Ординатура / Офтальмология / Английские материалы / Pediatric Ophthalmology Current Thought and A Practical Guide_Wilson, Saunders, Trivedi_2008

or weaken the contralateral yoke (left inferior rectus muscle recession; Fig. 14.2).

In patients whose paretic muscle function is still good, it is often better to weaken the yoke muscle since this minimizes the chances of creating a new deviation in the opposite direction.

14.3.2 Sixth Cranial Nerve Palsy

A patient has a mild esotropia due to right sixth cranial nerve palsy (Fig. 14.3a). The deviation is great-

est in right gaze. Surgical treatments could include resection of the right lateral rectus muscle, recession of the left medial rectus muscle, or recession of the right medial rectus muscle. If the field of greatest deviation is in right gaze, then resection of the right lateral and/or recession of the left medial rectus muscle are necessary (Fig. 14.3b). In some circumstances, the preferred approach is to weaken the action of the other eye.

14.3.3 Partial Third-Nerve Palsy

A patient has a mild inferior rectus muscle weakness of the right eye (Fig. 14.4a). There is a hypertropia on down gaze, but none in the primary position.

Strengthening the involved muscle or weakening its antagonist (superior rectus muscle) will create a deviation in primary gaze. The preferred option is to weaken the contralateral yoke (left inferior rectus muscle) using the fadenoperation (posterior fixation suture; Fig. 14.4b).

The concept of creating a matching weakness in the uninvolved eye (Principle 2: Balance the yoke muscles) is fundamental to achieving a wide range of single binocular vision in patients with paralytic strabismus.

Fig. 14.2a,b  Patients with a right fourth nerve palsy. a Note marked over action of the right inferior oblique on left gaze.

Treatment should include a right inferior oblique weakening procedure. b Patient has marked under action of the right superior oblique muscle. Treatment should include either a tuck of the right superior oblique or a recession of the “yoke” left inferior rectus

14.4 Moderate Decreased Duction

A moderate decrease in duction implies that the ocular rotation is reduced as much as 50−75%, but function is definitely still present. The treatment of a moderate paresis requires a strengthening procedure on the paretic muscle (Principle 1: Improve ocular rotation) in combination with either a weakening procedure of the ipsilateral antagonist, a weakening procedure of the contralateral yoke, and/or a weakening of the contralateral yoke’s antagonist. Weakening the antagonist muscle alone will result in improvement in the primary position alignment but a very limited range of binocular field since both muscles are now poorly functioning. In most circumstances it is better to weaken the contralateral yoke as opposed to the ipsilateral antagonist (Principle 2: Balance the yoke muscles).

Fig. 14.4a,b  Patient with vertical diplopia on downgaze but no deviation in primary gaze. a Note limitation of downward

movement of the left eye. b After right inferior rectus fadenoperation, the down gaze diplopia is eliminated

14.4.1 Fourth-Nerve Palsy

A patient with a right fourth-nerve palsy has a hypertropia worse in down and left gaze (Fig. 14.2b). Since the deviation is greatest in the field of the involved

right superior oblique muscle, a strengthening procedure (tuck) is appropriate. To minimize the creation of an iatrogenic Brown syndrome, weakening the contralateral yoke (left inferior rectus muscle), alone or in combination with the tuck, is also an option.

A recession of the right inferior oblique muscle will usually be the least helpful since there is almost no deviation up and to the left in its field of action.

If the antagonist muscle is contracted, then the restriction should be addressed necessitating a loosening procedure of that muscle. This will create a new deviation in opposite gaze for which treatment will be required (Principle 3: Anticipate problems).

14.4.2 Sixth-Nerve Palsy

A patient has large right sixth-nerve palsy with a tight right medial rectus muscle on forced duction (Fig. 14.5a) which will require a recession of the tight right medial rectus muscle along with a resection of the paralytic right lateral rectus muscle. If the deviation preoperatively was comitant and there is a

moderate esotropia in left gaze, then this will yield a satisfactory result; however, if the field of greatest deviation is in right gaze and there was little or no esotropia in left gaze, an exotropia will occur postoperatively in that direction (Fig. 14.5b). To address this problem, a left lateral rectus muscle recession (on adjustable suture) can be entertained, either at the time of the original surgery or as a second procedure. When performed at the time of the original surgery, it allows for the placement of the right medial rectus muscle in the best position to achieve as much movement on right gaze as possible, without worrying about an exodeviation being created in left gaze since that can be adjusted for by recessing the left lateral rectus muscle.

