Despite its prevalence, cortical visual impairment is often misunderstood and under diagnosed. So what is CVI and what should you do if you suspect a family member has cortical visual impairment?
Our Residency-Trained Pediatric Optometrist frequently sees patients with significant birth and developmental histories. These individuals, many of which have special needs, require a support team. We have noticed that these individuals often are thrust into an educational setting and various therapies without an understanding of how they use their vision. The family may have taken the child in for an eye exam, glasses may have been prescribed, but they have little understanding of how their child uses their vision. We often hear that the last eye exam revealed that the child's eyes are healthy, however they do not see 20/20. The doctor may not have given any further explanation as to why the vision is decreased and they may have not referred you to a Residency-Trained Pediatric Optometrist for further testing. In cases where cortical visual impairment is the cause of the decreased vision, a Specialized Vision Assessment with a Residency-Trained Pediatric Optometrist is needed to identify visual strengths and weaknesses. The unique way in which the person uses their vision can then be communicated to parents, educators and therapists so that they understand how to work with the child. Imagine how much more your child will get out of school and therapy if they can actually SEE what they are doing.
Cortical visual impairment is a decrease in vision secondary to damage to the visual pathway in the brain. Interestingly there is no ocular damage (damage to the eye itself) – this is why individuals with cortical visual impairment are told that their eyes are healthy even though they fail to see 20/20. Like many conditions, CVI is not the same for every patient. The condition has several causes and affects people in different ways – which is why a functional vision assessment with a Residency-Trained Pediatric Optometrist is needed to evaluate the person's visual strengths and weaknesses.
Cortical visual impairment used to be called cortical blindness. The term blindness is misleading because people with CVI are still able to use their vision; but in an altered way. CVI has a variety of symptoms. The most well known symptom is decreased vision. Certain visual targets can also be more challenging for these individuals. A full Snellen (letter) chart will be more difficult than a single symbol to assess vision because of a crowding phenomenon (they get confused when there is too much to look at). Other people may have a harder time viewing a stationary target and will have improved vision if moving or if they are moving (which can result in rocking).
Individuals with CVI may also have certain color preferences and be visually drawn to those colors (think of it as an extreme version of having a favorite color). As mentioned before, individuals with cortical visual impairment manifest different symptoms. In some cases, one person may have the exact opposite symptom as another. For example, some individuals enjoy light-gazing, while other individuals shy away from visual stimuli. This means that one person may be drawn to a busy visual environment while another will be drawn to a quiet visual environment.
These are just some of the symptoms that individuals with CVI demonstrate; the list is too long to name them all. It is also important to keep in mind that every day can be different for individuals with cortical visual impairment; they can have good visual days and bad visual days.
So what are the causes of CVI?
As mentioned before CVI is damage to the visual pathway. Fun fact, 40% of the brain is involved in the visual process. The most common cause of CVI is from an ischemic event in-utero. An ischemic event is lack of oxygen for a period of time. CVI can occur in-utero, during birth, or after birth. CVI can occur into adulthood. Besides an ischemic event a CVI can be caused from trauma, infection, or developmental malformations. A large percentage of individuals with cerebral palsy have CVI, which makes it difficult for them to access visual information.
So what can be done for these individuals?
The first place to start is a comprehensive eye examination with a pediatric eye care professional; either a Residency-Trained Pediatric Optometrist or a Pediatric Ophthalmologist. This dilated eye examination will evaluate the individual's ocular health to determine if the decreased vision is secondary to ocular disease. It will also determine if spectacles are indicated for visual improvement. Just because an individual has decreased vision secondary to CVI, or may have special needs, it does not mean they wouldn't benefit from an appropriate pair of glasses – so always start here. Following a comprehensive examination by a pediatric optometrist or pediatric ophthalmologist, a Specialized Vision Assessment with a Residency-Trained Pediatric Optometrist is indicated. A Specialized Vision Assessment will look further at the individual's visual skills to determine their visual strengths and weaknesses. Visual modifications can be prescribed to allow visual tasks to be easier. These modifications can be useful to educators, therapists, families, and other health providers.