1. Force transfer by constrained string (main design) - Results and Testing

The ideal method of testing the device would be to trial the device on patients with impaired blinks. However, due to the lengthy ethics approval processes required, patient testing of the device is not considered in the scope of this study.

Preliminary testing, to assess the relative effectiveness of closure methods to advise future study, was conducted by trialling the device on the author. The degree of closure and measures such as “comfort” and "ease of use" were considered.

Testing without actuator

Prior to attaching the actuator, the mechanism of closure was tested. Specifically, the following question was addressed:

Can a thread pulled through a system of patches with:

  • patch (1) fixing the thread origin on the nasal side;
  • patch (2) transferring downwards force to the eyelid; and
  • patch (3) ensuring the direction the thread was pulled was constrained

achieve eyelid closure?

This was tested by applying the patches in the described configuration and pulling the thread. The following video demonstrates the results. 

This demonstrates that actuating the thread connected to the patch configuration is able to generate closure.

It was noted here that the patch on the eyelid was being slightly disconnected, this was corrected by applying more band-aid adhesive. It could be beneficial to have adhesive running across the entirety of the underside of the patch for more even attachment. It would be desirable in future to test the effect of various constraint positions on the closure. 

Whether a system of patches actuated by a linear actuator is capable of achieving closure:

The actuator/glasses device outlined in the fabrication section was worn and connected to the patch thread via luer lock/tube attachment. During testing the thread was disconnected from the luer lock - the thread was reconnected directly to the actuator (as observed in the results videos). The thread was in a resting state such that applying a small amount of displacement to it would result in creating some tension on the eyelid. 

The actuator was activated to provide a posterior stroke, increasing from 6mm - 16mm. Partial eyelid closure began to be observed from ~8mm stroke.

Full closure was observed from 14-16mm stroke. 

Other files (for various degrees of partial closure, from 10mm - 14mm) are attached at the end. 


Effectiveness of Closure:

Full closure was achieved using 16mm of closure. 

Lower levels of displacement were not sufficient to achieve closure. This is double the Tollefson and Senders value of 8mm for linear sling based closure. It is expected that this is due to the displacement required to take up passive eyelid tension. Some displacement needs to be applied to the eyelid to take it from a "comfortable" stress-free state to a taut state prior to movement causing eyelid closure. This should be considered in device design. It is expected that the displacement requirements will vary from person to person, and also between applications of the device (e.g. through altered constraint positions). It would be of benefit to assess these variables through a study on multiple real people, where constraint positions are systematically varied and required displacement is observed. 

The closure did not meet the 80-100ms goal to replicate natural eyelid closure (it is expected approximately 600ms was the time). 

Comfort & Ease of Use:

While the device was noticeable, the closure motion did not elicit discomfort.

However, the ease of use was very low. It was challenging attaching the patches in the right configuration, with adequate adhesion, and then connecting the actuator system.  It took over 5 minutes to apply the device and occasionally de-adhesion would occur.

Two key areas require work:

1) An easy "on-off" interface system to allow application of the device

2) More effective materials selection and fabrication processes to allow for more reliable and easy to apply adhesion.

Validity of Self Testing:

The prototype devices were self-tested on a team member. It is possible that confirmation bias exists in reporting subjective values such as “comfort” and “noticeability” due to the involvement of the test subject (the author) with the project.

It was noticed that the right (unactuated) eyelid drooped slightly in time with the actuated eye on closure, this is likely due to the eyelids LPS muscle relaxing. This is similar to how the eyelid of an impaired patient would behave (where the LPS will relax but the eye will not close fully).

It is also likely that reporting on subjective parameters such as comfort may differ across subjects. Given the sample size of 1, it is not possible to determine whether reports on the “comfort” of specific design aspects are transferable to the wider population. For example, some people may feel more or less irritated by the presence of a Band-Aid on the lid. 

However, it is believed that the results are still valid and useful for early stage design decisions and demonstration of proof of concept. Details, such as the amount of displacement required and optimal location of attachment, are likely to vary and need to be assessed using other subjects drawn from the wider population.