April 29th
2010

Eye Physiology  ⁄  Accommodation and Convergence

Accommodation and convergence allow us to see objects clearly both near and far without diplopia (double vision). There is a direct relationship between the effort of accommodation and the effort of convergence. The effort of accommodation is measured in diopters, and the effort of convergence is measured in degrees. There are three main types of eye refraction: emmetropia (normal-sightedness), myopia (nearsightedness), and hyperopia (farsightedness). Emmetropia is the normal condition of perfect vision, in which parallel light rays are focused on the retina without the need for accommodation. When an emmetropic person is looking at a distant object, accommodation and convergence are resting. The axes of the eyes are parallel, and there is no effort of convergence (the angle of intersection is zero degrees). When the emmetropic (normal sighted) person is looking at a nearby object, some effort of accommodation and convergence is necessary.


accommodation-convergence

When the emmetropic person is looking at the distance of one meter, the effort of accommodation is 1.00 diopter, and the angle of convergence is about 4 degrees (if the distance between the pupils is 65 millimeters). At the distance of 0.5 meters, the effort of accommodation is 2.00 diopters with convergence of about 7 degrees. At a distance of 0.33 meters, the effort of accommodation is 3.00 diopters, and the convergence is 11 degrees. The picture below (Fig. 1, emmetropia) shows the relationship between the effort of accommodation and the angle of convergence.

In the next example, a myopic person with refraction -2.00 diopters is looking at an object at the distance of 0.33 meters. The effort of accommodation is only 1.00 diopters, and the angle of convergence is the same, 11 degrees. In this case, the relationship between accommodation and convergence is broken. Convergence corresponds to a small 1.00 diopter accommodation, and the visual axes try to intersect at a distance of one meter. This disparity is the cause of exophoria, a tendency of the eyes to deviate outward (Fig. 2, myopia 2.00 diopters, right eye is leading).

One more example: a hyperopic person with refraction +2.00 diopters is looking at an object at a distance of 0.33 meters. The effort of accommodation is 5.00 diopters, and the angle of convergence is the same 11 degrees; here too the relationship between accommodation and convergence is broken. But in this case, the convergence corresponds to a large 5.00 diopter accommodation, and the visual axes try to intersect at a distance of 0.2 meters. This disparity is the cause of esophoria, a tendency of the eyes to deviate inward (Fig. 3, hyperopia 2.00 diopters, right eye is leading).

accommodation-convergence-exophoria-esophoria

The elementary way to rebuild the normal relationship between accommodation and convergence is by correcting refraction using negative lenses in the case of myopia and positive ones for hyperopia. But there is another way: the development of volitional vergence with foveolar fixation restores visual acuity for better vision. I call it visual purism, the philosophy of natural perfect vision without any means of correction like eyeglasses, contact lenses, or refractive surgery. Want to be a visual purist? Then you should try some eye exercises using the dynamic fixation trainer.

People often see what they want to see or expect to see.

Dr. Arkadiy Davydov

13 Responses

  1. mat:

    05.05.2010 at 23:07 #

    Dear Doc,
    thanx for the new data.
    Have you made a dynamic fixation trainer?

  2. barraq:

    04.08.2010 at 12:29 #

    Q1/ why the light rays that coming from the far object are parallel while from near object are divergent .
    Q2/ at which distance of object in which the light rays that coming from it becomes convergent

  3. Doc:

    17.08.2010 at 13:45 #

    barraq,
    A1/ it’s just geometry. Light rays from a far object also diverge, but the divergence angle is negligible, so we can talk about parallel rays.
    A2/ light rays are always diverge, but converge after passing through a convex lens.

  4. Doc:

    17.08.2010 at 13:53 #

    Dear mat, I have partly made the dynamic fixation trainer.

  5. Henry:

    16.03.2011 at 23:51 #

    Having developed post traumatic enopthalmos, and diplopia in upgaze and far left gaze, and an orbital blowout fracture with possible nerve palsy and lateral rectus weakening, can you tell me please, will these exercises, and others like this strengthen my injured eye muscles, and help to return my vision to normal? Before this, I had perfect vision and was planning on pilot training.
    Hope you can help me,

    Thank You

    Henry Brenton

  6. Doc:

    20.04.2011 at 14:15 #

    Henry, unfortunately I can’t help you. The Dynamic Fixation Method helps to develop right visual skills in case of normal eye anatomy, not post-traumatic visual impairments.

