Other potential adaptations to improve visual function in higher environmental complexity may include strategies like clearing away excess clutter from a work spaces, or providing a plain background to view objects against, reducing noise levels, or other methods of monitoring and adapting for environmental complexity. One eye may perform significantly worse than the other, and depth perception can be very limited (although not necessarily zero). The field of view may be severely limited. The best vision might be in the centre (like tunnel vision) but more often it is at some other point, and it is difficult to tell what the person is really looking at. Note that if the person also has a common ocular visual impairment such as nystagmus then this can also affect which part(s) of the visual field are best. (Sometimes there exists a certain gaze direction which minimises the nystagmus, called a "null point.") Even though the field of view may be very narrow indeed, it is often possible for the person to detect and track movement. Movement is handled by the V5 part of the visual cortex, which may have escaped the damage. Sometimes a moving object can be seen better than a stationary one; at other times the person can sense movement but cannot identify what is moving. (This can be annoying if the movement is prolonged, and to escape the annoyance the person may have to either gaze right at the movement or else obscure it.)
Cortical visual impairment (CVI) is a form of visual impairment that is caused by a brain problem rather than an eye problem. (The latter is sometimes termed "ocular visual impairment" when discussed in contrast to cortical visual impairment.) Some people have both CVI and a form of ocular visual impairment. CVI is also sometimes known as cortical blindness, although most people with CVI are not totally blind. The term neurological visual impairment (NVI) covers both CVI and total cortical blindness. Delayed visual maturation, another form of NVI, is similar to CVI, except the childs visual difficulties resolve in a few months. Though the vision of a person with CVI may change, it rarely if ever becomes totally normal. The major causes of CVI are as follows: asphyxia, hypoxia (a lack of sufficient oxygen in the bodys blood cells), or ischemia (not enough blood supply to the brain), all of which may occur during the birth process; developmental brain defects; head injury; hydrocephalus (when the cerebrospinal fluid does not circulate properly around the brain, and collects in the head, putting pressure on the brain); a stroke involving the occipital lobe; and infections of the central nervous system, such as meningitis and encephalitis. Visual and Behavioural Characteristics
Visual and Behavioural Characteristics of CVI are individual and may include several (but not necessarily all) of the following:

The person with CVI may exhibit what at first appears to be frequent variable changes in vision.