Strabismus Surgery, Vertical
The term strabismus is derived from the Greek word strabismos, "to squint, to look obliquely or askance”: Strabismus means ocular misalignment, whether caused by abnormalities in binocular vision or by anomalies of neuromuscular control of ocular motility.
Vertical Strabismus refers to a vertical misalignment of the visual axis or vertical deviation. This could be comitant (deviation that is the same magnitude regardless of gaze position) o incomitant (it´s magnitude varies as the patient shifts his or her gaze). Most vertical deviations are incomitant.
It depends on each specific form of verical strabismus subtype. Generally we could said that any malfunction in extraocular muscles associated in vertical function in its origin, course, insertion, innervation, or central nervous system annomaly, secundary to any cause, could lead to a vertical strabismus presentation.
The deviation are described according to the direction of the nonfixating eye. If the ability to alternately fixate is present, the deviation is named for the usually hyperdeviating eye. The terms usually used accordingly the direction of deviation are called with a preffix
- Hyper- The eye is rotated so that the cornea is deviated superiorly and the fovea is rotated inferiorly.
- Hypo- The eye is rotated so that the cornea is deviated inferiorly and the fovea is rotated superiorly.
And a suffix acordingly to the presentation.
- -phoria A latent deviation that is controlled by the fusional mechanism so that the eyes remain aligned under normal binocular vision.
- -tropia A manifest deviation that exceeds the control of the fusional mechanism so that the eyes are not aligned under binocular conditions.
To understand its pathophysiology we must remember that each muscle has primary, secondary and tertiary functions in primary gaze position.
|Superior Rectus||Elevation Intorsion Adduction|
|Inferior rectus||Depression Extorsion Adduction|
|Superior Oblique||Intorsion Depression Abduction|
|Inferior Oblique||Extorsion Elevation Abduction|
- Depressors of each eye are the inferior rectus (IR) and superior oblique (SO) muscles.
- Elevators of each eye are the superior rectus (SR) and the inferior oblique (IO) muscles.
- Intortors of each eye are the superior muscles: SO and SR.
- Extortors of each eye are the inferior muscles: IO and IR.
- Normally, the 2 intortors and the 2 extortors of each eye have opposite vertical actions that cancel each other. If 1 intortor or 1 extortor is weak, it cannot act vertically and the vertical action of the other ipsilateral torting muscle becomes manifest.
With this in mind, we should understand, that any malfunction in its Origin, Course, Insertion, Innervation, or central nervous system annomaly, secundary to any cause, could lead to a vertical strabismus presentation.
As in all patients with strabismus, we must notice the age of onset, percentage of time eye(s) is deviated, misalignment present with distance viewing and/or near viewing, anomalous head positions, family history, medications, health problems, history of trauma and previous ocular treatments used.
First we have to make a general patient revisión: External exam – with special attention in compensatory head tilt. Visual acuity with current correction and best corrected visual acuity. Stereoacuity. Ocular preference. Ocular motility. Pupillary examination (Pupillary light réflex, Hirschberg and Krimsky). Worth four-dot test. Cover test / alternate cover test/ prism and alternate cover test / simultaneous prism cover test. Double Maddox Rods. Fundus examination - to evaluate for ocular torsion. Near point of convergence. Fusional vergences. Slit lamp examination. Cycloplegic Retinoscopy.
Ocular misalignment. Abnormal head position. Diplopia. Asthenopia.
It´s specific to each type of vertical strabismus and is based in all history and clinical examination previously mentioned.
Besides all the normal examination one of the tests that we must have in mind to examine a patient that has vertical strabismus is the 3 step test also known as Parks-Bielschowsky 3-step test. It must be performed while the patient is erect or else the vestibular input, upon which this test is heavily dependent, will be eliminated. This one was made to detect Cyclovertical muscle paralyses, however, we must have in mind that it´s not always diagnostic and can be misleading, especially in patients in whom more than 1 muscle is paralyzed, in patients who have undergone strabismus surgery, in the presence of a skew deviation, and in the presence of restrictions or dissociated vertical deviation. Each of the three steps consists of an alternate cover test measurement of the deviation in the indicated 9 gaze positions: primary position for step one, right and left gaze for step two, and head tilt (of about 45°) to each side for step three.
Step 1 Which eye has hyperdeviation?
- Identify weak depressors in higher eye (IR, SO) and elevators in lower eye (IO, SR)
Step 2 Is hyperdeviation greater in right or left gaze?
- Identify muscles that act in direction as hyperdeviation increases
- Right gaze: SR and IR of right eye, IO and SO of left eye
- Left gaze: IO and SO of right eye, SR and IR of left eye
Step 3 Is hyperdeviation greater with right or left head tilt?
