Rehabilitation Research Design & Disability (R2D2) Center

Modifying The Dynamic Gait Index For Improved Discrimination of Multifocal Eyeglass Conditions

Dennis B. Tomashek, MS, Kurt E. Beschorner, PhD, Roger O. Smith, PhD, Autumn Milanowski, MS

Abstract Methods

Background

Discussion

References

Results of Biodynamic Analyses

Objective: Create and test a 2nd generation modified Dynamic Gait Index (DGI-m2) for sensitivity to changes in gait when wearing multifocal lens glasses.Design: A 2X4 within-subjects repeated measures with two lens conditions (single distance & multifocal progressives) and 4 step/ramp conditions.Setting: The Biodynamics and Gait Lab on the UW-Milwaukee campus.Participants: 5 young novice adults and 2 experienced multifocal lens wearers.Outcome Measures: Gait measures, including Toe clearance, and maximumnormal force using motion capture andforce plate technology.Results: Increased toe clearance when stepping up (p=.05), and increased normal force when stepping down (p<.01) when wearing the multifocal glasses compared to single lens performance.

The Rehabilitation Research & Disability Design (R2D2) Center has developed a line of research addressing the possible role of multifocal lens glasses (Lined bifocals, trifocals, and unlined progressive lenses) on increasing the risk of falls for wearers. This detrimental effect was first studied in 2002 by Lord, Dayhew & Howland, who found that the odds of falling for elderly who wore multifocal lenses increased significantly(OR=2.26).Further research has been conducted on the effects of these type of glasses on stepping and gait behavior (Elliott & Chapman, 2009; Johnson, Buckley, Harley, & Elliott, 2008), and have been found to have detrimental effects, leaving the wearer more susceptible to falls.

The DGI is a well established tool for assessing gait, balance and fall risk in older adults (Herman, Inbar-Borovsky, Brozgol, Giladi, & Hausdorff, 2009). It has also been shown to be reliable for other populations, such as those with stroke (Jonsdottir & Cattaneo, 2007).

In an earlier study (Joerger, Smith, & Tomashek, in preparation) found that the original DGI reached ceiling limits when assessing young (18-22 years old) participants wearing bifocal lens glasses compared to single lens glasses. A follow-up study, (Brayton, Smith, & Tomashek, in preparation), modified the DGI by increasing the scoring from a 4- point to a 5-point scale. However, two groups, first time bifocal wearers and a control (non-wearer) group again encountered ceiling effects. A third bifocal study (Smith, Tomashek & Stalberger, in preparation), modified the DGI further in to the DGI-m. In addition to increasing the scoring range, the DGI-m:•Included two new tasks.

- A step-over task with a long, diagonal obstacle.- A step-up/step-down platform.

•Overlaid the DGI walkway and all obstacles with a checkered-pattern Amsler grid.•Introduced a visual distraction task for certain DGI tasks.

The main goal of this project is to develop a task that requires subjects to adapt to floor level changes, which we expect to be difficult while wearing multifocal lens glasses. To accomplish this, the researchers have modified the DGI in five ways:

1) Addition of a step/ramp task.2) Addition of motion capture analysis. 3) Addition of EMG analysis.4) A more continuous task.5) The use of force plates.

Figure 1. Photo of 3” and 6” ramp/step obstacles for modified DGI

Figure 2. Participant with motion capture markers and wireless EMGs performing the step/ramp task of the DGI-m2

The ramp/step apparatuses are interchangeable and reversible. Thus, 4 conditions can be assessed using these two platforms. The first apparatus has a 3” high step with a ramp pitched at 1” rise/run. The second apparatus has a 6” high step with a ramp pitched at 2” rise/run.The following results, both for the biomechanics and the DGI-m2, are for 5 participants. For the toe clearance and peak force analyses, a 2X2 ANOVA, with participants as a random factor was used.

Figure 4. Interaction of Lens Typeby Step Height for Mean Toe Clearance

Figure 5. Interaction of Lens Type by Step Height for Normalized Peak Vertical Force

Table 1. Mean Toe Clearance by Lens Type & Step Height

Table 2. Mean Normalized Peak Vertical Force by Lens Type & Step Height

Lens TypeStep

HeightMean Toe Clearance

Std. Deviation N

Single 3” 92.13 21.894 15

6” 81.19 21.164 15

Single Total 86.66 21.877 30

Progressive 3” 104.11 39.451 15

6” 115.08 20.122 15

Progressive Total 109.59 31.272 30

3” Total 98.12 31.935 30

6” Total 98.14 26.624 30

Total 98.13 29.149 60

Lens Type Step HeightMean Peak

ForceStd. Deviation N

Single 3” 1.25 .171 14

6” 1.49 .217 14

Single Total 1.37 .227 28

Progressive 3” 1.24 .108 15

6” 1.61 .275 13

Progressive Total 1.41 .274 28

3” Total 1.24 .139 29

6” Total 1.55 .249 27

Total 1.39 .250 56

Table 3. Results of 2 Univariate ANOVAs for Toe Clearance and Normalized Peak Vertical Force (n=5)

