Benign essential blepharospasm (BEB) is characterised by bilateral involuntary spasmodic contraction of the eyelid protractors where aetiology is not known. Hemifacial spasm (HFS), in contrast is usually unilateral with an identifiable underlying cause, including a vascular loop or tumor compression of the facial nerve [1-3].

Botulinum toxin (BT) and surgical extirpation of eyelid protractor muscles are the most effective treatments available [1-7]. Most patients with blepharospasm benefit from reduction of sensory triggers, particularly light, and tinted lenses can significantly reduce spasm in some patients [8-11]. Nearly 80% of patients with BEB report that bright light triggers or exacerbates their symptoms [3], and patients with BEB have been shown to be more light-sensitive than controls [8].

Bangerter occlusion foils (BOF) are translucent, plastic filters that adhere to the front of a spectacle lens. They block light transmission and reduce visual acuity in a graded fashion. We previously reported a case of facial palsy-induced bilateral blepharospasm, which improved with the placement of a hand a few centimetres in front of either eye (“occlusion-positive”) [12]. The subsequent placement of a BOF over one spectacle lens has allowed this patient to remain asymptomatic without the need for any other treatments, including BT injections.

We have since observed a similar reduction in symptoms using the BOF in other occlusion-positive (OP) patients with BEB and curiously also with HFS. The aim of this pilot study was to test the hypothesis that the BOF improves symptoms of BEB and HFS in OP patients, but not occlusion-negative (ON) patients, helping establish the clinical utility of the occlusion-sign in identifying patients most likely to benefit from the BOF.

Fifteen-patients (6 with BEB, 9 with HFS) completed the study. Six (40%) patients (5 female, 1 male) were occlusion-positive (OP) and 9 (5 female, 4 male) were occlusion-negative (ON). Of the 9 patients with HFS, 2 were OP and 7 were ON. Of the 6 with BEB, 4 were OP and 2 were ON. Mean age was 63.3 years (range 44-80 years) and 73.5 years (range 43-93 years) for the OP and ON groups, respectively.

The results of this pilot study support our hypothesis that occlusion-positive patients with BEB or HFS are more likely to experience a reduction in their symptoms from wearing the BOF, than those who are occlusion-negative. When measured subjectively with the CDQ-24 QOL, and objectively with observation of blink-rate, frequency and severity of spasm, OP patients showed a statistically significant difference in improvement for blink-rate and severity of blepharospasm compared to ON patients.

Anderson et al. [3] have suggested a simple conceptual approach to the multiple factors underlying the origin and manifestations of BEB. They propose that blepharospasm is due to a defective neurological circuit rather than a specific defective locus. Afferent stimuli, such as light and ocular irritation, are transmitted via the optic and trigeminal nerves to an as-yet-unidentified control centre, which may be located in the basal ganglia, midbrain or brainstem. Dysfunction of this centre results in failure of modulation of efferent signals transmitted by the facial nerve to the eyelid protractors, leading to involuntary eyelid contracture. This aberrant cycle becomes self-perpetuating as the resultant eyelid spasms create further irritation of the eyes, which will act as sensory stimuli [3]. Sensory triggers for BEB include bright light and ocular irritation [3, 8, 16]. Both FL41-tinted and grey-tinted lenses can significantly improve blepharospasm [9, 11].

Perhaps more curious is the finding of occlusion-positivity and the effect of the BOF in patients with HFS. HFS has traditionally been considered to be due to an identifiable underlying condition affecting the facial nerve. Furthermore, just as in facial palsy-induced blepharospasm, where in an isolated case we first found the BOF to be effective, patients with HFS also tend not to be light-sensitive or photophobic [12]. Interestingly, prior facial-palsy has been recognised in up to 1 in 4 cases of HFS and perhaps electrophysiology may play a more valuable role in identifying such patients and possibly helping further understand the basis of occlusion-positivity [15, 16]. However, we have also anecdotally observed that some patients with HFS experience reduction in their lower facial as well as eyelid spasm from wearing FL-41 tinted spectacle lenses. We believe that the role and thus modulation of sensory stimuli in HFS therefore remains an area that requires further study.