  7. Karin:

    27.04.2011 at 15:14 #

    When fixing on the black circle, should the entire circle be shaded. I often see a smaller shaded circle within the black circle, like a grey pool ball bouncing off the sides. When fixing I go from grey on the outside to small grey ball inside, It moves a lot too.

  8. Doc:

    29.04.2011 at 22:05 #

    Karin, this exercise is for understanding and feeling of eye movements. Ideally the smaller ball within the black circle tends to a point. This is the point of intersection of visual axes. You shouldn’t follow the movements of your eyes. On the contrary, you should try to take control of eye movements. For example, you can stop your eyesight on the edge of the black circle for few seconds and then move it to the other side of the black circle. It seems like you draw some geometric chords in the circle and the eyesight moves in the circle like pool ball on the pool table.

  9. Karin:

    25.05.2011 at 23:38 #

    Thank you.
    You are describing exactly what I saw: pool ball bouncing off the inside edge. Lighting in the house is not good so I used this idea on my walks and was able to see the STOP in a stop sign from a block away, I aimed at the sign with my walking stick with both eyes open, not squinting, and looked beyond the end of the stick. Now I can see the sign without the stick . In the four weeks I have been consistently exercising my eyes I am better able see street signs, leaf detail, birds on wires, squirrels. Bits and pieces of clear. Today I had 30 seconds of “clear vision”. I don’t have a blur rather I see a double image and have to focus my eyes to remove the double image.

    Can you suggest how I stop drawing “geometric chords”. Not sure what those are.

    Again thank you so much.

  10. Doc:

    27.05.2011 at 22:18 #

    Karin, my congratulations!
    The 30 seconds flash of clear vision after the four weeks of training is an excellent result. Generally, flashes of clear vision are my favourites.

    To avoid double vision, don’t move your sight outside the limit of the foveolar field. The area of foveolar vision is about the size of a thumbnail at arm’s length.
    About “geometric chords” – never mind.
    I wish you good luck!

  11. Mat:

    20.12.2013 at 23:51 #

    Dear Doc, I am very happy to be back on you site, as I have been tasting the blesses and successes of perfect vision but I am not there yet.
    First thing I got when I googled “forbestvision” is this elementary (and superlative) part about accomodation and convergence.
    Then I read an answer you gave to a certain Henry with pilot aspirations: “Henry, unfortunately I can’t help you. The Dynamic Fixation Method helps to develop right visual skills in case of normal eye anatomy, not post-traumatic visual impairments” (20.04.2011 at 14:15).
    With all due respect, when I read the answer, on the one hand I am glad to be an easier case, but on the other hand I feel sad that you didn’t tell him what I tried to tell you once, that any post-traumatic injury can be handled with Dianetics, sothat you CAN help him.
    The DVD I wanted to mail you back then as a token of appreciation for what you did for me so far, has been collecting dust on my shelf. As one can lend it from the library here in Copenhagen, I suppose you will be able to lend it from a library too. The latest edition is 4 hrs long and explains in great audio-visual detail what happens during an injury and how to use dianetic procedure to repair damage to any parts of our anatomy.
    We musn’t let people like Henry down, or any other people for that matter.
    Maybe he was a free bird who wanted to learn to fly again. Maybe one day he would have made a crucial difference in your life and in mine.
    So watch the new Dianetics DVD.
    Respectfully,
    Mat Finch, MA

  12. marc:

    23.03.2014 at 17:01 #

    The article says that myopic eyes have tendency to deviate outward.(“this disparity is the cause of exophoria, a tendency of the eyes to deviate outward (Fig. 2, myopia 2.00 diopters, right eye is leading”). But in other article you recommend fusion in divergence exercises for myopes. Why is it so? should not it be opposite? Because as far as i understand fusion in divergence should make eyes move more outward? am i right? thanks

  13. Doc:

    23.03.2014 at 22:14 #

    marc, I recommend the fusion in divergense to avoid a diplopia as a consequence of exophoria. The stable fusion is a base for binocular vision. Also keeping fusion in divergence improves the central vision too.

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