Diabetes and the Eye

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Diabetes is a disease that has grown and spread exponentially in the last 20 years, reaching epidemic proportions. Yet, many people do not know how devastating it can be and the effects it can have on the eye.

Background:

There are 2 main types of diabetes:

• Type 1 (Insulin dependent):
• Early onset (usually by teenage years)
• Autoimmune disease - the body attacks itself and causes destruction of the cells that make insulin
• Insulin is the chemical which promotes uptake of sugars from the blood into muscle and other tissues
• Treated with insulin replacement
• Can lead to death if not treated

• Type 2 (Non-insulin dependent):
• Later onset (usually over the age of 40)
• Body tissues develop resistance to insulin
• Very commonly associated with sedentary lifestyle, high fat diets, and obesity (No surprise its huge in North America!)
• Treatment:
• Early/mild: weight loss, diet changes, and exercise
• Moderate: All of the above plus oral meds that encourage glucose uptake
• Severe: All of the above plus insulin
• Significantly increases risk of heart attack, stroke, and kidney failure

The end result for both, if not well controlled, is high sugar (glucose) levels in the blood stream.

Normal blood sugar levels:

• Healthy patients should have glucose levels of approx 4 mM
• Diabetic patients are instructed to try to maintain them below 6 mM
• Uncontrolled diabetics often have glucose levels of 15-20 mM (if not higher)
  

The Eye:
While high sugar levels in the blood can affect the structure and function of cells and chemicals, the main concern in the eye is loss of integrity of the blood vessel walls.

The tiny retinal blood vessels can become leaky, thus allowing fluid, blood, and proteins to seep into the retina. If left uncontrolled, this can result in any combination of the following:

• Diabetic retinopathy:
• bleeding in the back of the eye, including leakage into the vitreous gel thus causing loss of vision
• lack of blood and oxygen delivery to areas of the retina
• death of retinal tissue - permanent loss of vision
• development of new, weaker blood vessels (neovascularization) which can cause further leaking and fibrosis of the retina
• Macular edema
  
• swelling of the macula (central part of retina) causing decrease of vision
• Retinal detachment:
• Fluid leakage behind the retina or fibrosis due to new blood vessels causing it to be pulled away
• Neovascular glaucoma:
• Due to the lack of oxygen delivery, new blood vessels begin to grow at the front of the eye and block the drainage of fluid causing increased pressure in the eye which can result in damage to the optic nerve - yet another way to cause vision loss
  

If the diabetes is adequately treated, some of the milder problems can be reversed and vision may be restored.

If you have diabetes, or know someone who does, it is very important to keep in mind the effect it can have on your eyes. Regular, annual eye exams are imperative and are no less than the standard of care of diabetic patients.

If there are any questions please feel free to ask. And as usual, please forward this information on to anyone who may find it useful.

Thanks for reading.

 

What does 20/20 mean?

This week's topic is something I get asked almost everyday. Unfortunately, the answer is never as simple as it may seem. I will do my best to explain it here.

Simple definition: 20/20 is the size of letter that the average person should be able to see when fully corrected (assuming that there are no visual opacities or retinal problems). It is what we aim to achieve when correcting patients with contact lenses, glasses, and laser surgery.

More specifically: A 20/20 letter is exactly 8.726mm in height at a distance of 20 feet.

FAQ:
Q: Does 20/20 mean "perfect vision"?
A: No, this is a common misconception. There really isn't such a thing as perfect vision. The sharpest estimated human visual acuity is about 20/8. Which, with a little math, equates to a minuscule 3.49mm letter at 20 feet!

Q: How is the size of the letter determined?
A: The letter size for 20/20 is based on the average spacing of the light-sensing cells in the retina, thus the average eye's ability to discern spaces between letters

Q: Why 20 feet?
A: That is the approximate distance at which the internal focusing system of the eye (used for near vision) is relaxed thus allowing your eyes to effectively see into the distance.

Q: What if I can't see any of the letters without my glasses? Does that mean I'm Legally Blind?
A: Vision without correction does not really provide any significant information about your eyes (other than the fact that correction may be needed).
The definition of Legal Blindness in Canada and USA is 20/200 in the better eye with correction. Thats 10 times the size of a 20/20 letter.

Q: Do I need to see 20/20 to drive?
A: No. This may come as a surprise. But, the legal requirement for driving is 20/40 in one eye. That's double the size of a 20/20.


Thanks for reading. Please feel free to pass this info on to anyone who may find it useful and don't hesitate to send me your questions and comments.