Mass Eye and Ear optometrist and researcher Lotfi Merabet, OD, PhD, MPH, is studying and raising awareness for cerebral visual impairment (CVI) and is helping lead a national charge to get the condition better recognized and treated.
When adults develop vision loss, it’s usually due to issues with the eye, but vision impairment in children is more often a result of problems in the brain, a condition known as cerebral or cortical visual impairment (CVI). Though CVI is the leading cause of vision impairment in children in the United States and other industrialized nations, many families struggle to have the condition diagnosed. Lotfi Merabet, OD, PhD, MPH, the Frederick and Thaddeus Jakobiec Chair in Ophthalmology at Mass Eye and Ear, is trying to change that.
Merabet was part of a group of researchers and advocates who put CVI on the National Eye Institute’s (NEI) radar in 2021, which resulted in a National Institutes of Health (NIH)-sponsored CVI Workshop in November 2023. The workshop, which Merabet co-chaired, brought together experts including ophthalmologists, optometrists, pediatricians, neurologists, teachers for the visually impaired, occupational therapists, and people with CVI and their caregivers. Together, they worked to develop an official definition of CVI, which was published recently in Ophthalmology, and laid plans to develop a national CVI registry and research resource.
In this Q&A, Merabet describes the challenges faced by people with CVI and discusses his research and efforts to bring the condition to light.
What causes CVI, and how does it impact people’s lives?
CVI is a brain-based visual impairment thought to result from complications during birth or early in development. When you think of the visual system, generally people tend to focus on the eye, but the eye is connected to the brain and they have to work together. An analogy I like to use is to think of your visual system as a digital camera. The camera lens is like the eye—it controls how much light goes in and where to focus—but it’s the camera body that analyzes the information that comes in. With CVI, there is something wrong with the camera body, but not necessarily with the lens, so the information is coming in, but the brain is not able to process it and create an image of the surrounding world that the person can recognize and understand.
CVI is very individualized in terms of presentation. Some kids tell us that everything looks washed out or fuzzy. Others tell us that they see very clearly, but they’re overwhelmed; everything looks like they’re in this collage of overlapping images.
What seems to be common, anecdotally and from our research, is that the visual system does fine when things are simple—like reading letters off an eye chart—but when you put that child in a crowded train station or store, their visual system doesn’t seem to have the bandwidth to process the information and make sense of the visual world around them.
Although CVI is considered a developmental condition, and some children’s symptoms improve with age, many have the condition for life.
What were the big takeaways from the NEI CVI workshop?
The first thing that this workshop has established is that CVI is a real condition, which is absolutely crucial. We now have an NEI-endorsed document that states CVI is real, and that eye doctors and healthcare providers need to recognize CVI and its criteria. Many of these children don’t qualify as visually impaired or blind because of definitions based on visual acuity and visual field, even though they’re clearly visually impaired. An important message to come out of this workshop is that someone can be visually impaired from a visual processing deficit and inability to extract information or make sense of the visual world.
The second takeaway is the importance of early diagnosis, because the earlier we recognize this condition, the earlier we can start putting various supports in place. A lot of what we’re seeing today is frustration from individuals and families who are going from doctor to doctor, trying to get a diagnosis, trying to understand what’s going on. In my mind, that’s time wasted.
What are the working group’s future plans?
The next step is to develop a diagnostic algorithm. In other words, how do we diagnose CVI given that everybody’s so different? How can we come up with a diagnostic strategy so that if someone in Washington or Florida sees the same child, they will come to the same conclusion?
Another piece is to develop a national registry. One of the current challenges is that we don’t know how many in the U.S. have CVI, and we don’t know much about how it changes as these children age. Having a registry will help us understand these things. Some estimates from the UK are actually quite astonishing—on the order of one in 30 school-aged children. That’s one child in every classroom.
How did you first get interested in studying CVI?
As an eye doctor and a neuroscientist, I’ve always been interested in vision and the brain. I initially started working with ocular blindness—profound blindness due to an eye disease—and trying to understand how the brain adapts to that. We hear that blind people hear better or have a keener sense of touch, and I was very interested in understanding the neuroplasticity and brain mechanisms that allowed that. And so I went around to various institutions, talking about this research, and invariably, there would be somebody asking, what about CVI? What about brain-based visual impairment? And I honestly had no idea what they were talking about. After a while, I said to myself, I need to learn more about this. And lo and behold, I realized that it wasn’t just a small population; it was the main cause of pediatric visual impairment. So about eight years ago, I pivoted from studying ocular-based visual impairment to brain-based visual impairment to try to address this very important public health issue.
Can you tell us more about your CVI research at Mass Eye and Ear?
There are two arms to our research. The first is brain imaging to understand how the brain’s wiring in CVI is fundamentally different from ocular-based blindness and also neurotypical development, and how the brain activates as a function of various visual tasks.
And then the second piece is developing functional assessments for CVI. Currently, when a child with CVI goes to an eye doctor, they read letters off an eye chart, and that’s pretty much it, but that’s only the tip of the iceberg as far as I’m concerned. To understand how CVI is impacting these children’s lives, we really need to get an understanding of how they use their vision in the real world.
To do that, we’re developing a series of functional assessments, using things like virtual reality and eye tracking. Virtual reality allows us to create much more realistic environments—for example, we have tasks where a child has to find a favorite toy in a toy box, and we can change the number of toys or the toys’ features to see what makes the task easier or more difficult. Eye tracking enables us to see what their eyes are looking at, what they’re not looking at, and how long they’re looking at objects, which provides us with objective assessments of how their eyes and brain are interacting with the visual world.
We really need these types of assessments to understand each child’s visual challenges, and from there, we can develop strategies and accommodations to help them in the classroom and daily activities. This individualized approach makes it obviously much harder, not just from a clinical assessment standpoint, but education and habilitation, but this is a situation where we really don’t have a choice. There is no single fix that’s going to work for everyone; we need to take each child on their own and provide strategies for them and their specific needs.
