# Fractal Dimension and Retinal Pathology: A Meta-Analysis
## 3 Results
### Results of Studies Conducting Fractal Analysis on Retinal Images  
Changes in the FD of the retinal vasculature in patients with retinal disorders are reported in Table 3. Setups for retinal imaging, vessel segmentation, and FD calculation were varied. Methodological variance was especially prominent for studies that employed OCTA as the imaging method, as often different studies considered different retinal vascular layers when calculating FD. Some studies also calculated FD on only the veins or arteries in an image, leading to the distinct parameters venular and arteriolar FD, apart from total FD. Digital fundus photography was the most common retinal imaging method, which was used by 14 out of the 28 studies with the most common field of view (FOV) being 45 degrees. The next most common imaging method was OCTA, which was used by 13 studies. Only one study used fundus fluorescein angiography (FFA) as the imaging method. Although methodological setups were relatively varied across the studies, there were some similarities. One setup that was used by 5 of the studies was the use of \begin{table}
\begin{tabular}{c c c c c c} \hline \hline
**Author** & **Study** & **N Subjects** & **Mean (SD)** & **Sex (M, F):** & **Population and Clinical** \\
**(Year)** & **Design** & **Pathologies** & **Cases/** & **Age in** & **Cases/** & **Controls** & **Characteristics** \\ \hline \hline \multirow{9}{*}{\begin{tabular}{c} [PERSON] et al. \\ (2020) \\ \end{tabular} } & \multirow{9}{*}{Case-control Hypertension} & \multirow{9}{*}{77/43} & Cases: 59.2 & \multirow{9}{*}{\begin{tabular}{c} Subgroup of an observational \\ study population that was \\ conducted in the village area \\ of Pingyin County in the \\ Southwest of Jinan, Shandong, \\ China. Inclusion in the \\ hypertensive group was \\ determined by having blood \\ pressure \textgreater{} 140/90 mmHgHg and \\ \textless{}180/110 mmHg, age from \\ 40–80 years, and no signs of \\ confounding comorbidities. \\ Mean arterial pressure defined \\ as diastolic blood pressure \\ plus one third of the diastolic \\ and systolic blood \\ pressure difference. \\ \hline \hline \end{tabular} } & \
\begin{tabular}{c} Patients from Wenzhou Eye \\ Hospital and students from \\ Wenzhou Medical University \\ were recruited. Control group \\ consisted of subjects with SER \\ between +0.50 D and \(-\)3.00 D \\ and highly myopic group \\ consisted of subjects with SER \\ less than \(-\)6.00 D. \\ \hline \hline \end{tabular} } \\ \hline \hline \multirow{9}{*}{
\begin{tabular}{c} [PERSON] et al. \\ (2016) \\ \end{tabular} } & \multirow{9}{*}{Case series} & Diabetic & 37 & (12.65) \\  & & Retinopathy & 8/29 & Controls: \\  & & & 32.27 (6.71) \\ \cline{1-1}  & & & & \\ \cline{1-1}  & & & & \\ \cline{1-1}  & & & & \\ \cline{1-1}  & & & & \\ \cline{1-1}  & & & & \\ \cline{1-1}  & & & & \\ \cline{1-1}  & & & & \\ \cline{1-1}  & & & & \\ \hline \hline \end{tabular}
\end{table} 
Table 2: Cont. the Singapore I Vessel Assessment (SIVA, National University of Singapore, Singapore) software combined with an optic disc centered annular ROI of 0.5 to 2.0 disc diameters. Another was the use of digital retinal photography combined with the fractal analysis package of the International Retinal Imaging Software (IRIS) for a circular ROI of 3.5 disc diameters centered at the optic disc, which was the choice of 4 other studies. Most of the studies (25 out of 28) calculated just the monofractal box-counting dimension of the retinal vascular tree and did not consider its multifractal properties. It should also be noted that 22 of the 28 studies examined retinal vascular parameters other than fractal dimension such as branching angles, caliber, and tortuosity. One study [28] was unique among the rest in that it examined the relationship between FD and a variety of different pathologies for the Singapore Malay Eye Study (SiMES) cohort. Another study [28] found a significant, independent association between decreased retinal FD and mobidities such as blood pressure and myopia.