Fluorescence Adaptive Optics Scanning Laser Ophthalmoscope for Detection of Reduced Cones and Hypoautofluorescent Spots in Fundus Albipunctatus

Abstract

IMPORTANCE Fundus albipunctatus (FA) is a form of congenital stationary night blindness characterized by yellow-white spots, which were classically described as subretinal. Although night blindness and delayed dark adaptation are hallmarks of this condition, recent studies have described a macular phenotype, particularly among older patients. Using a fluorescence adaptive optics scanning laser ophthalmoscope (FAOSLO), this study provides in vivo morphologic data at the cellular level in FA.OBJECTIVE To study the cone photoreceptors and the albipunctate spots in FA at single-cell resolution. DESIGN, SETTING, AND PARTICIPANTA woman in her 30s with FA underwent a complete ophthalmic examination, including conventional imaging tests, at the University of Rochester. A FAOSLO was used to obtain infrared reflectance images of the cone mosaic at the central fovea and along the superior and temporal meridians to 10°eccentricity. Cone density was measured at the foveal center, and cone spacing was calculated in sampling windows eccentrically. In the area of the albipunctate spots, autofluorescence FAOSLO images (excitation, 561 nm; emission, 624 Δ 40 nm) were simultaneously obtained. MAIN OUTCOMES AND MEASURESStructural appearance of cones, cone density and spacing, and reflectance and autofluorescence of albipunctate spots.RESULTS Cone density was reduced to 70% of the lower limit of the normal range at the foveal center (78.7 × 10 3 cones/mm 2 ; mean [SD] reference range, 199 [87] × 10 3 cones/mm 2 ), and cone spacing was increased eccentrically to 10°(sign test, P = .045). Individual cone central core reflectances appeared dim, suggesting loss of photoreceptor outer segments. The albipunctate spots were hypoautofluorescent. No photoreceptors or retinal pigment epithelium cells were identified at the locations of the albipunctate spots. CONCLUSIONS AND RELEVANCEAlthough the predominant clinical symptom of night blindness and the electroretinography results suggest a primary rod dysfunction, examination with a FAOSLO demonstrates that cone density is also reduced. This finding may represent an early sign of progression to macular phenotype in FA. The hypoautofluorescence suggests that the albipunctate spots do not represent lipofuscin.

Adaptive optics imaging of inherited retinal diseases

“…Using fluorescence AOSLO and cAOSLO, Song et al have reported decreased foveal cone density and increased cone spacing at 10° of eccentricity, despite this predominantly being a rod disorder. 64 No photoreceptors or RPE cells were visualised within the albipunctate spots. Another study also identified decreased perifoveal cone density and mosaic disruption using cAOSLO in RDH5 -associated fundus albipunctatus.…”

Adaptive optics imaging of the human retina

“…However, other imaging modes are wavelength dependent. Thus AOSLO systems can be readily adapted for fluorescence imaging of both endogenous (Morgan et al, 2009; Song et al, 2014) and exogenous (Dubow et al, 2014) fluorophores, and for identifying bleachable photopigment using retinal densitometry (Hofer et al, 2005; Roorda et al, 2001; Tuten et al, 2017). However to date there has not been much work using multiply scattered light, which tends to be more sensitive to absorption by retinal pigments (Elsner et al, 1992a; Remky et al, 1996).…”

“…With the AOSLO the most reliable methods for RPE visualization has been to use fluorescence as a contrast mechanism. There are two ways to do this, using the intrinsic fluorescence of lipofuscin (Morgan et al, 2009; Rossi et al, 2013; Song et al, 2014), and using ICG to stain the RPE cells (Tam et al, 2016).…”

Phenotypic diversity in autosomal-dominant cone-rod dystrophy elucidated by adaptive optics retinal imaging

“…In patient IV-5, the cone reflectance was diminished relative to surrounding rods, giving them a dark appearance. The presence of these ‘dark cones’ has been described by our group and others in a range of retinal degenerations 17 18 26 and may represent cones with reduced outer segment length or cones that lack outer segments. This hypothesis is supported by split-detector AOSLO that shows preserved cone inner segments underlying dark cones.…”

“…Selected study participants (three affected, three unaffected) underwent high-resolution retinal imaging with AOSLO according to published techniques. 17 Cone and rod photoreceptor reflectance images were acquired according to published image acquisition and montaging methods, using 796 nm illumination and a 1.8 Airy disk diameter confocal pinhole. 18 A strip of approximately 10°×1.5° along the nasal meridian was imaged in one eye of each study participant.…”