Modern Techniques of Strabismus Surgery

Transcription

1 Optometry in Practice Vol 2 (2001) Modern Techniques of Strabismus Surgery IB Marsh MB ChB FRCS FRCOphth Consultant Ophthalmologist, Walton Eye Unit, University Hospital Aintree, Liverpool, UK Accepted for publication 25 June 2001 Abstract There have been many recent changes in strabismus surgery, particularly in the management of vertical deviations and using injectable techniques. This paper aims to discuss initially the history of strabismus surgery followed by the discussion of superior oblique surgery, adjustable squint surgery, Faden procedures and the use of botulinum toxin. Indications for each of these particular techniques is discussed. Introduction Discussions about strabismus have been undertaken for many years. A motor imbalance between eyes was first noted in Ebers papyrus (Ebbell 1937). This document was thought to be written about 1550 BC and originally discovered by George Ebers in As such it pre-dates the writings of Hippocrates (the modern father of medicine) by about 1000 years. Hippocrates recognised a hereditary transmission of strabismus in some of his writings. He also described various types of ocular imbalance in conjunction with other systemic and local conditions. For example, he described ear infection, a hemiparesis and squint and also the development of strabismus in puerperal sepsis. Attempts to realign the visual axes by any means were not described (Adams 1946). Surgical intervention to attempt ocular alignment is thought to have begun in 1739 by John Taylor. He recognised that strabismus was a muscular abnormality and attempted to correct this by dividing the overacting muscle. It is said, however, that Taylor was a charlatan who merely snipped open the conjunctiva of the affected eye and then patched the opposite eye. The operated eye therefore took up fixation and the squint deemed to be cured. John Taylor was reputed to have left town before the patch was removed and the apparent cure found to be a fake (Helveston 1993). Eschenbach in 1752 divided an extraocular muscle to correct squint. Gibson repeated this surgery in However, the first recorded successful correction of strabismus with myotomy was by Diffenbach. He divided the medial rectus to correct an esotropia in a 7 year old boy. Not surprisingly a large exotropia was the result. The final outcome of the surgery may only have been a small improvement over the original pathology. The abnormal position of the caruncle, which was medially displaced, also contributed to the poor cosmetic appearance postoperatively (Helveston 1993). Towards the end of the 1800s reattachment of the divided extraocular muscle commenced and the measurement of the degree of recession became quantified. Resection of a muscle also became recognised and performed. Measurement of muscle resection was also undertaken. In all of these situations usually the horizontally acting muscles and only in rare cases the vertical recti were operated upon. The oblique muscles were considered to be a difficult anatomical problem and so surgery was not considered (Fink 1951). Early in the twentieth century inferior oblique weakening was used for the clinical indications of myopia and asthenopia. Not surprisingly there was very little success and the technique was abandoned. Initial attempts at surgical correction were hampered by primitive anaesthesia. No technique to render the patient unconscious was available and so all surgery was carried out rapidly with minimal anaesthesia and analgesia. As local anaesthesia and later general anaesthesia evolved so the surgery could be conducted at leisure with more accuracy. Surgical interventions for strabismus did not alter from these initial recessions and resections, apart from changes in incisions, the sizes of the muscle movement or resection and suture materials until the latter part of the twentieth century. Since those times the armamentarium of the Address for correspondence: Ian B Marsh MB ChB FRCS FRCOphth, Walton Eye Unit, University Hospital Aintree, Rice Lane, Liverpool L9 1AE, UK The College of Optometrists 79

