Delayed Visual Maturation: A Visual Inattention Problem


I’ve been fortunate now, on two consecutive days, to get a heads up from sharp New Jersey primary care O.D. colleagues who keep an eye out for articles of common interest.  Yesterday it was new evidence based support for amblyopia therapy.

Today Dr. Charlie Fitzpatrick sent the link to an article from Expert Review in Ophthalmology on delayed visual maturation (DVM) as a problem in visual inattention.  In a nutshell, the article describes what those of us in Pediatric Optometry have dealt with as cortical blindness or cortical visual impairment (CVI). There is no apparent reason why these infants don’t respond visually.  That is, they generally respond normally to retinal tests such as ERG, subcortical tests such as OKN, and visual cortical measures such as VEP.  The distinction might be made that DVM is a form of CVI that resolves over time.

This article notes that the defining characteristic of DVM is an inability to fixate and follow a target.  The authors do a nice job subdividing DVM into four categories:

Type 1 DVM: Visual fixation, attention, and tracking eventually develop, but these infants are at higher risk for learning disabilities and attention disorders.

Type II DVM: Resolution of visual delay is often slower and more incomplete than in Type I.  There is often seizure activity associated with cognitive disorders, and visual responses often improve as seizures are treated.  Hypoxia to the extrageniculostriate visual system is often involved.

Type III DVM: Infants in this category have associated congenital nystagmus and albinism.  Their vision starts to improve later, and to a lesser degree.

Type IV DVM: Infants in this classification include severe ocular disorders such as retinal dystrophies, optic nerve hypoplasia, and macular coloboma.

There are several interesting implications from this review:

1) DVM is a symptom common to a variety of neurologic abnormalities in which efferent and afferent visual pathways are largely intact.  The symptom itself is a problem of visual inattention that exists on a continuum in terms the time course of delayed development, and the degree to which visual attention is ultimately developed.

2) Top-down visual attention derives from multiple areas outside of the visual cortex, consisting primarily of an anterior and posterior network.  The anterior network includes he frontal and supplemental eye fields of the frontal cortex, as well globus pallidus, caudate, putamen, parts of the thalamus.  The posterior system consists of parietal cortex, superior colliculus, and pulvinar.  It is likely that visual inattention involves delayed maturation of, or damage to this network.

3) We are used to thinking of the concept of visual neglect in terms of acquired brain injury that results in inattention to a select region of the visual field.  A better understanding of DVM as total visual neglect, and its resolution, in those cases where fixation and following ultimately develops, may provide a better understanding of visual inattention with other populations.

An ophthalmologist who functions more like a developmental/behavioral optometrist, Lea Hyvarinen, has material that complements this article.  Here is a nice lecture she gave in San Francisco in 2003 on the assessment of CVI, and Dr. Hyvarinen has also presented on the trans-disciplinary nature of assessment.  A conference in which she participated last year highlighted these complexities.  Of particular interest will be her blog, Dr. Lea & Children’s Vision.

– Leonard J. Press, O.D., FCOVD, FAAO

 

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