Authors:
Richelle Baddeliyanage
Coordinator, Retinoblastoma Champion Program
Retinoblastoma Survivor

Dr. Ben Thompson
Professor and Associate Director for Research, University of Waterloo
Adjunct Professor, McGill University
Professor, University of Auckland

Dr. Ari Chakraborty
Brain Canada Fellow, University of British Columbia
Adjunct Assistant Professor, University of Waterloo

Introduction:
Richelle interviews Ben and Ari to learn more about their monocular (one eyed) vision development research.

Research Overiew:
The goal of our retinoblastoma-related research is to understand how the removal of one eye in childhood effects subsequent development of the visual system. During the early years of life, the brain learns how to interpret information from the eyes and modifies its structure and function to optimize vision. Eye conditions in childhood that impair the ability of the two eyes to work together (binocular vision) such as the misalignment of one eye (strabismus) or unequal focusing power between the two eyes (anisometropia) can disrupt this developmental process and cause vision impairment later in life. The loss of one eye in childhood may have similar effects. Alternatively, the brain may learn to use the remaining eye normally because there are no conflicting signals from the other eye. To investigate this question we used a multimodal approach, comprising behavioral and neuroimaging experiments, to compare the visual system in children with one eye with an age-matched control group. A particular focus of our research was motion perception because previous research from York University, led by Dr. Jennifer Steeves had reported motion perception deficits in adults with a history of monocular enucleation. We investigated whether motion perception was affected earlier in development by inviting school-aged children with one eye to participate in our study. We found that all of our participants had normal clinical measures of vision (visual acuity, contrast sensitivity etc.), however our participants with one eye had a different pattern of results on our motion perception measure. Motion perception was normal when images moved from the temple towards the nose, but worse than normal when motion was from the nose towards the temple. Our neuroimaging data suggest that this difference in the development of motion perception involves a region the cerebral cortex called the middle temporal area. Our results have improved our understanding of vision in people who experience monocular enucleation in childhood. The results also help us to understand the role of binocular vision in normal visual development and provide a neural signature that may be useful to detect binocular vision problems in children with two eyes.

Question & Answer:

Richelle: Can you speak to the importance of your research and how it affects retinoblastoma patients.

Ben & Ari: Unilateral enucleation for retinoblastoma typically takes place in early childhood when visual brain areas are rapidly developing. The human brain has evolved to process information from two eyes. Therefore, unilateral enucleation has the potential to considerably alter visual system development. Our research aims to map the effect of unilateral enucleation on visual development. In particular, our studies are designed to identify whether unilateral enucleation effects vision in healthy eye of children with a history of retinoblastoma. Any effects that are detected could potentially be addressed using rehabilitation techniques such as visual perceptual learning – targeted training of specific visual functions.

Richelle: You mention that a study led by Dr. Jennifer Steeves found “motion perception deficits in adults with a history of monocular enucleation”. Did the adults also have normal motion perception when images moved from the temple towards the nose, but worse than normal motion perception when images were moved from the nose towards the temple? Did these adults have an enucleation in childhood?

Ben & Ari: The 2002 study by Dr Steeves reported a similar bias in motion perception towards nasalward motion, whereby the motion perception was better when moving dots moved towards the nose than when those dots moved towards the temple. All but one of the participants in the study had an enucleation in childhood.  Our theory is that the motion perception asymmetry occurs because of altered visual input to the brain when it is still undergoing rapid development in childhood. We predict that unilateral enucleation in adulthood would not have the same effect because the development of visual brain areas is complete.

Richelle: Your research results indicate that motion perception is challenged in children who have lost one eye early in life. Would you expect similar results in patients that didn’t have an enucleation but had very poor vision in one eye (e.g., only light perception)? Has research examined if other senses such as hearing compensate for the loss of vision?

Ben & Ari: This is a very interesting question and one that we are actively pursuing. There are a number of conditions that can cause a difference in vision between the two eyes in childhood. These include an eye turn (strabismus), a blurred image in one eye due to refractive error and childhood cataract affecting one eye. A difference in the images seen by each eye in childhood can alter the development of visual brain areas resulting in abnormal processing of information from the affected eye within the brain, a condition known as amblyopia. A number of studies have identified motion perception deficits in individuals with amblyopia, however motion asymmetry has not yet been studied. We currently have three active projects investigating this question. These projects currently focus on participants with a history of childhood cataract in one eye.

Richelle: In children who have had monocular enucleation, are there any aspects of visual function that are enhanced during development?

Ben & Ari: Although we did not observe any enhancement of vision in our study of children, previous studies have reported better visual acuities in adults with a history of childhood monocular enucleation in comparison to a control group who completed testing wearing an eye patch.

Richelle: Are there any exercises/activities that can help mitigate the effects of monocular vision? Alternately, do you imagine any advancements in the future that would mitigate motion perception deficits in monocular enucleation?

Ben & Ari: It is certainly possible that training on vision tasks using a technique called perceptual learning could improve motion perception in children with a history of monocular enucleation. The next step for us it to understand the origin of the motion perception asymmetry within the brain. We have been pursuing this question using a brain imagining technique called Magnetoencephalography (MEG). Once we understand the origin of the asymmetry, we may be able to design techniques to treat it.

Richelle: What information is useful for parents trying to understand challenges resulting from their monocular vision? As you know, the Canadian Retinoblastoma Research Advisory Board is committed to patient engagement in research including the translation of research findings. How can we make sure retinoblastoma patients are aware these challenges?

Ben & Ari: This is an excellent question. Through forums such as this blog, we hope to make our research accessible to parents. We are also always open to new ideas on how best to communicate our research to parents.

Richelle: What are your recommendations for further studies that focus on the removal of one eye in childhood?

Ben & Ari: A key issue that we face as researchers is being able to enroll enough participants in our studies to reach scientifically valid conclusions. Future research should endeavour to include more participants. In addition, the rapid development of advanced neuroimaging techniques provides us with an excellent opportunity to understand the effects of childhood unilateral enucleation on the structure and function of the brain. This information could then be used to guide the development of treatments for any vision problems that are detected in the healthy eye of children with a history of unilateral enucleation.

To learn about opportunities at the Human Visual Neuroscience Laboratory at the University of Waterloo, email hvnl@uwaterloo.ca.