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Autofluorescence photography

With autofluorescence fundus imaging, argon blue light with a wavelength of 488nm is projected at the back of the eye, where it is converted by lipofuscin and other natural fluorophores to light having a different wavelength. Images are captured using confocal scanning laser ophthalmoscopes, such as the 'Spectralis Heidelberg Retinal Angiograph'.

 

Lipofuscin is a by-product of retinal photoreceptors discs, which at the end of their useful life are removed by the retinal pigment epithelium.  Increased amounts of lipofuscin ('orange pigment') accumulate when the retinal pigment epithelium is diseased, as happens over choroidal tumours such as melanomas. The presence of conspicuous clumps of orange pigment is a sign of maligancy and therefore helps to distinguish malignant melanomas from benign naevi. Although such orange pigment is usually visible with standard ophthalmoscopy and colour photography, autofluorescence imaging makes this abnormality easier to detect and provides a means of documentation. This can be useful with pale lesions, in which 'orange pigment' actually appears brown.

 

  autofluorescence

Autofluorescent, brown lipofuscin over an amelanotic melanoma

 

Lipofuscin can accumulate in a diffuse manner to induce diffuse autofluorescence, which over a melanocytic tumour is highly suggestive of malignancy. 

 

Other autofluorescent retinal pigment epithelial lesions include:

  • drusen (wax-like deposits in the retinal pigment epithelium). However, some drusen are non-fluorescent or even hyofluorescent.
  • fibrous metaplasia (abnormal transformation of retinal pigment epithelial cells into fibroblasts, forming scar tissue)
  • areas of hyperpigmentation, caused by clumps of retinal pigment epithelial cells.