The BOF degrades visual acuity by reducing light transmission, and may improve blepharospasm by reducing noxious light or other complex visual stimuli mediated by the trigeminal and optic nerves into the aberrant blink cycle. All patients in the study had used tinted lenses with variable success. As no measurements of light-sensitivity were made, it is not possible to comment on whether the OP patients were more light-sensitive or had more light-induced spasm than ON patients, but this may have influenced response rates between the two groups.

Many questions remain unanswered about the mechanism of action of the BOF on reducing spasm, and these should be the subject of further study. Firstly, if reduction in light transmission is their main effect, why do they work with unilateral wear, and would we have expected a greater effect if they had been worn bilaterally, as tinted lenses are? Inducing visual blur bilaterally would be impractical and unacceptable to most patients. It has also been our experience that unilateral wear evokes a sufficient response in those patients responsive to the BOF, and that this response is the same regardless of the side of wear (left or right), even in our HFS patients. These observations suggest that the underlying mechanism for the BOF is much more complex than just reduction in light transmission or vision. It may well simply act as a distraction, but nevertheless, this possible distraction-effect remained for the duration of the study and further studies may help define long-term benefit.

We acknowledge significant flaws in this study. Confounding factors that may have influenced outcomes in the two groups include placebo effect, selection bias, and duration of wear and strength of BOF. As patients were aware of the working hypothesis on enrolment into the study, and were not masked to their occlusion status, a placebo effect in the OP group may have contributed to their better overall results.

The better results obtained in the OP groups may also have been due to selection bias, as 50% of the OP group (3/6) had already been using the BOF for blepharospasm with good effect prior to enrolment.

It would be expected that patients who wore the BOF more consistently, and who tolerated more reduction in visual acuity, would gain more effect. Whilst a greater proportion of the OP group (80%) wore the BOF full-time compared to the ON group (67%), and the mean strength of foil used was also stronger in the OP group (0.45) than in the ON group (0.58), the small numbers of patients in both groups did not allow meaningful statistical analysis of this difference. However, duration of wear and strength of BOF prescribed is patient-driven and reflects what is acceptable to patients in everyday life. Enforcing a certain strength and duration of wear between the OP and ON patients in this study may have increased the accuracy of our results, but would not have reflected how we would practically prescribe this treatment to our patients. The strength of BOF worn ranged between 0.3-0.6 in the OP group, equating to a unilateral reduction of vision of 20/30-20/80 (mean 20/40). This did not affect patients’ ability to carry out normal daily tasks; however, patients often opted not to use the BOF during activities such as work, where clear binocular vision was essential. In our study we excluded patients who were predominantly monocular, however, unilateral blur may contribute to loss of depth perception and impair mobility in patients who are already impaired, many of whom may also be elderly. This further limits the suitability of BOF or other uniocular occlusion modalities.

With no conceivable cure in sight and current treatments offering variable symptomatic control, any treatment which is safe, effective, affordable and acceptable to patients, is a welcome addition to the evidence-based management of this difficult condition. The BOF meets many of these criteria. There were no significant side effects from wearing the BOF in this study, but practical problems, such as the accumulation of dirt and bubbles under the stick-on foil, which increased visual blur, occurred. This was easily rectified by changing of this cheap foil (approximately 4 US dollars each). Whilst one OP patient in this study has not required any BT since wearing the BOF, all other patients have required ongoing BT injections for optimal blepharospasm control. We anticipate that the impact of the BOF will be as an adjunctive to the mainstay treatments of BT and surgery. It remains to be seen whether the BOF can reduce the amount or frequency of BT required in responsive patients, but this would clearly be beneficial.

In conclusion, the results of this small pilot study suggest that patients with idiopathic blepharospasm or HFS may demonstrate the phenomenon of occlusion-positivity. Those positive are more likely to experience a reduction in spasm with a BOF than occlusion-negative patients. Whilst further study with larger patient numbers is required, we suggest that patients with BEB or HFS be examined for occlusion status, and that the BOF be considered as an adjunctive treatment in patients who are occlusion-positive.

Royal College of Ophthalmologist’s Annual Congress, May 2008.