|When patients with facial nerve palsy reach the contraction phase, the skin of the lower and upper eyelids may contract due to stiffening or loss of elasticity of the tarsus. Photo: James Heilman, MD. Click image to enlarge.|
As early as three months following the onset of facial nerve palsy (FNP), patients can experience effects such as skin contraction and muscle stiffness. During this contraction phase, many will also experience horizontal shortening of the lower eyelid margin. A recent study published in Eye confirmed this finding, leading its authors to believe that measuring punctum-to-canthus distance may have utility in the evaluation of soft tissue contraction following FNP.
The study included the data of 24 patients diagnosed with FNP without a history of surgery that could manipulate the length of the lower eyelid margin (i.e., periosteal flap or lateral tarsal strip). The mean age of the cohort was 52.5 years, and 54% were female. Using a straight plastic ruler, the horizontal length of the lower eyelid margin was measured from the lower lacrimal punctum to the lateral canthal angle, which the researchers referred to as “PC distance.” Lids were measured on a gentle stretch, which straightens the eyelid margin in all three dimensions without distorting the eyelid or closing the palpebral aperture.
Compared with fellow eyes, those affected by FNP had a significantly shorter PC distance on average (27.5mm vs. 26.0mm) with a mean difference of 1.5mm between the eyes. Notably, three of 24 patients had been diagnosed less than one year prior to their ocular exams and were still in the paralytic phase of FNP. In these individuals, affected eyes did not demonstrate shortening of the lower eyelid margin (mean difference: 0mm), providing evidence to support the hypothesis that this measurement is not affected prior to the contraction phase. When looking only at patients in the contraction phase, the mean difference in PC distance was 1.7mm (range: 0 to 4mm) between affected and fellow eyes.
The researchers also observed a statistically significant difference in lid-margin-to-brow distance in affected vs. fellow eyes (28.8mm vs. 31.2mm), signifying the presence of contraction of the ipsilateral upper eyelid skin. The mean difference between the lid-margin-to-brow distance of both eyes was 2.5mm. Similar to the trend observed in the lower eyelid, affected eyes of patients in the contraction phase showed a greater reduction in lid-margin-to-brow distance than those in the paralytic phase (2.7mm vs. 1mm). A weak association was found between reduction in lower eyelid PC distance and reduction in upper eyelid lid-margin-to-brow distance.
“Whilst this is a relatively small consecutive case series, this study's findings are supported by the fact that there were no cases in which PC distance was greater in the affected eye than the fellow eye, and in cases where a reduction in PC distance was found, a reduction in upper eyelid lid-margin-to-brow distance was also observed to be present,” the researchers pointed out in their paper. “On the former point, the fact that there were no cases in which PC distance was greater on the affected side than the fellow side provides evidence that horizontal laxity and eyelid length do not increase in FNP.” Because of this, the researchers advise clinicians to consider that shortening the eyelid may not be the appropriate solution for these patients.
In summary, the team concluded that FNP patients may present with horizontal shortening of the lower eyelid in the contraction phase due to stiffening or loss of elasticity of the tarsus. “Punctum-to-lateral-canthus distance adds an additional tool in the overall assessment of soft tissue contraction following FNP and raises the clinician's awareness of the possibility of horizontal contraction,” they added.
Jamison A, Patel BCK, Malhotra R. Horizontal shortening of the lower eyelid margin in facial nerve palsy. Eye. July 6, 2023. [Epub ahead of print].