Biomedical Engineering Reference
In-Depth Information
1.1.3
Binocular and Stereoscopic Vision
One of the most important functions of the human visual system is binocular vision.
This enables us space perception and orientation.
The development of human binocular vision has two phases. In the first phase, it
is the development of monocular vision. After birth components of the child's vision
system mature. A newborn is capable of short-term monocular fixation, the squint
in the other eye is physiological (strabismus spurius). Fixation becomes active from
the beginning of the 2nd month, the child observes persons and moving objects.
However, tracking movements aren't continual. The immaturity of brain centres
causes low visual acuity. From the beginning of the 5th week, the child is capable of
foveolar fixation. The critical phase of visual development sensitivity occurs in the
2nd and 3rd months. Visual acuity rapidly improves. Any pathological states in this
period could affect visual development and lead to a disorder of the brain's vision
centre and the development of amblyopia. There is a second phase after achieving
a sufficient state of monocular vision. The afferent visual pathway connects to
binocular cortical cells sensitive to stimulation of both eyes and to monocular
cells sensitive to stimulation of one of the eyes. Binocular cortical cells are
present in a newborn. The utilization of these cells depends on the anatomical and
physiological condition of the eyes as well as on retinal stimulation and the parallel
position of the eyes, which changes with age. Binocular vision progresses along
with the development of optomotorical coordination. Visual development becomes
pathological when any disturbance during normal development occurs. The visual
centre is suppressed and amblyopia, strabismus, anomal retinal correspondence or
alternating vision could evolve.
The development of normal visual development can be arrested by:
1. Optical obstruction - refractive disorder, cataract, unsuitable optical correction,
eye occlusion
2. Neural obstruction - retinal or visual pathway disorders
3. Congenital deviation - skull, orbit or a tumour
4. CNS disorder - during brain dysfunction
Single binocular vision conditions:
-
Motor
1. Free eye movements in all directions
2. Normal function of motor pathways and coordination centres for accommo-
dation and convergence
3. Parallel eye position for distance vision
-Sensory
1. Normal vision of both eyes
2. Foveal fixation of both eyes
3. Approximately identical size of retinal images
4. Normal retinal correspondence
5. Regular binocular reflexes
