Measuring Vision in the Classroom
The Need for a Common Standard
Research in optometry and medicine has shown that the only way to determine whether a child has a sufficiently robust visual foundation is to assess very specific elements of visual health and function that represent potential obstacles to reading, and by extension, learning. The Orinda study of 1959 (Blum, 1959) was the progenitor of the ‘Modified Clinical Technique’ (MCT) which provides an economical means of determining gross risk by including assessment of refractive error and detection of strabismus. The MCT does not, however, require assessment of rapid motor skills, phoric posture, or other essential elements of muscular control such as vergence that can have a great negative impact on reading performance. (Basics elements of visual behaviour are covered later.)
While not all elements of the comprehensive examination are practical for on-site assessments of large groups, detailed assessment of refractive error, nervous function, and ocular motilities can be obtained in a relatively brief time and should be considered compulsory. When problems arise, gathering of more detailed information is warranted on an individual basis. Refraction with cycloplegia (‘dilated’ or ‘drop’ examination) for borderline cases is an effective means of increasing reliability of referrals and reducing costs overall. Use of more recent autorefractor technology combined with cycloplegia in school screening is a powerful tool in accomplishing this.
In order to ensure all children are properly assessed for potential significant VIL, all should be assessed periodically following the guidelines in the table below, beginning shortly before Grade 1.
|Table 2:||Recommended Elements in Assessing Visual Readiness for Early Elementary.|
Comprehensive assessment programs, as compared to current screening methods, are prudent fiscally and with respect to health and education outcomes. Still, tightening school and health budgets encroach upon school nursing and monitoring programs, and more effort is now spent on making vision screening faster and more efficient. But this comes at the price of increased numbers of false negatives and higher costs for intervention for academic, behavioural, and health concerns resulting from unchecked VIL over the child’s lifetime. Abbreviated screening protocols then, such as simple sight tests administered by untrained personnel, may well represent false economy while providing little to no benefit to those who need the help most.
As far as terminology goes, ‘color blindness’ is an inappropriate term as people are not generally blind to color, even though some people will show the inability to perceive some hue combinations – known as Color Vision Deficiency (CVD). CVD, like myopia, is relatively easy to spot in the classroom with no specialty testing or training required. For very small children, or for parents at home, testing can be a simple matter of having the child match colors to objects by pointing, comparing, sorting, or selecting. For example, Froot Loops or Nerd candies can be placed on a white sheet, and the child is asked to remove/eat only those of a certain color. This is not, however, an accurate test and any concerns regarding color vision should be documented using a standard test, such as Ishihara Pseudo Isochromatic (IPP) plates, or the Farnsworth D15 cap test. Pediatric IPP plates are available for low cost and are recommended standard equipment for developmental professionals.
Color perception deficits can be classified as either congenital or acquired. Congenital CVD is the most common form, and is due to physiologic genetic differences that prevent retinal light receptors from responding to light in the same way neurotypical eyes do. Acquired CVD is an indication of pathology – either through disease or toxicity. Children with new problems with color perception need to be assessed on a priority basis.
Up to 8 % of boys will show some sort of difficulty with color perception, 8X more than girls. In the classroom, CVD has a limited impact for the simple fact that very few tasks require the ability to accurately identify or compare color differences. There are some consequences of CVD relating to career choice that will limit options for those affected – electricians and commercial pilots, for example, must show no restrictions in color differentiation.
See this PDF for a more detailed CVD tutorial and description of color vision testing protocols: Color_Vision_Deficiency_Tutorial