The importance of minimizing the creation of a new deviation in the one field of gaze where the patient previously had single vision cannot be emphasized enough.

Fig. 14.5a,b  Patient with a right sixth nerve palsy and a tight right medial rectus muscle. a Note marked limitation of abduction of the right eye. There is no deviation on left gaze. b Motility after a recession of the right medial and resection of the

right lateral rectus muscles. Note that the patient now has an intermittent exotropia in the primary position and an exotropia on left gaze. This will require a left lateral rectus recession

14.5 Absent Muscle function

A severe duction limitation usually indicates no function of the muscle, except if significant restriction is also present, and on ocular rotations the eye cannot be moved into the field of action of the muscle. An example of a severe limitation is a sixth nerve palsy with no abduction of the eye past midline, negative forced duction testing, and sluggish response to an OKN drum rotated temporal to nasal with the viewing eye in adduction. The OKN drum elicits an abducting saccade which, if weak or absent, provides indirect evidence of severe muscle function impairment. If there is no muscle function then some form of alterna-

tive force needs to be created. There are basically two options for this: a large resection (or tightening of the involved rectus muscle) or a transposition procedure.

In an example of sixth-nerve palsy, a patient has complete right sixth-nerve palsy (Fig. 14.6, top).

Since there is no abduction of the right eye a transposition procedure was performed, moving the right superior and inferior rectus muscle to the right lateral rectus muscle. A residual esotropia persists in right gaze (Fig. 14.6, middle). Transpositions or resections will not normally result in full movement and a weakening procedure of the contralateral yoke will be necessary to enhance the effect (Principle 2: Balance the yoke muscles; Fig. 14.6, bottom).

Fig. 14.6  Patient with a right sixth nerve palsy. a Right gaze shows severe limitation of ocular movement to the right. b Post-transposition procedure with improved movement but

still esotropic on right gaze and now exotropic on left gaze. c After a left medial and lateral rectus muscle fadenoperation

While recession is generally used to weaken the yoke muscle, another effective way is the use of the fadenoperation (Fig. 14.6). This procedure is especially effective in lateral rectus muscle paresis and can provide an additional enhancement [1]. In patients with mild limitation and a small deviation in the primary position it can be combined with a recession.

In more severe limitations it can be used to expand the field of single binocular vision in the direction of the paralytic muscle since its major advantage is that it does not increase the risk of an unwanted deviation on opposite gaze (Principle 3: Anticipate problems).

If the ipsilateral antagonist muscle is contracted or tight, then a recession of this muscle will be necessary and can be assessed at the time of the original transposition procedure. If anterior segment ischemia is a concern, Botulinum toxin can be injected into the antagonist muscle to achieve a temporary weakening and can be performed at the time of or before the transposition surgery. If injected prior to the surgical procedure, it can assist in assessing residual muscle function of the paralytic muscle.

Patients usually develop a deviation on opposite gaze after transposition procedures combined with recession of the antagonist muscle or after large resections of the paralytic muscle (Figs. 14.5, 14.6). This deviation can be proved or eliminated by a recession of the contralateral antagonist of the yoke. Often this requires a fairly large recession to control. If the eyes are straight in the primary position and the deviation is only present in one direction, then a fadenoperation on the muscle can be used (Fig. 14.6).

Large resections can be substituted for a transposition procedure if the muscles to be transposed are also poorly functioning. This is typically the case in partial third cranial nerve palsies where multiple muscles are involved. Transposing an already weakened muscle usually accomplishes little and limits further surgical options because of anterior segment vascular supply considerations. In such situations very large resections can be used with good results (Fig. 14.7). These resections may need to be repeated as they tend to “loosen” with time since the muscle has no real function.

14.6 Multiple Muscle Paresis

In patients who have more than one paretic muscle, the outcome goals need to be altered, as it is usually impossible to return the patient to full function. Emphasis should be placed on aligning the eyes centrally and in the down-gaze position. Alternative forces are usually necessary and will require either a transposition or a large resection. Each muscle is assessed independently with the results combined to design a unified surgical approach.

