Part 1 of this series considered the initial assessment and then referral of cataract. Part 2 considers what happens next.
Preoperative assessment
The preoperative cataract surgery assessment consists of two parts. The first tends to be nurse led and assesses the patient’s general suitability to undergo a surgical procedure and prepares the patient for surgery. Different hospitals will have different admission criteria and will be influenced by whether or not the hospital can provide general anaesthesia or support those with extremely restricted mobility. The other part involves a multi-disciplinary team and focuses on the ophthalmic workup of the patient. Some units do each part on separate visits and others will do both at one appointment to minimise the number of hospital trips needed as often, patients are reliant on relatives for transport.
Nurse-led assessment
Medical history
A full medical and ocular history is elicited to assess whether or not the patient has any conditions that might contraindicate surgery or influence risk factors. Allergies are noted, in particular allergies to latex, sticking plasters and previous hypersensitivity reactions are highlighted. Blood pressure, pulse rate and blood sugar tests are carried out with diabetic patients undergoing a finger prick test (Figure 1) to ascertain their blood glucose levels.
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Hypertensive patients must have well controlled blood pressure to undergo surgery. A blood pressure reading is routinely taken at the initial assessment for all patients and then checked again on the day of surgery prior to going into the operating theatre. Patients who are on anti-coagulant therapy such as warfarin must present with their international normalisation ratio (INR) record book. The INR should be within the patient’s desired therapeutic range as set by their GP and this ensures that the patient is not exposed to undue risk of excessive bleeding during or after surgery.
All the gathered information is considered by the surgeon and discussed with the patient during the consent process.
Social care needs
Some elderly patients live alone and do not have anyone to stay with them for the first 24 hours after surgery or do not have the dexterity to administer their own eye drops. In such cases, arrangements need to be made for a relative to stay overnight and, sometimes, for a district nurse to attend the patient for the duration of the postoperative period that the patient requires eye drops. This could be as often as four times a day for up to six weeks.
The patient is also evaluated for their ability to co-operate with the procedure and lie reasonably flat and still during surgery. It is also important to identify those patients with potential communication issues such as hearing loss or not understanding English. It is imperative that the patient is able to understand and follow any instructions that the surgeon may give during the operation. If necessary, an interpreter is provided.
The nurse informs the patient what will happen on the day of surgery and about the surgical procedure itself. Most patients, although a little nervous about having surgery, are prepared to accept that they will be fully conscious during the procedure. A few patients may be overly anxious, particularly if they have a tendency to be claustrophobic (as the face is covered with a drape during surgery). These patients will need to undergo further assessment, possibly with an anaesthetist, to look at their suitability for either sedation or a general anaesthetic.
Ophthalmic workup
Vision assessment
The measurements required are the patient’s unaided, best corrected and pinhole vision. Spectacle prescription prior to cataract formation is also useful when the cataract has caused significant refractive change as it may influence the end point that is aimed for. Refraction may be carried out at the preoperative assessment if the patient does not have significant cataract and the decision for surgery is borderline, or if another pathology is suspected. Refractive information is also important where the patient has already had one eye treated and is not emmetropic and it is also checked against the biometry data for overall consistency.
Biometry
Keratometry and axial length measurements are used to calculate the IOL power required for each eye, so accurate data are vital for a good outcome. Therefore, soft contact lens wearers are advised to leave their lenses out for a minimum of one week and hard or RGP lens wearers for four weeks due to the possibility of corneal warpage rendering the data inaccurate. Optical biometry is most commonly used in hospital units as it is a non-invasive and highly reproducible method of measurement. However, accuracy relies on the instrument being able to penetrate the cataract along the visual axis and good patient fixation. Inaccurate measurement or no measurement at all can be an issue with dense cataract formation. Keratometry accuracy can also be affected if the patient has a deformed cornea or a very poor tear film.
Where optical biometry is not possible, ultrasound methods can be employed to measure the axial length of the eye. A-scan biometry can be easily carried out by a contact method (Figure 2) but reproducibility is difficult to achieve as it relies on the probe being placed in exactly the same position on the corneal vertex along the visual axis each time. An immersion method is more accurate as it avoids corneal compression during measurement. This involves placing a scleral shell between the eyelids which is filled with saline; the probe is then immersed while care is taken not to touch the cornea. The quality of an A-scan can be adversely affected by macular pathology such as macular degeneration or oedema.
