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Hanieh Mirhajianmoghadam, Suman Adhikari, Alexander W Schill, Gwen Musial, Hope M Queener, Nimesh B Patel, Jason Porter; Comparison of cone packing and foveal architecture between normal eyes with short and long axial lengths. Invest. Ophthalmol. Vis. Sci. 2018;59(9):4749. doi: https://doi.org/.
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© ARVO (1962-2015); The Authors (2016-present)
Multiple factors, including axial elongation, have been suggested to influence the formation and maturation of the normal human fovea. However, there is a lack of data examining both foveal structure and cone density within and between eyes with short versus long axial lengths (AL). To better understand overall foveal architecture and the potential role of axial elongation in its development, we examined whether differences existed in overall foveal morphology and cone packing between short and long eyes.
Split detector and confocal adaptive optics scanning laser ophthalmoscope images of foveal capillaries and cone photoreceptors were acquired over the central 3 degrees in one eye of 7 normal subjects with short ALs (22.54 ± 0.17 mm) and 12 normal subjects with long ALs (25.13 ± 0.38 mm), aged 18-40 years. The border of the foveal avascular zone (FAZ) was manually traced in capillary perfusion images to quantify FAZ area, perimeter, circularity and aspect ratio. Cone packing metrics (Bound density, Nearest Neighbor Distance (NND), Furthest Neighbor Distance (FND), Intercell distance (ICD), Intercell regularity, Voronoi cell area regularity) were calculated at 0.15, 0.2 and 0.3 mm eccentricities in 4 major meridians. Volume scans of the central macula (6 x 6 mm, 128 B-scans) were acquired using spectral domain optical coherence tomography (Cirrus HD-OCT) to measure foveal pit volume, depth, diameter, area and slope. Biometric measurements (Lenstar) were used to calculate retinal magnification factors.
Bound cone density (cones/mm2) was significantly different between eyes with short and long ALs at 0.2 and 0.3 mm eccentricities (0.15 mm: 72,465 ± 6,625 vs 65,122 ± 6,636; 0.2 mm: 68,015 ± 4,013 vs 59,094 ± 6,692 [P<.01]; 0.3 mm: 56,089 ± 4,836 vs 47,773 ± 3,725 [P<.01]), as was ICD. FND was significantly different at 0.3 mm eccentricity (P<.01). Mean FAZ and foveal pit metrics were similar between short and long eyes. Eyes with larger FAZ areas had larger pit volumes, areas and diameters only in long AL eyes (P<.05). However, cone packing tended not to be correlated with foveal pit or FAZ metrics in short or long AL eyes.
The results suggest that retinal stretching due to axial elongation may affect cone photoreceptor packing for eccentricities ≤ 0.3 mm, whereas FAZ size and foveal pit shape may be primarily driven by factors other than AL.
This is an abstract that was submitted for the 2018 ARVO Annual Meeting, held in Honolulu, Hawaii, April 29 - May 3, 2018.
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