Real World Vision and Task Performance in the Elderly

Overview
Description of Elder Vision
Take Home Points
Size Matters
The Change in Vision Across Time
Vision and Driving
Development of New Vision Tests
The SKILL Card
The Attentional Visual Field Test
SKI Study Personnel
Publications Related to Study

Overview

The "SKI" (Smith-Kettlewell Institute) Study aims to investigate vision under conditions of everyday task performance in older persons. Our goal to find out more about how different aspects of vision (especially those other than acuity) change with age, how they affect performance on visual tasks, how they interact with other aspects of health and functioning, and whether predictions can be made about future visual impairment and task performance based on present measures of vision. We are especially interested in developing or identifying vision tests that better represent vision under real world, non-ideal conditions and measure aspects of vision of which older persons complain. Some of the tests used are illustrated here:

The SKI study has several unique aspects:

1. The study sample is older than that of other studies of vision in aging. The 85+ age group is well represented (148 of 900 subjects)
2. A broad range of vision measures, selected to relate to ‘real life’ viewing conditions, and measures of visual performance were used.
3. Vision was tested under the conditions that individuals operate in daily life, with habitual correction and binocular viewing).

The study design is longitudinal; to the extent that they remain available, individuals are tested repeatedly (3 times) over an interval of several years, so that the change in vision over time may be studied. Each of the participants in the vision study has also been followed in a large longitudinal study of health and functioning conducted by the Buck Center for Research in Aging.

Description of elder vision

How does the vision of older individuals differ from that of young adults?

Though our intuition that vision declines in old age is correct, it is not entirely correct.

This figure shows the relative rates of decline across age for 10 different aspects of vision. The data were collected from a random sample 900 community-dwelling elders living in Marin County, Ca. The sample has been grouped into 5 year age bins. For each age, the factor by which that group’s median performance is poorer than normative values for young adults is shown.

Take home points:

• On all measures, vision in older people less than age ~75 is not very different from that of young adults.
• Beyond age 75, and more so beyond age 85, the degree to which elders are worse off than young varies greatly among the different types of vision task.
• median high contrast acuity-the standard measure of vision, the minimum character size for identification of black letters on a white background under good lighting — declines very little, even into very old age (green triangles). The median value for the oldest group is a factor of 2 worse than visual acuity for young adults.
• reducing letter contrast to ~18% (gray letters on a white background) approximately doubles the loss. Low contrast acuity for the eldest group is ~4 times worse than that of young normal (white diamonds, green line).
• surrounding the low contrast letter chart with a background of glare greatly exacerbates the vision loss in elders; the median value for the oldest subjects is ~18 worse (20/720) than young normals (20/40) in the presence in glare. More than half of the very old are rendered ‘legally blind’ by the presence of glare. The impact of glare on vision in elders is largely accounted for by the increased scatter by the ocular media, especially the crystalline lens.
• the loss of integrity of retinal function is made evident by the dramatic increase in glare recovery time with age. Whereas young people recover vision in less than or equal to 10 seconds, 50% of 90-year olds have not recovered vision after 1.5 minutes.
• aging significantly reduces the effective visual field under conditions of divided attention (white circles, red line), and coarse stereopsis (depth perception) is also greatly impaired.

Size matters

How large does type need to be to compensate for the loss of vision with age? It depends on, among other things, the contrast of the letters and the lighting conditions. The following illustration, based on data from the SKI Study, shows the relative letter sizes required under different levels of contrast and lighting conditions, for two of the age groups illustrated in the previous figure: the youngest (mean age 62.5) and those aged 80-85.

The change in vision across time

When re-tested after several years, most individuals sow only small declines in standard acuity — letter chart vision. However, even among those with good acuity, some show substantial loss of vision. We find that other measures of low contrast vision are excellent predictors of future major vision loss. In other words, individuals who scored poorly on these tests (SKILL Dark Chart, contrast sensitivity, or depth perception) at the first test were more likely to suffer an acuity loss at the next test. Such measures may therefore become even more important for clinicians in helping to identify which patients to follow carefully. These measures also predicted a decline in ability to read.

