Sunday, September 16, 2007

Preventing Vision Loss

A story from Reuters last week:

Study Finds Spinach, Eggs Ward Off Cause Of Blindness

Some excerpts:
"Two nutrients found in eggs, spinach and other leafy green vegetables offer some protection against the most common cause of blindness among the elderly, researchers said on Monday."

"Age-related macular degeneration affects 1.2 million Americans, mostly after age 65."

Macular Degeneration Vs. Diabetic Retinopathy

While macular degeneration (MD) is a scourge upon the elderly, I question whether it is the most common cause of blindness in the US. Given the large and growing number of people with diabetes in this country, I would say that diabetic retinopathy (DR) has likely surpassed MD as the most common cause of blindness, at least new cases of blindness.

If we look at how many adults in this country are thought to have diabetes:
"The total prevalence of diabetes among people aged 20 years or older, United States, 2005: 20.6 million; 9.6 percent of all people in this age group have diabetes."
- National Diabetes Statistics
And we apply a prevalence rate for blindness-causing diabetic retinopathy to that number:
"Among an estimated 10.2 million US adults 40 years and older known to have DM [in 1999-2000], the estimated crude prevalence rates for retinopathy and vision-threatening retinopathy were 40.3% and 8.2%, respectively."
- National Eye Institute: The Prevalence of Diabetic Retinopathy Among Adults in the United States
We arrive at 9.99 million (40.3% plus 8.2% of 20.6 million adults) or roughly 10 million US adults with some form of diabetic retinopathy in 2005. Even if we apply the more conservative 8.2% prevalence rate for those with advanced vision complications, we still surpass the 1.2 million afflicted with macular degeneration.

Age Group Afflicted

Where age-related macular degeneration usually occurs in an older age group (65+ years), diabetic retinopathy can and does strike a younger population.

The ADA states:
"After 20 years of diabetes, nearly all patients with type 1 diabetes and >60% of patients with type 2 diabetes have some degree of retinopathy."
- American Diabetes Association: Diabetic Retinopathy
Type 1 diabetes is usually diagnosed in people under 30, and often in young teenagers.

Type 2 diabetes can strike at any age. The average age for diagnosis has moved from the 40s and 50s in recent years towards a younger population, with diagnoses occurring in children as young as 2 years old.

Type of Vision Loss

Finally, the two conditions, MD and DR, don't result in similar forms of vision loss. In addition to blurred vision that occurs with both conditions, MD results in central vision loss; DR results in dispersed areas of vision loss.

Here's a normal view:

Here's that same view through the eyes of someone with macular degeneration:

Here's that same view through the eyes of someone with diabetic retinopathy:

You can turn your head and compensate for central vision loss. Compensation for dispersed loss is more challenging.

In sum:
  • ~1.2 million Americans have MD
  • ~10 million Americans have DR
  • MD strikes an older population
  • DR can strike anytime throughout a person's life
  • MD results in central vision loss
  • DR results in widespread vision loss,
So, if diabetic retinopathy strikes more people, at a younger age, with potentially greater repercussions if left untreated, that would say to me it's probably more important to keep blood glucose consistently under 140 mg/dl (diabetes or not), if you're concerned about your sight, than it is to make sure you're getting enough lutein and zeaxanthin.

Not that I'm panning spinach. Actually, I am panning spinach, as much as will fit, along with kale and collards. Greens do a body good!
Photo of spinach from Mahanandi, a very beautiful and inspirational Indian cooking blog.
Photos of vision loss from NIH National Eye Institute via Wikipedia.

No comments: