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The human eyes provide the brain with two independent, slightly different images of an object called stereo vision. This process leads to the sensation of depth enabling us to determine how close or far an object is. The differences in the two retinal images are called horizontal disparity, retinal disparity, or binocular disparity. The differences arise from the eyes' different positions in the head. Stereoscopic visualization is commonly referred to as depth perception.
A stereoscope is a device by which each eye can be presented with different images, allowing stereopsis to be stimulated with two pictures, one for each eye.
The monocular (2D) visualization, found in current MIS systems, lacks of depth perception. This significantly reduces the surgeon’s ability to determine the size and precise location of anatomical structures, thus impairing his ability to diagnose and operate efficiently.
Stereovision is illustrated in this diagram.
Stereopsis appears to be processed in the visual cortex in binocular cells having receptive fields in different horizontal positions in the two eyes. Such a cell is active only when its preferred stimulus is in the correct position in the left eye and in the correct position in the right eye, making it a disparity detector.
When a person stares at an object, the two eyes converge so that the object appears at the center of the retina in both eyes. Other objects around the main object appear shifted in relation to the main object. In the following example, whereas the main object (dolphin) remains in the center of the two images in the two eyes, the cube is shifted to the right in the left eye's image and is shifted to the left when in the right eye's image.
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The two eyes converge on the object of attention. |
The cube is shifted to the right in left eye's image. |
The cube is shifted to the left in the right eye's image. |
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We see a single, Cyclopean, image from the two eyes' images. |
The brain gives each point in the Cyclopean image a depth value, represented here by a grayscale depth map. |
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Because each eye is in a different horizontal position, each has a slightly different perspective on a scene yielding different retinal images. Normally two images are not observed, but rather a single view of the scene. Nevertheless, stereopsis is possible with double vision. This form of stereopsis was called qualitative stereopsis by Kenneth Ogle.
Monocular image can mislead
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