Archive for October, 2009

I’ve never needed glasses for reading… why now?

Monday, October 26th, 2009

By Dr. Ryan W. Nelson

 

The most common reason for reading glasses in a person who has never needed them before is a phenomenon known as presbyopia.  Presbyopia causes near vision blur when distance vision is either normal or corrected.

The cause for presbyopia is a faulty focusing system.  The focusing system of the eye is made of two major components, the “lens” and the muscle that controls it called the “cilliary body”.   The ciliary body is triggered to contract when focusing on objects at near and it directly controls the lens.  It is ultimately the lens’ flexibility which allows us to see at both distance and near automatically.  Over time, the lens becomes less flexible and is no longer able to focus light like it once could, which results in blurred vision.

In the optometry profession we say, “three things are certain: death, taxes… and presbyopia”.  Given enough time, presbyopia catches up with us all.  Most individuals will experience the early signs of presbyopia between 40 and 50 years old.  It starts when you have to hold things further away in order to see them clearly.

Near vision blur is correctable with glasses and contact lenses.  The difference is that now two prescriptions are needed: one for distance, and one for near.  Let us help you at your next eye examination.

What does 20/20 really mean?

Wednesday, October 21st, 2009

 

By Dr. Ryan W. Nelson

 Dr. Ryan Nelson

 

 

 

 

 

Quality of vision is most often measured using Snellen acuity.  The Snellen system uses standard letter sizes at a fixed distance of 20 feet to quantify an individual’s ability to see. For example, if you have 20/20 vision, at 20 feet you can see what the normal eye can also see at 20 feet.  Confusing?  You bet it is.  Here is another example.  If your vision is poorer, say 20/40, then the normal eye can see at 40 feet what you can only see at 20 feet. 

Some individuals are able to achieve better than 20/20 vision.  A visual acuity of 20/15 means that you can stand back at 20 feet and read the same sized letter that a normal person has to move 5 feet closer to see.  Impressed?  Did you know that the human eye has been measured to a resolution of 20/7!  

Most Snellen charts use various letters, but tumbling “E” and picture optotypes can help optometrists test the vision of young children more easily. Snellen acuity is not the only way to test vision either.  In fact, there are many methods; some even measure other aspects of vision, such as contrast sensitivity.

To test your eyes, schedule an appointment at our office today.

 

Iowa Eye Care Eye Chart

Iowa Eye Care Eye Chart