Contribution of optical coherence tomography angiography OCT-A in diabetic maculopathy

Peak Cone Density Predicted from Outer Segment Length Measured on Optical Coherence Tomography

PURPOSE

To compare peak cone density predicted from outer segment length measured on optical coherence tomography with direct measures of peak cone density from adaptive optics scanning light ophthalmoscopy.

METHODS

Data from 42 healthy participants with direct peak cone density measures and optical coherence tomography line scans available were used in this study. Longitudinal reflectivity profiles were analyzed using two methods of identifying the boundaries of the ellipsoid and interdigitation zones to estimate maximum outer segment length: peak-to-peak and the slope method. These maximum outer segment length values were then used to predict peak cone density using a previously described geometrical model. A comparison between predicted and direct peak cone density measures was then performed.

RESULTS

The mean bias between observers for estimating maximum outer segment length across methods was less than 2 µm. Cone density predicted from the peak-to-peak method against direct cone density measures showed a mean bias of 6,812 cones/mm2 with 50% of participants displaying a 10% difference or less between predicted and direct cone density values. Cone density derived from the slope method showed a mean bias of -17,929 cones/mm2 relative to direct cone density measures, with only 41% of participants demonstrating less than a 10% difference between direct and predicted cone density values.

CONCLUSION

Predicted foveal cone density derived from peak-to-peak outer segment length measurements using commercial optical coherence tomography show modest agreement with direct measures of peak cone density from adaptive optics scanning light ophthalmoscopy. The methods used here are imperfect predictors of cone density, however, further exploration of this relationship could reveal a clinically relevant marker of cone structure.

Evaluation of Posterior Ocular Blood Flow in Diabetic Retinopathy Patients Without Macular Edema Using Optical Coherence Tomography Angiography

AIM

The objective of this study is to investigate and compare the superficial and deep vascular structures of the retina, as well as the changes in the choriocapillaris (CC) and optic disc microvasculature, using optical coherence tomography angiography (OCTA) in patients diagnosed with diabetes mellitus (DM) without diabetic retinopathy (DR), patients with non-proliferative and proliferative DR, and healthy individuals.

MATERIALS AND METHODS

This prospective study conducted between July 2020 and July 2021 included patients diagnosed with type 2 DM without DR, as well as patients with mild nonproliferative, moderate nonproliferative, and proliferative DR without macular oedema. A control group of 25 age- and gender-matched healthy individuals was also included. OCTA parameters of the patients were examined.

RESULTS

In the DR groups, compared to the control group, there was a significant decrease in macular superficial, deep, and CC perfusion areas as the severity of DR increased (p<0.001). The vascular density (VD) of the superficial capillary plexus (SCP) and deep capillary plexus (DCP) exhibited a statistically significant decrease in all quadrants of the DR group compared to the control group (p = 0.033 for SCP in the fovea, p<0.001 for all other quadrants). The superficial and deep FAZs showed a significant expansion in the DR group compared to the control group (p = 0.003 for superficial FAZ, p<0.001 for deep FAZ). As the severity of DR increased, there was a statistically significant decrease in the perfusion areas of the optic nerve head (ONH), radial peripapillary capillary (RPC), and vitreous segments (p<0.001 for ONH, p = 0.031 for RPC, p<0.001 for vitreous). There was a statistically significant decrease in RPC VD in all quadrants as the severity of DR increased. Moreover, as the severity of DR increased, a statistically significant decrease in the VD of the ONH was observed in all quadrants except for the inferior nasal (p = 0.094), inferior temporal (p = 0.111), superior temporal (p = 0.18), and temporal (p = 0.284) quadrants.

CONCLUSION

Our study demonstrated the involvement of macular and optic nerve perfusion areas (PA) and VD in diabetic patients. OCTA proved to be a valuable and noninvasive imaging modality, providing an easy and repeatable assessment of posterior segment vascular changes in patients with DR.

Study of Foveal Avascular Zone Growth in Individuals With Mild Diabetic Retinopathy by Optical Coherence Tomography

Purpose

The purpose of this study was to investigate the association between foveal vessels and retinal thickness in individuals with diabetic retinopathy (DR) and control subjects, and to reveal foveal avascular zone (FAZ) growth in early individuals with DR.

Methods

The regions with a thickness less than 60 µm were marked from the intima thickness maps and named FAZThic. The avascular zones extracted from the deep vascular plexus were designated as FAZAngi. The boundary of the two FAZ forms a ring region, which we called FAZRing. The FAZ growth rate was defined as the ratio of the FAZRing area to the FAZThic area. Thirty healthy controls and 30 individuals with mild nonproliferative DR were recruited for this study.

Results

The FAZThic area in individuals with mild DR and control subjects showed similar distribution. The FAZAngi area in individuals with mild DR are higher than that in control subjects on the whole, but there was no significant difference (P > 0.05). The FAZRing area in individuals with mild DR was significantly higher than that in control subjects (P < 0.001). However, there is still a small amount of overlap data between the two groups. For the FAZ growth rate, the individuals with mild DR were also significantly larger than the control subjects (P < 0.001). But there were no overlapping data between the two groups.

Conclusions

The growth of FAZ in individuals with mild DR can be inferred by comparing FAZAngi with FAZThic. This method minimizes the impact of individual variations and helps researchers to understand the progression mechanism of DR more deeply.