Monocular elevation deficiency (MED) or double elevator palsy (an older term) is when one eye fails to elevate in all horizontal orientations of the eye. This leads to one eye pointing downward, relative to the unaffected eye (hypotropia). Previously, it was thought both the deficiency in the superior rectus muscle and inferior oblique muscle was responsible for this condition, hence the term 'double elevator palsy.' However, literature has established that weakness in either one or both elevator muscles and elevation restrictions can cause the disease leading to a change of name to ‘monocular elevation deficiency.’
This rare condition is a type of strabismus where the eye(s) are misaligned. It is found in both genders equally, and mostly affects children from seven months and 21 years, although it can also be congenital. Though inconclusive, research suggests that the right side more than the left, is affected in congenital cases. Other research indicates that the condition has a preference for the left side in acquired cases.
Also Known As
- Double elevator palsy
- Type 1 with poor Bell’s phenomenon (medical sign), an extra lower eyelid fold when attempting an upgaze, and generally a restrictive form
- Type 2 a paretic (partial paralysis) form with Bell’s phenomenon absent
- Type 3 is often congenital and a combination form
Causes & Risk Factors
MED is primarily caused by the paralysis or restriction of the superior rectus, inferior oblique elevator muscles, or both. Some children are born with the condition (congenital), while others can acquire it. In congenital cases, MED is reportedly sporadic, although some cases of twins having it have been cited. For congenital MED cases, the cause may be a defect in the affected region, restrictions of the inferior rectus that cause the inability to elevate the eye, and primary superior rectus paresis (partial paralysis).
Causes of acquired MED include diseases such as high blood pressure, arteritis, and thromboembolism. Other conditions and situations can also cause the disease, such as syphilis, sarcoidosis, and certain midbrain tumors like pineocytomas. There is no evidence so far that MED is a hereditary disorder.
MED is associated with several disorders such as ptosis and Marcus Gunn jaw-winking. There is no known association between MED and neurological or systemic conditions.
Signs & Symptoms
Signs and symptoms may include:
- Abnormal head posture
- Diplopia (double vision)
- Vertical eye misalignment
- Inability to elevate the affected eye
Diagnosis is made through the following:
- Medical and ocular history
- A slit-lamp examination
- A complete ophthalmic examination
- A test of ocular motility (eye movement)
- Use of an indirect ophthalmoscopy to examine the inside of the back of the eye
- Measurement of deviation using tests such as the Hirschberg test on uncooperative children
- Refraction tests to check for the presence of refractive errors such as myopia, hyperopia, and astigmatism
- Assessment of visual acuity using the Snellen chart. For uncooperative children, a fixation pattern can be used
- An external clinical examination to check for the symptoms. Diagnosis of MED is primarily made through a clinical diagnosis with importance attached to differentiating it from other conditions that present with similar symptoms. These disorders include Brown syndrome, vertical Duane syndrome, and craniofacial abnormalities where the inferior oblique and superior rectus are absent from birth. Others include congenital fibrosis of extraocular muscles, third nerve palsy, myasthenia gravis, labyrinthine disorders, cerebellar tumors, etc.
The goal of treatment is to improve vision by increasing the binocular vision field. This is accomplished through improving the affected eye's position in primary gaze (when looking straight ahead of the face).
If amblyopia is present, the better-seeing eye can be patched to strengthen the affected eye. Underlying refractive errors are treated with glasses.
MED is managed through surgery if the chin-up posture of the head and/or hypotropia are significant. Other factors that may necessitate surgery include amblyopia induced by deviation, binocular fields that are restricted, diplopia in primary gaze, and vertical deviation in primary gaze. Often, the surgeon will operate on the affected eye. However, s/he may perform surgery on the other eye as well for full correction of the deficit. The type of elevation deficit will determine the kind of surgery to be performed. Types of surgery include inferior rectus recession, a Knapp procedure, a partial tendon transposition, etc.
Prognosis & Long-Term Outlook
MED treatment can have positive outcomes if the correct surgical method is selected. Thus, there is a need for accurate diagnosis for satisfactory results.
Prevention & Follow Up
Follow-up is scheduled by the ophthalmologist and will depend on the type of procedure and patient response.