Foveal Microvasculature And Its Relationship To Retinal Thickness

Abstract

 

Purpose:

 

To investigate the association of foveal capillary network and retinal thickness in healthy subjects. To better understand the neurovascular interplay at the foveal pit by examining the relation of asymmetries in the FAZ to asymmetries in retinal thickness.

 

Methods:

 

In vivo foveal microvasculature imaging was performed on 14 subjects (14 eyes; age range 21-57) using an adaptive optics scanning laser ophthalmoscope (AOSLO). Standard deviation maps of the AOSLO images were used to generate the foveal capillary network. Foveal avascular zone (FAZ) diameters along the horizontal (FAZ_Hori) and vertical (FAZ_Vert) meridians were measured. Asymmetry index (AI) of the FAZ was computed by the ratio of the longer to shorter diameter. Thickness of retinal layers was measured using a Heidelberg Spectralis. Inner neural layer (INL) thickness and outer nuclear layer (ONL) thickness were measured at the edges of the FAZ corresponding to the locations of the FAZ margins on the horizontal (INL_Hori and ONL_Hori) and vertical (INL_Vert and ONL_Vert) SDOCT scans on the same (Figure).

 

Results:

 

The foveal capillary network was readily visualized in all subjects. As expected there was individual variation in size of the FAZ and also in the shape of the FAZ which produced large variation in the relative horizontal and vertical sizes. The mean±SD of AI was 1.33±0.22. In respective horizontal and vertical meridians, the mean±SD (um) of the FAZ diameters was 587±230 and 564±174; the INL thickness was 69±12 and 70±16; the ONL thickness was 104±17 and 106±14; While the ratio of INL_Hori/INL_Vert was positively correlated with the ratio of FAZ_Hori/FAZ_Vert (r = 0.84, p<0.05), no significant correlation was found between the ratio of ONL_Hori/ONL_Vert and the ratio of FAZ_Hori/FAZ_Vert (r = -0.35, p=0.11)_.

 

Conclusions:

 

In contrast to the ONL thickness, our results suggest that the INL thickness follows the asymmetry of the FAZ diameter along the two principal meridians.  

 

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