Axial length associations with retinal layer thicknesses from spectral domain optical coherent tomography (SD-OCT) macular scans in the Beaver Dam Eye Study (BDES)

Abstract

 

Purpose

 

To describe retinal layer thickness by ocular biometric measures in a population based study of older adults.

 

Methods

 

Refraction, ocular biometric measurements, and SD-OCT imaging were performed in participants aged 63-100 years at the 2008-2010 BDES examination (n=1913). Macular scans were automatically segmented using the Iowa Reference Algorithms which identify 10 retinal layers: nerve fiber (NFL), ganglion cell (GCL), inner plexiform (IPL), inner nuclear (INL), outer plexiform (OPL), outer nuclear (ONL), inner segment/outer segment (ISOS), outer segment junction (OSJ), outer photo receptor (OPR) and retinal pigment epithelial (RPE). Scans of eyes with confounding conditions (eg, epiretinal membranes) and scans with a low tissue contrast score or other artifacts affecting segmentation (eg, severe motion, Z-plane offset) were excluded. Axial length divided by the radius of corneal curvature (ALCR) is a unit-free measure of the axial elongation that is highly correlated with myopia. Each eye was included in analyses, using generalized estimating equations (GEE) to account for correlation.

 

Results

 

A total of 1700 scans with both segmentation and ALCR data were included in analyses. The figure shows each layer’s thickness (z-score) as ALCR increases for the Early Treatment Diabetic Retinopathy Study grid regions that correspond to the center, inner and outer rings. Thickness patterns differed among the layers. The NFL thickness increased in each region, while the GCL, IPL, INL and OPL thicknesses all decreased in the outer, increased in the center and did not change in the inner ring as ALCR increased. The outer retinal layers (ONL, ISOS, OSJ, OPR and RPE) had smaller changes as ALCR increased (often non-significant) and showed different patterns than the inner retinal layers.

 

Conclusions

 

Thinning of the retina with increasing ALCR was present in most retinal layers, especially with the outer grid regions. A tilted disc may impact measurements, especially in the center grid region. Further work is needed to understand functional implications of the thinning.  

 

Thickness measures (z-score) for each layer. Each point represents increasing ALCR categories with median refraction in diopters (D).