Vision and driving

Older persons self-restrict their driving based on several aspects of their vision, but not on the basis of deficits on attentional fields (measuring divided attention performance — one of the most important correlates of accidents). Testing and education is therefore needed.

Development of New Vision Tests

The words ‘vision test’ conjure an image of a chart on an exam room wall with black letters on a white background. The use of the ‘standard visual acuity chart’, originally for the measurement of refractive error and optimization of refractive correction, has become ubiquitous in clinical and institutional (e.g. The Department of Motor Vehicles) settings. But, the ability to resolve high contrast targets under optimal illumination is but a very small part of vision. Look around the room you’re sitting in and you’ll notice that much of what we see is subtle differences in shading or brightness. Walk out of this room and into the next, particularly in the home environment, and you’ll notice that the lighting changes and in many cases is rather dim.

The SKILL Card

The SKILL (Smith-Kettlewell Institute Low Luminance) Card was designed to assess vision under conditions of low contrast and lighting under standard office or exam room lighting. The test consists of s standard high contrast near acuity chart on one side and a chart of gray letters on a dark background on the other. The reflectance of the ‘dark chart’ is 1/10th that of the ‘light chart’ and so effectively simulates testing in a dim environment.

This test is available upon request. For more information or to order a SKILL Card, contact Dr. Lori Lott at 415-345-2000.

Haegerstrom-Portnoy G., Brabyn J., Schneck M.E. and Jampolsky A. The SKILL Card: A Test of Low Luminance, Low Contrast Acuity Under Ordinary Room Illumination. Invest Ophthalmol Vis Sci . 1997; 38(1):207-18.

The Attentional Visual Field Test

Our sensitivity to targets presented away from the point of focus depends on the extent to which our attention is also drawn to the point of focus. We have developed and applied a relatively simple tool for rapid assessment of the effective field of view under conditions of divided attention. The test apparatus is a modified Synamed perimeter. Bright suprathreshold stimuli are presented along each of 5 meridia. The standard field test requires subjects to press a button upon detection of peripheral targets while maintaining fixation on a steady red central target. The attentional field task requires the subject to keep track of and report (at the end of the test) the number of times the central target is briefly extinguished while continuing to respond to peripheral targets. The impact of divided attention is determined by comparing the sizes of the standard and attentional fields.

Some findings in older people are presented in the following Figures.

Field SIZE. The size of the standard visual field (red regions) changes little with increasing age (left to right). The upper (60º) meridian shrinks more than other parts of the field. However, attentional fields — measured with the same peripheral stimuli, but while subjects attend to a central counting task (blue regions) shrink dramatically with age. For the oldest subjects, the attentional field is only half the diameter (1/4 the area) of the standard field.

Field INTEGRITY. The bar graphs show the percentage of field locations not detected under standard (left) and attentional (right) conditions. The near periphery (central 20º, yellow), mid periphery (20-40ºeccentricity, red) and far periphery (beyond 40º, green) are considered separately. Few standard field points are missed, even among the oldest subjects , and those that are missed are in the far periphery (i.e. though fields shrink slightly they do not have no 'holes' within them). Under conditions of divided attention however, fields not only shrink but become 'holey'. Note also that more near-peripheral than mid-peripheral points are missed.

We also have found that older individuals who continue to drive have larger attentional fields than those who have had to or chosen to give up driving.

People involved in the SKI Study

SKI Study personnel:

• John Brabyn PhD
• Marilyn Schneck PhD
• Gunilla Haegerstrom-Portnoy OD PhD
• Lori Lott PhD
• Jean Brennan OD
• Cathy West MD PhD
• Ginny Gildengorin PhD
• Ruth Youngquist
• Bebe St. John
• Martin Winderl
• Al Alden