One of the reasons that visual difficulties are overlooked is the superficial or simplistic notion equating vision with activity in the occipital cortex at the rear of the brain. Don’t get me wrong — I’m a big fan of V1 and all of the processing that goes on in the rest of the “Vs”. But that’s only a small portion of what constitutes vision. The sketch above is from a generally informative blog about Autism Spectrum Disorders that describes individuals with ASD as often having extreme visual strengths. Such extremist statements mask the extent of difficulties experienced by individuals with ASD. One cannot dissociate the influence of executive control and other avenues of top-down knowledge on visual perception, one reason why the visual brain is so easily subjected to illusions.
I mentioned yesterday a chapter in a wonderful book on visual impairment, and there are many other chapters in the book that bear on the subject at hand. As a prelude, take a look at this excellent discussion by an optometrist on autism and vision, who worked for many years with visually impaired children who exhibited autistic behaviors. The legal definition of visual impairment centers on reduced visual acuity and/or defects in peripheral vision, and you can gain alot more information about visual impairment and autism at the neurodiversity website. There’s a brilliant chapter in the Visual Impairment book (Clinics in Developmental Medicine No. 186) by August Colenbrander, a physician-scientist at the Smith Kettlewell Eye Institute in San Fran who differentiates between Ocular Visual Impairment (OVI) and Cerebral Visual Impairment (CVI) – the former being problems rooted in the eyeball and the latter being problems rooted in visual pathways/connections through the brain and the rest of the body (a la Harry Wachs).
Regarding visual function, Colenbrander notes: “Because visual acuity is measured so often, some regard it as a general measure of the quality of vision. This is not true; visual acuity is only one of many visual functions … Disorders of functional vision tend not to be enquired about or assessed by ophthalmologists. Hence, the measurement of visual functions is often used as a substitute for prediction or estimation of function.” Colenbrander offers a chart with a general scale of visual function, in which he notes the concept of lost cognitive reserves, and visual problems that may manifest when the individual is under stress. Here are some other key concepts in the book that should be required reading for all eyecare professionals, particularly ones who try to infer visual function from visual acuity and straight healthy eyes:
From the Introduction by Dutton & Bax: “Vision certainly plays a role in disturbed social interactions, which are seen in many neurodevelopmental disorders, such as autism, but its role has yet to be fully elucidated.”
“The fact that training is now known to lead to brain growth accompanied by greater cell size and greater numbers of synaptic connections in the occipital area indicates that strategies which optimize habilitation may affect ultimate visual outcome.”
“We were particularly aware that, while ‘simple’ problems affecting visual acuity, contrast sensitivity, and visual fields are identified, the role of perceptual and cognitive visual functions in many disabilities may not be recognized or understood. We think particularly, for example, of the many children on the autistic spectrum who have problems with vision and visual interpretation, as these problems tend to be enveloped in the general description of the condition, such as autism, and not focused on diagnostic issues in their own right … Simply thinking of children on the autistic spectrum as having fundamental visual problems, rather than purely behavioral issues, changes the cast of one’s mind as one approaches such a child.”
From the chapter by Jacobson & Flodmark on children with white matter damage (WMDI): “It is common that visual acuity at near is lower than acuity assessed at distance, a finding that cannot be explained by problems with accommodation only, as spectacles correcting for near distance seldom normalize near acuity. Low near acuity and crowding may make reading of print difficult.
“Many studies have described cognitive and perceptual visual impairment associated with WMDI. Children with WMDI, even those with relatively well-developed optotype acuity (emphasis added) often have dorsal stream dysfunction with profound difficulties in moving through three dimensional spaces, with difficulties judging depth … It is important to recognize that problems in daily life for a child with visual dysfunction caused by WMDI are not primarily related to visual acuity (emphasis added), but are dominated by cognitive visual deficiencies.”
From the chapter by Mastuba & Soul: “Children with CVI have a unique set of behavioral characteristics. Some may initially present with roving eye movements. As their visual function improves, their visual attention and curiosity also progresses, as if vision ‘starts to make sense’. This improvement may be linked to better organization of visual information, which times time to develop … ”
“Even with improvement in visual interests, children with CVI may show variability in visual function, even during the course of the day. Spontaneous visual activity often occurs in short duration. Visual function may diminish depending on environmental and health conditions, such as a noisy room or an intercurrent illness … Sometimes visual learning in its own right can be fatiguing. Although children may be able to visualize distant objects they may have difficulty identifying them. In general, visual interests and activities are better for nearer objects, even for children who lack significant refractive errors (emphasis added). This mechanism appears to reduce the crowding effect. So, when several toys are presented, children may be able to focus on only one. Those with limited visual interests may choose not to use their vision, preferring to close their eyes to focus on listening. Others regularly choose to explore visual objects through touch.”
“Since many children with CVI do not have stereopsis and fusional vergence, they can present with strabismus. In the presence of poor visual attention, children with CVI may have an exotropia. With better visual attention, esotropia is more common … When vision is reduced or absent, it can influence body tone, eye movements, and primitive reflexes.”
“Posture plays an important role in vision rehabilitation. There is a relationship between vision and neck control. Poor positioning of the child may impeded visual function, and proactive positioning and seating is required to optimize visual function.”
… So the next time you see someone indicate that a child with learning problems has normal vision, or describe a child as having significant (yet alone extreme) visual strengths, give them a link to this volume of Clinics in Developmental Medicine, so they can read some of their own relevant literature. There are signs that a few of our optometric colleagues are forging some very key relationships with pediatric ophthalmologists that will help change the visual landscape. More on that in a future blog.