Toe Clearance Maximum Normal Force

F Significance F Significance

Lens Type (Single vs. Progressive)

4.987 .040* .244 .628

Step Height (3” vs. 6”) .000 .999 14.76 .001*

Lens Type X Step Height Interaction

4.186 .000* 4.835 .000*

Figure 7. Mean scores on the DGI-m2 tasks for 2 Lens Conditions

Discussion

Motion Capture analysis techniques found significant differences in participants stepping up performance between the single lens and progressive lens conditions (see table 1 above). Higher toe clearance when wearing the progressive lens glasses indicates more uncertainty of the actual step height, causing participants to use a more cautious approach, thus over-compensating to avoid a possible trip. In addition, the higher toe clearance when wearing progressive lenses was associated with a longer distance from the step to the stance foot (r=.67), another indication of uncertainty as to the exact location of the step.Force plate data collected in the stepping down condition indicated a strong interaction between the higher step height and wearing progressive lens glasses (see table 2 above). The vertical force was correlated with vertical heel velocity (r=-.55), an indication that, due to the uncertainty of the actual distance to the ground, the participants did not adjust their foot dissent speed appropriately, causing a higher force at greater speed. Both the stepping up and stepping down data are indicative of uncertainty of physical distances as perceived through the lower portion of the progressive lenses, thus increasing the risk of a trip or fall.

Results of Ratings of Performance on the DGI-m

Figure 6. Mean scores on the DGI-m2tasks for 2 Lens Conditions

Lens Type Mean Std Deviation t Sig

Single Lens 43.90 1.342 3.443 .026

Progressive Lens 41.20 2.515

Table 4. Means, standard deviation, and results of dependent samplest-test for total DGI-m2 scores for 2 Lens Conditions (n=5)

A significant difference was found for the total scores of the 9 DGI-m2 tasks as rated by an expert rater. For individual DGI-m2 tasks, only in Task 5 “Complete pivot turn during gait” were significant differences found in gait performance for the 2 lens conditions. Other tasks, which included vertical or horizontal head turns (Tasks 3 & 4), and stepping over obstacles (Tasks 6 & 8) also showed differences, but did not reach significance. For all of these tasks, participants performed worse when wearing the progressive lens glasses. These results show that the progressive lens glasses affect the functional gait performance of young novice wearers to a point that is noticeable to an observer. Of particular interest were the tasks that caused changes in head orientation and focal point, and those in which judgment of an obstacle’s height and position were targeted. The results obtained from this pilot study, both the high-tech methodologies of Motion Capture and Force Plate technologies, and the more traditional rating of functional gait by an observer, indicate that even in young, healthy adults, the progressive lenses cause obvious changes in gait that have been associated with increased risk rate for falls in the older adult population. Future research will include older adults, both experienced and non-multifocal lens wearers, to compare their performance with that of the younger adults.In addition, further refinement of the DGI-m will continue, in order to produce a reliable instrument to measure the adaptation to wearing multifocal lenses that will be useable by clinicians and therapists.

Lord, S.R., Dayhew, J., and Howland, A. (2002). Multifocal Glasses impair edge contrast sensitivity and depth perception and increase the risk of falls in older people. Journal of the American Geriatrics Society 50, 1760-1766.

Jonsdottir, J. & Cattaneo, D. (2007). Reliability and validity of the Dynamic Gait Index in persons with chronic stroke. Archives of Physical Medicine and Rehabilitation, 88, 1410-1415.

Elliott D.B. & Chapman, G. (2009) Adaptive gait changes due to spectacle magnification and dioptric blur in older people. Investigative Ophthalmology & Visual Science

Herman, T., Inbar-Borovsky, N., Brozogol, M., Giladi, N. & Hausdorff J.M. (2009). The Dynamic Gait Index in healthy older adults: The role of stair climbing, fear of falling, and gender. Posture, 29, 237-241.

Johnson, L., Buckley, J.G., Harley, C., & Elliott, D.B. (2008). Use of single-vision eyeglasses improves stepping precision and safety when elderly habitual multifocal wearers negotiate a raised surface. Journal of the American Geriatrics Society, 56(1), 178-179.

Contact

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