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A Modular and Adjustable Ptosis Crutch as a Non-Surgical, Low Cost Solution for Elevating the Upper Eyelid in Myasthenia Gravis.

1 Introduction

1.1 Background

Myasthenia gravis (MG) is a treatable autoimmune disorder that affects the neuromuscular junction. MG is characterised by fatigue and generalized weakness of voluntary skeletal muscle (Pruitt and Ilsen 2010; Nemet et al. 2014). Estimates from North American data suggest that the prevalence of MG is around 200 per million people (Phillips 2003). The incidence in South Africa is similar to the rest of the world (Mombaur et al. 2015). While MG affects individuals of all racial groups, patients of African genetic ancestry, particularly juveniles, are more likely to develop an ocular muscle complication of MG compared to their European counterparts (Heckmann 2012). The most common symptoms of the ophthalmoplegic complications of MG are difficulty with moving the eyes and blepharoptosis.

1.2 Description of the Clinical Problem

Blepharoptosis, abbreviated to ptosis, describes the condition of a lowered upper eyelid(s), beyond the normal position [Figure 1] (Walsh et al. 2006; Ahmad et al. 2011). Ptosis may present as a unilateral or bilateral condition. Surgical correction of ptosis is often contraindicated in MG patients with severe weakness of the muscles involved in eye closure and in patients with active disease. In these cases, a non-surgical solution to elevating the ptotic eyelid above the visual axis is required (Moss, 1982). A ptosis crutch that is attached to the lens or frame of the spectacles seems to offer an appropriate solution to elevating the upper eyelid above the visual axis.

Although the ptosis crutch itself is not a novel idea, there is no record of a commercial ptosis crutch that is developed and available in South Africa. Furthermore, no evidence could be found of a modular or adjustable ptosis crutch in the global market. The literature suggests that crutches are currently manufactured and fitted on a case-by-case basis (Moss, 1982; Lapid, 2000; Kumar, 2010). Unfortunately, custom making crutches requires the patient to have access to the appropriate facilities as well as the funds to supports this option. These are two luxuries that a large proportion of the South African population, as well as other developing countries, do not have. The ptosis crutches that are available are permanently fixed to the frame or lens of the spectacle, thus limiting the use of the crutch to one pair of spectacles [Figure 2].

1.3 Study aim

The aim of the present study was to design and construct a modular ptosis crutch for the South African myasthenia gravis population. The crutch should elevate the upper eyelid to clear the visual axis.

1.4 Objectives of the study

The primary aim of the study was the design of a modular and adjustable ptosis crutch for MG patients, which could be produced using low-cost manufacturing methods. The three research objectives were to:

i. Determine the anthropometric measures that would inform the ptosis crutch design.

ii. Design and prototype a modular and adjustable ptosis crutch suitable for the MG population.

iii. Verify the efficacy of the ptosis crutch within the clinical setting. The ability of the ptosis crutch to perform its intended would be determined in terms of usability, effectivity, and efficiency.

1.5 Ptosis crutch requirements

The ptosis crutch requirements and design parameters, outlined below, were defined with the input from the clinician, designer, and user.

i. Elevate the ptotic upper eyelid to clear the visual axis [Figure 3].

ii. Triaxle adjustability

iii. Affordable, thus the attachment needed to be compatible with a standard spectacle frame.

iv. Comfortable

By satisfying the device requirements, the ptosis crutch would fulfill the usability requirements of efficiency, effectiveness, and user satisfaction. Relevant ergonomic design principles were used to ensure that the ptosis crutch fitted the users' needs as best as possible, these included participatory ergonomics, heuristic evaluation, and usability testing.

2 Methodology

The research project included both clinical and design methodologies. Prior to testing the participants gave informed consent; in the case of a minor, the guardian provided consent [HREC REF: 240/2015]. The characteristics of the participants are displayed in Table I.

2.1 Clinical methodology

The purpose of the clinical methodology was to:

i. Obtain the anthropometric measures to inform the ptosis crutch design.

ii. Determine the impact the ptosis has on the participant's visual function, activities of daily living and quality of life.

iii. Verify the efficacy of the final design within the clinical setting.

