# Fractal Dimension and Retinal Pathology: A Meta-Analysis
## 4 Discussion
### Meta-Analysis  
To answer the question of whether retinal FD changes significantly in a quantitative manner, a meta-analysis was conducted for each retinal disease category to derive a summary effect size using the available studies. A negative summary effect size was found for diabetic retinopathy and myopia, suggesting decreased retinal fractal dimension for patients with those pathologies while the results for diabetes mellitus, glaucoma, hypertension are uncertain. Some limitations of this analysis include combining the retinal vascular layers into one group, estimation of mean (SD) FD, study heterogeneity, as well as low sample size for diabetes, glaucoma, and hypertension. Taking the combined average of mean (SD) FD calculations over different retinal vascular layers is a source of error as the fractal dimension over the whole retina can be greater than over its constituent layers. Estimating the mean (SD) FD for a study given median (IQR) FD can also lead to errors  
\begin{table}
\begin{tabular}{c c c c c c c c} \hline \hline \multirow{2}{*}{**Disease**} & \multirow{2}{*}{\begin{tabular}{c} **Authors** \\ **(Year)** \\ \end{tabular} } & \multirow{2}{*}{\begin{tabular}{c} **No. of** \\ **Cases** \\ \end{tabular} } & \multirow{2}{*}{\begin{tabular}{c} **Mean (SD)** \\ **FDM—Cases** \\ \end{tabular} } & \multirow{2}{*}{\begin{tabular}{c} **Heart (SD)** \\ **FD—Cases** \\ \end{tabular} } & \multirow{2}{*}{\begin{tabular}{c} **Effect Size** \\ **(SE)** \\ \end{tabular} } & \multirow{2}{*}{\begin{tabular}{c} **Summary Effect** \\ **Size (SE)** \\ \end{tabular} } \\ \cline{1-1} \cline{5-7}  & \begin{tabular}{c} [PERSON] (2012) \\ \end{tabular} & \(1949\) & \(963\) & \(1.404\) (\(0.0441\)) & \(\begin{matrix}1.4082\\ (0.0465)\end{matrix}\) & \(\begin{matrix}-0.0042\\ (0.0018)\end{matrix}\) & \(\begin{matrix}-0.0054\\ (-0.00125, 0.0017]\end{matrix}\) \\ \cline{2-7}  & \begin{tabular}{c} [PERSON] (2020) \\ \end{tabular} & \(77\) & \(43\) & \(\begin{matrix}1.6895\\ (0.0689)\end{matrix}\) & \(\begin{matrix}1.706\) (\(0.0346\)) \\ \end{tabular} & \(\begin{matrix}-0.0165\\ (0.0112)\end{matrix}\) & \(\begin{matrix}-0.0125, 0.0017]\end{matrix}\) \\ \hline \multirow{4}{*}{\begin{tabular}{c} Glaucoma \\ \end{tabular} } & \begin{tabular}{c} [PERSON] (2012) \\ \end{tabular} & \(72\) & \(2841\) & \(\begin{matrix}1.4067\\ (0.0433)\end{matrix}\) & \(\begin{matrix}1.4054\\ (0.0426)\end{matrix}\) & \(\begin{matrix}0.0013\\ (0.0051)\end{matrix}\) & \(\begin{matrix}\\ -0.0051\end{matrix}\) \\ \cline{1-1} \cline{5-7}  & \
\begin{tabular}{c} [PERSON] \\ et al. (2002) \\ \end{tabular} & \(25\) & \(29\) & \(1.694\) (\(0.0229\)) & \(1.669\) (\(0.0309\)) & \(0.025\) (\(0.0075\)) & \(\begin{matrix}-0.0049\) (\(0.0191\)) \\ \(-0.0423, 0.0324]\end{matrix}\) \\ \cline{1-1} \cline{2-7}  &
\begin{tabular}{c} [PERSON] (2013) \\ \end{tabular} & \(123\) & \(2666\) & \(1.37\) (\(0.10\)) & \(1.41\) (\(0.04\)) & \(\begin{matrix}-0.04\\ (0.0041)\end{matrix}\) \\ \hline \hline \end{tabular}
\end{table}
Table 4: _Cont._in the meta-analysis. Furthermore, the demographics of each study vary widely in age and ocular history. This combined with the many variables that go into each stage of data acquisition/processing when performing fractal analysis leads to large heterogeneity. Due to this, we reiterate that a standardized procedure for retinal fractal analysis should be developed to facilitate inter-study comparison and support future meta-analyses.