Reply: Comparison of macular morphology between femtosecond laser–assisted and traditional cataract surgery (2013)

The remarks of the Australian group are valuable thoughts, which are mainly triggered by a new technology that is still in its developmental phase. Below, we reflect on the concerns raised by the authors. First, it is important to emphasize that our study was aimed at assessing macular morphology in postoperative subclinical macular edema, not CME, which we clearly described in the manuscript. Consequently, the study was not intended to assess the risk for postoperative CME; we aimed to show the morphological changes and their differences following femtosecond laser–assisted and standard cataract surgery. Our answers to the points made by the authors are as follows. 1. Fluorescein angiography has been the gold standard in macular diagnostics for many decades. However, based on the words of Carmen Puliafito, one of the inventors of OCT, “OCT has become one of the most important decision-making technologies used in ophthalmology.” In recent times, OCT has also revolutionized the diagnosis of subclinical macular edema, replacing angiography in the diagnostic armamentarium thanks to its quantitative and noninvasive nature. In studies by our group as well as by others,1–3 OCT has shown there might be subclinical macular edema present even after uneventful phacoemulsification surgery. We agree that CDVA is the major outcome measure after cataract surgery. However, we did not perform any statistical comparison as it could have been misleading, partly due to the well-known fact that intraocular lenses (IOLs) are significantly better centered after femtosecond laser–assisted cataract surgery, which results in better visual outcomes.4,5 Better centration can be especially useful with the implantation of premium IOLs. In the latter case, to use all the benefits that premium IOLs may provide, we need a predictably consistent technique for all steps of cataract surgery. Slight tilt or decentration could cause severe problems in postoperative visual acuity. 2. Patients were randomly enrolled in the 2 groups. The observers were masked during the follow-up as OCT operators and those performing the segmentation procedure were not informed of the procedure performed by the surgeon. As can be seen from the mean follow-up times and the standard deviations (SDs), the follow-up times were not statistically significantly different (P>.05, paired t test). The OCT examinations were performed 4 to 8 weeks after surgery, similar to studies reporting the peak incidence of postoperative macular edema,2,3 and therefore we do not think the follow-up times biased the analyses. Furthermore, follow-up time was also included in the multivariable model but showed no significant effect on macular thickness in any locations. We did not correct our analyses for systemic illnesses as we had excluded patients with general pathologies such as diabetes mellitus and other systemic autoimmune diseases and uveitis during the preoperative assessments. It is important to emphasize that the excellent review by Flach6 indeed identified 20 risk factors for CME, but most of them are general concerns about research methodology (eg, the thoroughness of the search for this syndrome, research methodology), are outdated (eg, extracapsular versus intracapsular surgery, exposure to excessive intraoperative or postoperative light), or are not applicable to our study because of the reported fact of uncomplicated surgeries in all enrolled patients (eg, the presence of vitreous to the wound, the presence or absence of an intact posterior capsule). 3. Indeed, it is technically possible to obtain OCT scans of the macula even with dense cataracts and dilated pupils by scanning near the pupillary border. However, these scans can be applied for qualitative but not quantitative analyses, partly due to the poor image quality and the cutoff artifacts produced by the effects of pupillary aperture. We have previously shown that high signal strength (signal strength value greater than 6) is needed to avoid artifacts in macular image segmentation performed by our custom-built Octrima software7; this is why we did not do preoperative assessments. These facts are described in the “Patients and Methods” and “Discussion” sections of the paper and are addressed in the text dealing with the potential shortcomings of the study. In addition, taking into account that media opacity impacts image quality and the precision of measurements obtained after segmentation, it is evident that assessing preoperative measures from low-quality images is not useful for further postoperative comparisons. 4. We clearly stated the use of time-domain OCT technology in the “Patients and Methods” section of the paper and addressed it among the potential shortcomings of the study. We have previously shown the high reproducibility of Octrima measurements and even its comparability with spectral-domain OCT technology.8–10 Particularly, despite the worse resolution of time-domain OCT, we could achieve a high correspondence of retinal layer segmentation with Fourier-domain OCT in elderly subjects, who are supposed to have poor fixation cooperation.10 Therefore, we do not agree with Lauschke et al. that Octrima provides less accurate readings and slice reproducibility. Octrima is simply a custom-built software that analyzes images from OCT devices. It does not read or scan eyes but simply provides measurements of the retinal structure from OCT images. Authors should be aware that although spectral-domain OCT provides higher resolution images, this ability does not always ensure robust segmentation. The variability of measurements is due to the operator and the device. Therefore, claiming high reproducibility and accuracy is a major fault when the operator factor is not taken into account even when using spectral-domain OCT technology. We used Octrima because of its validated precision of measurements in contrast to the lack of widely accepted and validated OCT segmentation tools for both time- and spectral-domain OCT technology. We also emphasize that OCT measurements were performed by a highly experienced operator and meticulous attention was paid to foveolar centration. The methodology used to provide the most accurate measurements by time-domain OCT technology is clearly described in our previous papers; eg, scans with an SD of more than 10% in central point thickness measurements are excluded and repeated to maintain minimal variability of fixation. 5. There is little evidence available regarding the pathological changes of the photoreceptor-containing outer nuclear layer as observed by OCT segmentation and therefore more results are needed to objectively evaluate outer nuclear layer pathology by OCT. Besides, we have shown the high repeatability of outer nuclear layer measurements by Octrima being well below 6%, and therefore a 9% change can indeed imply a meaningful pathological change. In contrast, the papers cited by Lauschke et al. are based on the diagnosis of CME, which does not compare to our study setup. The paper by Ouyang et al.,11 on which Lauschke et al. base their argument regarding the normal range of previously reported OCT measurements, deals with the comparison of CME detection by angiography versus OCT and does not contain any retinal thickness or segmentation data. On the other hand, the paper by Kusbeci et al.,12 cited for the same purpose by Lauschke et al., is based on total retinal thickness measurements by spectral-domain Cirrus OCT (Carl Zeiss Meditec), which is known to produce different retinal thickness measurements10,13 compared with the Stratus OCT and therefore also cannot be used for comparison with our study. Besides this, Kusbeci et al.12 dealt with sectoral thickness data in the perifoveal area and not an average thickness of the perifoveal and pericentral rings as in our study, which further reduces the comparability of their study with ours. To sum up, we did our best to emphasize the potential shortcomings of our study and we are convinced we have done our best to provide reliable and clinically meaningful results and discussion. Our results may improve our understanding of the pathogenesis of postoperative macular thickening, which may lead to CME potentially influencing visual acuity. The femtosecond laser has always created dispute in ophthalmology. When it was used for the first time in flap creation, many of us doubted the acceptance because of the higher price. However, as it became available for corneal transplant surgery, the acceptance was positive and general. The comparison cited by the authors to the bent 27-gauge needle is a bit exaggerated. In fact, why use a $100 000 phacoemulsification device when extracapsular surgery can be performed by an experienced surgeon with comparable safety and good visual results at a fraction of the cost of phacoemulsification? We agree with Lauschke et al. that there is a need to perform larger studies in the future to make more meticulous observations, as femtosecond laser technology in cataract surgery is a new technology and still in its infancy. Our team is determined to research and publish the first clinical and scientific results to provide details that are as accurate as possible to the ophthalmic community. Results can, of course, be debated, but technological development cannot be denied or stopped.