Superficial Vascular Plexus Associated with mfERG Foveal Avascular Zone Size

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Ophthalmology office. Masked patient and doctor – Covid 19 in consultation. Refractive telescope, slit lamp, fundus, AMD, diabetes of the eye, retinal scanner, Volk lens, Cover test, glasses, blur. Old person. (Photo by: Pascal Bachelet/BSIP/Universal Images Group via Getty Images)
The study evaluates blood vessel layers of the FAZ to explore their correlation with mfERG measures in patients with prediabetes and early type 2 diabetes.

This article is part of Optometry Advisor’s conference coverage from the 2021 meeting of the American Academy of Optometry, held in Boston from November 3 to 6, 2021. The team at Optometry Advisor will be reporting on a variety of the research presented by the primary eye care experts at the AAO. Check back for more from the AAO Optometry 2021 Meeting..

A structural and functional relationship exists between foveal avascular zone (FAZ) size from the superficial vascular plexus (SVP) and the whole eye amplitude (AMP) of the multifocal electroretinogram (mfERG), according to findings presented at the American Academy of Optometry 2021 annual meeting, held in Boston from November 3-6.

Researchers conducted a study that included 7 control participants, 11 with prediabetes, and 7 with well-controlled, type 2 diabetes with no retinopathy or edema. All participants (N=25) had 20/25 vision or better. The researchers collected HbA1c levels, using the Siemens DCA HbA1C Analyzer, which were used to classify participants into the 3 groups (controls: <5.7%, prediabetes: 5.7-6.4%, type 2 diabetes: >6.4% or physician diagnosis). Optical coherence tomography angiography (OCT-A) was performed for each participant, and FAZ was measured by hand for SVP and deep vascular plexus (DVP) separately and together. 

Retinal function was also assessed with mfERG using a burian allen electrode, which recorded a 103 hexagon stimulus and a 4-minute m-sequence at near 100% contrast. AMP and implicit time (IT) were calculated for the fovea and the whole eye average, and additional markers of overall ocular health, including blood pressure, total cholesterol, and contrast sensitivity, were evaluated. For each participant, all testing was performed on the right eye.

The study observed a positive correlation between the FAZ measured from each plexus and HbA1c. For all metrics, there was a stronger correlation with the SVP and DVP (P <.001, r2=0.33). There was a negative correlation between AMP, averaged over both the whole eye (P <.001, r2=0.42) and the fovea (P <.012, r2=0.21). Researchers noted no statistically significant relationship between SVP and IT, and SVP was negatively correlated with contrast sensitivity (P <.001, r2 = .41). Finally, there was no correlation with measures of blood pressure or cholesterol. 

The relationship with SVP was stronger than DVP, which indicates that the association is not only driven by the outer layers, but by the entire retina in diabetes, according to the study.

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Zagst A, Smith J, Wang R, Harrison W. Foveal avascular zone size and mferg metrics in diabetes and prediabetes. Poster presented at: The American Academy of Optometry  2021 annual meeting; November 12-15; Boston. Board #94.