Inverse Bell's Phenomenon
Inverse Bell’s phenomenon:
Disease Entity: Disease: Inverse Bell’s phenomenon is a rare ophthalmic phenomenon that causes reflexive globe hypotropia during forced eyelid closure. Normal Bell’s phenomenon, Bell’s reflex, or palpebral oculogyric reflex, is normal upwards and lateral deviation of the eyes upon forced eyelid closure to avoid corneal exposure. Therefore, inverse Bell’s phenomenon refers to an abnormal downwards and inwards movement of the eyeball upon forced eyelid closure. Can be found in both children and adults, inverse Bell’s phenomenon is associated with numerous ocular and systemic conditions, including and not limited to peripheral facial nerve palsy, conjunctival scarring, trauma, tabes dorsalis, eyelid swelling, ectropion of the upper lids, and extensive ptosis surgery; however, it can also be seen as part of the normal physiological response to eyelid closure.1 2
Levator resection to treat ptosis is one of the most frequently performed surgeries in ophthalmology with a potential early complication of transient inverse Bell’s phenomenon. Typically, inverse Bell’s phenomenon is seen bilaterally and returns to normal in days to months without intervention following recovery postoperatively. Overall, the prognosis of inverse Bell’s Phenomenon is good with recovery, to normal.9 Nevertheless, lubrication of the eye is recommended to prevent corneal damage.4
Anatomy The oculomotor nerve, third cranial nerve, or CN III has three primary motor functions and no sensory function: 1. Innervation to the pupil and lens (autonomic, parasympathetic) 2. Innervation to the upper eyelid (somatic) 3. Innervation of the eye muscles that allow for visual tracking and gaze fixation (somatic)
The oculomotor nerve exits the brainstem near the midline at the base of the midbrain just caudal to the mammillary bodies. It passes through the cavernous sinus and proceeds through the supraorbital fissure to reach the orbit.10 The oculomotor nerve elevates the upper eyelid by innervating the levator palpebrae superioris muscle and supplementation by the superior rectus muscle. Innervation to medial rectus, inferior rectus, and inferior oblique muscles adduct, retracts, and elevates the eye during adduction, respectively.10
Additionally, cranial nerves IV (trochlear), VI (abducens), and VII (facial) are also associated with the misdirection of oculomotor movements. Isolated injury to CN III nerve or its nucleus in the midbrain are rare, so most lesions result in complete limitation of eye movement, dilated pupil, and ptosis. CN IV or trochlear nerve similarly has its nucleus in the midbrain, innervating the contralateral superior oblique muscle and allowing for movement of the eye inferiorly when the eye is adducted. A lesion to CN IV results in vertical diplopia. The final cranial nerve responsible for ocular movement is CN VI or abducens, which originates in the pons and innervates the lateral rectus muscle. An abducens lesion presents with inward deviation of the eye at rest. The linkage between CN III and VI is the median longitudinal fasciculus allowing for the extraocular muscles to coordinate.11,13,14 Injury to any of these nerves, nuclei, or tracts could lead to abnormal eye movements.
Etiology There are numerous etiologies of inverse Bell’s phenomenon including peripheral facial nerve palsy, conjunctival scarring, and ptosis surgery, with ptosis repair being the most well-documented and common cause.8 Additionally causes include cicatricial entropion of the upper eyelids, Salzmann nodular disease, thyroid disease, or following surgical correction of monocular elevation deficiency (MED) and hypotropia.
Inverse Bell’s phenomenon has been hypothesized to correspond to the location of Salzmann’s nodules. Patients presenting with superior Salzmann nodules have been observed to exhibit inverse Bell’s phenomenon, whereas a normal Bell’s phenomenon presented with inferior nodules.7
Pathogenesis A proposed explanation for inverse Bell’s phenomenon is injury to the oculomotor nerve innervating the superior rectus muscle causing malfunction of the trigemino-oculomotor projection alongside hyperemia of the superior fornix, resulting in abnormalities between the superior rectus movement and the eyelid.4
Similarly, an abnormality in the relationship between CN IV and VII cranial nerve nuclei could result in an abnormal response from the superior oblique and inferior rectus muscles.10
Nevertheless, damage to the soft tissue, edema, or inflammation relation to the superior rectus could also be a potential cause for the inverse Bell’s phenomenon considering levator resection causes some degree of intraoperative tissue manipulation.1 Typically, inverse Bell’s phenomenon resolves in a similar timeline to the resolution of postoperative lid edema and ecchymosis following levator resection or frontalis sling suspension procedure.1
Epidemiology Bell’s phenomenon has variability across the population, with about 10% of normal individuals exhibiting deviation from the norm.2 Approximately 8% of individuals have a downwards or inverse Bell’s phenomenon response naturally.2 The variation among the downwards ocular movements is drawn below in Figure 4.
The youngest documented case occurred in a six-year- old kid following congenital levator resection.1 This suggests that inverse Bell’s phenomenon can affect any age ranging from childhood to adulthood.