Clinical testing was carried out on two separate occasions, namely pre-design and post-testing. Photographs of the participants were captured while seated in a marked frame. The purpose of using the measurement frame was to provide a fixed frame of reference to standardize the measurements. The measurements that were recorded for each participant are displayed in Table 2.

2.1.1 Pre-design clinical testing

The initial testing session involved measurement of the natural eyelid position in primary gaze, to determine the amount of eyelid elevation that was required. The position of the eyelid was measured using the measures of marginal reflex distance (MRD) and vertical palpebral fissure (VPF). Three photographs of each participant were taken, the best quality photograph was used for analysis, and the remaining photographs were discarded. The participants were required to fixate their gaze on the lens of the centre camera, thus standardizing the direction of gaze to primary gaze. The position of eye gaze was standardized to primary position to reduce the direction of gaze altering the position of the upper eyelid (Coombes et al., 2007).

During the pre-design testing session, the participants were issued a qualitative questionnaire. The purpose of the questionnaire was to determine the impact that ptosis has on their visual field, activities of daily living and quality of life. The questionnaire focused on activities and symptoms that might be adversely affected by ptosis. The design of the questionnaire was based on the National Eye Institute Visual Function Questionnaire (NEI-VFQ-25) and the 10-item Neuro-Ophthalmic Supplement to the NEI-VFQ-25 surveys (Mangione, et al, 2001). An item was not required to be answered if the patients did not perform the activity.

2.1.2 Post-design clinical testing

The post design clinical testing referred to the functional assessment of the ptosis crutch. The testing involved digital photograph analysis of the participant's ptotic eye under two conditions, specifically with no crutch and when wearing the ptosis crutch. The ptosis crutch was fitted to a standard spectacle frame that was used during all of the testing sessions.

The experimental setup and procedures for capturing the photographs were consistent with that carried out in the pre-design testing. Following the photographic assessment, each participant was required to complete a questionnaire. The questionnaire was intended to gain qualitative feedback on the functionality and user experience of the ptosis crutch. The questions related to the visual ability of the patient while wearing the crutch as well as the ease of use and aesthetic appearance of the crutch. After the clinical testing was complete, each participant was issued with a crutch/ pair of crutches that was fitted to their spectacle frame.

Following the clinical testing, each participant was issued with a crutch/ pair of crutches that was fitted to their spectacle frame. In the circumstance that the participant did not wear spectacles, the participant was given a pair of spectacles with a clear lens, to which the crutch was fitted. After a minimum period of a one-month, the participants were contacted to learn whether they were using the crutch. The participants were required to answer questions relating to the user experience of the crutch. 8 participants satisfied the criteria of 'one month minimum use' at the time of publication.

2.2 Design methodology

The design methodology was an iterative process that depended on the input from the user, clinician, and designer. Participatory ergonomics was an important component in the design of the ptosis crutch. The device was intended to be used by the user without any assistance, thus it was critical to ensure that the end user informed the ptosis crutch design from the design concept stage.

Heuristic evaluation of the ptosis was performed as part of the iterative and evaluation process, where the design concepts were matched against the device requirements. 87 design failures were incurred before the final ptosis crutch design was realised. In the circumstance that the crutch failed to meet the requirements, the reason for failure was noted and the necessary iterations were made. Every design failure resulted in an improved iteration of the successive ptosis crutch design.

3 Design outcome

The design outcome was an adjustable ptosis crutch made up of three modular components [Figure 4]. The ptosis crutch was tested in the clinical setting (n = 12 MG patients). The marginal reflex distance increased by 1.96mm [+ or -] 1.11mm when wearing the ptosis crutch. Figure 5 displays an MG patient with and without the aid of the ptosis crutch.

The activities that were perceived as having the greatest impairment prior to using the ptosis crutch included reading, watching television as well as walking up/down stairways. The activities that were least affected were identifying objects as well as shaving and styling hair.

