Purpose:
To determine the normative database of cone packing cell density and investigate the demographic or clinical factors that influence cone cell density in the normal human eye as measured by an adaptive optics scanning laser ophthalmoscope(AOSLO) equipped with a dual liquid crystal on silicon-spatial light modulator (LCOS-SLM) (Canon Inc., Tokyo, Japan).
Methods:
192 eyes of 192 subjects with no ocular pathology were enrolled. Cone packing density was measured in areas 0.5 mm, 1.0 mm, and 1.5 mm from the foveal center and in each of 4 meridians at each distance. In addition, to assess the spatial arrangement of the cone mosaics, the nearest-neighbor distances (NNDs) and the Voronoi domains were examined by Photoreceptor analysis software (Designed by Canon Inc., Tokyo, Japan, version 1.5).
Results:
Cone packing density decreased from 28198 ± 3288.27 to 15596 ± 1504.42 (mean ± SD) cells/mm2 from the 0.5mm to 1.5mm zone (p<0.001) with a slight tendency to show a higher density of cones along the horizontal meridian. A negative correlation was observed between age and density but was not statistically significant (r=-0.117, p=0.14). There was, however, a statistically significant negative correlation(r=-0.367, p=0.003) between axial length and cone density. There was no significant difference (all, p>0.05) in cone density between sex, ocular dominance, and ethnicity. Average NND and Voronoi area gradually increased (all, p≤ 0.001) with increasing retinal eccentricity which signifies increasing cone cell size and a less dense packing arrangement. Contrarily, the ratio of mean NND for each subject divided by the triangularly packed NND was significantly decreased (p<0.001) with an increase in eccentricity which indicates a larger departure from a perfectly triangular arrangement of the cone mosaic.
Conclusions:
The present study reports normative data for cone packing density with AOSLO using dual LCOS-SLM in normal human subjects. Cone packing density decreases as a function of retinal eccentricity and axial length. The effect of age on cone density is limited in the area beyond 0.5mm from fovea center. In addition, the results of NND and Voronoi analysis can be a good index for the spatial arrangement of cone mosaics. These data may be useful when interpreting cone packing density for the diagnosis and management of various retinal diseases.
Keywords: photoreceptors • imaging methods (CT, FA, ICG, MRI, OCT, RTA, SLO, ultrasound) • macula/fovea