Should macular optical coherence tomography be part of routine preoperative cataract assessment?

Macular examination is a key part of preoperative assessment of patients with cataract. Subtle macular pathology may be overlooked, especially in the presence of media opacity. This may mislead the clinician towards unwise clinical decisions, as in the case of undetected diabetic macular oedema or choroidal neovascularization. We examined the value of routine macular optical coherence tomography (OCT) in patients with cataract in whom no macular pathology is suspected clinically. Specifically, we wished to determine how often the routine preoperative use of OCT leads to changes in management decisions or in prognostic information provided to patients in the consent process. Patients were recruited from general ophthalmology clinics, which receive referrals from general practitioners, optometrists or private specialists. Clinical assessment at the outpatient clinics includes a full, mydriatic ocular examination by ophthalmologists or ophthalmology registrars. All our patients were diagnosed with visually significant cataract and scheduled for cataract surgery. The study team selected consecutive patients attending the preoperative assessment clinics on random days during the study period (May to September 2010). We included 232 cataractous eyes of 162 patients in the study. The average age was 73 years. Visual acuity ranged from 6/6 to finger counting, with a median of 6/9, and 73% of eyes had visual acuity between 6/9 and 6/18. Fourteen eyes of 13 patients were excluded from the study because of poor OCT image quality or poor fixation and movement during OCT testing. We also excluded patients with clinically evident maculopathy. Macular examination was performed using spectral domain OCT. We examined the images, and, where macular abnormalities were detected, the information was conveyed to the treating ophthalmologists, whose decision was then recorded. Macular abnormalities were detected by OCT in 10 of 218 eyes (4.6%, 95% confidence interval 1.81–7.37%). The clinical and OCT findings are summarized in Table 1. The average time interval between clinical examination and OCT was 102 days (range 15–302 days). Treating ophthalmologists decided to cancel or defer cataract surgery based on the OCT findings in five eyes of four patients with diabetic macular oedema, neovascular age-related macular degeneration (AMD), epiretinal membrane and macular hole. Those patients were referred to medical or surgical retinal consultations. In the other five patients, the prognostic aspect of the informed consent for cataract surgery was revised in light of the OCT information. Biomicroscopical detection of subtle macular abnormalities through a cataract is challenging. Failure to identify them may result in erroneous treatment decisions or in unrealistically high expectations for postoperative visual improvement. When compared with expert clinical assessment, OCT has been shown to be significantly more accurate in diagnosing surgical macular pathology and prompting correct treatment decisions.1 Whereas in the pre-OCT era, postoperative ‘macular surprises’ could perhaps be excused by the difficulty of examining the macula through a cataract, the availability of OCT makes such surprises largely preventable, and therefore less defensible. Cataract surgery accounts for the majority of malpractice claims in ophthalmology in the USA. Unrealistic patient expectations are commonly the underlying factor.2 There is therefore a risk that avoidable failure to detect macular abnormalities will become an increasingly common reason for postoperative patient dissatisfaction. Unsuspected macular findings were detected in 4.6% of eyes in this unselected cohort. Five eyes (2.3%) had OCT findings, which changed the primary diagnosis from cataract to a macular disease, resulting in a change in the treatment plan. In the remaining five cases, the postoperative prognosis was believed to be less certain than initially thought, and the patients' informed consent was revised accordingly. Our average time from clinical examination to OCT was approximately 3 months. It is theoretically possible that in some patients, maculopathy developed between the clinical examination and the time of OCT scanning. We believe the likelihood for this is low, given that macular diseases detected in our patients develop slowly. In five eyes, maculopathy, rather than cataract, was interpreted in hindsight as explaining the original visual symptoms. Of note, 90% of our maculopathy patients were diagnosed by specialist general ophthalmologists. Therefore, our findings cannot be explained by lack of clinical experience. A limitation of this study is the inclusion of patients with mild to moderate cataracts. Most patients had visual acuity ranging from 6/9 to 6/18. Such cataracts usually permit both clinical and OCT examination of the macula, and may therefore allow for misdiagnosis and a false sense of security if the diagnosis is based on clinical examination alone. It is possible that the rate of unsuspected macular findings would be even higher if patients with denser cataracts were included. It may be extrapolated from our data that a hypothetical surgeon performing 300 cataract operations a year may expect to misdiagnose a serious macular problem as cataract in six to seven surgical cases per year. With 110 000 cataract operations performed in Australia each year,3 the expected incidence of such serious misdiagnoses is 2530 cases per year for the Australian health system. We believe this may pose a significant risk from a doctor's perspective or that of a large health system. In summary, we have shown that the routine use of macular OCT before cataract surgery improves the accuracy of the preoperative diagnostic process and helps avoid misdiagnosis and postoperative macular surprises. As OCT is rapidly becoming the gold-standard examination for macular anatomy, we believe its usage should be considered as part of a complete ocular assessment prior to cataract surgery.