Purpose : In most cases of geographic atrophy (GA) adaptive optics ophthalmoscopy (AOO) reveals the presence of a mosaic of hyperreflective spots 2-4 µm large at the level of the Bruch’s membrane, that we termed punctuate hyperreflectivity (PHR). The origin of this “pseudomosaic” is uncertain. Basal laminar deposits (BlamD) are an age-related sub-RPE, continuous material deposit located between the RPE basal lamina and the inner layer of Bruch's membrane. During GA, the BlamD persists after disappearance of the RPE, forming a continuous layer with a spiky inner surface.
Aim: To discuss the possible origin of the PHR in eyes with GA.
Methods : Ten GA patients (12 eyes) were imaged with SDOCT and AOO, both flood and scanning based. A qualitative analysis and correlation between imaging techniques was done. Directional imaging was done in order to evaluate the Stiles-Crawford effect. The long-term change of the PHR was also documented. In vivo data were compared to histologic findings from the literature.
Results : Within atrophic area a bright hyperreflective granular structure mimicking the normal cone photoreceptor mosaic was consistently observed in 10 out of 12 eyes by both AOO modalities throughout large areas. The PHR appeared more contrasted by SLO-based AOO, while the overlying melanin-containing cells were better visible by flood AOO. The density of the punctate hyperreflectivity was within the range of the normal cone density (12676 PHR/mm2). The PHR could be seen through pigmented cells. Multidirectional imaging showed no consistent directional changes of the pseudomosaic reflectance, as opposed to what is observed in normal cones. The PHR was stable over months. In one case, it could be demonstrated that the PHR was visible under the RPE, i.e. before atrophy developed.
Conclusions : SDOCT scans and histopathologic studies consistently show the absence of photoreceptors in atrophic areas. Moreover, several histologic preparations published in the literature demonstrate the persistence of the BLamD in areas of atrophy, which corresponds to a hyperreflective band without RPE on OCT scans, for instance in "plateaux". We hypothesize that the BLamD spiky inner surface might generate similar mosaic-like reflectance by AOO. It has also been shown that cells may be located between the Bruch’s membrane and the BlamD, hence suggesting the interest of BlamD imaging.
This abstract was presented at the 2019 ARVO Annual Meeting, held in Vancouver, Canada, April 28 - May 2, 2019.