Ординатура / Офтальмология / Учебные материалы / Эндокринная офтальмопатия - мультидисциплинарный подход 2007

Fig. 1. In attempting elevation, a restriction of the inferior rectus muscle causes a deficit of elevation and, pushing the eye into the orbit, a temporary rise in intraocular pressure.

Observe the orbital region of the patient while he is looking straight ahead (primary position of gaze): this is important for a gross impression of the presence of monolateral or bilateral proptosis, the type of dislocation of the eyeball (if present), and/or the presence of a manifest strabismus (looking at the corneal reflex).

Examine ductions (ductions are monocular movements of the eye): this is done by patching the controlateral eye and asking the patient to look at a penlight that is moved along the diagnostic positions of gaze, starting from the primary position. If the eye does not reach the maximal excursion, a restrictive disorder of the opposite rectus muscle is very probable. The test may be also performed in a quantitative way with an arc perimeter following the indication of Mourits et al. [2].

Examine versions (versions are binocular movements of the eyes): this is done by asking the patient to look at a penlight that is moved along the diagnostic positions of gaze starting from the primary position. It gives different information in respect to duction testing, because it evaluates the relative position of both eyes during ocular rotations. This is fundamental for the surgical plan, because in the frequent case of multiple or bilateral restrictions you must tailor your surgery, not only in order to reduce the angle of strabismus (working on the most involved muscle) but also to make ocular movements more concomitant as possible, with the aim of obtaining a useful field of single binocular vision. So, e.g., if we are facing a symmetric restriction of the inferior rectus muscle (IRM) in both eyes (OO), the patient may have a good field of single binocular vision and may not need surgery; or if the restriction is asymmetric,

operating only on one eye you must plan your surgery in order to symmetrize and not to normalize ductions in the most affected eye because in this latter case you will get a vertical hypercorrection.

Cover tests are essential for determining the presence of strabismus, its type and for an objective measurement of the angle. There are substantially 3 types of cover test: (1) The cover-uncover test which aims to detect manifest strabismus: it is performed by covering one eye and looking at the other eye in order to see if it makes a movement of refixation. In this case, a manifest strabismus is detected. The manoeuvre is repeated on the other eye, after allowing a moment of binocularity. (2) The alternate cover test which aims to detect latent strabismus (the ocular deviations that are masked by fusion). In this test, the eyes are covered alternately without giving moments of binocularity (this is in order to dissociate fusion). The test is positive for latent strabismus when there is evidence of refixation movements. (3) The prism cover test which measures the deviation in both latent and manifest strabismus: it is performed in the same way as the alternate cover test, interposing a bar prism in front of one eye and finding the prism that neutralizes the refixation movement.

Measurement of intraocular pressure in upgaze: an increase more than 3 mm Hg in upgaze may indicate the presence (also not evident in ocular motility assessment) of a restriction of the inferior rectus muscle.

Forced duction test: this test is fundamental for assessing the presence of a restriction. It may be performed under local or general anaesthesia and consist of taking the perilimbal conjunctiva with a forceps and trying to move the eye passively in the direction of action of the extraocular rectus muscles. If there is some resistance the presence of a restriction of the antagonist muscle is confirmed. This test has to be performed before surgery for confirming the presence of a restriction, and during and at the end of surgery in order to assess that the restrictions have been relieved.

How Can You Avoid Diagnostic Errors in Complex Cases?

In order to avoid errors we must remember:

(1)In GO impairment of ocular motility is always due to restriction and never to hyperfunction or paralysis.

(2)Multiple restrictions are often present and must be detected for a correct surgical plan.

(3)Some signs may be misleading [3] and may induce a wrong diagnosis. Among these we consider:

(a)Apparent overaction of the inferior oblique muscle (IOM): On examination, these patients show an apparent hypertropia of the adducted eye

Fig. 2. Restriction of inferior rectus muscle gives hypotropia of the affected eye which increases in abduction: this may simulate inferior oblique overaction (pseudo overaction of the inferior oblique muscle; above). This is a bilateral case and surgery on both inferior rectus muscles solved the problem (below).

simulating inferior oblique muscle (IOM) hyperfunction, common in concomitant strabismus. The hypertropia of the adducted eye in GO is usually due to a restriction of the controlateral IRM: in this case IRM has to be weakened (fig. 2) and surgery on IOM will result in a disaster [4].

