I’ll take Binocular Vision for $1000, Alex. And … it’s the Daily Double! So for $2000, faithful blog reader, here is your clue: He is considered the father of modern optical science. That’s right! It is Ibn al-Haytham, known in the West as Alhazen, an 11th century polymath who authored what is considered to be the first authoritative treatise on Optics. You’re viewing here the frontispiece of Optical Thesaurus, incorporating al-Haythem’s monumental work translated into Latin.
Isaac Newton famously remarked: “If I have seen further, it is because I stand on the shoulders of giants”. Ibn al-Haytham was one of those giants, celebrated as a centerpiece of the International Year of Light in 2015.
I had read of al-Haythem’s work before, but never in as elaborate an historical context as in a new book by the science historian Dominique Raynaud, Studies on Binocular Vision: Optics, Vision and Perspective from the Thirteenth to the Seventeenth Centuries. Raynaud traces al-Haytham’s experiments in refraction and binocular vision in graphic detail.
As Raynaud reviews in Chapter 5, al-Haytham also differentiated between heteronymous or crossed diplopia, and homonymous or uncrossed diplopia. That’s a very powerful fact that we use in vision therapy a number of ways not only in figuring out visual projection diagnostically, but in vision therapy as well regarding physiological diplopia. Aside from giving the patient feedback about where her eyes are postured in space, it’s also a fun way of keeping kids’ attentive to and honest about what they’re seeing! Let’s take for example using the TBI bulbs along the z-axis, like an electronic Brock String.
Visualize that you’re having the patient looking at the bulbs through anaglyphic glasses with the red filter over the right eye. If the patient fixates the far or back bulb and appreciates a single lustrous color, she’s under converged or in exo posture relative to the front or near bulb. That bulb is therefore seen in crossed diplopia so the red bulb appears on the left side and the green bulb on the right side (heteronymous projection). The opposite occurs when the patient fixates and maintains fusion on the near bulb. She is then insufficiently diverged or in eso posture relative to the far bulb, which is now seen in uncrossed diplopia so the red bulb appears on the right side and the green on the left side (homonymous projection).
In Chapter 6, Raynaud credits al-Haytham with the providing the substrate for understanding binocular correspondence between the two eyes, as well the basis through which Panum was able to derive the concept of fusional areas of space. Ibn al-Haytham certainly was a giant on whose broad shoulders we all stand today.