The qualitative feedback on the ptosis crutch indicated that all the participants were interested in using the ptosis crutch on a long-term basis. Following the clinical testing, each participant was issued with a ptosis crutch for long term use

The usability feedback from the 8 MG patients that had been using the crutch for a month or longer reflected a variety of results. The outcome of the usability testing is presented in Table 3. The reasons for non-use included 1] the crutch broke, 2] wearing the crutch caused the eye to tear, 3] The user was not accustomed to wearing the crutch/wearing glasses and 4] the user had trouble adjusting the crutch appropriately thus the crutch was uncomfortable to wear for long periods of time. The reasons noted for occasional and minimal use included 1] the patient was not yet accustomed to wearing the ptosis crutch, 2] the patient's eyes were watering when the eyelid was elevated.

3.1 Prototyping the ptosis crutch

The ptosis crutch was prototyped using a combination of 3D printing and manual manufacturing. Acrylonitrile butadiene styrene (ABS) was the material used for 3D printing. The crutch bar was constructed from 1.5mm galvanized wire.

The crutch bar was coated in polyvinyl chloride (PVC) tubing. It was the rapid production and interaction with the user (MG patient) that lead to the development of the final product. Figure 6 displays the final ptosis crutch prototype attached to the superior border of the spectacle frame.

4 Discussion of design outcome

4.1 Socio-economic impact

MG affects individuals of all racial groups, however, the outcome to therapy of the disease differs across races. Patients of African genetic ancestry, particularly juveniles, are more likely to develop ocular muscle complications of MG when compared to their European counterparts. The association of treatment resistant and ocular muscle complications in MG patients of African ancestry emphasized the need for a local, low-cost solution to elevate the eyelid. The ptosis crutch described by this project provides an important step in offering a standard rather than an ad-hoc solution to elevating the ptotic eyelid of MG patients. The device will be made available on an open source innovation platform. This will ensure that the ptosis crutch is easily available, by allowing ptosis patients or interested institutions to download the ptosis crutch STL file free of charge. Although the device described herein is a solution to alleviating ptosis associated with MG, the application of the ptosis crutch could be of use to individuals with ptosis of other aetiologies.

4.2 Usability requirements

The ptosis crutch was designed following a user-centred design process. The heuristic evaluation of the ptosis crutch prototypes, throughout the design process, allowed the for the identification of any usability concerns. The specific usability requirements of effectiveness, efficiency and user satisfaction were explored to determine whether the ptosis crutch could be considered successful in meeting the needs of the user. Each of these components is discussed below.

4.2.1 Effectivity

Effectivity was defined as the ability of the ptosis crutch to effectively elevate the upper eyelid to clear the visual axis. The ptosis crutch was successful in elevating the eyelid to clear the visual axis. There were circumstances where the ptosis crutch needed to be altered to the specific requirements of the user. While the initial clinical testing of the ptosis crutch showed a promising outcome for the device, it is ultimately the long-term feedback on the device that will provide a more valuable indication on the usability of the device.

4.2.2 Efficiency

The efficiency of the ptosis crutch describes the device's use of resources. The term resources referred to the materials and manufacturing methods that were utilized. The ptosis crutch can be considered as efficient as it cost 0.9 USD [11,90 ZAR at the time of print] to produce. This is noticeably less than the fee of existing devices, which cost between 30-100 USD [396,67-1322,22 ZAR at the time of print] (World Optic, 2016; Porter & Salter, 2005; Pelak, et al., 2001). It must be noted that the ABS crutches were fragile and there were reports of the device breaking after a few days of use.

4.2.3 User satisfaction

User satisfaction describes the user's subjective feeling of the ptosis crutches usefulness. The device needed to meet the user's performance expectations as well as being comfortable and easy to use. For the purpose of the current study, it was important to communicate to the participants that the ptosis crutch was not intended to restore the functionality of the muscles involved in eyelid elevation, but rather to act as an aid to manually elevate the eyelid in order to improve their visual function.

