Persistent Dark Cones in Oligocone Trichromacy Revealed by Multimodal Adaptive Optics Ophthalmoscopy

Abstract

Dark cone photoreceptors, defined as those with diminished or absent reflectivity when observed with adaptive optics (AO) ophthalmoscopy, are increasingly reported in retinal disorders. However, their structural and functional impact remain unclear. Here, we report a 3-year longitudinal study on a patient with oligocone trichromacy (OT) who presented with persistent, widespread dark cones within and near the macula. Diminished electroretinogram (ERG) cone but normal ERG rod responses together with normal color vision confirmed the OT diagnosis. In addition, the patient had normal to near normal visual acuity and retinal sensitivity. Occasional dark gaps in the photoreceptor layer were observed on optical coherence tomography, in agreement with reflectance AO scanning light ophthalmoscopy, which revealed that over 50% of the cones in the fovea were dark, increasing to 74% at 10° eccentricity. In addition, the cone density was 78% lower than normal histologic value at the fovea, and 20–40% lower at eccentricities of 5–15°. Interestingly, color vision testing was near normal at locations where cones were predominantly dark. These findings illustrate how a retina with predominant dark cones that persist over at least 3 years can support near normal central retinal function. Furthermore, this study adds to the growing evidence that cones can continue to survive under non-ideal conditions.

Characterizing Cone Spectral Classification by Optoretinography

“…These cones were located in their counterpart image, and analyzed for their spectral type using ORG. Such cones with abnormal reflections have been observed in healthy and diseased eyes[39, 40, 42]. They have previously been shown to have normal function also[41, 42].…”

Widespread subclinical cellular changes revealed across a neural-epithelial-vascular complex in choroideremia using adaptive optics

“…4d ) 43 . In addition, from the AO-OCT images, measurements of outer retinal length (ORL) were performed, defined as the distance between the inner segment/outer segment junction (ellipsoid zone) and the RPE bands 44 . ORL measurements in both labeled and non-labeled photoreceptor regions from five female carriers further showed no statistically significant differences between these two groups ( P = 0.45).…”

“…ORL was measured in AO-OCT as the distance between the inner segment/outer segment junction (ellipsoid zone) and the RPE bands 44 .…”

Patches of Dysflective Cones in Eyes With No Known Disease

“…Despite the sources of cone reflectivity variability described above, it is generally the case that regions in AOSLO and optical coherence tomography (OCT) images that exhibit a lack of normal reflections from the photoreceptors correspond to regions that lack functional cones. Multiple publications have confirmed this for many different diseases, including retinitis pigmentosa, 13 , 14 choroideremia, 15 , 16 cone–rod dystrophy, 17 , 18 age-related macular degeneration, 19 achromatopsia, 20 oligocone trichromacy, 21 fundus albipunctatis, 22 and Stargardt disease. 23 , 24 …”