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A very dense cataract could also absorb sound waves, making a good reading impossible and in such cases a B-scan needs to be carried out instead. B-scan ultrasound is most useful when direct visualisation of intraocular structures is difficult or impossible. It can accurately image intraocular structures and give valuable information on the status of the lens, vitreous, retina, choroid, and sclera. It is primarily used for diagnostic purposes (when pathology is suspected) but the images obtained can also be measured to provide axial length data.
Once the data has been captured, the IOL power can be calculated using one of several formulae. Choice of formula in phakic eyes that have not undergone any corneal refractive surgery depends upon the axial length value and according to surgeon preference. Some formulae utilise the anterior chamber depth and corneal diameter measurements in an attempt to further improve accuracy. For example, the printout in Figure 3 shows the variation in calculated IOL power between the different formulae. While the SRK/T formula is commonly used, it is generally accepted that the Haigis and Hoffer Q formulae are more accurate for eyes that have an axial length of less than 22mm, and the Holliday formula better for axial lengths of more than 26mm.
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Calculation can be made even more precise. Each IOL type has a set of constant values that are recommended by the manufacturer and are applied to each of the formulae. To improve accuracy of refractive outcomes, there is a worldwide online database on which registered surgeons can enter their outcome data. The collective data is then analysed and constants adjusted. Each surgeon can also factor in their own refractive outcomes and the constant can be ‘optimised’ for individual surgeon and IOL combinations. However, not all hospitals/surgeons use optimised constants.
In most cases, the intention is to leave the patient near to emmetropia unless contraindicated. For example if the surgical plan is for one eye only and the other eye has significant hypermetropia or myopia, then anisometropia may cause problems with spectacle wear if the operated eye is left plano. For those patients with significant corneal astigmatism, corneal topography is also useful so that the surgeon can plan the position and depth of their corneal incisions. Limbal relaxing incisions can be effectively used to reduce astigmatism but not all surgeons will aim to deliberately reduce astigmatism as this may be considered as refractive surgery, which is outside the remit of NHS cataract service provision. However, no more than 1.00DC of astigmatism should be induced by the procedure.1
Surgeon’s assessment
Ocular examination
The surgeon carries out an examination on the anterior and posterior eye, where any exclusions to surgery are looked for and any risk factors evaluated. If no fundus view is visible, a B-scan or retinal projection testing can be used to give an assessment of retinal function. The latter is useful if the patient has a very mature cataract with vision of perception to light only. A pen torch is shone from different directions of gaze and the patient asked to identify which direction the light is coming from. Intraocular pressure measurements and pupil function are also checked at this appointment.
Risks and exclusions
This section will look at the factors that may increase the risk of complications during or after surgery. The list is not exhaustive, but covers the more commonly encountered conditions.
Non-pathological conditions
- High ametropia – Eyes which are highly hypermetropic are smaller and tend to have shallower anterior chambers. This increases the risk of pupil and endothelial trauma2 during surgery, with the latter leading to a risk of prolonged corneal oedema postoperatively. Accurate IOL power calculation is also more difficult in very long or short eyes and so the surgeon may look at the calculations of several formulae before deciding making a decision.
- Previous refractive surgery – Standard IOL calculation formulae are not sufficient in these cases3 and more advanced formulae that require additional data must be used. The more information that is available about the pre-refractive surgery status of the eye, the greater the accuracy of the formulae. Additional information such as the last prescription prior to refractive surgery, K readings and pre-cataract postoperative refractive outcome is ideal. The challenge of calculating the IOL power needed in an eye after refractive surgery has yet to be met fully, and so patients that have undergone corneal refractive surgery must be carefully counselled with respect to potential refractive surprise.
- Poor pupil dilation – At the ocular assessment, any difficulty in achieving good pupil dilation is noted. Insufficient pupil dilation restricts the view for surgery and increases the risk of a posterior capsular tear. Iris hooks can be employed and the pupil stretched, but this increases the risk of iris trauma.
