Assessment of Internal Reflectivity of the Various Cellular Layers of the Retina Using Optical Coherence Tomography

Abstract

 

Purpose:

 

To investigate direct measurement of the internal reflectivity of the various cellular layers of the retina in normal eyes with the StratusOCT^TM system.

 

Methods:

 

6 mm retinal scans (centered at fovea) using the radial lines protocol were obtained from normal volunteers with a StratusOCT^TM system. Normal subjects (10 eyes) were healthy volunteers with normal ocular examination. To compare different scans in the same subject or among different subjects, each reflectivity value was a percentage of the local maximum of each image. Relative internal reflectivity of the various cellular layers of the retina was measured on OCT images after automatically and/or interactively segmenting these layers with a software program of our design. The raw reflectivity data was extracted from each of the OCT images and statistical analysis was performed.

 

Results:

 

Mean relative internal reflectivity values were obtained for each retinal sublayer in normal eyes: Mean relative internal reflectivity was highest for the IS/OS layer in all the eyes analyzed. The variation of the mean reflectivity within the different retinal sublayers was small. RPE_CC internal reflectance (relative to IPL reflectance) varied among normal subjects (mean difference of 6 ± 2%). There was no evidence that a higher RPE_CC reflectance is associated to a lower choroidal signal in normal subjects.  

 

Conclusions:

 

The reflectivity is an important retinal feature that is not currently used in the analysis of OCT data. Furthermore, thickness alone is not a perfect predictor of visual field loss. The methodology presented could be used to build a normative database with a significant number of normal, control eyes to compare various macular data. Relative internal reflectivity along with thickness information of the various cellular layers of the retina may provide useful information about the pathological changes in retinal morphology. The quantification of such pathological changes mediated by abnormal reflectivity patterns could permit both a better detection and follow up of layers injury as well as understanding of the diseased retina.

 

Keywords: imaging methods (CT, FA, ICG, MRI, OCT, RTA, SLO, ultrasound) • image processing • retina