Electrical activity of the orbicularis muscles before and after installation of ocular prostheses

Abstract

This study examined the electrical activity of the superior (SO) and inferior (IO) orbicularis oculi muscles before and after installing ocular prostheses in patients who had undergone unilateral enucleation. Twelve volunteers requiring prostheses were selected. Their electrical activity was monitored at rest and during normal opening and closing of the eyelids, rapid opening and closing of the eyelids, and squeezing. Data were recorded before and 7, 30, and 60 days after the ocular prosthesis was installed. Two-way analysis of variance was performed to verify whether there were any significant differences between the muscles and periods, and means were compared by Tukey–Kramer honestly significant difference (HSD) tests ( P < 0.05). Results from the initial period differed significantly from those after prosthesis installation in all clinical situations. The SO had significantly higher electrical activity levels than the IO in all clinical situations but squeezing. The authors observed the same values during the initial period for the condition of rest (SO 8.42/IO 5.93) and the highest values for the condition of squeezing after 60 days (SO 131.50/IO 117.12). Rehabilitative treatment promoted an increase in the electrical activity of the orbicularis oculi muscles, restoring part of the muscle tone and motor function to muscles of the affected area.

Orbital defects are embarrassing to patients because they affect the face, which is essential to human relationships. The absence of an ocular globe can lead to atrophy of the orbicularis muscles of the eye, thereby altering the muscle tone of the facial area. The palpebral cutaneous musculature is of supreme importance to facial appearance and expression, and it protects the ocular cavities. Three ocular–orbital–palpebral surgeries are related to ocular bulb removal: evisceration, comprising the partial removal of the ocular bulb with conservation of the sclera; enucleation, comprising the total removal of the bulb with only the capsule and oculomotor muscles remaining; and exenteration, comprising the removal of all contents of the orbital cavity and the circumjacent tissue.

To rehabilitate patients with deformities of the ocular bulb, an ocular prosthesis may be used. Prosthesis use improves the patient’s aesthetic appearance, helping their psychosocial development and improving their quality of life. The prosthesis does not restore the original function of vision, but it keeps the anophthalmic cavity filled, restoring lacrimal direction and preventing lacrimal fluid accumulation in the cavity.

Few studies in the literature have examined the activity of the orbicularis oculi muscles after prosthesis installation, and all of them have been based solely on clinical observations. Thus, the purpose of this study was to determine whether the muscle tone is influenced by prosthesis installation. Accordingly, the electrical activities of the superior and inferior orbicularis muscles (SO and IO, respectively) were evaluated before and after ocular prostheses were installed in patients with unilateral enucleation of the ocular bulb. The study hypothesis was that rehabilitative treatment with an ocular prosthesis would affect the electrical activity of the orbicularis muscles.

Patients and methods

Participant selection

The study included 12 volunteers (age range 50–65 years) with unilateral enucleation of the ocular globe (time since ocular globe loss 6–24 months) and an indication for a prosthesis, based on anamnesis and clinical examinations. Exclusion criteria were as follows: prior use of an ocular or expander prosthesis; extreme atresia of the anophthalmic cavity; and an inability to perform the tests due to insufficient cognitive ability. Volunteers received information about the treatment to be used and signed a consent form, in accordance with the recommendations of the institutional ethics committee for human research.

Electromyographic examination

Electromyographic (EMG) examinations were performed with the MyosystemBr1 electromyograph (DataHominis Tecnologia Ltda, Uberlândia, Minas Gerais, Brazil) ( Fig. 1 ). EMG signals were conditioned using instrument amplifiers, which were programmable via software, and analogue band-pass filters with 10-Hz high-band and 1000-Hz low-band frequencies. Signals were digitized with a sampling frequency of 2 kHz, with 12 bits of resolution and simultaneous signal sampling. For data collection, the equipment gain was adjusted to 2000 times. To visualize and process the EMG signal, Myosystem I software version 2.12 was used.

Fig. 1
MyosystemBr1 electromyograph and bipolar surface electrodes.

Bipolar surface electrodes (DataHominis Tecnologia Ltda) were used for EMG recording. Electrodes were positioned on the SO and IO muscles of both eyes (the enucleated eye and the healthy eye) ( Fig. 2 ) . The EMG signal was captured in four clinical situations: rest, normal opening and closing of the eyelids (OCE), rapid opening and closing of the eyelids (ROC), and squeezing. Each situation was recorded for 10 s. EMG examinations were performed before and 7, 14, 30, and 60 days after the ocular prosthesis was installed and in use. The EMG record of the orbicularis muscle of the patient’s healthy eye was used as the control.

Fig. 2
Bipolar surface electrodes positioned on the superior (SO) and inferior (IO) orbicularis oculi muscles of the eye.

Manufacture of the ocular prosthesis

An ocular prosthesis was made individually for each patient, according to the technique described by Goiato et al.

