Page 179 - Characterization of genetic neurodevelopmental disorders at adult age, with a focus on 22q11.2 deletion syndrome - Emma Boersma

The eye as a window to the brain
performed the retinal blood vessel assessments (A.A.). Images of the right
eye were used for analyses. In case the quality was poor, the left eye image
was used.
Four vascular parameters were calculated, as described previously:12, 16, 20,
21 central retinal artery and central retinal vein equivalent (CRAE and CRVE;
both measures of vessel diameter), fractal dimension (FD; measure of the
branching pattern and vessel density) and vascular tortuosity (measure
of the vessel trajectory). Vessel length was determined with customized
semi-automated MATLAB 2022a software (MathWorks, Inc., Natick,
Massachusetts, United States). 20
CRAE and CRVE were calculated with the revised Knudtson‐Parr‐Hubbard
formula and averaged over the six largest arterioles and venules in the zone
between 0.5- and 2-disc diameters from the optic disc.22 In order to adjust
for magnification differences of the two cameras, image resolution and
refractive errors, a calibration factor was multiplied by individual CRAE and
CRVE to convert values in pixels to micrometers (μm).12 FD was calculated
with automated MATLAB 2018a software, using the box-counting method,
in which images are divided into multiple equally sized square boxes. 23 The
number of boxes containing the skeletonized line tracing was counted and
the process was repeated for different sized squares. FD was calculated
as the gradient of logarithms of the number of boxes and the size of the
boxes.16 Vascular tortuosity was calculated as the ratio of the arc length
(i.e., actual length of the vessel) divided by the chord length (i.e., length of
a straight line drawn from the start to end point of the vessel, Figure 1)
averaged over all vessels. 24, 25
Optical coherence tomography
An HRA+OCT Spectralis Tracking Laser Tomography camera (Heidelberg
Engineering, United States of America) was used to obtain peripapillary
RNFL thickness and macular thickness. Thickness of peripapillary RNFL
was evaluated as a 3.4 mm diameter circle surrounding the optic disk
which was segmented into four sectors: superior, inferior, temporal, and
nasal (Figure 2). The superior and inferior sectors were further divided
into temporal-superior, nasal-superior, temporal-inferior and nasal-inferior
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