The initial feedback from the participants indicated that the ptosis crutch improved their vision. The participants reported the device as being comfortable and indicated that they were interested in using the device on a long-term basis. The participant feedback after the crutch had been used for a minimum of one month showed mixed results. One participant found the crutch useful when reading and completing tasks around the house. Four participants indicated that they were no longer using the crutch as it had broken, however when they had been wearing the crutch, they had found it to be useful. Two participants indicated that they were not yet accustomed to wearing the ptosis crutch. One participant indicated that they were experiencing tearing when their eyelid was elevated. It is thought that manufacturing the device with more durable materials will improve the adjustment mechanisms as well as resulting in fewer crutch breakages.

5 Conclusion and future work

The present study sought to design a low cost, modular and adjustable ptosis crutch for the MG patient population. Although the ptosis crutch is not a new device, the final crutch described herein has several novel aspects. This multidisciplinary project used a bio-psychosocial approach, in that it acknowledged the anatomy and biomechanics of the eye as well as the social and psychological considerations of the MG patients.

The clinical verification of the ptosis crutch was successful in that the device satisfied the design requirements. There is future work that would be beneficial to the success of the device. The areas for future work, as suggested by the primary researcher, are listed below:

i. Initial MG patient feedback has shown promising results for the ptosis crutch. It is ultimately the long-term feedback from the users that will confirm the success of the device.

ii. Explore the possibility of manufacturing the ptosis crutch using durable materials. This will remove the open source access of the ptosis crutch but it has the potential to improve the appearance and durability of the ptosis crutch. The benefits versus the costs of a new manufacturing method should be investigated, once the long-term feedback from the users has been determined.

iii. The application of the ptosis crutch to persons with ptosis with aetiologies other than MG should be explored.

It appears that the ptosis crutch, described by this project, has the potential to offer a much-needed biomechanical solution to an African clinical problem. However, the exploration of the recommended future work will contribute towards ensuring that the device is usable on a long-term basis.

Acknowledgements

National Research Foundation Scarce Skills Scholarship. NRF grant number: SFH15070112253; NRF CSUR Grant no: CSUR13082630873 for supporting this study. Muller's Optometrists for donating the spectacle frames.

References

Ahmad, K.; Wright, M., & Lueck, C. J. (2011). Ptosis. Practical Neurology, 11(6), 332-340.

Coombes, A. G.; Sethi, C. S., Kirkpatrick, W. N., Waterhouse, N., Kelly, M. H., & Joshi, N. (2007). A standardized digital photography system with computerized eyelid measurement analysis. Plastic and Reconstructive Surgery, 120(3), 647-656.

Heckmann, J. M.; Hansen, P.; Van Toorn, R.; Lubbe, E.; Janse van Rensburg, E. & Wilmshurst, J. (2012). The characteristics of juvenile myasthenia gravis among South Africans: Research. South African Medical Journal, 102(6), 532-536.

Mangione, C. M., Lee, P. P., Gutierrez, P. R., Spritzer, K., Berry, S., & Hays, R. D (2001). Archives of Ophthalmology, 119, 1050-1058)

Mombaur, B.; Lebowski, M.; Liebenberg, L.; Vreede, H. & Heckmann, J. (2015). Incidence of acetylcholine receptor-antibody-positive myasthenia gravis in South Africa. Muscle and Nerve, 51(4), 533-537.

Moss, H. L. (1982). Prosthesis for blepharoptosis and blepharospasm. Journal of the American Optometric Association, 53(8), 661-667.

Nemet, A.; Kaiserman, I.; Mimouni, M.; Segal, O. & Vinker, S. (2014). High prevalence of myasthenia gravis among rural adult populations. Journal of Clinical Neuromuscular Disease, 16(2), 47-50.

Pelak, V. S., & Galetta, S. L. (2001). Ocular myasthenia gravis. Current treatment options in neurology, 3(4), 367-376.

Phillips, L. H. (2003). The epidemiology of myasthenia gravis. Annals of the New York Academy of Sciences, 998(1), 407-412.

Porter, N. C., & Salter, B. C. (2005). Ocular myasthenia gravis. Current treatment options in neurology, 7(1), 79-88.

