This prospective study relates to a catchment population that represents one third of the New Zealand population and involved approximately 20% of New Zealand ophthalmic surgeons. Therefore, other than the slightly greater proportion of Maori and Pacific Islanders in the reported population, we believe this study is reasonably representative of subjects presenting with cataract and their subsequent management in the Public Health Service within New Zealand
The results of this study confirm that the population undergoing cataract surgery in the public sector in Auckland is predominantly elderly and female. Subjects with Maori and Pacific Island ethnicity present approximately 10 years earlier for cataract surgery than European-Caucasian subjects and this may be explained, at least in part, by the dramatically higher proportion with diabetes mellitus.4
Indeed, 58% of Pacific Islanders and 38% of Maoris exhibited diabetes mellitus compared with only 10% of European-Caucasian subjects. Subjects presenting for cataract surgery have other significant systemic co-morbidities, with almost half being treated for systemic hypertension and more than a third providing a history of other cardiac or cerebrovascular disease.
Access to cataract surgery within the public health system is constrained by a government directed points system in New Zealand.2
Interestingly, at the commencement of this study, all subjects fell just below the points based prioritisation threshold for cataract surgery, yet exhibited significant visual impairment in the cataract affected eye (Fig 1). While basing prioritisation upon objective criteria, rather than merely upon position on increasingly growing public waiting lists, has obvious merit, this form of healthcare rationing may still deny access to surgery by patients with genuine need.2
While the scoring system current at the beginning of this study included assessment of aspects of functional ability, such as driving, the BSCVA of the affected, and the contralateral eye, contributed the majority of points. Unsurprisingly, in this context, the visual acuity in the eye intended for surgery was worse than 6/24 in 53% of eyes assessed in this study, whereas the threshold for cataract surgery in Australasia has generally been reduced to 6/6–6/9 in symptomatic patients.5
Although, in some subjects, there may be cultural reasons for delayed presentation with cataract, many of the subjects in this study had presented for surgery up to 3 years earlier, but with a mean BSCVA of 6/9 in the contralateral eye, none reached the prevailing threshold for surgery.
Small incision phacoemulsification (97.5%), with implantation of a foldable IOL, under sub-Tenon's local anaesthesia (95%), has become the favoured technique within Auckland. Although sub-Tenon's anaesthesia is becoming increasingly popular in New Zealand, the United Kingdom, and elsewhere, a recent assessment of trends in cataract surgery (1998), with respect to the USA, Japan, and Denmark, suggested that only ophthalmologists in Japan use predominantly sub-Tenon's anaesthesia as frequently.6
In the present study a higher proportion of clear corneal temporal incisions than superior scleral tunnel incisions was observed, highlighting local surgical preference. However, Riley et al4
have demonstrated that this population exhibits a median refractive astigmatism of 1.2D that is against the rule in 50% of eyes; therefore, the choice of a temporal approach corneal incision may offer a minor beneficial effect on corneal astigmatism in appropriate cases. In the current study, 76.7% of subjects exhibited 0.75D or less change in refractive astigmatism after small incision phacoemulsification.
Interestingly, a recently published questionnaire survey of all New Zealand ophthalmic surgeons reported that, in 1997 and 1998, only 24% routinely used sub-Tenon's anaesthesia for cataract surgery and only 33% used anterior limbal or clear corneal incisions.1
The conflicting results of the current study may reflect regional differences in the approach to cataract surgery or, more likely, the rapidity with which cataract techniques evolve, with both sub-Tenon's local anaesthesia and clear corneal phacoemulsification being increasingly adopted nationally. Initial concerns that clear corneal incision might produce significantly greater astigmatism than scleral tunnel incisions seems unfounded. Current techniques of clear corneal incisions produce similar astigmatic change7,8
to scleral tunnel incisions and, as noted previously, such induced change may actually be beneficial in the older eye with against the rule astigmatism.4,8
Review on day 1 after phacoemulsification identified a single case of early endophthalmitis but no other sight threatening adverse events. It is notable that 4.3% of eyes had an IOP greater than 30 mm Hg. Overall, nine eyes (1.9%) required a suture for a wound leak. All of these eyes had undergone temporal approach, clear corneal, phacoemulsification, whereas, no eyes with superior scleral tunnel approach demonstrated aqueous humour leak. Although 16% of corneal incisions were sutured intraoperatively, 2.4% (nine eyes) of corneal incisions required a suture to address wound leak on day 1. This suggests that perhaps a lower threshold for intraoperative placement of a suture, or a modification of wound architecture, should be observed in this population when clear corneal, sutureless phacoemulsification surgery is performed. However, this has to be balanced with the knowledge that all corneal sutures will require subsequent removal and 5.8% of eyes in this study exhibited more than 1.0D of suture induced astigmatism, which was statistically associated with BSCVA of less than 6/12 in almost half of these eyes. Herbert et al9
have recently highlighted the importance of day 1 review, noting 1.5% of subjects with an IOP greater than 30 mm Hg, 0.26% with painless iris prolapse, and 1.8% that required modification of the topical steroid regimen.
