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2024
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Sakshi Vasiu Master's Thesis Final PDF_Sakshi Vasiu.pdf
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"Purpose: To evaluate retinal ganglion cell function in diabetic patients with no retinopathy.
Methods: The full-field photopic flash electroretinogram (ERG) was recorded from 11 diabetics patients (55.75 ± 14.77) and 11 age-matched controls (50.17 ± 15.18) with a ColorBurst TM handheld stimulator (Diagnosys LLC). The visual stimuli consisted of 40 ms duration red (640 nm) test stimuli of strengths ranging from 0.25 cd/m2 to 1500 cd/m2 delivered on and constant rod-saturating blue (470 nm) background of 7cd/m2. The Intensity response function of the PhNR and the b-wave amplitudes plotted as a function of stimulus strength were fitted with a generalized Naka-Rushton equation of the form V(I)/Vmax = In /(In +Kn ) and the fit parameters of K, n and Vmax were compared between the diabetic patients and control subjects. Visual field sensitivity was measured by behavioral perimetry using the Humphrey Visual Field Analyzer 10-2 and 24-2 SITA-standard tests. Structural parameters of the retina, namely area of the foveal avascular zone (FAZ), superficial vascular plexus density (SVD), deep vascular plexus density (DVD)and Retinal Nerve Fiber Layer (RNFL) thickness were measured with the Heidelberg OCTA. Linear regression analysis was used to study the correlation between affected ERG fit parameters and aspects of visual field sensitivity and retinal structural parameters.
Results: The mean ages were not significantly different between the diabetic patients and control subjects. The average value of the PhNR semi-saturation constant for the diabetic patients and control subjects were 83.64+39.96 and 32.21+20 and the difference was statistically significant (p=0.0054). The average value of the PhNR slope for the diabetic patients and control subjects were 0.83+0.19 and 1.39+0.17 and the difference was statistically significant (p=0.0000018). PhNR Vmax was not statistically significantly different between the diabetic patients (30+7.12) and controls (30.18+6.45). The parameters of the Naka-Rushton fits to the b-wave responses were not significantly different between the two groups. A positive correlation was seen between the semi-saturation constant of the PhNR in diabetics and self-reported HbA1c% (r=0.72, m=22.8, p=0.029) and a negative correlation was observed between the semi-saturation constant of the PhNR and 10-2 mean sensitivity (r=0.67, m=-0.03, p=0.02). A positive correlation between the semi-saturation constant and SVD (r=0.66) and DVD (r=0.67) were seen in control subjects, whereas negative correlation was seen in diabetics eyes (r=0.5 and r=0.4).
Conclusion: Retinal ganglion cell sensitivity is compromised in diabetic patients with no retinopathy as indicated by an increase in the value of the full-field PhNR semi-saturation constant while responses of their input neurons, namely bipolar cells, as reflected by the b-waves is relatively normal. Compromise of retinal ganglion cell function may underlie the earliest visual sensitivity changes diabetic patients. Further longitudinal studies are warranted to determine whether changes in ganglion cell function precedes changes in superficial and deep vessel density.
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