A recent study in The International Journal of Retina and Vitreous explored various retinal vessel geometric parameters and their associations with diabetic retinopathy (DR).
Give me some background first.
Diabetes mellitus (DM) is a metabolic disorder characterized by impaired insulin production or sensitivity, leading to increased blood sugar levels.
- The rising global prevalence of DM calls for earlier detection of DR, an associated complication that affects the microvasculature of the retina
Optical coherence tomography angiography (OCT-A) is a non-invasive imaging modality capable of visualizing retinal microvasculature in vivo.
And the retinal geometry parameters of interest in this case?
Those would be:
- Vessel tortuosity (VT), which reflects microvasculature instability and blood flow changes following vessel remodeling
- Fractal dimension (FD), which reflects the extent of branching of retinal vessels and is implicated in risk for cardiovascular disease
Now, talk about the study.
Researchers in Indonesia conducted a retrospective study using OCT-A scans of DM patients. ImageJ and Fractalyse software were used to measure VT and FD on the scans.
A vitreoretinal specialist classified DR severity based on fundus exam findings using the The International Clinical Diabetic Retinopathy and Diabetic Macular Edema Disease Severity Scales.
Who was included in the study?
The study involved 96 DM patients (161 eyes) who were part of a previous study called the Diabetic Ocular Renal Surabaya (DiORS).
Patients were classified into five categories by DR severity:
- No-DR (52.7%)
- Mild nonproliferative DR (NPDR) (0.09%)
- Moderate NPDR (18.6%)
- Severe NPDR (11.1%)
- Proliferative DR (PDR) (0.07%)
Demographic and laboratory data collected included age, gender, hemoglobin A1c (HbA1c), and best-corrected visual acuity (BCVA).
Patients were excluded if they had:
- Poor quality OCT-A scans
- Incomplete medical records
- Other retinal disease (ex. retinal detachment, macular degeneration)
- Motion artifact
Findings?
The differences in VT and FD among the five categories of DR severity were analyzed using Kruskal-Wallis and Chi-Square tests.
- VT was significantly elevated in all DR groups (p<0.05) compared to the No-DR group.
FD of both the superficial capillary plexus (SCP) and deep capillary plexus (DCP) were studied.
- While FD of the SCP was not statistically different (p>0.05) compared to the No-DR group, FD of the DCP in the moderate NPDR, severe NPDR, and PDR groups were significantly lower.
Tell me more.
Increased VT in DR is consistent with the fact that elevated pressure, inflammation, and reduced oxygenation (which contributes to retinopathy) also result in vessel remodeling (ie. vessel tortuosity).
Additionally: Significant findings in FD may have been found in the DCP only as the DCP has a lower vascular density than the SCP and is thus more susceptible to damage.
- These results suggest that microvascular changes, particularly in the deeper retinal layers, may precede or indicate DR progression.
Any limitations?
The authors reasoned that the use of ImageJ may not be practical for efficient vessel geometry characterization in the clinical setting; however, the development of an automated image analysis would enable quick study of VT and FD in DM patients.
The study also had a small and imbalanced sample size, and lacked a traditional healthy control group that limited the comparison to nondiabetic patients.
Lastly: Although images with motion artefacts were excluded, some projection artifacts still remained and may have compromised the accuracy of the FD calculations.
So what's the take home from this?
These findings support the use of OCT-A as a screening tool, along with VT and FD (especially in the DCP) as biomarkers for early detection of DR—and, thus, critical to slowing disease progression.