Evaluation of retinal structure and function in prediabetes

Variations in Retinal Oxygen Saturation in a Diverse Healthy Population

Purpose

Local retinal oxygen saturation is a research technique, which has the potential as a biomarker for diabetes. However, normative data has not been established. This study examined differences in oxygen saturation around the macula and characterizes the relationship between age, race, refractive error (RE), sex, blood pressure (BP), prediabetic status and oxygen saturation.

Methods

Fifty-nine subjects aged 22-69 (38.8 ± 14.7 years) were included who were racially diverse and with equal gender distribution. None had eye disease. Oxygen saturation was taken with the Zilia Ocular in 4 locations around the macula 3.1 degrees from the fovea and they were also averaged. BP, RE, and HbA1c were noted. Regression analyses for oximetry and other factors were completed as were t-tests with multiple comparison corrections.

Results

There were significant variations in oximetry measures by race, with higher pigmentation levels associated with lower oximetry values (p < 0.01). There was no relationship between oximetry and sex (p = 0.34), RE (p = 0.67), BP (systolic p = 0.61, diastolic p = 0.71) nor prediabetic status (p = 0.87). Oximetry was associated with age when controlling for race (P < 0.002). Nasal-temporal variations showed nasal oximetry to higher than temporal measures (P < 0.01).

Conclusion

This study revealed race/pigmentation is an important influence on oximetry measures. Retinal location also caused variations, likely due to proximity to larger vessels nasally. No differences in sex, RE nor BP were observed to alter local oxygen saturation. However, age was correlated when considered with race. This study will inform our future work in different disease states and is an important first step in evaluating this technology.

Foveal avascular zone size and mfERG metrics in diabetes and prediabetes: a pilot study of the relationship between structure and function

PURPOSE

Previous studies have demonstrated functional and structural retinal changes in type 2 diabetes (T2DM). However, less is understood in prediabetes, which is an important precursor to T2DM. Here, we evaluate the microvasculature structure of the foveal avascular zone (FAZ) and how it is correlated with retinal function as measured by the multifocal electroretinogram (mfERG) across levels of glucose dysfunction to uncover how T2DM and prediabetes alter this structure-function relationship.

METHODS

33 subjects were included: 9 controls, 12 prediabetes, 12 T2DM with no retinopathy or edema. Subjects were aged 30-70 years, had BCVA of 20/25 or better, and had no confounding ocular conditions. Blood was collected via fingerstick to determine Hemoglobin A1c (HbA1c), which was used along with previous diagnosis, to determine study grouping. Optical coherence tomography angiography (OCTA) was used to analyze the FAZ area and was corrected for refractive error. FAZ area was measured by hand using the Heidelberg Spectralis software. mfERG (VERIS 6.3) metrics implicit time (IT) and amplitude were evaluated in the foveal region, macular region, and averaged over the posterior pole of the right eye. Regression analysis was performed between each study group parameter to determine relationships, and t tests with corrections were used to compare groups.

RESULTS

FAZ area (superficial plexus) was negatively correlated with mfERG posterior pole amplitude (p < 0.01, R2 = 0.30), foveal amp (p = 0.02 R2 = 0.17) and macular amplitude (p = 0.02 R2 = 0.18) across all 33 study subjects. FAZ and mfERG metrics were not significantly different between study groups in this cohort except for IT, which was more delayed in the diabetes group compared to other groups.

CONCLUSION

FAZ area is correlated with mfERG amplitudes but not IT. This suggests a link between the structural metrics and retinal function. Longitudinal follow-up work would be helpful to determine the timing of these changes in prediabetes.