Risk Factors In approximately 17% of people, the Bell’s phenomenon downwards response have been associated with ocular surface abnormalities (e.g., . inferior keratitis, reduced tear production, redundant conjunctiva, and severe corneal ulcer resulting in evisceration).2 Furthermore, it may present as a complication of other ocular diseases including, but not limited to, peripheral seventh nerve palsies, tabes dorsalis, eyelid swelling, scarring of conjunctiva, ectropion of upper lid, and most commonly after ptosis repair.6 7
Additionally causes include cicatricial entropion of the upper eyelids, Salzmann nodular degeneration, Thyroid eye disease, or following surgical correction of monocular elevation deficiency (MED) and Hypotropia in Med Type II.
Ptosis repair for congenital ptosis, residual ptosis, or repeat surgical attempts to correct ptosis are more likely to develop inverse Bell’s phenomenon.4 According to a 1965 study, the overall prevalence of inverse Bell’s phenomenon is 2% in normal ptosis repair postoperatively.8 However, other studies suggest that inverse Bell’s phenomenon is correlated with the amount of levator resection.20 In a study of large levator resections spanning from 18mm - 28mm, only two of the 32 patients presented with inverse Bell’s phenomenon.20
Diagnosis: History Inverse Bell’s phenomenon is often seen in the immediate postoperative period of extensive levator resection. A detailed history of the patient’s past procedures as well as a preoperative assessment of their Bell’s reflex would be crucial to determine whether the inverse Bell’s phenomenon is deviation for the norm for that patient, or if it was part of the normal variation of extraocular movements during forced eyelid closure.
Physical examination: Gross physical examination of the Bell’s phenomenon can be observed when the examiner ask the patient to close his eyes while he simultaneously elevates the patient’s upper eyelids with his finger and thumb.2 If the exam is positive for inverse Bell’s phenomenon, the examiner will observe the downward rolling of the eyeball during forced eyelid closure.4 There should be no restriction of eye movement on any gaze.8
Clinical Diagnosis Diagnosis of inverse Bell’s phenomenon is typically a clinical diagnosis. Pre and postoperative assessment of the Bell’s reflex is paramount following ptosis surgery and also for diseases involving progressive external ophthalmoplegia and oculomotor palsies, complications of lagophthalmos following corneal abnormality.2
Diagnostic procedures Following physical postoperative ocular examination of globe movements upon eyelid closure various imaging studies can be used to determine whether the positive inverse Bell’s phenomenon is due to a neuro reflexive, iatrogenic, or other cause. - Electrodiagnostic testing to stimulate CN III, IV, and VI to determine the level of oculomotor nerve injury - Electronystagmography - Magnetic resonance imaging (MRI) could be performed for the following: - Patients younger than 50 years - History of cancer - CN III, IV, and/or VI nerve palsy - Optic nerve edema - If no marked improvement is seen after 3 months or other nerves become involved (Citation: Abducens eyewiki)
Management: General treatment: No proven treatment or medical therapy for inverse Bell’s phenomenon. Typically, inverse Bell’s phenomenon will spontaneously resolve in a few days to a few months following ptosis surgery.1 An article published in 2019 found that spontaneous resolution of inverse Bell’s phenomenon three weeks following surgery potentially correlates to the decrease in tissue edema and inflammation.20
However, “copious lubricating eye drops, and frequent examination of the eye is required until it gets resolved.”4
Complications: The most likely complication due to inverse Bell’s phenomenon is the appearance of exposure keratitis following corneal exposure post-levator resection due to inadequate protection by the lower eyelid. This complication can be managed through heavy lubrication in the postoperative period.4 5 20
Prognosis The prognosis for inverse Bell’s phenomenon depends on the underlying etiology. In most cases of inverse Bell’s phenomenon patients will return to normal following days to months without medical intervention.
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24 Abraham, S. V. (1931, July). Bell's Phenomenon and the Fallacy of the Occlusion Test. American Journal of Ophthalmology, 14(7), 656-664. https://doi.org/10.1016/S0002-9394(31)91154-9. 25 Deb, I. (2015). The Importance of Monocular Elevation Deficiency (MED) in Congenital Ptosis. AIOC, 73. 26 Gupta, J. S., Chatterjee, A., & Kumar, K. (1965, May). Inverse Bell's Phenomenon as a Protective Mechanism. American Journal of Ophthalmology, 59, 931-933. 27 Morawala, A., Sharma, A., & Naik, M. N. (2019). Inverse Bell’s phenomenon: a rare complication of levator resection surgery in a case of congenital ptosis. BMJ Case Reports, 12(11). https://doi.org/10.1136/bcr-2019- 232451 28 Victoria, A. C., Chuck, R. s., Rosenberg, J., & Schwarcz, R. M. (2011, July). Timing of eyelid surgery in the setting of refractive surgery: preoperative and postoperative considerations. Current Opinion in Ophthalmology, 22(4), 226-232. https://doi.org/10.1097/ICU.0b013e328347b275 29 Yum, C. L., Kwok, T. Y., & Yuen, H. K. (2022, 12 29). Reversal of inverse Bell’s reflex after sling removal and scar lysis in an 11-year-old patient: a case report. Hong Kong Journal of Ophthalmology, 26(2). https://www.hkjo.hk/index.php/hkjo/article/view/328