In an example of third cranial nerve palsy, a

65-year-old patient has a right third nerve palsy. The patient is unable to elevate and adduct the right eye

(Fig. 14.8). He shows an exotropia that appears relatively similar in all horizontal gaze positions and a marked right hypotropia. He will need an alternate force for the right superior rectus muscle because there is no function, and a resection of the right medial rectus muscle with either a right lateral rectus muscle recession or a left lateral rectus muscle recession. Since a transposition can be combined with a resect/recess procedure, the entire surgery can be performed on his right eye, involving only two of the rectus muscles. The medial rectus muscle is resected and transposed superiorly to the medial border of the superior rectus muscle, and the lateral muscle is transposed to the lateral border of the superior rectus muscle and then recessed with reference to the spiral of Tillaux. A fadenoperation on the left inferior rectus muscle was performed in anticipation of a greater vertical problem on downgaze after the above surgery. Post-operation he had an improved field of single vision (Fig. 14.8b).

Other combinations of partially functioning muscles can be approached in the same manner. The underlying general principles are to improve ocular rotation whenever possible and to weaken overacting yoke muscles. Surgery on antagonist muscles can be used to enhance the resection effect but runs the risk of creating a deviation in a field where one did not previously exist. If this is necessary, then surgery on the contralateral antagonist will also be needed.

In another example, A 40-year-old man has left third cranial nerve palsy. The patient is unable to elevate, depress, and adduct the left eye (Fig. 14.9a). He will need either a large resection of the left medial rectus muscle or an alternate force (transposition) for the left medial rectus muscle because there

Fig. 14.7a,b  Patient with bilateral third-nerve palsy. a Preoperative motility. Since there is no elevation and depression, transposing the superior and inferior muscles medially will not help with adduction. Large resections of the medial rectus muscles are the only possibility and can be performed without

also weakening the lateral rectus muscles. b Post-operative motility. Note excellent alignment in the primary position with some horizontal movement. Excessive weakening of the lateral rectus muscles would have resulted in marked limitation of movement in all directions

Fig. 14.8a,b  Patient with right partial third-nerve palsy. a Note marked inability to elevate and adduct the right eye. There is a very mild limitation of depression. b After transposition of the right medial and lateral rectus superiorly. The medial rectus

was also resected for the exotropia. Note that the depression weakness would be exaggerated due to the elevation effect of the transposition. This was treated with a fadenoperation on the left inferior rectus

is no function. Since the superior and inferior are also not functioning well, a resection of the left medial rectus muscle was performed (Principle 1: Improve function). In addition, a large recession of the yoke right lateral rectus muscle (Principle 2: Balance the yoke muscles) and a recession of the right medial rectus muscle plus a fadenoperation on the right inferior rectus muscle was performed (Principle 3: Anticipate problems) (Fig. 14.9b).

Care should be exercised in recessing the antagonist muscle, especially in vertical deviations in thirdnerve palsies which appear to have only an isolated muscle involved. Sometimes there is asymmetric involvement with one of the vertical muscles more paretic than the other. A recession of the “normal functioning” vertical muscle may result postoperatively in a more than anticipating underaction of this muscle. If at all possible, recessing the contralateral yoke muscle will obviate this complication.

Take Home Pearls

•A successful surgical procedure for paralytic strabismus must give the patient a sufficiently large area of single binocular vision to allow them to function without diplopia over a range of at least 20°.

•A careful analysis of the ocular motility deficit with particular attention to the amount of residual ocular rotation is extremely important in selecting a procedure which will yield the maximum benefit.

•Whenever possible, improve the eye movement in the field of action of the paretic muscle(s) (Principle 1).

•Always consider weakening the partner yoke muscle (Principle 2).

•Anticipate creating new deviations with your surgery and use that to help correct the

incomitant strabismus or plan to add additional procedures to address it (Principle 3).

•Assessing residual muscle function determines how the muscles should be modified.

–Good function: strengthen the muscle (resection or weaken the antagonist) or weaken the yoke.

–Poor Function: alternative force.

•The field of greatest deviation helps determine which muscles should be modified.

–Opposite gaze: weaken the antagonist and/or weaken the yoke.

–Same gaze: strengthen the muscle and weaken the yoke.

–No difference: strengthen the muscle and weaken the antagonist.

•Avoid just weakening the antagonist muscle in patients with paretic muscles which

are poorly functioning. This will create a very small binocular field since the eye will not move well in either direction.

•Very large resections can be very useful in situations where there is poor or no muscle function; these may have to be repeated to achieve long-term success.

•The OKN drum can be helpful in differentiating paresis from restriction.

Have the eye gaze in the direction opposite the paresis and rotate the drum toward that direction. This will elicit a saccade in the direction of the paretic muscle which, if brisk, indicates that the ocular rotation limitation has a restrictive component.

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