rate of lens implant dislocation after cataract surgery in these eyes, which may occur up to several years later.72 Hence, it has been suggested that any evidence of lens instability during surgery should prompt the surgeon to use a capsular tension ring or consider an alternative position for the lens implant. ANAESTHETIC CONSIDERATIONS For cataract surgery, several methods of anaesthesia are available and depend on surgeon preference. Most cases are done under local anaesthesia, with general anaesthesia reserved for patients intolerant of local anaesthetic for any reason. The preference for local anaesthesia is not only the faster recovery time for the patient but also the decreased risk of systemic complications of general anaesthesia and the decreased cost. Our preference is for topical anaesthesia, using tetracaine eye drops followed by intracameral lignocaine 1% preservative free. The main advantage of topical anaes© 2010 The Authors



PRE-OPERATIVE CONSIDERATIONS Patient factors

Are they suitable for local anaesthesia. Are they on medications such as tamsulosin?

Ocular factors

Dilated examination for pseudoexfoliation, phacodonesis, ocular pathology requiring treatment prior to surgery (e.g. diabetic macular oedema, active uveitis, retinal tears)

INTRA-OPERATIVE COMPLICATIONS Posterior capsular rupture

Rates vary from