The Effects of Diabetic Retinopathy Stage and Light Flicker on Inner Retinal Oxygen Extraction Fraction

PURPOSE: We determined the effects of light flicker and diabetic retinopathy (DR) stage on retinal vascular diameter (D), oxygen saturation (SO(2)), and inner retinal oxygen extraction fraction (OEF). METHODS: Subjects were categorized as nondiabetic control (NC, n = 42), diabetic with no clinical DR (NDR; n = 32), nonproliferative DR (NPDR; n = 42), or proliferative DR (PDR; n = 14). Our customized optical imaging system simultaneously measured arterial and venous D (D(A), D(V)) and SO(2) (SO(2A), SO(2V)) before and during light flicker. Inner retinal OEF was derived from SO(2) values. Light flicker–induced ratios of metrics (D(A)R, D(V)R, SO(2A)R, SO(2V)R, OEFR) were calculated. RESULTS: Arterial D was larger in NPDR compared to NC (P = 0.01) and PDR (P = 0.002), whereas D(V) was similar among groups (P ≥ 0.16). Light flicker increased D(A) and D(V) (P ≤ 0.004), but D(A)R and D(V)R were similar among groups (P ≥ 0.09). Arterial SO(2) was higher in all groups compared to NC (P ≤ 0.02) and higher in PDR compared to NDR and NPDR (P<0.001). Arterial SO(2) did not change with light flicker (P ≥ 0.1). Venous SO(2) was higher in NPDR and PDR compared to NC and NDR (P ≤ 0.02). Light flicker increased SO(2V) in NC, NDR, and PDR (P ≤ 0.003), and SO(2V)R was lower in NPDR compared to NC and NDR (P ≤ 0.05). Inner retinal OEF was lower in NPDR compared to NDR and PDR (P ≤ 0.02). Light flicker decreased OEF (P ≤ 0.03), but OEFR was greater in NPDR compared to NC and NDR (P ≤ 0.03). CONCLUSIONS: The findings of alterations in retinal D, SO(2), OEF, and their light flicker–induced responses at stages of DR may be useful to elucidate the pathophysiology of DR.