Pruitt, J. A. & Ilsen, P. F. (2010). On the frontline: What an optometrist needs to know about myasthenia gravis. Optometry-Journal of the American Optometric Association, 81(9), 454-460.

Walsh, G; Rafferty, P. R & Lapin, J. (2006a). A simple new method for the construction of a ptosis crutch. Ophthalmic and Physiological Optics, 26(4), 404-407.

World Optic (2016). About ptosis eye crutches, Retrieved from http://www.worldoptic.com/eyewear-modifications/eyeglasses-ptosis-drooping-eye-lid crutches.php#.V9gFS_l95QJ.

Megan Findlay (1)

Medical Devices Lab, Division of Biomedical Engineering, Department of Human Biology, University of Cape Town, Cape Town 7925, South Africa

megsfindlay@gmail.com

Jeannine Heckmann, FCN, PhD2

Division of Neurology, Department of Medicine, University of Cape Town, Cape Town 7925, South Africa

jeanine.heckmann@uct.ac.za

Sudesh Sivarasu, PhD (1)

Medical Devices Lab, Division of Biomedical Engineering, Department of Human Biology, University of Cape Town, Cape Town 7925, South Africa

sudesh.sivarasu@uct.ac.za

http://dx.doi.org/10.4314/esa.v28i2.5

Caption: Figure 1. A Photograph of an MG patients (primary gaze) with bilateral ptosis (photograph used with permission from the patient).

Caption: Figure 2. A ptosis crutch permanently attached to the spectacle frame [taken from Walsh, 2006].

Caption: Figure 3. A model illustrating the desired outcome of the ptosis crutch. The ptosis crutch was intended to elevate the eyelid from the position illustrated by image A to the position illustrated by image B. Image B does not represent a normal eyelid position, but an eyelid elevated above the visual axis.

Caption: Figure 4. A model of the ptosis crutch. A] Crutch bar. B] Control and connection between the spectacle attachment and the crutch bar. C] Attachment to spectacles.

Caption: Figure 5. Photographs of an MG patient in primary gaze. A] Without the aid of the ptosis crutch. B] With the aid of the ptosis crutch attached to the superior border of the spectacle frame.

Caption: Figure 6. A photograph of the ptosis crutch attached to the spectacle border. A] Front view. B] Superior view.
Table 1. The anthropometric measures that were recorded for each
participant.

Pre-design Testing          Participant Information

Number of participants      Male: 6
                            Female: 10

Age                         42 [+ or -] 23 years

Race group                  Black: 14
                            Caucasian: 2

Post-design Testing

Number of participants      Male: 3
                            Female: 9

Age                         43 [+ or -] 24 years

Racial group                Black: 10
                            Caucasian: 2

Table 2. The anthropometric measures that were recorded for each
participant.

Measurement            Description of           Reason for observation
                       measurement

Vertical palpebral     The distance from the    Upper eyelid position
fissure                bottom of the upper
                       eyelid margin to the
                       top of the bottom
                       eyelid margin

Marginal reflex        The vertical             Upper eyelid position
distance               measurement between
                       the centre of the
                       pupil and the upper
                       eyelid margin

Horizontal palpebral   The distance from the    The length of the
fissure                lateral to the medial    crutch.
                       border of the eye
                       aperture

Vertical corneal       A vertical line          The centre of the
diameter               measuring the limbus     cornea is approximated
                       to limbus distance       to the centre of the
                                                pupil. The measurement
                                                informed the elevation
                                                required to clear the
                                                visual axis

Table 3. The ptosis crutch frequency of use by 8 participants. The
frequency of use was reported after the participants had been using
the crutch for a minimum of one month.

Frequency of crutch use                  Number of patients

Used full time                                   0
Used occasionally (4 hours per day)              6
Used minimally (<4 hours per day)                2
Not used                                         0
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Author:Findlay, Megan; Heckmann, Jeannine; Sivarasu, Sudesh
Publication:Ergonomics SA
Date:Dec 1, 2016
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