Cataract characteristics
- Brunescent cataract – Very mature cataracts with a hard nucleus require a longer duration of phacoemulsification and require a higher energy input. This increases the risk of a burn at the corneal incision site through which the phaco probe is inserted. Phaco burns cause shrinkage at the incision site, leading to difficulties in closing the wound as well as corneal trauma.
- White cataract – Cataract that has calcified with maturity has a bright white appearance and is so hard that it may not be possible to phacoemulsify the lens nucleus. In such cases a larger incision must be made, through which the lens nucleus in its whole state is removed. This larger 10-12mm incision requires sutures, unlike the self-sealing 2-3mm incision used in phacoemulsification.
- Posterior subcapsular cataract – This type of cataract can be very firmly attached to the posterior lens capsule. This increases the risk of a posterior capsular rupture during surgery which may lead to the need for an anterior vitrectomy.
Systemic conditions
- Diabetes –There is a possibility that some patients undergo surgery with pre-existing diabetic retinopathy that is not detected preoperatively due to the fundus view being obscured by cataract. This is of consequence as patients with pre-proliferative diabetic retinopathy are at increased risk of progression to proliferative postoperatively and must be monitored closely afterwards. Diabetics also have an increased risk of cystoid macular oedema, postoperative uveitis and early posterior capsular opacification.4,5
- Systemic hypertension – Blood pressure needs to be well controlled as a raised level during surgery increases the risk of haemorrhage and may even lead to an expulsive episode during the operation. It is checked again on the day of surgery as some patients could suffer from ‘white-coat syndrome’, which may lead to surgery being cancelled. Even those patients with controlled hypertension are at risk of a moderate rise prior to surgery.
- Anti-coagulant therapy – This increases the risk of haemorrhage, but stopping the drug prior to surgery is not appropriate and so anaesthesia options requiring a sharp needle are unlikely to be offered to the patient.
- Tamsulosin – Used to treat benign prostate enlargement, the alpha adrenergic antagonist causes the iris dilator smooth muscle to relax, resulting in floppy iris syndrome.6 This may lead to progressive pupil miosis during surgery which does not respond well to normal methods of pupil stretching.7 This causes visualisation problems during surgery and complications are more likely.
Ocular co-morbidities
- Blepharitis/meibomian gland dysfunction – This is a significant risk factor for postoperative endophthalmitis8,9 and should be treated prior to surgery. If a patient does not comply with any lid hygiene measures introduced, it may lead to their surgery being cancelled on the day.10
- Corneal dystrophies – With any dystrophy that affects the endothelium such as Fuchs’, or if the patient already has a low endothelial cell count, there is an increased risk of prolonged postoperative corneal oedema.11 There is some inevitable loss in cell count with cataract surgery and this, coupled with an already compromised endothelium, could lead to decompensation and a loss of corneal clarity in the worst-case scenario.
- Pseudoexfoliation syndrome – Pupil dilation issues can occur with this group of patients. They also tend to suffer from zonular weakness which increases the potential for IOL tilt or displacement and after many years there is also a risk of complete IOL dislocation.12 There is also an increased risk of secondary glaucoma postoperatively.
- Anterior uveitis – Patients with a history of recurrent uveitis are more likely to suffer prolonged inflammation postoperatively and are at an increased risk of uveitic glaucoma too. If there is a great deal of protein matter in the anterior chamber, it can deposit on the IOL surface and compromise vision.13
- Primary open-angle glaucoma – Intraocular pressure can be raised for up to a week following cataract surgery, which can pose a problem for those eyes that are susceptible or already have a compromised optic nerve head.14 Other potential complications include increased aqueous filtration through a bleb during surgery and then a decrease in bleb performance postoperatively (see Figure 4).15,16
- Previous vitrectomy – These eyes are more prone to increased nuclear sclerosis and a weakened lens capsule which can lead to a more complicated surgery. Surgery can also be a little unpredictable due to issues with anterior chamber depth fluctuation and possible intra-operative pupil miosis.17
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The consent process
Once the patient has had their suitability for surgery confirmed, the surgeon will discuss in detail the potential benefits versus the risks, explaining in detail those that are specific to that patient due to co-morbidity. For eyes that are only just meeting the criteria for NHS surgery, the benefit of surgery may not outweigh the potential risks. It is also important to set the patient expectation with respect to refractive outcome. Spectacle independence after surgery is not a given and those with significant astigmatism are likely to still need spectacles for distance postoperatively unless they opt to self-fund a toric IOL implant. All patients are warned that they will need reading spectacles after surgery. This consent process is critical in ensuring that the patient fully understands the nature of the surgery so that they can decide whether or not to proceed.