(b)Pseudoparalysis of the superior oblique muscle (SOM): The diagnosis of paralysis is usually made after performing the three-step test of Parks; this test is valid for diagnosis of a paralytic cyclovertical disorder but is unattainable in restrictive disorders. In this case the disorder is again due to a restriction of the controlateral IOM. It is often accompanied by torticollis with head tilt towards the controlateral shoulder. Again, operating on SOM may result in a disaster and surgery has to be performed on the controlateral IRM (fig. 3).

(c)Excyclotorsion on attempted upgaze: This finding may be interpreted as a paretic involvement of a SOM but once again it is due to a homolateral restriction of the IRM. It is due to hyperactivation of the IOM in attempted elevation, when the superior rectus muscle (SRM) is unable to elevate the eye: the problem is solved weakening the omolateral IRM [3].

How Can You Evaluate the Need for Surgery?

The need for surgery is evaluated considering:

(1)The disability of the patient which is usually related to the diplopia field.

(2)The prognosis for a favourable result.

(3)Rarely the aesthetic problem.

Fig. 3. A positive head tilt test may simulate a controlateral superior oblique palsy at the Parks’ three-step test (above). In GO, a positive head tilt test is due to inferior rectus muscle restriction and is confirmed by the fact that surgery on this muscle will result in a negative head tilt test and reduction of torticollis (below).

Disability is the most important factor when considering surgery: it is usually linked to the field of diplopia more than to the angle of strabismus (this because the same angle of strabismus may or may not give diplopia in different patients due to the entity of fusional amplitudes). The extent of diplopia may be quantified by examining the field of single binocular vision (FSBV). This test is performed with an arc or bowl perimeter: the patient, with both eyes open, is asked to look at a target which is moved from the area of the field of gaze in which it appears single toward the area in which it appears double. In this manner, the limits of the area of single binocular vision can be determined and reported in a graph (fig. 4). Obviously, diplopia in the primary position of gaze and/or in downgaze is the most disabling.

Disability may also be due to an anomalous head posture (torticollis oculi, not infrequently causing pain in the back of the neck) and this may be a strong indication for surgery (fig. 3).

The prognosis progressively worsens from pure horizontal deviation, to pure vertical deviation and to mixed deviation (figs. 5, 6). Particularly problematic are those eyes with multiple heavy restriction and deficit of ductions in the opposite direction of gaze or in all directions of gaze (frozen eyes): in these eyes one must be very careful when performing surgery because, for the restriction of the homolateral antagonist, a mild degree of weakening surgery may induce a conspicuous hypercorrection.

Fig. 4. Field of single binocular vision in a patient with left inferior rectus muscle restriction before (left) and after (right) a lengthening procedure on the left inferior rectus muscle.

Fig. 5. A mixed deviation (horizontal and vertical) before (left) and after (right) surgery.

Fig. 6. A mixed deviation (horizontal and vertical) before (left) and after (right) surgery. This patient did not attain SBV after surgery: however, he ignored diplopia and after further surgery on the right inferior lid he was happy with the result.

The prognosis for a favourable result other than the type of deviation is related to the presence of potential single binocular vision (SBV). This may be checked neutralizing the angle with a prism and asking the patient if he is seeing double. Obviously, this test may be misleading but usually it is a good indicator of a possibly good result.

Moreover, any decision has to be made on the basis of patient’s needs, and surgery must be asked for by the patient himself.

When Is the Right Time for Surgery?

At least 6 months after normalization of thyroid function, loss of activity of GO and stabilization of ocular motility. For the stability of the results, it is important to operate when GO is inactive.

What Can You Realistically Expect from Surgery?

Obviously, the results expected vary in relationship to the form of ocular motility disorder. More often a good result may be considered by the attainment of a useful field of SBV, comprising both primary position and downgaze [5]. It is important immediately after surgery to obtain an area of single binocular vision: this area, also if limited, will usually enlarge with time, due to development of fusional amplitudes (fusional amplitudes are plastic: when there is no area of SBV they are not utilized and will reduce; after surgery, when an area of SBV is present, they will increase with exercise in casual seeing).

How Should You Advise the Patient?

Very often GO patients have unrealistic expectations from surgery, sometimes generated by optimistic press releases from physicians. Speaking about extraocular muscle surgery, the surgeon must specify that:

(1)It is an incompletely predictable surgery: in the best series success is about 80–85% with one surgery and rises to 92–93% with more than one procedure. Obviously, it depends not only on the appropriateness of the surgical plan but also on factors related to the patient that may not be detectable on preoperative examination.