- Identify torting muscles that act in direction as hyperdeviation increases
- Right head tilt:
- Intorsion of right eye (SR and SO)
- Extorsion of left eye (IO and IR)
Circle involved muscles at each step described previously, and the muscle with 3 circles is the one with palsy.
There are many entities that can lead to vertical strabismus. We´ll review the principal entities, it´s clinical presentation and general treatment.
Inferior Oblique Muscle Overaction (overelevation in adduction)
There are 2 kinds of muscle overaction:
- Primary: It´s mainly overfunction of inferior oblique, not associated with superior oblique muscle paralysis.
- Secondary: It´s present when there´s a paresis or palsy of the inferior oblique muscle's antagonist superior oblique muscle or yoke superior rectus muscle.
Develops in about 72% of congenital esotropes, 34% of accommodative esotropes, and 32% of intermittent exotropias developed between 1-6 years.
Usually asymptomatic in primary gaze, but we will see the eye elevated in adduction, both horizontally and in upgaze, also almost never present subjective symptoms of ocular torsion, but they do have objective evidence of excyclotorsion of the involved globes that extends from the center of the disc.
Primary inferior oblique overaction is usually asymmetrical and may be unilateral at onset (23%), also could be bilateral and symmetric.
The presence of fundus excyclotorsion in children with congenital esotropia may predict the later development of inferior oblique overaction.
V-pattern strabismus is often associated with inferior oblique overaction and yields greater exodeviation in upgaze.
There are many grading systems to classify this in general there are classified in 4 grades 1+ -to 4+. Treatment is surgical: a weakening procedure of inferior oblique, depending on severity and surgeon preference.
The weakening procedures in order of less to more are recession 3mm posterior and 2 mm temporal to anterior border of inferior rectus or recession of 10 mm, recession of 14 mm, myectomy, denervation/extirpation. Anterior transposition may be performed if dissociated vertical deviation is also present.
Inferior Oblique Muscle Underaction (Palsy or paralysis)
Few Patients may have true inferior oblique palsy. Usually idiopathic but may follow orbital trauma, viral illness, or other neurologic problems
Patients may have a hypodeviation in primary position if fixing with the nonparetic eye, secondary overaction of the antagonist superior oblique muscle, and an A-pattern exotropia with better elevation in abduction than adduction. May be unilateral or bilateral. Forced duction testing is negative, unless the superior oblique is contracted.
Indications for treatment of inferior oblique muscle paralysis are abnormal head position, vertical deviation in primary position, and diplopia. Primary treatment is surgery, recession of the contralateral superior rectus or weakening of the ipsilateral superior oblique is the usual procedure. Also some will respond adequately with vertical prisms.
Superior Oblique Muscle Overaction (IV Nerve overaction)
Usually asymptomatic, in some in some we will find vertical strabismus in primary position, also we´ll find incyclotorsion of fundus and this could be associated to an A-pattern strabismus. Children who have neurologic dysfunction have been found to have increased incidence of superior oblique muscle overaction
If the condition is significant, the superior oblique may be weakened by tenotomy, tenectomy, graded recession, or lengthening with biological plastic (Silastic) bands.
Superior Oblique Muscle underaction, IV Nerve Palsy or paresis
It´s the most common cyclovertical paralysis. It can be congenital or acquired. Most cases are congenital (idiopathic) or post-traumatically acquired. Another causes less commonly are associated with central nervous system, vascular problems, diabetes, brain tumors, direct trauma, congenitally lax or attenuated muscle/tendon and craniofacial abnormalities. To differentiate if it´s congenital or acquired we could ask the patient for some old photographs to find an abnormally contralateral head tilt (“ocular torticolis”), observe facial asymetry, also large vertical fusional amplitudes indicate chronicity. It´s important because recently diagnosed paralysis that cannot be attributed to known trauma suggests the possibility of a serious intracranial lesion.
Usually present as ipsilateral hypertropia and excyclotorsion. Vertical diplopia or vague reports of “eyestrain” and difficulty reading in downgaze are the most common complaints. Preferred head position consisting of a contralateral head tilt toward the shoulder opposite to the side of the weakness could be found by most patients. Very large vertical vergence amplitudes could develop from 15 to 20 prism diopters (normal value being 3–4 prism diopters) Ipsilateral side is vertically shortened and hypoplastic. This one could be uni or bilateral. Unilateral cases usually have less than 5º of excyclotorsion. In billateral cases at least have 5º of excyclotorsion, and if exceeds 10° or 15° a bilateral fourth nerve palsy is strongly suggested. Also Bielschowsky, head-tilt test yields positive results on tilt to each side, and we could also found esotropia in downgaze.
