But sometimes objects aren¹t necessarily real. Let¹s look at ³The Magic Eye², those 3-D composite images that you stare at, and then.......pufffff......as if magic, a picture with depth and space appears from a flat photograph!
It¹s not magic, of course, it¹s just stereoscopic vision. Two views are able to be deciphered from the single picture because you have artificially created double vision. Normally, when you view an object at a fixed distance in front of you, bot h eyes turn in slightly (converge) so that they¹re aimed squarely on the object. The focusing system also adjusts for that distance. By holding the picture close and turning your eyes so that they are aimed at an imaginary place in front of you, you& #185;ve de-focused and un-crossed (diverged) your eyes to create a double vision view of the picture. Your brain combines the two images and decodes the not-so-random patterns into a 3-D view! So why not 3-D television and movies?? Stay tuned, it¹ s coming soon!
Depth perception is the process by which you understand the relative distances of objects in space and how they relate to each other. With binocular, stereoscopic vision, the task is simple. There is very clear spatial presentation. But along with this true 3-D view of things, our brain has learned to process visual images by comparing the relative sizes, horizontal and vertical orientations, object overlap and shadows projected within the field to further define our perceptions of the world around us. These are monocular functions: only one eye is needed.
Back to the original question: If you have the use of only one eye, you¹ve probably learned to understand spatial reality, but how you ³get it² is different than those of us with full binocular vision.
2 View a scene with great depth, for example an outdoor viewscape with trees or other large objects in the background and some smaller objects in the foreground. The far-point background should be a clear sky (some clouds floating by would be a nice touc h!) Stare out into the distant sky and view the scene with one eye covered. At first, it may appear noticeably flat but soon you¹ll begin to see some ³depth.² Now view the scene with both eyes. You will notice an immediate, significant 179;expansion of depth¹² as it may be called. This is the true binocular stereo effect kicking in.
There are a number of causes for amblyopia. These include: visual deprivation in early childhood (for example, a child born with a cataract or corneal scar), strabismus (see below), uncorrected refractive error, and neurological disorders within the eye o r in the connections to the brain. Most of these causes result from early childhood deficits. Amblyopia can develop in an adult as a result of neurological trauma, nutritional deprivation or chemical insult. The primary chemical insults are nicotine ( 9;tobacco amblyopia²) alcohol, and salicylate poisoning. There are also cases of hysterical or psychogenic vision defects.
The vision system needs to see equally and simultaneously from both eyes. If only one eye has an optical focus error, or their degree of error is significantly different, the eyes don¹t work together. The fix: eyeglasses or contact lenses. When clea r vision develops in one eye but not the other, the condition called amblyopia occurs. In amblyopia, even when the brain receives a clearly focused image, it can not process that information. In certain circumstances, amblyopia can be helped. The treatme nt consists of hyper-stimulation of the weaker eye and de-stimulation of the stronger eye. This is accomplished by patching the good eye and/or through intense training of the weaker eye and the encouragement of neurological integration. The success of th e treatment of amblyopia varies (see comments below) and is considered very rarely functionally successful if it is a long standing deficit. But then again some people do walk after being paralyzed and recover from severe neurological impairments caused b y strokes. In modern medicine, many things are possible.
Sometimes, the focus is correct but the eye muscles don¹t maintain ³ocular visual axis alignment.² One eye is turned out or turned in. This is called strabismus. The causes include: early childhood disruption of vision in one eye, congenit al defect in the length or function of one of the muscles that turn the eyes, neurological damage in the connections to the muscles or in the brain, or uncorrected large refractive errors, especially hyperopia. The last cause is called ³accommodative esotropia² and is a common and easily correctable form of strabismus. The fix for the various causes of strabismus is relative to the cause. If there is a farsighted correction, spectacle or contact lenses are indicated. If the muscle is too long or short, surgery is sometimes indicated. Exercises to strengthen weak muscles and/or facilitate neurological integration, or prism lenses to adjust the angle of the incoming image are other remedies. Sometimes these remedies are combined in a treatment pl an. Ophthalmologists are the practitioners who generally perform ³strabismus surgery.² Optometrists who specialize in developmental issues often treat the functional deficits. The success rates vary, and, as adults, some people seek a remedy sol ely for the cosmetic effect. A diagnosis and treatment plan will disclose outcome in a case by case situation, often with reasonably good certainty. As a basic statistical guideline, the earlier the problem is detected and mitigated, the better the progno sis for ³single, clear, simultaneous binocular vision.² As a ³rule of thumb,² children between age two and five are the best candidates for correction resulting in usable binocular vision. Adults desiring a cosmetic improvement are lik ely to be very pleased with the surgery.