Surgery
The Worldwide Health Organization produced a 19-step checklist in 2008 with the aim of reducing death and serious complications during surgery (Figure 5). It has now be implemented by the majority of health care providers across the world.
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In general, the patient pathway is as follows. When a patient is checked into theatre, their identity is confirmed and an ID tag placed on the wrist. The patient’s blood pressure and pulse rate are checked and a pulse oximeter is later attached to the patient’s finger. The surgeon checks the patient’s eye if required and then the consent form is checked for correctness and signatures. The eye to be operated on is marked up and the pupil dilation regime is then commenced. The relevant section of the WHO checklist is completed before the patient enters the operating room, and again before the first incision.
During the procedure, the patient’s face is covered with a drape with a cut-out section for access to the eye to be operated on. Oxygen is piped under the drape to aid breathing and so unless the patient is claustrophobic they are generally comfortable. The surgery begins with the application of topical anaesthesia and cleaning of the eyelid margins with iodine.
Anaesthesia
Most cataract surgery in the UK is carried out as day case surgery under local anaesthesia. General anaesthesia or other sedation is not recommended unless patients cannot keep still or are excessively nervous. The choice of local anaesthesia varies according to surgeon preference, patient factors and hospital facilities. Some surgeons are happy to use purely topical anaesthetic eye drops which have the advantage of being easy to administer and being more comfortable for the patient. However, the eye is not immobilised and so some surgeons prefer to add in a sub-Tenon block to achieve some level of akinesia. This involves injecting an anaesthetic into the space between the sclera and Tenon’s capsule.
Sometimes a subconjunctival haemorrage can be seen in the infero-nasal conjunctiva after surgery. It is here that the conjunctiva is lifted with a pair of forceps and a small incision made with scissors which may also damage a conjunctival blood vessel. A slightly curved cannula (Figure 6 on the left) is then inserted through the incision and manoeuvred around to the back of the globe before releasing the anaesthetic.
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Sub-Tenon anaesthesia is safer than retrobulbar or peribulbar anaesthesia, where a sharp needle is used to directly inject into the extraocular muscle cone or with the latter technique, the orbicularis muscle. These sharp needle techniques can only be performed by an anaesthetist or a specially trained ophthalmic surgeon and carry a risk of globe perforation, severe haemorrhage, and increased discomfort to the patient.
Cataract extraction
In the UK, phacoemulsification is the procedure of choice for most surgeons undertaking cataract surgery. Although the procedure is more complex than intra- or extracapsular cataract extraction and requires more training and skill, the intra-operative risks are lower and the postoperative recovery of the patient is faster in terms of both ocular integrity and visual function. The smaller incisions needed for phacoemulsification and foldable lens implants mean that induced astigmatism is much lower than with previous methods.
The cataract is accessed by making 2-3mm incisions near the limbus through which the instruments can be placed. The anterior capsule is opened up (capsulorrhexis) and the phacoemulsification needle inserted into the lens. The harder the nucleus, the greater the energy needed to break it up. In some cases, if the lens nucleus is very hard, a ‘chopper’ needle is used to break it up first. During surgery, the endothelium is protected from the impact of surgery by a viscoelastic substance which has been injected to inflate the anterior chamber and to provide a mechanical buffer. Once the phacoemulsification is complete, the surgeon cleans the lens capsule of any lens substance that is visible and then exits the eye. As the incisions are self-sealing, sutures are rarely needed.
The final section of the WHO checklist is completed and the patient is taken to a recovery bay. Before the patient leaves, the surgeon carries out a post-surgery eye examination and ensures that the patient is pain free. The patient is discharged with their postoperative eye drops and comprehensive written instructions which include information on the drug regime, expected signs and symptoms, a list of do’s and don’ts, and an emergency contact telephone number. A postoperative follow-up will have also been arranged for the patient to attend in 3-4 weeks’ time.
