Quantitative Analyses of Fundus Autofluorescence

Ali Ayata, Ophthalmologist,

Other Contributors:

April 24, 2008

Dear 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

Conflict of Interest

None declared