Hyperdeviation in primary position without torsional component could be treated with prisms to relieve diplopia. Surgery indications: Abnormal head position, significant vertical deviation, diplopia, and asthenopia. Remembering that after an acquired palsy/paresis develops a period of observation lasting at least 6 months before a surgery decision is made as there may be some recovery of function, and to make sure of stability of measurement. Most people can tolerate 7° of torsion. If the deviation in primary position is less tan 15 PD weakening the inferior oblique in the same eye may be sufficient. However, if the child is young and head tilt is very prominent, superior oblique tuck may be considered. For purely excyclotorsional deviation, one should consider Harada-Ito procedure: lateral transposition of anterior portion of SO tendon. If the deviation is larger than 15 PD, 2 muscle surgery may be required - in addition to weakening ipsilateral inferior oblique (or tucking superior oblique), could consider weakening contralateral inferior rectus. Unusually severe cases with a vertical deviation greater than 35~ in primary position, 3-muscle surgery usually is required. In this situation, one could consider recession of the overacting antagonist inferior oblique muscle, ipsilateral superior oblique (yoke) tendon tuck, and either ipsilateral superior rectus recession or contralateral inferior rectus recession, as dictated by forced duction test results. Bilateral superior oblique muscle paralysis requires surgery on both eyes, graded for unequal severity.
Dissociated Vertical Deviation (Dissociated vertical divergence, DVD)
Dissociated vertical deviation is an innervational disorder found in supranuclear control of eye position; this can occur isolated in 40% of patients or associated with any strabismus form that develops early in life. The most common associated is infantile esotropia, it´s presented in 50% of this patients. Seldom present at birth, DVD is frequently a new finding after the age of 2–3 years.
It´s usually bilateral though frequently asymmetric. It may occur spontaneously (manifest DVD) or only when 1 eye is occluded (latent DVD), also could be exacerbated in periods of visual inatention, with or without daydreaming or fatigue. Either eye slowly drifts upward and outward, with simultaneous extorsion, sometimes a horizontal movement is presented in the exotropic direction. We must notice that as the vertically deviated eye moves down (and intorts) to fixate when the previously fixating fellow eye is occluded, the latter makes no downward movement, and no upward movement when cover is moved back to the eye with DVD. This violates Hering’s law.
The deviated eye is suppressed, so visual symptoms seldom occur.
If the movement is chiefly horizontal and the term dissociated horizontal deviation (DHD) is used; if it is chiefly torsional, the term dissociated torsional deviation (DTD) is used.
Measurement of DVD is difficult and imprecise, the prism power that makes the residual vertical drift symmetrical can be used as an estimate of the deviation.
The deviation can also simply be graded on a 1+ (least) to 4+ (most) scale.
Aim of nonsurgical therapy for DVD is to strengthen the patient’s fusional mechanisms, elimination of any concurrent strabismus and optimization of vision through accurate refractive prescription and treatment of amblyopia. Changing fixation preference by penalization is effective mostly in unilateral or highly asymmetric. Indications for surgery are visual symptoms, physical discomfort from a large deviation, or disfigurement. If one eye is used habitually for fixation, surgery may be performed only on the opposite eye. If either eye is used at times for fixation, both eyes may need to be operated on, but asymmetrically. Procedures include large recession of the superior rectus muscle, and if that is not sufficient, resection of the inferior rectus. Anterior transposition of the inferior oblique insertion may be performed if DVD is present in conjunction with inferior oblique overaction.
- Inferior Oblique Muscle Overaction (overelevation in adduction)
- Inferior Oblique Muscle Underaction (Palsy or paralysis)
- Superior Oblique Muscle Overaction (IV Nerve overaction)
- Superior Oblique Muscle underaction, IV Nerve Palsy or paresis
- Dissociated Vertical Deviation
- Oblique Muscle Pseudo-Overaction
- Monocular Elevation Deficiency (Double Elevator Palsy)
- Orbital Floor Fractures
- Brown Syndrome
- Third Cranial Nerve Paralisis
- Thyroid Eye Disease
- Congenital Fibrosis Syndrome
- Mobius Syndrome
- Superior Oblique Myokymia
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- Noorden GK von. Binocular vision and ocular motility, Ch 18. St Louis: Mosby-Year Book; 1996:392–429.
- Monte A. Del Monte, M.D., Steven M. Archer, M.D, Atlas of Pediatric Ophthalmology and Strabismus Surgery, USA, Churchill Livingstone, 1993.
- Creig S Hoyt, MD. MA., David Taylor. FRCOphth. FRCS. DSc(Med), Pediatric Ophthalmology and Strabismus. Fourth Edition, San Francisco, Elsevier Limite, 2013.