I’m a 48-year old woman who’s not overweight and was diagnosed with Type 2 diabetes one and a half years ago. My vision has been blurry for the past one and a half years. It’s clear in the morning if fasting readings are 90 to 100 mg/dl [5.0 to 5.6 mmol/L], but gets blurry after eating breakfast and remains so for the rest of the day. I’ve seen four ophthalmologists including retina and glaucoma specialists. They said I have mild retinopathy (no glaucoma or cataracts) and, the only way that my vision would clear up, is to keep my sugars under control.

My endocrinologist says my A1c is fine at 5.9 and my blood sugars, which are 90 to 100 mg/dl [5.0 to 5.6 mmol/L] fasting and 150 to 180 mg/dl [8.3 to 10.0 mmol/L] postprandial, are under control with 10 units of Lantus daily and Glucovance 2.5/500, twice a day. He said I could try two units of NovoLog with breakfast and dinner in addition to the Lantus and Glucovance. It’s a few weeks now since I started NovoLog and my vision is as bad as ever. I do not have anemia or any thyroid problems. What could be causing the blurriness for such a long time?

It is difficult to know what is causing your blurred vision after eating breakfast without examining your eyes, but I will suggest a few likely possibilities based on your descriptions:

Postprandial lenticular swelling – hyperglycemia can draw fluid into the eye’s internal lens, resulting in refractive fluctuations (a transient change in your optical prescription) that may be mild or severe, resulting in blurred vision; diabetics with sub-optimal glycemic control are notorious for this; if your blood glucose readings are above 150 mg/dl [8.3 mmol/L] two hours after eating, regardless of your A1c your glycemic control is sub-optimal; I think your endocrinologist’s idea of adding NovoLog at breakfast makes perfect sense but, unfortunately, this does not seem to have resolved the problem.

Diabetic macular edema – this form of retinopathy causes fluid leakage within the most critical part of the retina responsible for detail vision, the macula. If severe enough, the retina specialist would have recommended laser treatment; less severe cases do not benefit from laser, but may cause postprandial blurring; tight blood sugar control is again the remedy.

Diabetic corneal dysfunction – the clear windshield at the front of the eye, the cornea, is often affected by hyperglycemia that causes cellular damage and/or dry spots on the corneal surface that lead to blurred vision; this does not always improve with tight blood sugar control and is often under-diagnosed in diabetics, in my experience. If your visual clarity improves after blinking (or with a lot of blinking), even momentarily, this strongly suggests poor corneal optics and/or a deficiency of normal tears; if so, this will respond often to artificial tear supplements, tear duct plugs that increase corneal moisture, omega-3 fatty acid intake (salmon, sardines, flax seed or omega-3 supplements), and better blood sugar control. Ask the doctor to check you for “dry eye syndrome.”

You should ask your eye doctor to check you first thing in the morning, when things seem clear, and then again after you eat breakfast, when your vision is blurry. If your optical prescription changes from one visit to the next, the cause is most likely #1 above. Otherwise, it’s probably #3 or, less likely, #2. I would suggest bringing this e-mail with you to you next appointment. Don’t be too worried about this particular symptom – I know it’s frustrating and annoying, but it sounds as if you have ruled out any serious, vision threatening eye disease at the least. A persistent and caring eye doctor ought to be able to help you figure this out.

PC