Why 20/20 isn’t perfect-What is visual acuity?

Courtesy of riekhavoc (caughtup?) on Flickr

Courtesy of riekhavoc (caughtup?) on Flickr

Measuring normal vision

When patients come to see me, I need to have a way to compare how they see in relation to someone with normal vision.  So, like most eye doctors, I use a number system called Snellen visual acuity.  This measure of the clarity of vision uses black letters on a white background.  If you have ever had an eye examination, it is when the doctor asks you to read the letters on the chart that starts with a big “E”.  The letters are called optotypes and they have a very specific design that takes into account the size of the lines and the space between them.  While there are other types of visual acuity measurements, this is the most common.

20/20 isn’t perfect

The measure most people want to achieve with Snellen visual acuity is 20/20 vision.  While 20/20 is pretty darn good vision, in reality, 20/20 is not exceptional vision so much as it is more like the lowest possible visual acuity a person can have and be considered normal.  In fact, many people have the potential to see somewhere between 20/16 and 20/12 which means that they see even better than 20/20!

Paul B. (Halifax)

Paul B. (Halifax)

What do the numbers mean?

People also ask me to explain what the numbers mean.  As an example, take a person with 20/40 vision.  A person with 20/40 is at a disadvantage compared to a person with normal, 20/20 vision.  In fact, a person with 20/40 vision would have to stand 20 feet away from something that a person with normal vision can stand 40 feet away from and still see.

A number of factors like eye disease, the eye’s length and curvature, and the quality of connection between the eye and the processing centers in the brain come together to determine visual acuity.  Some factors, like nearsightedness, come with easy solutions like glasses.  Others, like macular degeneration, are much more complex and simple solutions like glasses only offer minimal improvement.  If a patient has very poor visual acuity, they may need magnifiers and telescopic lenses to help.

So,  the next time you go to the optometrist, give the 20/15 line a shot.  Good luck!

~David Ardaya, OD
California Optometric Association
http://eyehelp.org
http://www.coavision.org

It’s just the FACTS: Vision & Learning Go Hand in Hand

August has been recognized as the Vision & Learning month.  It would seem appropriate since many children return to school in August or shortly thereafter.  In addition to getting new clothes and supplies for our kids, this yearly routine should spur us to take our children in for a comprehensive eye and vision examination.

Vision is a highly complex and intricate process.  So, it is not surprising that reading and learning is dependent on not only having excellent 20/20 vision, but also accurate eye movement, eye focusing, eye teaming, and visual motor skills.

It’s just the plain ole fact that there is a direct correlation between vision and learning.

Courtesy of woodleywonderworks on Flickr

Courtesy of woodleywonderworks on Flickr

Did you know that…

  • “25% of students in grades K-6 have visual problems that are serious enough to impede learning.” – American Public Health Association
  • Approximately “80% of children with a learning disability have an  undiagnosed vision problem.”– Vision Council of America
  • “1 in 4 children has an undiagnosed vision problem which can interfere with learning and lead to academic and/or behavioral problems.”  – College of Optometrists in Vision Development
  • Studies show that “children who had visual perceptual and eye movement difficulties did poorly on standardized tests.” – Dr. Lynn Hellerstein, FAAO, FCOVD, Past President of COVD
  • “When vision problems go undetected, children almost invariably have  trouble reading and doing their schoolwork.  They often a display fatigue, fidgeting and frustrations in the classroom – traits that can lead to a misdiagnosis of dyslexia or other learning disabilities.” – American Optometric Association
  • A “child with a vision based learning problem has excellent verbal skills, causing parent and educators to think the child must be lazy, have ADD/ADHD, or is learning disabled.”
    – College of Optometrists in Vision Development

A cursory vision screening is just not enough to detect vision-related learning difficulties.  Early prevention of a child’s vision problem is so important for school readiness, learning and academic success.  So make it an integral part of your child’s back-to-school preparations.  Buy school supplies, outfit your child with new clothes, and most important, take your child to see a doctor of optometry for a thorough eye and vision examination.

~Judy Tong, OD, FAAO

(Special thanks to my colleagues Drs. Carmen Barnhardt, Eric Borsting, Ray Chu, and Rebekah Louie.)

Getting children ready to go back to school

Summer seems to have just started, but the new school year is only a month away. Many of us get ready for this time by making sure our kids have the right clothes, books and school supplies to start the year off right, but we forget to make sure that our kid’s eyes are working well so that learning in school is easy, comfortable, and fun!

The back to school season is a great time to schedule your child’s eye health and vision exam. Optometrists are able to make sure that not only is your child seeing as clear  as possible, but that all of their other visual skills are working properly to handle the demands of the new school year.

"Reading is Fun" Photo Courtesy of John-Morgan on Flickr

“Reading is Fun” Photo Courtesy of John-Morgan on Flickr

The following are some of the important visual skills necessary for learning in the classroom:

  • Visual acuity — The ability to see clearly at any distance. Seeing 20/20 is only one portion of all of the visual skills necessary for classroom success, but sometimes the only area that is assessed by typical “vision screenings.”
  • Eye Tracking — The ability to follow with the eyes a slow moving object such as the teacher moving around the front of the classroom and the ability for the eyes to follow along a line of print while reading without skipping or re-reading
  • Focusing Flexibility- the eyes ability to maintain focus on objects in the distance and at near as well as shift focus quickly from point to point.
  • Eye teaming — The skill needed to aim both eyes together at the same time.  This is a needed skill for lining the eyes up while reading across of page of print and also to have the very high level of depth perception needed for sports.
  • Eye-hand coordination — The skill needed to coordinate the visual system and the motor system when writing, copying, or playing sports.
  • Visual perception — The skill needed to sort, understand and remember information that is coming into the visual system.

Making sure all of these areas are working at the highest level will help ensure that your child has a successful school year.

~By Lisa Weiss, OD, FAAO