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Author's response
Submit responseDear Editor
We thank Dr Ayata for the thoughtful comments of our article. He had three questions that we would like to answer as follows:
1) Figure 1 was quite important for the paper because it shows the exact location of the macular pigment in monkeys (courtesy of Francois Delori, PhD). We are sorry for the lack of the image in the on-line paper version but it was probably due to the PDF saving process.
2) We do not think there is any inconsistency between results and conclusion because that was exactly what we expected. If a pseudohole is a macular lesion where there is no loss of foveal tissue, the presence of foveal AF indicates the absence of macular pigment in the fovea. Being the pigment located in the outer plexiform layer and outer nuclear layer in the fovea (fig 1), that means we were dealing with lamellar rather than pseudo macular holes. Our paper just underlined the finding that OCT alone is inadequate to differentiate pseudo from lamellar holes. As to this respect AF imaging may be useful because reveals a loss of foveal tissue.
3) We are aware of the different aspects of AF-imaging after dark and light adaptation. As Dr Ayata properly pointed out, the visible changes in AF imaging in light and dark adapted eyes are minimal in the fovea and the lack of macular pigment in lamellar macular hole is in the fovea. The AF ratio was used to correlate AF intensities with residual retinal thickness at the bottom of the defect. The reason why we did not use raw images for AF quantitative measurements was related to the great difficulties in visualizing foveal defect in non normalized images. The ratio could have affected the results of these correlations but not the presence of foveal AF itself.We thank again Dr Ayata for his interest in our article.
Ferdinando Bottoni ,MD
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Quantitative Analyses of Fundus Autofluorescence
Submit responseDear Editor,
We read with great interest the recently published article by Bottoni and associates. However, we would like to express our concerns regarding their article entitled “Diagnosis of macular pseudoholes and lamellar macular holes: is optical coherence tomography the gold standard?” Br. J. Ophthalmol. published online 1 Feb 2008; doi:10.1136/bjo.2007.127597. [1] In this article, the authors investigate whether fundus autofluorescence imaging (FAF) differentiates between macular pseudo hole (MPH) and lamellar macular hole (LMH).
(First of all, figure 1 has not been presented. I guess it could be a technical error owing to the PDF rendering process).
Second, although corrected value of the foveal AF intensity was not found to be significantly different between the two groups (ie, pseudoholes and lamellar holes), authors concluded that AF imaging may add useful information as to the differential diagnosis of MPH from LMH. Moreover, they stated that the presence of foveal AF is consistent with a loss of foveal tissue and therefore a diagnosis of LMH. We believe there is an inconsistency between results and conclusion.
Third, several factors should be considered for evaluating FAF intensities in different examination and patient. Detector gain, pupillary alignment, refraction of the eye, lens status and number of the averaged image could be interfere pixel intensity of the FAF signal and those should be standardized before quantitative analyses of FAF images. [2] In the aforementioned article, standardization of the FAF images has not been clearly stated.
Ratio between the region of interest and background intensity appears reliable for single mean image quantification. However, bleaching of the photopigments due to the continuous visible light excitation may influence results and leads miscalculation. Bleaching with blue light is minimal at the fovea and is maximum approximately 12 degrees away from the fovea in the horizontal and vertical meridians. [3] Increment of the pixel intensity of the FAF image is depending on excitation time and amplitude of the fotobleaching is related amount of the photopigment and varies individually. According to our results (article in process), nearly 40% increment (range 18.8 % to 75.9 %) in FAF luminosity occurs during first thirty seconds of the excitation. For this reason, obtaining standard FAF images with accurate luminosity requires at least 30 second fundus illumination to bleach the photoreceptor pigments.
Considering these biasing factors (acquiring standardized FAF images, using accurate raw image processing algorithm) may provide more reliable results. Different analyse technics (i.e. circularity, eccentricity or transition pattern analyse) may grant the difference.
We thank Bottoni and his associates for their interesting article.
References
1. Bottoni F, Carmassi L, Cigada M, Moschini S, Bergamini F. Diagnosis of macular pseudoholes and lamellar macular holes: is optical coherence tomography the gold standard? Br J Ophthalmol. 2008 Feb 1; [Epub ahead of print] doi:10.1136/bjo.2007.127597
2. Schmitz-Valckenberg S, Holz FG, Fitzke FW. Perspectives in Imaging Technologies. In: Atlas of Fundus Autofluorescence Imaging, Holz FG, Spaide RF, Bird AC (editors). Springer – Verlag, Berlin 2007:325-34
3. Theelen T, Berendschot TT, Boon CJ, Hoyng CB, Klevering BJ. Analysis of visual pigment by fundus autofluorescence. Exp Eye Res. 2008;86:296-304.
Ali Ayata, MD ali_ayata@yahoo.com Gulhane Military Medical Academy Haydarpasa Training Hospital Department of Ophthalmology Istanbul-Turkey
Sinan Tatlipinar, Melih Unal, Dilaver Ersanli, Ahmet H Bilge Competing interest:None
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