Note: This is part of a series. You can read part one here.
In part one, we took a look at how vision differs from eyesight, the nine elements of athletic visual skill, and what visual skills are important for shooters. In this second installment we will explore ways you can go about assessing your vision with the primary goal of improving binocular vision.
Testing your vision
There are four easy screenings to asses your vision:
- Simplified binocular vision and depth perception test
- Eye dominance test
- Phoria test
- Suppression test
If upon trying these tests you think you may have a problem with your vision, you should seek out a practitioner who is experienced with vision training and therapy.
Checking your binocular vision/depth perception
To perform this test, you will use your finger (or thumb) and the green circle below.
To begin, hold your finger in front of the circle, between your eyes and the screen. Focus your eyes on the circle. You should see the circle clearly in the middle between two images of your finger. The finger(s) will appear semi-transparent and slightly blurry.
Note: Some people find this very easy to do, others have to work at it.
Next, focus on your finger. The two previous images should merge together into one finger, while the circle splits into two. Try shifting your focus between the circle and the finger a few times and note how easy or difficult it is.
If you can you see both finger images, you have binocular/stereo vision and both eyes are “switched on,” i.e. working together.
If you experience any of the following, you may have a depth perception problem:
- One finger is easier to see than the other
- One finger is larger than the other
- Fingers sometimes appear and disappear
- One finger tends to go directly over the circle while the other finger is far to the left or right.
- You can only ever see one finger
These symptoms are often caused by one eye dominance, in which case you may be able to train your other eye to pick up its share of the workload. Find a “functional optometrist,” or a Z-Health practitioner who has been through the “S-Phase” course, for more information.
If you can’t create binocular vision, you will definitely want to perform the other three tests, as a deficit in any of them could contribute to an inability to produce binocular vision.
Remember the SAID principle: Even if you have great binocular vision at rest, that doesn’t mean you have great vision at high levels of exertion! Those of you who “pass” the binocular vision test should try completing all tests both at rest and after intense exertion.
- Go where you can see an object that’s at least 10 to 20 feet away.
- Clasp your hands together, make a triangle between them a couple of inches wide, and extend your hands to arm’s length.
- Keeping both eyes open, use the triangle to visually frame the object.
- While making sure you keep the object framed, alternate closing one eye at a time.
- The object will remain in view when you use your dominant eye and disappear when using the non-dominant eye.
Basic eye anatomy
Each eye has six muscles that control its movement. Just like a hamstring, an eye muscle gets tight and weak when is not “worked” enough. An eye muscle that is chronically tight can pull the eye off target, causing you to perceive the world as closer or farther away than it actually is.
Phoria testing looks for signs of esophoria and exophoria. Esophoria refers to eye muscles that are tight and pull the eye inward (toward the nose). Exophoria refers to eye muscles that are tight and pull the eye outward (toward the temple).
To do phoria testing, you need a partner to help.
- Begin by looking at an object that is straight ahead and 10-20 feet in front of you. Keep your eyes focused on this spot during the entire test.
- Have your partner hold something flat a couple of inches in front of one of your eyes. When the eye is “covered,” the brain will stop using the eye and instead switch to paying attention to the video stream the uncovered eye is sending. This will cause the covered eye to relax more, allowing it to be pulled in the direction of muscle tightness.
- After 5-10 seconds, quickly move the cover to the other eye.
- Watch the eye that is being uncovered. Note the direction of eye movement (if any) as this will indicate the flavor of phoria (exophoria or esophoria).
If the eye moves from inward (toward nose) to centerline, this is esophoria. If the eye moves from outward to centerline, this is exophoria.
Esophoria will cause targets to appear closer than they really are whereas exophoria will cause targets to appear farther away than they really are.
To perform a suppression test, you will need to either make a Brock string or buy one. Making one is straightforward and easy. All you need is about a 10-foot length of string or twine, preferably white. You then need to get at least three colored beads—red, blue and green. Wood ones that are about 1/3″–1/2″ in diameter work fantastic, but of course you can pick one up on Amazon for under $10!
With Brock string in hand, here is what you need to do:
- Tie up one end to a stationary object that is a little above or below eye level for you.
- Hold the other end of the string and pull it tight to your nose. You’ll need to have enough room to step back far enough to pull the string tight.
- You may need to adjust the beads. Bring the first one as close to you as you can comfortably focus on and take the last one as far away as you can see clearly. The middle one can go in the middle for now.
- When holding the Brock string to the center of your nose (make sure you don’t have the string offset a little to the right or left), stare at the center of the first bead like the photo below.
- When focusing on the center of the bead, the hole where the string passes through, you should see two sets of strings — one coming from the left and one from the right. Both strings should look like they cross inside the bead. Exiting the bead, it should look like a string going from center to the left and another from center toward the right, like an X (see photo below).
- Once you can focus on it clearly, jump to the next bead and regain your focus until you see the X as described in step five.
- Note: The last bead may look more like two strings coming into the bead and one string coming out the back. That may be normal around the 10-foot mark and isn’t a concern.
- If you consistently see two strings going in and two coming out, then you are creating binocular vision and do not have any suppression.
- If one string is missing, or it is almost transparent or fading in and out, then the vision from the eye on that side is being suppressed or ignored by the brain.
- If the string you are able to see intermittently switches from left to right, then you may have Intermittent Central Vision Suppression (ICS).
- If the strings cross before or after the bead, you can try touching a point on the string that is behind the bead and in front of the bead to see if that clears.
- If you see two sets of beads and strings, you will want to have your eyes checked by a qualified professional such as a functional optometrist or functional neurologist.
Remember the SAID principle? You always get better at exactly what you do. Don’t forget to try some of the screenings for binocular vision in your most used shooting positions. Just because it tests fine in a static seated or standing position doesn’t mean it will be the same in your shooting positions and vice versa.
In part three of this series, we will examine some exercises you can use to enhance your gaze stabilization and some possible ways to integrate that into your shooting practice.
Technical Contribution: Troy Dodson of Brain Based Fitness Rx
(Images courtesy of: mediacollege.com, visionhelp.wordpress.com, oculist.net, anatomybodypics.net, weeatplants.com, nationalguardsf.com)
Asbury, T. & Frederick, D. R. (2002). Strabismus, General Ophthalmology. McGraw-Hill. Retrieved from http://www.oculist.net/others/ebook/generalophthal/server-java/arknoid/amed/vaughan/co_chapters/ch012/ch012_print_01.html
Depth Perception Test. (n.d.). MediaCollege.com. Retrieved from http://www.mediacollege.com/3d/depth-perception/test.html
Kirscher, D. W. (1992). Sports vision training procedures. Optometry clinics: the official publication of the Prentice Society, 3(1), 171-182.