Tuesday, 7 January 2014

Cortical Visual Impairment

Definition
Cortical visual impairment (CVI) is bilateral decreased visual response due to an abnormality affecting the part of the brain responsible for sight. It is one of the most frequent causes of visual impairment in children from developed countries.

Delayed visual maturation (DVM)
DVM is similar to CVI except the visual disorder/symptoms improve and resolve by the age of one year.

Normal vision
The eyes take a picture of an object. That message is sent to the brain by way of the optic nerves. The brain recognizes the image and integrates it with other sensory messages (auditory or hearing, proprioceptive or sensing where the object is in relation to the body, etc). The brain then responds to the sensory input by sending a motor response to the appropriate part of the body.




Vision in CVI
The eye structure in CVI is usually normal. The eye takes a normal picture of the object and sends the message to the brain. The message is not properly processed or integrated because of the abnormal brain function. Many children with CVI have difficulty visually “latching on” to an object and also filtering out peripheral visual stimuli to isolate the object.

Cause
CVI can be caused by any process that damages the brain. Examples include: stroke, decreased blood supply, decreased oxygenation, brain malformation or infection, hydrocephalus (increased pressure in the brain), seizure, metabolic disease, head trauma and other neurologic disorders.
  
Visual characteristics associated with CVI

• Variable level of vision loss, often demonstrating fluctuations over time
• Poor attention to visual stimuli, particularly complex visual stimuli
• Delay in response to visual stimuli
• Improved visual function in familiar settings with familiar objects
• Preference for looking at lights
• Preference for viewing objects at close range and odd angles
• Better vision when viewing moving objects than stationary objects

Treatment
Treatment of any underlying neurologic disease is essential and should be organized by the primary care physician. It is also important to start early intervention to help stimulate visual development. The appropriate state or local agency should be contacted for available services. It is difficult initially to predict future visual function. Vision improvement may be seen in some children.


Helpful Stimulus for the Children with CVI

• Large, high contrast, lighted, reflective and moving objects; e.g. mobiles
• Touch or sound to attract child’s attention
• Visual materials presented in a simple uncluttered manner with increasing complexity as            tolerated
• Presentation of visual material from different directions/angles
• Variable level of light in environment (some children do better with a lighted toy in dim room        initially)
• Extra time for responses to visual stimuli
• Avoidance of over stimulation
• Avoidance of visual tasks when child is hungry, tired, frustrated, etc.


Importance of Eye Examination in Children with CVI
Some children with CVI have other associated visual disorders such as structural eye disease, misaligned eyes, or a significant refractive error.  A Pediatric Ophthalmologist can evaluate the eyes to see if they are healthy, or if there is an abnormality in the eye that is contributing to the visual issues.  Treating these associated conditions may include glasses or eye muscle surgery and can help maximize visual function.


 

Courtesy: aamerniazi.blogspot.com