Adaptive optics find reflectivity differences between drusen types in AMD

By Lucy Piper, Senior medwireNews Reporter

Adaptive optics (AO) provide insight into the differences in reflectivity between medium–large drusen and reticular pseudodrusen in patients with age-related macular degeneration (AMD), researchers report.

AO imaging improves the transverse resolution of conventional retinal imaging by measuring the ocular wavefront aberrations and compensating for them in real time with active optical elements, allowing detailed analysis of macular lesions and cone photoreceptor appearance, they explain.

Giuseppe Querques (Centre Hospitalier Intercommunal de Creteil, France) and colleagues used the technology to study the appearance of medium–large drusen and reticular pseudodrusen in 14 AMD patients.

En face AO of a total of 19 images of medium–large drusen in eight eyes of six patients showed that they were highly hyper-reflective round to oval lesions. The lesions were either centred and/or surrounded by continuous or discontinuous hyporeflectivity. Cone photoreceptors were unambiguously detected overlying and on the border of the lesions and appeared as continuous “bright” hyper-reflective dots over a “dark” hyporeflective or isoreflective background, like a cone mosaic. In three eyes of three patients, cone photoreceptors were also detected as continuous “dark” hyporeflective dots overlying medium–large drusen.

In a total of 14 en face AO images from eight eyes of eight patients, pseudodrusen deposits appeared as isoreflective lesions. Like medium–large drusen they were surrounded by a continuous or discontinuous hyporeflective halo. However, pseudodrusen differed from medium–large drusen in having no “dark” hyporeflective dots.

In both cases, the hyporeflective halo corresponded with the loss of the inner and outer segment (IS/OS) interface on spectral-domain optical coherence tomography images, the researchers note in the British Journal of Ophthalmology.

Cone photoreceptors did not appear to explain differences in reflectivity, the team points out, as the decrease in cone appearance on the border of the two types of drusen, compared with visibly healthy zones within the vicinity, was similar, at 15.7% for medium–large drusen and 16.2% for pseudodrusen.

The researchers say that the differences in the overall appearance of medium–large drusen and reticular pseudodrusen support current evidence that they “exhibit different localisations of material collections (ie, under vs above the RPE [retinal pigment epithelium]).”

They add that these differing AO imaging features could reflect varying degrees of impairment in the RPE and photoreceptors.

“[T]he status of the RPE and IS/OS layer appears to be equally important in reticular pseudodrusen and conventional drusen regarding their imaging properties”, Querques et al comment.

“Therefore, utilising multiple imaging technologies may enable a more definitive understanding of the prognostic value of these lesions and their respective clinical impact on macular function.”

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