Variation of cone photoreceptor packing density with retinal eccentricity and age

Abstract

Purpose: To study the variation of cone photoreceptor packing density across the retina in healthy subjects of different ages.

Methods: High-resolution adaptive optics scanning laser ophthalmoscope (AOSLO) systems were used to systematically image the retinas of two groups of subjects of different ages. Ten younger subjects (age range, 22-35 years) and 10 older subjects (age range, 50-65 years) were tested. Strips of cone photoreceptors, approximately 12° × 1.8° long were imaged for each of the four primary retinal meridians: superior, inferior, nasal, and temporal. Cone photoreceptors within the strips were counted, and cone photoreceptor packing density was calculated. Statistical analysis (three-way ANOVA) was used to calculate the interaction for cone photoreceptor packing density between age, meridian, and eccentricity.

Results: As expected, cone photoreceptor packing density was higher close to the fovea and decreased with increasing retinal eccentricity from 0.18 to 3.5 mm (∼0.6-12°). Older subjects had approximately 75% of the cone density at 0.18 mm (∼0.6°), and this difference decreased rapidly with eccentricity, with the two groups having similar cone photoreceptor packing densities beyond 0.5 mm retinal eccentricity on average.

Conclusions: Cone packing density in the living human retina decreases as a function of age within the foveal center with the largest difference being found at our most central measurement site. At all ages, the retina showed meridional difference in cone densities, with cone photoreceptor packing density decreasing faster with increasing eccentricity in the vertical dimensions than in the horizontal dimensions.

Figure 1.

(a) Wide-field fundus image of subject 5. High-resolution AOSLO images were acquired in the boxed region. (b) High-resolution AOSLO image of fovea and inferior retina, acquired within the boxed region in (a). Scale bar, 200 μm.

Figure 2.

Exponential fitting of cone packing density at the nasal retina from subject 5. Cone packing density (×10³ cones/mm²) is plotted as a function of retinal eccentricity (mm). (●) The actual cone densities at different retinal locations; × the interpolated cone density at 1.6-mm eccentricity.

Figure 3.

Cone distribution measured 6 months apart at the same retinal location, 1 mm eccentricity in nasal retina of subject 7. (A) Earlier image; (B) later image. Separate counting for the two images produced density estimates within 2%.

Figure 4.

Cone photoreceptor images from a 0.81-mm eccentricity of the nasal retina for all 20 subjects. Individual images are 200 × 200 μm. Numbers below each panel are the cone packing density of each subject at this location in cones per square millimeter. Top two rows: group 1 (22–35 years); bottom two rows: group 2 (50–65 years). Scale bar, 100 μm.

Figure 5.

Top: montage of cone photoreceptors from the fovea to approximately 12° for subject 3 (axial length 23.85 mm). Bottom: cone photoreceptor images of subregions of the montage indicated by the squares in the top row montage with the corresponding numbers. Scale bar: top, 200 μm; bottom, 100 μm.

Figure 6.

Cone packing density at different retinal eccentricity along four meridians from both groups. The cone density from (A) superior, (B) inferior, (C) nasal, and (D) temporal retina is shown. Group 1 was aged 22 to 35 years, group 2, 50 to 65 years. Cone densities replotted Curcio et al. are shown.

Figure 7.

Mean cone densities from two groups as a function of eccentricity, with 0 as the center of fovea and ±1 SE shown as an error bar. (A) The vertical meridian retina. (B) The horizontal meridian retina. Shown are the average cone density in subjects from group 1 (22–35 years) and group 2 (50–65 years).

Figure 8.

Cone photoreceptor images from one older subject and one young subject from the superior retina. (A) Older subject, 0.27 mm; (B) older subject, 0.9 mm; (C) younger subject 0.27 mm; and (D) younger subject 0.9 mm.