Metamorphosia and Optical Coherence Tomography

Letters to the Editor Metamorphosia and Optical Coherence Tomography Dear Editor: I read with interest the article by Watanabe et al.1 describing the correlation between metamorphopsia and epiretinal membrane (ERM) optical coherence tomography (OCT) findings. The authors concluded that metamorphosia induced by ERM may be related to the edematous areas of the inner nuclear layer detected with spectral-domain OCT. Although the study is well-designed, I have the following comments and questions. For measurement of the thickness of the inner retinal layer, the authors examined 5 horizontal B-scan cross-sections on 3D OCT, and vague points vertically, which were described by the authors as follows: “as many points as possible on each of the horizontal B-scan cross-sections.” Although the authors commented on this point as a limitation of the study, a more precise parameter for statistical comparison between groups should be used. In addition, no comments were included in the article to address prevention of selection bias when the authors measured the thickness by manual caliper. I am wondering how to match the Amsler chart findings with the OCT mapping; and I suggest that the authors explain more precisely the definition of the area correlating to metamorphosia, which was a very important factor in their statistical results. Furthermore, in a case of broad metamorphosia (see Fig 2, Case 3 in this article1), measurement of the thickness of the inner nuclear layer, outer plexiform layer, and outer nuclear layer by caliper seems very difficult. I agree that establishment of an objective method for detection of metamorphosia is clinically important and that spectral-domain OCT is useful for detection of objective changes in the inner retinal layers. Furthermore, from the aspect of surgical indication and prognosis, the author’s morphological classification of ERM seems to be a good approach. However, I recommend the authors present simpler and more reliable methods for clinical application of their findings. YOUNG-HOON PARK, MD, PHD Seoul, Korea Reference 1. Watanabe A, Arimoto S, Nishi O. Correlation between metamorphosia and epiretinal membrane optical coherence tomography findings. Ophthalmology 2009;116:1788 –93.

Author reply Dear Editor: We thank Dr. Park for his interest in our manuscript.1 As he pointed out, a more precise and selection bias-free parameter to represent thickness of the inner retinal layer should be employed for statistical comparison. To measure the thickness of the inner retinal layer as precisely as possible, we first reviewed each B-scan crosssection throughout a 3-dimensional (3D) spectral-domain optical coherence tomography (SD-OCT) data map by dragging the mouse and determined the inner retinal layer in

each scan. Then, we measured the thickness of each segment in as many points as possible in regularly spaced five B-scan cross-sections to evaluate the trend of thickness change and to detect possible inaccuracies in the thickness measurements due to the indistinct borderline. Data from points very far from adjacent points were excluded. We agree that the use of a manual caliper to measure the inner retinal thickness is a limitation of the present SD-OCT method. The Amsler chart detects subjective metamorphopsia in the central 20-degree of visual field, and 3D SD-OCT approximately scans the corresponding retinal region. Based on this assumption, we correlated the position of local metamorphopsia on the Amsler chart with the position of 3D SD-OCT map, although this correlation may not be complete as Dr. Park noted. However, we believe that our findings provide an index to recognize the severity of metamorphopsia in patients with epiretinal membranes. Currently, we are reinvestigating the correlation between the thickness of the inner retinal layer and the position of metamorphopsia by using automated 3D intraretinal layer segmentation theory to minimize selection bias.2 Advancement of both soft- and hard-ware in SD-OCT to overcome problems we are facing is anticipated. AKINARI WATANABE, MD Hyogo, Japan References 1. Watanabe A, Arimoto S, Nishi O. Correlation between metamorphopsia and epiretinal membrane optical coherence tomography findings. Ophthalmology 2009;116:1788 –93. 2. Garvin MK, Abramoff MD, Wu X, et al. Automated 3-D intraretinal layer segmentation of macular spectral-domain optical coherence tomography images. IEEE Trans Med Imaging 2009;28:1436 – 47.

Pseudomonas Endophthalmitis Dear Editor: We read with great interest the article by Pinna et al.,1 describing an outbreak of post-cataract surgery endophthalmitis caused by Pseudomonas aeruginosa. The authors investigated 20 patients with acute postoperative endophthalmitis who underwent cataract surgery. Based on the antibiotic susceptibility by classic agar diffusion (Kirby-Bauer) method, all strains were multidrug-resistant to cefazolin, chloramphenicol, tetracycline, aminoglycosides, and fluoroquinolones; conversely, most of them were susceptible to polymyxin B. Despite the prompt use of intravitreal antibiotics, 10 patients had evisceration or phthisis of the affected eye. Our concerns regarding some issues they presented are the following: 1. In their case series, pars plana vitrectomy was only performed in 2 patients. However, in patients with poor initial visual presentation (light perception) and/or moderate-to-severe vitreous inflammation in acute bacterial endophthalmitis, pars plana vitrectomy with intravitreal antibiotics and corticosteroids are usually recommended. Based on susceptibility testing of ocular fluids, secondary intravitreal anti-

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