stereoscope near far
Stereoscope Near-Far is part 2 of the “trick” Robert A. Kraskin, OD (Bob) worked through with his patients who wanted to function more symmetrically. It enabled those who demonstrated asymmetrical use of the self to go down a new path; helping them discover more symmetrical control and use of themselves. Stereoscope Near-Far relates to several other activities both horizontally and vertically in the Opsis Protocol.
The key element here is that the stereoscope is simply used to set the stage for the observations of what happens as the person alters the relationship between the relative alignment of the their two visual channels as projected out into space. Kraskin understood fundamentally that we do not do VT to a patient, but we arrange conditions to allow the patient to make changes. Sue Barry (Stereo Sue) echoed this throughout her book “Fixing My Gaze” and in any talk she gives about how she recovered her vision. We the optometrists and vision therapists need to stop doing the movements of the targets during the VT. Putting the patient in the driver’s seat, so that they learn how to control their visual system is the key of our VT.
Many other methods use devices which simply place targets at the right place and hope that by achieving overlap of some parts of images, in a passive way, that the person will build their binocularity. Active movements, which reflect the changes the patient is making by moving in space, provide the patient with essential feedback helping them discover their control. The stereoscope is simply used to separate what each of the two channels is viewing. The fact that the objects are clearly fixed in position in space and that any changes in their relative position are indeed because of changes the person is moving, raises the probability that the patient sees themselves as the controller.
This is the basic set up of the stereoscope. The +5.00 Diopter sphere lenses collapse space to include optical infinity in the 20 cm physical Z-axis depth. The septum in the middle blocks each eye from seeing the target in front of the other eye/channel.
Left eye view is only of the red backlit shape. The septum to the right blocks the view of the pencil, which is in front of the right eye.
Right eye view. Septum is to the left and blocks the view of the red backlit shape.
We have the patient look into the stereoscope and tell us what they see. Prior to getting to this step it is critical that the patient have developed and can demonstrate the ability to converge at will, regardless of their relative starting position of the visual axes. The “power on” side of the movement is the ability to converge and then they “let-go” of the convergence to allow the eyes to move outwards or to diverge. Brief periods of power on followed by extended periods of let-go in free space are fundamental to benefitting maximally from this activity. Eye Control is the major pre-requisite activity for this.
It is important that the targets used here are just two different things. We are not looking to align or “fuse” anything. We want simultaneous perception of both targets being seen in relation to each other. Here the red filter is in front of the left eye. It is brighter and takes up more visual space than the mechanical pencil being held in front of the right eye. With some patients, it might be better to have the red filter in front of the right eye. Over time you will get a good sense of the starting position for your patients. Experiment with the filter going on the right or left side with a good number of patients.
Here is a closeup of one potential combined view, with the red filter being seen by the left eye/channel and the mechanical pencil being seen by the right eye/channel. The goal is not to have them in a particular alignment, but to see both at the same time in close proximity or overlapping like this, when looking easily, in the “let-go” manner.
NOTE: The mechanical pencil had to be repositioned to get this picture and for optimal comparison it should have been placed vertically and rotated so that the printing on the pencil is in the same position as the pencil shown in the picture to the left.
The key point here is that the picture is showing what the person would see in a highly converged or “power-on” position of the eye. The more convergence the person makes the more the two objects should appear to move apart from each other with the object on the left moving to the left and the object on the right moving to the right.
“Let-go” and they come back towards each other and maybe even cross through each other to a different starting point than seen in the picture to the left.
The goal: conscious control of moving the images relative to each other. The stereoscope simply allows the person to see the consequence of their actions.
CLINICAL PEARL: Some people may even observe size changes in the targets as they go to the power on and to the let-go positions. See if you see these changes, which at first people describe as subtle, but over time, they see them more and more easily.