Background and Overview:
Prior to attempting the main soft exopatch device, the concept of external eyelid closure was explored by considering the possibility of achieving closure by attaching a connector to the lid (e.g. a Band-Aid with string) and pulling laterally using an actuator.
The linear sling method, using a sling harvested from temporalis muscle fascia, has been used to create a working prototype of implantable active closure devices using electroactive polymers [2].
It involves harvesting patients muscle fascia, inserting it into the eyelid and pulling it laterally to drag the eyelid closed. A schematic (taken from Tollefson and Senders, 2007) outlining the concept is shown below.
It may be possible to use the same method to provide closure externally, by attaching a lateral pulling actuator to the external surface of the upper eyelid, possibly using string and Band-Aid for purposes of prototyping.
To achieve closure using an implant device, a linear actuator, must provide 6mm of unidirectional displacement and 654mN of force to a sling inserted into the upper eyelid [2].
The proposed method could involve the following key materials and geometry:
- Actuator: A linear actuator situated laterally to the lateral canthus of the eye, (able to achieve 6mm of displacement)
- Method of Attachment: String, attached to the inferior palpebral portion of the upper eyelid
- Closure Motion: Transfer of force and displacement from the linear actuator to the upper eyelid via the string.
The key requirements, are as follows:
- Actuation Displacement: Either 6mm lateral displacement, or a 6mm vertical displacement component. There is dispute regarding this requirement.
- Force: 20-100gmf force if activated simultaneously with blink, 56-150gmf force if activated while the levator is active
- Actuation Time: Ideally within 80-100ms
The device is illustrated as per the following general schematic, representing the actuator connected to some element on the lid. The actuator would act in the right hand direction of the image.