Model answers
(The correct answer is in bold text)
1 Which of the following systemic medications requires a patient to present their INR record book?
A Beta-blockers
B Warfarin
C Prednisolone
D Frusemide
2 Which of the following statements regarding a soft contact lens wearer undergoing cataract surgery is true?
A Limbal neovascularisation renders the patient inoperable
B Low modulus lenses require no resting period preoperatively
C A week without wear before biometry is usually recommended
D Biometry is best undertaken with the contact lens in situ
3 For which of the following axial length is the Holliday formula most appropriate for IOL power calculation?
A 20 mm
B 22mm
C 25mm
D 27mm
4 Which of the following is most likely to require an incision wound suture?
A White cataract
B Brunescent cataract
C Posterior subcapsular cataract
D Early nucleosclerotic cataract
5 Which of the following systemic conditions may require a treatment resulting in miosis and surgical complications due to iris stretching?
A Hypertension
B Diabetes
C Prostate enlargement
D Rheumatoid arthritis
6 Which of the following may increase the risk of post-operative IOL displacement or luxation?
A Anterior uveitis
B Pseudoexfoliation syndrome
C Fuchs' endothelial dystrophy
D Meibomian gland dysfunction
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References
1 Royal College of Ophthalmologists Cataract surgery guidelines 2004.
2 Wladis EJ, Gewirtz MB, Guo S. Cataract surgery in the small adult eye. Surv Ophthalmol, 2006; 51: 153- 61.
3 Langenbucher A, Haigis W, Seitz B. Difficult lens power calculations. Curr Opin Ohthalmol, 2004;15:1- 9.
4 Dowler, J, K Shemi, PG Hykin, and AMP Hamilton. The natural histopry of macular oedema after cataract surgery in diabetes. Ophthalmology, 1999;106: 663-668.
5 20. Dowler, J, PG Hykin, and AMP Hamilton. Phacoemulsification versus extracapsular cataract extraction in patients with diabetes. Ophthalmology, 2000;107: 457-462.
6 Chang DF, Campbell JR. Intraoperative floppy iris syndrome associated with tamsulosin. J Cataract Refract Surg, 2005; 31:664–673.
7 31. Chadha V, Borooah S, Tey A et al. Floppy iris behaviour during cataract surgery: associations and variations. Br J Ophthalmol, 2007; 91:40-42.
8 Sparrow JM. Monte-Carlo simulation of random clustering of endophthalmitis following cataract surgery. Eye, 2007 21: 209-213.
9 Speaker MG, Milch FA, Shah MK, Eisner W, Kreiswirth BN. The role of external bacterial flora in the pathogenesis of acute postoperative endophthalmitis. Ophthalmology, 1991 98: 639-649.
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11 Seitzman GD. Cataract surgery in Fuchs’ dystrophy. Curr Opin Ophthalmol, 2005;16:241-5.
12 Küchle M, Viestenz A, Martus P, et al. Anterior chamber depth and complications during cataract surgery in eyes with pseudoexfoliation syndrome. Am J Ophthalmol, 2000; 129: 281-5.
13 Van Gelder RN, Leveque TK. Cataract surgery in the setting of uveitis. Curr Opin Ophthalmol, 2009; 20:42-5.
14 Tennen DG, Masket S. Short-and long-term effect of clear corneal incisions on intraocular pressure. J Cataract Refract Surg, 1996; 22: 568-70.
15 23. Mandal AK, Chelerkar V, Jain SS, Nutheti R. Outcome of cataract extraction and posterior chamber intraocular lens implantation following glaucoma filtration surgery. Eye, 2005;19:1000-8.
16 24. Klink J, Schmitz B, Lieb WE, Klink T, Grein HJ, Sold-Darseff J, Heinold A, Grehn F. Filtering bleb function after clear cornea phacoemulsification: a prospective study. Br J Ophthalmol, 2005;89:597- 601.
17 Grusha YO, Masket S, Miller KM. Phacoemulsification and lens implantation after pars plana vitrectomy. Ophthalmology, 1998:105: 287-94.
Michelle Hanratty is the senior optometrist at Optegra Birmingham and an examiner for the College of Optometrists