(2)An acceptable result is to obtain a useful field of single binocular vision (so diplopia in lateral and superior gaze may probably persist).

(3)In some cases, there may be the need to operate on both eyes and more than one muscle per eye (maximum 2 rectus muscles).

(4)If adjustable sutures are planned there will be an adjustment under topical anaesthesia on the following day.

(5)The surgical plan may be modified during surgery if the surgeon detects some restrictions which were not detected during the preoperative examination.

The Surgical Plan: What Procedures Are Recommended?

The surgical plan is the focal point: surgery has to be planned taking in account that:

(1)It is important to aim at obtaining an area of single binocular vision with a single surgery: this area, also if limited, will usually enlarge with time, due to development of fusional amplitudes with spontaneous exercise in casual viewing; for that reason we have to operate on more than one muscle and on both eyes at one time, if needed; in adult patients you can perform surgery safely only on two rectus muscles in each eye, for the fear of anterior segment ischaemia [6]. You must plan your surgery and reoperations thinking that you must not detach more than two rectus muscles from the globe (this must be taken in account also in eventual subsequent procedures, because there is no evidence that this will avoid anterior segment ischaemia).

(2)Usually only weakening procedures (recessions, recession on adjustable sutures, lengthening procedures) are performed, due to the restrictive nature of the disorder. Pay attention, a strengthening procedure (that has invariably to be coupled to a weakening procedure on the antagonist) will usually result in a marked hypercorrection; moreover, in such a situation, having operated on two rectus muscle of the same eye, any other surgery on the remaing rectus muscles will be precluded.

(3)Misleading signs (pseudo inferior oblique overaction, pseudo superior oblique paresis, excyclotorsion during elevation, head tilt on a shoulder) are due to restriction of the inferior rectus muscles and not to involvement of an oblique muscle.

(4)In vertical deviation always aim for a slight hypocorrection. After surgery there is very often a slow updrift of the operated eye and this may result in late hypercorrection. A mild hypocorrection will afford single binocular vision in downgaze and primary gaze (with or without a temporary prism) and the area of single binocular vision will enlarge with time. I worry about a late hypercorrection if I get a full correction of the vertical deviation on the day after surgery [7].

(5)The procedures recommended are, as stated, weakening procedures: these comprise recessions, recession on adjustable sutures, lengthening procedures and conjunctival recession. In the last years much has changed in

Fig. 7. Adjustable suture. The muscle is recessed with a loop anchored to the original insertion. A temporary knot affords intra-operative and early post-operative adjustment.

Fig. 8. Lengthening procedures are useful in some cases, particularly when, after decompression, the tendon is displaced, or in presence of very strong restrictions: in these circumstances it is important to maintain an arc of contact and lengthening the tendon is indicated.

strabismus surgery with the introduction of topical anaesthesia and adjustable sutures. Topical anaesthesia (eventually implemented with subtenonian injection and general sedation) allows intra-operative assessment of the results, while adjustable suturing allows fine tuning of the results on the following day (fig. 7). Lengthening procedures are useful in some cases, particularly when, after decompression, the tendon is displaced (fig. 8), or in the presence of very strong restrictions.

Fig. 9. Late vertical hypercorrection and left lower lid ptosis after weakening procedure on the left IRM.

(6)Weakening of both the inferior and medial rectus muscles may cause a divergence in downgaze (the so-called A pattern of deviation) with diplopia in the reading position. To avoid this problem, it is important to transpose the medial rectus muscle insertion upward during the weakening procedure: in this way, the adduction in downgaze will be reinforced [8].

What Are the Possible Complications of Surgery and How Can I Avoid or Manage Them?

There are two types of surgical complications: those common to every strabismus surgery (e.g. perforation of the sclera, postoperative infections, and adherence syndrome) and those more frequent or more dangerous in GO patients. The latter include:

(1)Lost or slipped muscle: This is really a threatened complication: usually the slipped muscle will retract deeply into the orbit without the possibility of being recovered. Very often the presence of a contracture of the homolateral antagonist will cause a marked overcorrection: this is very difficult to treat surgically and for this reason every effort has to be made in order to prevent muscle slippage.

(2)Late vertical hypercorrections (fig. 9): Late vertical hypercorrection may be due to concomitant restriction of the homolateral antagonist or restriction of the controlateral inferior rectus muscle (fig. 10). The treatment is based on prism prescription in mild cases or more often in a new surgical procedure: in order to plan surgery, we again must detect the muscles involved and take in account that not more than 2 rectus muscles for each eye can be severed from the sclera.