Data analysis

Two-way repeated-measures analysis of variance (ANOVA) was performed to verify whether there were statistically significant differences between the muscles and periods (time points) for each clinical condition. The means were compared by Tukey–Kramer honestly significant difference (HSD) tests using SPSS version 19.0 statistical software (SPSS Inc., Chicago, IL, USA). All the results were analysed at a significance level of 0.05.

Results

Table 1 shows the electrical activity values for each clinical condition (rest, OCE, ROC, and squeezing), muscle (location analysed, SO and IO), and time point (initial, 7, 14, 30, 60 days and control).

Table 1
Electromyographic activity (μV) of the orbicularis muscles for analysed clinical conditions at different times after installing the ocular prosthesis. a
Condition Muscle Period (days) Control
Baseline 7 14 30 60
Rest SO 8.42 ± 2.12 10.03 ± 2.13 10.62 ± 1.81 10.82 ± 1.88 10.89 ± 1.85 10.87 ± 1.90
IO 5.93 ± 1.62 7.82 ± 2.30 8.16 ± 2.03 8.19 ± 1.84 8.22 ± 1.96 8.55 ± 1.82
OCE SO 9.27 ± 1.93 12.18 ± 2.15 12.69 ± 1.94 12.89 ± 1.88 12.89 ± 1.98 12.62 ± 1.53
IO 7.89 ± 2.02 10.39 ± 2.15 10.77 ± 1.99 10.83 ± 1.98 10.94 ± 2.04 10.94 ± 1.48
ROC SO 13.32 ± 2.92 22.74 ± 3.51 24.93 ± 2.89 25.77 ± 3.41 25.81 ± 3.49 25.18 ± 3.40
IO 10.88 ± 2.96 15.84 ± 3.81 17.99 ± 4.32 18.49 ± 4.63 18.78 ± 4.94 18.48 ± 2.95
Squeezing SO 76.68 ±17.02 118.97 ± 14.93 127.78 ± 22.44 130.05 ± 23.01 131.50 ± 21.05 135.51 ± 24.25
IO 65.85 ± 19.01 108.80 ± 15.38 113.96 ± 21.17 116.66 ± 20.82 117.12 ± 19.41 124.73 ± 23.50
SO, superior orbicularis; IO, inferior orbicularis; OCE, normal opening and closing of the eyes; ROC, rapid opening and closing of the eyes.

a Data are shown as the mean ± standard deviation. The control was the contralateral healthy eye.

ANOVA revealed a significant difference ( P < 0.0001) in the electrical activity values for time point in all clinical conditions ( Tables 2–5 ). There was significantly higher electrical activity according to the muscle in all clinical situations but squeezing (ANOVA, Table 5 , muscle P > 0.05). In addition there was no significant difference in the interaction of all factors for the clinical conditions of rest, OCE, and squeezing ( P > 0.05) ( Tables 2, 3 and 5 ). However, there was a statistically significant difference in the interaction of all factors for the ROC condition ( Table 4 ). The electrical activity levels of the ROC condition exhibited significantly higher values for the SO muscle than the IO muscle for each time period, excepting the baseline ( Tables 1 and 4 ).

Table 2
Results of two-way repeated-measures ANOVA for the rest condition.
Variation factors df SS MS F P -value
Muscle 1 218.415 218.415 10.485 0.004 *
Between subjects 22 458.275 20.831
Period 5 108.909 21.782 56.813 <0.0001 *
Period × muscle 5 0.903 0.181 0.471 0.797
Within subjects 110 42.174 0.383
ANOVA, analysis of variance.

* P < 0.05 denotes a statistically significant difference.

Table 3
Results of two-way repeated-measures ANOVA for the OCE condition.
Variation factors df SS MS F P -value
Muscle 1 116.268 116.268 5.962 0.023 *
Between subjects 22 429.028 19.501
Period 5 201.858 40.372 69.379 <0.0001 *
Period × muscle 5 1.788 0.358 0.615 0.689
Within subjects 110 64.009 0.582
ANOVA, analysis of variance; OCE, normal opening and closing of the eyes.

* P < 0.05 denotes a statistically significant difference.

Table 4
Results of two-way repeated-measures ANOVA for the ROC condition.
Variation factors df SS MS F P -value
Muscle 1 1390.741 1390.741 23.977 <0.0001 *
Between subjects 22 1276.058 58.003
Period 5 1874.628 374.926 83.371 <0.0001 *
Period × muscle 5 103.563 20.713 4.606 0.001 *
Within subjects 110 494.677 4.497
ANOVA, analysis of variance; ROC, rapid opening and closing of the eyes.

* P < 0.05 denotes a statistically significant difference.

Jan 17, 2018 | Posted by in Oral and Maxillofacial Surgery | Comments Off on Electrical activity of the orbicularis muscles before and after installation of ocular prostheses
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