The design of the current study, where reporting of intraoperative complications by the operating surgeons was followed by a comprehensive postoperative independent ophthalmic examination, may have advantages in terms of accuracy and consistency over comparable studies of self reporting alone. The observed rates of adverse surgical events are comparable to similar published studies, which have reported posterior capsular rupture rates of between 0% and 9.8% of cases and clinically apparent cystoid macular oedema in 0.6% to 6% of eyes.3,10–14
The overall posterior capsular rupture rate in the current study was 4.9%, and comparison of this complication as encountered by consultant surgeons, relative to fellows and registrars under supervision (4.7% v
5.4%), highlighted no statistical differences. However, it should be noted that trainees generally performed surgery on more straightforward cases and the lack of statistical difference in such small numbers does not preclude a clinical difference. Assessment of complications by trainee surgeons of registrar (resident) grade in other large studies of phacoemulsification have highlighted an incidence of intraoperative posterior capsular rupture of up to 10%.10,12
Interestingly, a Royal College of Ophthalmologists (UK) report, by Desai et al
, noted a posterior capsule tear rate of 4.4% in a National Cataract Study in a healthcare system fundamentally similar to New Zealand's.13
More recently, Ionides et al
, in a series of 1420 cataract procedures, noted a similar overall capsular rupture rate of 4.1% in a major UK training hospital and in this series posterior capsule tears occurred in 5.3% of cases performed by surgeons in training.14
In the current series, automated anterior vitrectomy was performed in 75% of cases of capsule rupture and there was no clinical or statistical association between capsular tear and either CMO or a final BSCVA of less than 6/12. In contrast, Ionides et al
reported that eyes with a posterior capsule rupture were 3.8 times more likely to have a final BSCVA less than 6/12.14
Preoperatively, a large number of advanced brunescent or white cataracts resulting in BSCVA of 6/60 or poorer (24%) were identified. This may bias the complication rate when comparing studies, as these advanced cataracts may be associated with increased risk of adverse surgical events (Tables 4 and 5). This may also account partly for the relatively large numbers of phacoemulsification procedures that required a suture (15%), since more dense nuclei often require phacoemulsification for a longer period at higher power, with greater potential for wound retraction. Unfortunately, since more than one type of phacoemulsification machine was used, phaco parameters could not be compared or correlated in the current study. However, interestingly, in terms of adverse events in more complex cataracts, Chakrabarti et al
in a retrospective study of 222 advanced white cataracts, reported incomplete capsulorhexis in 28% of eyes, but a posterior capsule rupture rate of only 1.9% following clear corneal phacoemulsification.
In this study group, two thirds of eyes achieved 6/12 UAVA and 88% of eyes achieved a BSCVA of 6/12 or better after cataract surgery. However, if those eyes that had a poor visual prognosis preoperatively, because of known coexisting ocular disease, are removed from analysis, the proportion with BSCVA of 6/12 or better increases to 94%. However, while the mean postoperative BSCVA was 6/7.5 for all eyes in the study, special consideration should be given to those patients (1.5%) who had lost lines of BSCVA, thought to be a consequence of the surgical intervention, at the latest follow up. A longer follow up period may show some further improvement in those with CMO in which BSCVA was significantly adversely affected (1.3%).
Only visual acuity and objective measures such as refraction have been reported in this study; however, additional measures such as functional acuity, symptom score, and patient satisfaction are also valuable ways of providing a more comprehensive assessment of outcome following cataract surgery.16,17
Indeed, the risk of dissatisfaction with outcome of cataract surgery is related to low visual acuity and age related maculopathy in the better eye preoperatively while, overall, the postoperative BSCVA in the operated eye is the single most important factor in terms of patient satisfaction.18
In this respect, at least 5.0% of eyes in the current study exhibited age related macular degeneration that affected BSCVA preoperatively, and 1.5% of eyes overall had poorer vision postoperatively thought to be related to the surgical intervention. We have assessed the whole study group by satisfaction and functional questionnaires and this will be the subject of a future communication.
Although phacoemulsification has a lower risk of retinal detachment than conventional extracapsular surgery, a series of 1418 phacoemulsification procedures, with approximately one third having undergone Nd:YAG laser capsulotomy, recorded a long term risk of retinal detachment of 0.4%.19
Owing to the limited follow up, only to the point of outpatient discharge, longer term complications, such as retinal detachment, or the requirement for Nd:YAG laser posterior capsulotomy, were not identified in the current prospective study.
In summary, this Auckland based study highlights that cataract surgery in the New Zealand Public Health Service utilises contemporary surgical techniques, with 97.3% of eyes undergoing small incision phacoemulsification surgery with insertion of foldable intraocular lenses. The results of cataract surgery continue to improve with the predominant use of local anaesthesia (99.8%), which, with small incision phacoemulsification, facilitates day case surgery, early rehabilitation, and improved visual results.20,21
Despite significant medical co-morbidity and relatively advanced cataracts in the population under investigation, surgical complication rates for both experienced and trainee surgeons were found to be consistent with international standards. In this elderly population, 94% of eyes without preoperative non-cataract pathology achieved 6/12, or better, BSCVA, at latest follow up.