Letter to the Editor
In vivo evaluation of photoreceptor mosaic in early onset large colloid drusen using adaptive optics
Article first published online: 23 AUG 2011
Copyright © 2012 Acta Ophthalmologica Scandinavica Foundation
Volume 90, Issue 4, pages e327–e328, June 2012
How to Cite
Querques, G., Massamba, N., Guigui, B., Lea, Q., Lamory, B., Soubrane, G. and Souied, E. H. (2012), In vivo evaluation of photoreceptor mosaic in early onset large colloid drusen using adaptive optics. Acta Ophthalmologica, 90: e327–e328. doi: 10.1111/j.1755-3768.2011.02228.x
- Issue published online: 28 MAY 2012
- Article first published online: 23 AUG 2011
Drusen are extra cellular deposits that accumulate between the retinal pigment epithelium (RPE) and the inner collagenous layer of Bruch’s membrane (Gass 1973). They usually appear after the age of 50 years and are considered as the initial pathologic stage of age-related macular degeneration (AMD) (Pauleikhoff et al. 1990). Rarely, drusen may also present an early (<50 years) onset (i.e. basal laminar drusen and malattia leventinese). We recently reported on the angiographic features of a new type of early onset drusen, that we called large colloid drusen (Guigui et al. 2010). The pathology as well as the clinical significance of such drusen is not known.
Adaptive optics (AO) is used in retinal imaging systems to limit the impact of ocular aberrations on signal resolution (Liang et al. 1997). AO technology leads to acquisition of high-resolution retinal images and allows visualizing the mosaic of cone photoreceptors or RPE cells (Liang et al. 1997).
Our purpose was to investigate the characteristics of the photoreceptor mosaic in a patient with large colloid drusen as imaged with AO illumination fundus camera.
A 29-year-old man was referred to our Department with diagnosis of retinal drusen. No medical history or familial retinal disease was noted. Visual acuity was 20/20 in both eyes. Fundus biomicroscopy revealed an aspect of large colloid drusen in both eyes, sized 200–300 μm, mainly located in the temporal perifovea.
These drusen were homogenously hyperfluorescent on the late phases of fluorescein angiography. On the late phases of indocyanine green angiography, the large colloid drusen were either hyperfluorescent or hypofluorescent surrounded by a discreet hyperfluorescent halo (Fig. 1). High-definition spectral domain optical coherence tomography (Spectralis SD-OCT; Heidelberg Engineering, Heidelberg, Germany) showed multiple large dome-shaped RPE detachments (Fig. 1), with a marked thinning of the inner segment (IS)/outer segments (OS) junction overlying the large colloid drusen (28 ± 12 μm mean IS/OS thickness over drusen versus 52 ± 25 μm in the adjacent areas).
In this patient, retinal images of the left eye were taken with the Imagine-Eyes (Imagine Eyes, Orsay, France) flood-illumination AO ophthalmoscope from 3° to 8° temporal to the fixation point. Normally, retinal cones are seen as the bright spots on AO images. Individual cones (bright spots) within the mosaic (regions containing a close-packed arrangement of bright spots) were identified manually and the average nearest-neighbour spacing was determined; thus, in turn, cone density was chosen over cone spacing as a measure of photoreceptor distribution.
This quantitative analysis was compared with that from one age-matched and refraction-matched control subject. As the axial length of subjects was not measured, we used the standard eye [schematic (275 μm/degree)] as previously reported (Drasdo & Fowler 1974). Overall, AO revealed a preservation of perifoveal cones over the large colloid drusen (Fig. 1) at 4–6° temporal to the fixation point (cone density was 18 267 ± 1187 cones/mm2), compared with an age-matched and refraction-matched control subject (cone density was 20 628 ± 1392 cones/mm2 at 4° temporal to the fixation point).
Adaptive optics is a noninvasive technique that allows observing retinal pathology directly at a cellular level and provides a measure of photoreceptor loss in retinal diseases. Using AO, we previously reported that in AMD drusen, the cone layout and photoreceptor mosaic are disrupted, with residual cone photoreceptors appearing sometimes isolated, sometimes grouped into tight aggregates (Massamba et al. Invest Ophthalmol Vis Sci. E-abstract 2009). Generally, cone photoreceptors are visible in areas between drusen, and the mosaic image sharpness is significantly less uniform across the field than in younger, healthy retinas (Massamba et al. Invest Ophthalmol Vis Sci. E-abstract 2009). Interestingly, here, using AO, we demonstrated the preservation of cones over drusen in a patient with early onset large colloid drusen [a new type of young-onset not age-related drusen recently described by our group (Guigui et al. 2011)], as well as an overall preservation of perifoveal cones over the large colloid drusen at 4–6° temporal to the fixation point.
Similar findings have been recently reported (Godara et al. 2010) in a 45-year-old asymptomatic woman with basal laminar drusen. Also, in this case presenting early onset drusen, the authors found that the mosaic was visible across the entire surface of the drusen, and, in turn, that the cones were still present despite morphological disruption on OCT (IS/OS thinning).
The different AO features may suggest a different pathology and possible evolution between AMD drusen and this peculiar type of early onset drusen. Further analyses are needed to confirm our preliminary findings on large colloid drusen.
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