Evaluation of Discrepancies Between Fluorescein Angiography and Optical Coherence Tomography in Macular Edema in Uveitis

This letter refers to the article “Discrepancies between Fluorescein Angiography and Optical Coherence Tomography in Macular Edema in Uveitis,” by Ossewaarde-van Norel and associates. The authors analyzed the time-domain optical coherence tomography (TD OCT) and fluorescein angiography (FA) scans of 112 eyes with active or inactive uveitis for the presence of macular edema and observed discrepancies between the findings of the 2 investigational tools in nearly 46% of eyes. We congratulate the authors for the concept of the study, but have a few comments to make.

First, the authors did not mention the TD OCT scanning protocol that was used for image capturing and analysis. Using TD OCT, 6 radial line scan images can be acquired using 2 protocols: the fast macular thickness protocol in which 128 A-scans for 1 line scan are obtained and the macular thickness protocol in which 512 A-scans for 1 line scan are acquired. The fast macular thickness protocol decreases the chances of motion blur, but compromises on image resolution. If the fast macular thickness protocol was the sole protocol used for image acquisition and analysis, it may have led to an increase in false-negative results (higher chances of cysts being missed) and would be a serious limitation of the study.

Second, we also believe that a high proportion of FA-positive and TD OCT-negative reporting could be the result of missing cysts in the perifoveal area. The 6 radial line scan protocol has a propensity of missing perifoveal pathologic features, which are present in the intervening area between the 2 line scans.

Third, the authors’ statement regarding their inability to test their hypothesis of atrophic retinas with macular edema and negative TD OCT results because of increased central retinal thickness being a selection criterion may not be entirely true, because it was not the only selection criterion and in all the patient subgroups (FA positive/TD OCT positive, FA positive/TD OCT negative, FA negative/TD OCT positive), the lower range of thickness was less than 249 μm (the defining thickness for macular edema in this study).

Fourth, the clinical application of the study would be more relevant if the pattern of discrepancies in eyes with an initial episode of intraocular inflammation, a recurrent episode of uveitis, and inactive uveitis were described separately.

In a study at our center, we compared the FA and spectral-domain (SD) OCT image findings in patients with active intermediate uveitis with macular edema (unpublished). We observed discrepancies in 4 (7%) of 56 cases. In 1 eye (1.7%), there was presence of fluoroscein leakage without cystoid macular edema on SD OCT, and in 3 eyes (5.1%), the SD OCT showed cysts without fluoroscein leakage. A low proportion of discrepancy in our series can be attributed to the study population, comprising mainly patients with a primary attack of intermediate uveitis and early presentation. The other reason is the use of SD OCT, which detects intraretinal cysts better and is able to acquire better images in hazy media compared with TD OCT. The absence of leakage with presence of cysts in our patients can be ascribed to treatment response with corticosteroids with a residual anatomic defect.

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Jan 9, 2017 | Posted by in OPHTHALMOLOGY | Comments Off on Evaluation of Discrepancies Between Fluorescein Angiography and Optical Coherence Tomography in Macular Edema in Uveitis

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