The Functional Classification of Brain Damage-Related Vision Loss
Colenbrander, August, Journal of Visual Impairment & Blindness
Vision loss can be considered from many different points of view, each of which reveals a different aspect. To gain a comprehensive picture, all these aspects need to be taken into account. Consider the scenario of a woman with age-related macular degeneration who enters a physician's office to make an appointment. The staff at the front desk thinks about when to schedule her. The physician thinks about which treatment to select. The office manager may worry whether the woman's insurance will pay. The daughter asks whether her mother can still drive. The vision rehabilitation worker thinks about which visual devices and training will be needed. These are all different aspects of a single clinical case.
Recently, increased attention has been paid to the many ways in which cerebral disorders can affect visual behavior. This article presents a functional classification (see Box 1) of these effects and of how the vision loss caused by cerebral conditions differs from that caused by more familiar ocular conditions. Brain damage--related vision loss can have many causes: cerebral visual impairment in children, traumatic brain injury in adults, or a cerebrovascular accident in elderly people. Whatever the cause, we professionals in the field of visual impairment are reminded that vision is not just a function of the eyes, but that the most complex part of visual functioning resides in the brain.
ASPECTS OF VISION LOSS
As a framework for this discussion, various aspects of vision loss in general need to be considered. I use the term aspects because the aspect that we see not only informs us about the object, but gives us insights into the point of view of the beholder.
The first aspect is that of structural changes at the organ level, such as scarring, atrophy, or loss. Here, the focus is on the tissue, and a pathologist is needed to look at the structure of the organ. However, the structural changes do not tell us how well the eye can function. We need to widen our view to the aspect of visual functions. To do so, we need an eye care professional to measure parameters, such as visual acuity, visual field, and contrast sensitivity.
Yet, knowing how well the eye functions does not tell us how well the person functions. Thus, we need to consider the person and his or her abilities to perform tasks, such as reading, mobility, and recognizing faces. For this aspect, various low vision professionals are needed to work with the patient, to provide various devices, and to teach various skills. Beyond that, we need to look at the consequences in a societal context. Do these changes affect the person's participation in society, causing social isolation, job loss, or a reduced quality of life? How can we be sure that we reach the end goal of all our interventions, which is not just an anatomical correction, but satisfied patients who are content with the effect on the quality of their lives?
For this discussion, it is useful to distinguish the organ-related aspects of vision loss from the person-related aspects; with regard to the organ-related aspects, we speak of visual functions, and with regard to the person-related aspects, we speak of functional vision. The traditional medical focus is on the organ of vision, its structure and functioning. The rehabilitation focus extends this view to the functioning of the person. The traditional focus on organ function benefits from an anatomical classification, in which eye conditions, which can involve either the optics of the eye or the retina, are separated from cerebral conditions, which can involve either the optical pathways or the cortical structures. It should be noted that cerebral causes may involve more than just the cortex, which means that we should refer to cerebral, rather than cortical visual impairment.
Various activities may cover more than one aspect. With regard to reading, the measurements of print size and reading speed describe an aspect of organ function. …