Structural and function correlation of cone packing utilizing adaptive optics and microperimetry

Aim. To assess the functional aspects of cone mosaic and correlate cone packing with retinal sensitivity utilizing microperimetry in emmetropes at different eccentricities. Methods. Twenty-four healthy volunteers underwent microperimetry (MAIA Centervue, Italy) and assessment of photoreceptors using adaptive optics retinal camera, rtx1 (Imagine Eyes, Orsay, France), at 2 and 3 degrees from the foveal centre in 4 quadrants: superior, inferior, temporal, and nasal. Data was analyzed using SPSS version 17 (IBM). Spearman’s correlation tests were used to establish correlation between mean cone packing density and retinal sensitivity at different quadrants. Results. Thirteen females and 11 males (age range 20–40 years) were included. The cone density was found to be significantly different among all quadrants (temporal = 25786.68/mm2 ± 4367.07/mm2, superior = 23009.35/mm2 ± 5415.81/mm2, nasal = 22838.09/mm2 ± 4166.22/mm2, and inferior = 21097.53/mm2 ± 4235.84/mm2). A statistical significance was found between orthogonal meridians, that is, temporal, nasal superior, inferior (44106.88/mm2). A drop in retinal sensitivity was observed as the eccentricity increased . It was also found that as cone packing density decreased retinal sensitivity also decreased in all quadrants. This was observed at both 2 and 3 degrees. Conclusion. It is of crucial importance to establish normative variations in cone structure-function correlation. This may help in detection of subtle pathology and its early intervention.

1. Introduction

Adaptive optics (AO) is emerging as an objective tool in assessment of the architecture of the photoreceptor layer of retina. It can be used to quantify the cone mosaic including the density and packing arrangements. Studying the cone mosaic shows different reflectance patterns with wide temporal and spatial variations. Multiple AO systems have described this variation in the cone reflectivity to be secondary to differences in the phase of phototransduction, length of the outer segment, disc shedding, wavelength of the light, and so forth [1–3].

By just studying the cone mosaic, we are unable to assess the functional aspect of a visible cone and correlate whether a visible cone is a functional cone.

Our study aims to assess the functional aspects of the cone mosaic and correlate the cone packing with the retinal sensitivity utilizing microperimetry (MAIA) in emmetropes at different eccentricities.