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Research Connecting Blood Sugar Level with Organ DamageRewrote retinopathy section as follows:
Diabetic Retinopathy Develops at "Prediabetic" Blood Sugar LevelsThe first conclusive evidence for this finding was reported based on Diabetes Prevention Project data at the ADA 65th Annual Scientific Sessions. It found that:
Over three years of subsequent follow-up of 302 DPP participants, 13% of prediabetics who developed type 2 disease were found to have diabetic retinopathy, and nearly 8% of "prediabetics" also were found to have diabetic retinopathy, though they never developed diabetes per diagnostic criteria.
The diagnostic criteria used by the DPP to define "prediabetic" was a fasting plasma glucose test result that ranged between 100 and 125 mg/dl (5.5-6.9 mmol/l and/or a glucose tolerance test result showing impaired glucose tolerance: glucose tolerance test values at two hours that fell between 150 and 199 mg/dl (8.3-11 mmol/l).
This finding would suggest that prolonged exposure to post-challenge blood sugars over 150 mg/dl are highly dangerous to your retina, with or without a diabetes diagnosis, but even more so with a type 2 diabetes diagnosis.
ADA Scientific Sessions: Retinopathy Found in Pre-Diabetes. Elizabeth Thompson Beckley. DOC News August 1, 2005. Volume 2 Number 8 p. 1
Even more worrisome is the meta analysis published by Tien Y. Wong, that found that "More than 60% of retinopathy cases were among patients with fasting plasma glucose levels below 7.0 mmol/L (126 mg/dL). This review of many published studies found that the three studies [with over 11,000 participants] together, 7.4% to 13.4% of participants had retinopathy at glucose levels below 5.6 mmol/L (100 mg/dL).
Relation between fasting glucose and retinopathy for diagnosis of diabetes: three population-based cross-sectional studies Wong TY, et al Lancet 2008; 371: 736-743.
That means something like one in ten people who were most likely to have only abnormalities of post-meal blood sugars, since the most common pattern of developing diabetes is for fasting blood sugars to remain near normal for years while post-meal blood sugars rise into the prediabetic and even diabetic range.
You can read more about patterns in which diabetes develops on this page on this web site: The Patterns in which Diabetes Develops
Further confirmation that diabetic retinopathy occurs at blood sugar levels well below those defined as "diabetic" by the Amerian Diabetes Association was provided by an analysis of 2005-2006 NHANES data which was published in October 2009.
This study looked at 1,066 individuals with or without diabetes aged 40 years or more. "A1C, FPG, and 45° color digital retinal images were assessed."
This study found a prevalence of retinopathy of 11% in the whole group and 36% in those with diabetes diagnoses.
Most significantly, this study found that:
The steepest increase in retinopathy prevalence occurs among individuals with A1C equal to or greater than 5.5% and FPG equal to or greater than 5.8 mmol/l [104 mg/dl]. A1C discriminates prevalence of retinopathy better than FPG.
Association of A1C and Fasting Plasma Glucose Levels With Diabetic Retinopathy Prevalence in the U.S. Population: Implications for diabetes diagnostic thresholds Yiling J. Cheng et al.
Diabetes Care November 2009 vol. 32 no. 11 2027-2032. doi: 10.2337/dc09-0440
An even larger metastudy, published in late 2010 based on he records of "44,623 participants aged 20 to 79 years with gradable retinal photographs" examined the correlations between signs of retinopathy and the subjects' fasting, 2 hour glucose tolerance test, and A1c results.
Glycemic Thresholds for Diabetes-Specific Retinopathy: Implications for Diagnostic Criteria for Diabetes:The DETECT-2 Collaboration Writing group. Stephen Colagiuri et al.
Diabetes Care Published online before print October 26, 2010, doi: 10.2337/dc10-1206
The conclusion of the 2010 study was this:
A narrow threshold range for diabetes-specific retinopathy was identified for FPG and HbA1c but not for 2-h PG. The combined analyses suggest that the current diabetes diagnostic level for FPG could be lowered to 6.5 mmol/L [117 mg/dl] and that an HbA1c of 6.5% is a suitable alternative diagnostic criterion.
This was because
glycemic thresholds for diabetes-specific retinopathy were observed over the range 6.4-6.8 mmol/L [115 - 122 mg/dl] for F[asting]P[lasma]G[lucose] 9.8-10.6 mmol/L [176.4 - 191 mg/dl] for 2-h PG, and 6.3-6.7% for HbA1c.
