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Chronic exposure to hypoxia causes corneal thinning in patients with hemifacial spasm
Patients with hemifacial spasms and chronic exposure to hypoxia may show signs of corneal thinning, according to a study conducted at Noor Ophthalmology Research Center at Noor Eye Hospital in Tehran, Iran.
“To the best of our knowledge, thickness of corneal sublayers and corneal endothelium morphology in patients with HFS [hemifacial spasm] have not been evaluated by any previous study,” the authors wrote. “In this study, we aimed to determine whether the corneal topographic parameter values, individual corneal layer thicknesses and its endothelial layer morphology are different in patients with HFS than in the control contralateral eye.”
Researchers evaluated 56 eyes in 28 patients (16 women and 12 men), all with HFS in one eye as the study eye and with one normal contralateral eye as the control eye, according to the study. All patients were scanned with the Pentacam Scheimpflug camera, and a corneal endothelium cell count was recorded. The thickness of the corneas of each patient was measured between 10:00 a.m. and 11:00 a.m. by a single clinician.
Corneal sublayer thickness was measured with the anterior segment module of a spectral domain OCT device. Researchers compared variables between the study eyes and the control eyes of each patients. P values of less than 0.05 were recorded as significantly important to the study.
They noted significant increases in steep K, Kmax and astigmatism in patients with HFSv.
Researchers also found that astigmatism values were higher in the study eyes of each patient with HFS than in the control eyes (P < 0.05). Corneal thickness and corneal stromal thickness measured in the study eyes were significantly thinner than the control eyes (P = 0.04 and P < 0.001, respectively).
They said that chronic exposure to hypoxia may induce corneal stromal thinning, “through extracellular matrix remodeling and losses in collagen framework content in patients with HFS.”
The authors noted that the patients in their study were not staged according to the severity of their HFS.
“The severity of the disease might affect the corneal findings depending on the level of hypoxia,” they said. – by Erin T. Welsh
Disclosure: The authors report no relevant financial disclosures.
Perspective
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This study looks into potential changes in corneal morphology/topography secondary to HFS. It suggests that HFS is associated with increased steep K and corneal astigmatism from greater eyelid pressure during involuntary forceful contractions. In addition, the study proposes that HFS is associated with changes of the anterior corneal surface, specifically thinning of the total cornea and specifically the corneal stroma. No change was found in the corneal endothelium with specular microscopy, suggesting the corneal thinning was secondary to chronic hypoxia-associated keratocyte loss due to ocular surface exposure to lower oxygen levels.
These findings may have clinical significance as applied to refractive surgery, contact lens fitting and intraocular lens calculations in HFS patients. The awareness of irreversible corneal changes in HFS patients enforces the criticality of early diagnosis and treatment.
As optometrists, we need to remember the importance of testing all cranial nerves and looking specifically for subtle findings indicating an abnormality with the facial nerve, especially because HFS usually begins as abnormal fasciculations of the orbicularis oculi muscle. If identified early, HFS patients can be referred to neurology or neurosurgery, and treated with botulinum toxin or microvascular decompression surgery before the HFS leads to changes in corneal morphology or other problems.
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Ulusoy D, et al. Eye & Contact Lens. 2019:doi: 10.1097/ICL.0000000000000597.
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