Macular dystrophies are a heterogeneous group of hereditary disorders involving the macular area at different levels and with variable severity. Diagnostic tools, including fluorescein angiography, FAF, electrofunctional tests, and OCT can provide information regarding the morphological changes characterizing each dystrophy. Infrared examination of the human ocular fundus has provided interesting results in the past [12
]. More recently, the F10 SLO has been used non-invasively to examine the posterior pole with a retro-mode technique at an infrared wavelength, providing accurate characterization of the retinochoroidal structures [4
]. The F10 is based on a newly developed RMI procedure using an infrared laser to provide a pseudo three-dimensional image.
The pseudo-3D image is obtained by assembling multiple pictures generated by the retinal layers at different depths and collected by the F10-detector through the retro-mode aperture. This consists of a central stop blocking the direct light reflection and a laterally oriented oval-shaped opening, which allows the scattered light spreading in only one direction to cross.
In previous reports, RMI was able to characterize the cystoid macular edemas secondary to polypoidal choroidal vasculopathy, retinitis pigmentosa or retinal vascular disorders, including diabetic maculopathy and retinal vein occlusion [4
]. Tanaka et al have described a specific ‘fingerprint’ pattern related to macular retinoschisis in myopic eyes, which consists of radiating retinal striae centered on the fovea and many light dots and lines that run in parallel to the striae or form a whorled pattern surrounding the radiating striae [6
]. In eyes affected by dry age-related macular degeneration, RMI featured the progressive enlargement and confluence of drusen over a short term observation, suggesting a possible role in the monitoring of subtle drusen changes in the progression of AMD [8
Our results reveal that RMI is also able to detect abnormalities in retinal dystrophies. In particular, the main finding of RMI is a pseudo-3D pattern of all the lesions at the posterior pole. Any accumulation of material within the retina appeared as an elevated area, with different shapes and sizes, showing irregular and darker borders. On the other hand, atrophic regions turned out to be accurately outlined by the precise visualization of the choroidal vasculature, both in the macula and outside the macular region when the fovea was spared.
Comparison with other imaging techniques can be interesting. Indeed, BL-FAF is considered to be related to the amount of lipofuscin within the RPE cells [9
], whereas NIR-AF patterns have been interpreted as corresponding to the extent of melanin deposition [3
]. Interestingly, we did not find a clear correlation between RMI, and BL-FAF or NIR-FAF imaging. Bearing in mind that both BL-FAF and NIR-FAF signals correspond to the fluorescence of specific molecules (lipofuscin and melanin, respectively), the presence of other molecules contributing to the whole mass of each specific alteration cannot be visualized by the two FAF techniques. RMI thus seems to be a technique able to depict the full extension of the abnormal material amassed. Moreover, RMI provides a more precise imaging of the elevated lesions than biomicroscopic examination, precisely detecting even small alterations that can be missed in a simple ophthalmoscopic examination.
OCT can also produce 3D imaging of retinal abnormalities, providing insights useful in the diagnosis of macular diseases. In view of the fact that some alterations are located at a different depth of the retina, certain authors have argued that it is not always easy to see all the changes in a single OCT section [5
]. OCT and RMI may thus be considered complementary techniques, together providing a fast and non-invasive examination of the fundus.