20/20 vision

Lil' Wayne and cataracts

"You can't see me baby boy, you got them cataracts" - Lil' Wayne in Best Rapper Alive

Who said rap music is bad for you? I think its educational! Lil' Wayne may not know exactly what a cataract is, but he definitely has the right idea.

A cataract is the clouding of the lens that is inside the eye. As the lens becomes more clouded, vision becomes blurred due to light being blocked or scattered. This is the same lens that we use to focus at near objects. The same lens that stops working around the age of 45 and forces people to start wearing reading glasses (See: presbyopia in the "All Kinds of Blurry" post).

Everyone will develop cataracts at some point in their lives if they live long enough. How much and how fast depends on the individual and the environment. Medical conditions like diabetes can cause cataracts to develop faster. Sunlight is the main environmental factor. So, grab those sunglasses!

Congenital cataracts - It is possible to be born with a cataract. I recently saw a 5 year old boy who had a cataract in one eye. Another reason why kids should have regular eye exams.

Traumatic cataracts - Getting hit in the eye can cause a cataract. Wear protective lenses whenever possible!

How do you treat cataracts?

The only treatment is removal. The cloudy lens is removed and new clear plastic lens is inserted in its place. The surgery takes about 10-15 minutes per eye and requires an incision less than half a millimeter in size!

Who knows, maybe next week Kanye West will rap about Macular Degeneration... Stay posted!

 

"I spent a G on these frames, but my vision is priceless" - Lil' Wayne

 

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.