eYe to eYe

Most people associate migraines only with headaches.  But there is a visual component to migraines that may occur alone or can be followed by a headache.

The visual aura or ocular prodrome is described as swirling, pulsating lights, “heat-waves”, or geometric patterns (e.g. zigzag lines) in one’s vision that can last for 5 – 50 minutes.  In a classical migraine, these lights are followed by a severe headache.  In an ocular or visual migraine, there is little or no headache.  Often persons who experience an ocular migraine have never suffered from a classical migraine.

 Migraines can be triggered by anything from sunlight to stress, including eating certain foods.  When you experience the visual aura there are a few simple steps to take to lessen the duration of the visual disturbances and/or avoid a terrible headache that could last for days…

• Find a quiet dark room.
• Position a warm compress across your forehead and covering your eyes.
• Remain there uninterrupted for 15-30 minutes or until your symptoms subside.

 Keeping a diary of your episodes may help you determine your “trigger”.   Once you know what triggers a migraine attack, you will be able to avoid it.

“Flashing lights” in your vision may also be caused by a retinal problem.  Call our office immediately with any visual disturbance that persists more than 60 minutes to rule out a retinal problem such as a tear or detachment.

If your migraine headaches persist or continue to worsen, see your primary care physician for treatment options.

The Urban Dictionary defines “overrated” as anything that is given too much credit and hype.   Things in this category that come to mind for me are the Yankees, Twitter, and cranberry sauce.

Another thing that can be overrated is seeing 20/20 on a vision screening.  The key context here is on a vision screening.  Visual acuity is only one of many tests that are conducted as part of a comprehensive eye examination.  Too often I hear parents say “my child read 20/20 on the eyechart at school so she doesn’t need an eye exam.”   While the ability to see clearly in the distance is important, it does not give any indication of how well the eyes focus up close, or work together. It also does not give any information about the health of the eyes.

The American Optometric Association states the following concerning vision screenings ….

There is often misunderstanding about what passing a vision screening means. The information obtained from a vision screening can be compared to the information obtained from a blood pressure measurement. Because your blood pressure may be in normal range, it cannot indicate that you do not have other health problems. It provides a single measure of one aspect of your overall health. Just like a complete physical is needed to evaluate total health, only a comprehensive eye and vision examination can evaluate your overall eye health and vision status.

There are many eye doctors who believe that vision screenings can do more harm than good because they can lead to a false sense of security.   A  person can have 20/20 vision and still have glaucoma, a retinal tear, macular drusen, a melanoma in the eye, diabetic retinopathy and a whole slew of other eye diseases.

This eye can see 20/20 and could pass a vision screening even though it has severe bleeding from diabetes.

Please don’t “over-rate” seeing 20/20 on a vision screening.   Vision screenings should never substitute for a comprehensive eye examination.

Most people know that 20/20 vision means good vision.  20/20, however, does not mean “perfect” vision… it means “standard” vision.

In my last post we learned that Herman Snellen defined standard vision as the ability to correctly read a line of optotype characters when they subtend 5 minutes of arc and are separated by 1 minute of arc.  OK, that sounds very scientific but what does it really mean?  It refers to the size of the letters (specifically “optotypes” which can also be numbers, pictures, etc.) that are large enough to take up 5 minutes of arc (think of the distance between numbers on the clock) and have a separation between their parts (like the gaps in an “E”) which are 1 minute of arc (think of the hash marks between the numbers of a clock).

5 minutes of arc refers to the angle from the top to the bottom of an optotype.

A practical (real-life) way to think of 20/20 is that if you see 20/20 it means that you can see at 20 feet away what the “normal” or “standard” person can see 20 feet away.  If you see 20/40, you have to be at 20 feet to see what that “normal” guy can see at 40 feet away and if you are 20/15 (better than 20/20), you can see something from 20 feet away that Joe Average needs to be at 15 feet to see.  This is why 20/20 does not mean “perfect” vision…because some people can see better than 20/20.  Baseball legend Ted Williams  had 20/10 vision and birds of prey are believed to have better than 20/5 vision (but it’s hard to get them to read the eyechart).

So why do we say 20/20?  The first (or top) number refers to our testing distance.  The standard testing distance in the United States is 20 feet.  Since most exam rooms are not 20 feet long, mirrors are often used in optometric offices in order to attain “20 optical feet.”   If we test vision with only a 10 foot distance, the top number should be written as a “10″.  The bottom number refers to the size of the letter relative to the minutes of arc concept.   10/10 is the same as 20/20.  In Europe, 6 meters is used for testing and standard vision is written as 6/6.

Another misconception about “20/20″ is that one “20″ is for the right eye and the other “20″ is for the left eye.  This is not correct.  Each eye has its own acuity level.   For example, I will record a person’s visual acuity as 20/20 right eye; 20/20 left eye; and 20/20 with both eyes.

Next post….”Why 20/20 is overrated”.