Recently, the investigators in two studies have taken another approach: They searched databases for patients with neovascular AMD and analyzed whether and for how long the patients had been pseudophakic.
9 25 This eliminated the problem of analyzing only small numbers of patients with neovascular AMD. However, if the study sample is drawn only from patients who acquire neovascular AMD, it may be difficult to determine the effect of a risk factor (e.g., cataract surgery). In addition, it would be necessary to determine how many individuals underwent cataract surgery without the development of neovascular AMD. In the two studies, different strategies were chosen to obtain these data: Kaiserman et al.
9 used the diagnosis records of a health maintenance organization (HMO) to find matched control subjects for patients who had had cataract surgery. The patients were matched for age, gender, and chronic diseases (hypertension, hyperlipidemia, diabetes, and ischemic heart disease), but not for the presence or severity of AMD. From this study, it was concluded that patients with cataract surgery had a higher rate of photodynamic therapy (PDT) for neovascular AMD. Several factors limit the value of this study: Data were analyzed per patient, not per eye. Thus, a patient undergoing cataract surgery on his right eye who was later treated for neovascular AMD in his left eye would have been counted as a patient with both conditions in the same eye. The control cases were not matched for retinal disease, especially AMD. This is an important limitation as individual patients may have a different susceptibility for development of AMD. Because the HMO did not cover PDT for other causes of choroidal neovascularization, it was assumed that in all cases, PDT was indicated for subfoveal AMD. This may not have been the case. In another study,
25 610 cases of subretinal neovascularization of other origin (e.g., angioid streaks, myopia, chorioretinal scars) were found in a search of a database of 3154 angiography reports. Sutter et al.
25 analyzed the difference in lens status (phakic or pseudophakic) in patients with neovascular AMD. No significant difference in lens status was found between eyes with neovascular AMD and fellow eyes with early AMD. Moreover, pseudophakic eyes in which neovascular AMD developed had not been pseudophakic for a significantly longer period. These results are in agreement with our findings. A limitation of our study is that, at baseline, the surgical and nonsurgical patients may have differed in the distribution of clinical subtypes of early AMD. The clinical subtypes of early AMD were not routinely classified and fundus photographs with fluorescein angiography were obtained only when neovascular AMD was suspected during fundus biomicroscopy. Patients in the surgical group were older, and they had worse visual acuity before phacoemulsification. These differences may have introduced a bias, in that patients in the surgical group may have had more advanced stages of early AMD and thus a higher risk of the development of neovascular AMD. Even if this bias existed, it had only a limited effect on our findings, as no significantly increased incidence of neovascular AMD was found in surgical eyes. Correction of this bias may further reduce the effect size. Moreover, the improved visual acuity after surgery suggests little impact of possible prior retinal disease. It has been suggested that obscured vision of the fundus in some patients with cataract causes late-stage AMD to be unrecognized until cataract surgery is performed.
27 This notion is supported by our findings. Four of 28 eyes with postoperative neovascular AMD most probably already had neovascular AMD before surgery. These patients were not excluded from our study because in clinical practice, neovascular AMD was not diagnosed before surgery, and a decision was made to offer cataract surgery. To exclude these patients because in hindsight they had neovascular AMD before surgery would introduce criteria for cataract surgery that cannot be used in the clinical situation, where obviously a decision about cataract surgery has to be made when the cataractous lens might interfere with retinal examination. However, it is important to note that this inclusion of these four eyes would result in finding more cases of neovascular AMD in surgical patients. Thus, there may actually have been bias toward a higher incidence of neovascular AMD in patients with cataract when indeed we could not find a significant difference. We selected only patients from our database who had taken follow-up examinations for at least 1 year after surgery. This selection may be a source of bias, if those patients in whom neovascular AMD developed after cataract surgery in our institution chose to seek medical care elsewhere. Although we cannot completely rule out this possibility, it seems unlikely, because the Recklinghausen Eye Centre is the major provider of medical and surgical retina services locally. As it happens, most diagnoses from a search of our database for pseudophakia and AMD were patients who were referred to us with a diagnosis of AMD after having had cataract surgery elsewhere. These patients were not included in the study because there was insufficient information about the severity of AMD before cataract surgery and evolution of their disease.