2 IB Marsh Oblique Non absorbable sutures Tucked Oblique Figure 1. Resection of the superior oblique Figure 2. oblique tucking strabismus surgeon has been strengthened by the addition of superior and inferior oblique surgery, adjustable squint procedures, Faden surgery and the use of botulinum toxin injections. All four of these new techniques will be described and discussed. Oblique Surgery Both strengthening and weakening of the superior oblique muscle have been described and used (McLean 1948). The commonest form of surgery used is a strengthening procedure. Resection of the superior oblique is difficult as the muscle tendon fans out at the insertion to form a wide thin band of tissue, which stretches from just behind the superior rectus insertion on the lateral side, back towards the equator (Figure 1). Complete tucking of the muscle or advancement of part of the muscle to a more advantageous position produces a more powerful muscle without recourse to resection. oblique tuck The indication for a superior oblique tuck is a weakness of the muscle, which is maximal in the position of action of that muscle. The superior oblique acts to depress the eye when the globe is adducted. It also has the action of inward rotation of the eye. If the left eye has a weakness of the superior oblique muscle then the patient may have vertical diplopia maximal in position of dextro depression. The problem with this concept is that muscle sequelae can alter these findings. A weak superior oblique may also have ipsilateral inferior oblique overaction, contralateral inferior rectus overaction and contralateral superior rectus weakness. The position of maximal deviation is therefore influenced by the development of these sequelae. The evaluation of these patients always includes a measurement of angle of deviation in all nine positions of gaze and includes vertical, horizontal and torsion measures. The assessment should always be undertaken fixing with each eye in turn. Causation It is important in the evaluation of these patients to establish the possible causation of the weakness. The two likely aetiologies are congenital and acquired. Congenital superior oblique weakness is characterised by a history of relatively sudden onset of troublesome constant vertical diplopia often with previous episodes of intermittent problems prior. The patient will usually not have torsion or tilting of the double images. Examination of old photos will often reveal a longstanding abnormal head posture. The patient will exhibit a tilt of the head to the side opposite to the muscle weakness. Sometimes the chin will be depressed to attempt to join the separated images. The condition is almost always unilateral and the lack of torsion is almost diagnostic. The patient may also have characteristic mild under development of the face on the side of the paresis. The patient seeks attention when the condition becomes decompensated. 80

3 Optometry in Practice Oblique known as acquired Brown s syndrome can occur. In Brown s syndrome the affected eye cannot elevate in the adducted position. Significant problems in upgaze were thought to be unacceptable. Recent developments of the surgical procedure have added an intra operative forced duction test to ensure that the operated eye can be passively elevated in adduction while the patient is under anaesthesia (Saunders et al. 1985). The complication of acquired Brown s syndrome has almost disappeared with this refinement. Other procedures Lateral Acquired superior oblique weakness is usually due to closed head trauma. Rarely other systemic conditions may cause the condition but unless clinical examination reveals any other findings then scanning is not usually undertaken. The trauma likely to cause this problem is fairly severe and often of the whiplash type. The development of symptoms is immediate and severe. Torsion is more prominent symptomatically than the vertical element and the patient often is unable to take up a head position to relieve the diplopia. Sometimes the patient will place the chin in a depressed position if the weakness is bilateral. The anatomical position of the fourth nerve, that exits from the brain posteriorly, makes it vulnerable to backwards and forward motion of the cerebral apparatus in the whiplash type injury. The fourth nerve also leaves the brain by a number of rootlets that decussate or cross to the opposite side. The left nucleus therefore innervates the right superior oblique and vice versa. Because of this unusual anatomy the condition of acquired superior oblique weakness is common. Examination of the patient with an emphasis on detection of bilaterally is vitally important. In these patients a period of observation of up to twelve months with continued monitoring of the ocular deviation is vital to assess recovery and monitor development of sequelae. Complications Advanced anterior part of SO tendon Figure 3. Fell s modification of the Harada Ito Procedure Following its introduction, superior oblique tucking (Figure 2) was initially thought to cause significant postoperative problems (Helveston 1984). If the muscle is tightened excessively during the tuck procedure then a condition In the condition of congenital superior oblique weakness the indication for the tuck procedure is a patient who has the largest vertical deviation in contralateral depression to the affected muscle. This can be augmented by combining the procedure with an ipsilateral inferior oblique weakening operation if the patient also has significant overaction of this muscle with a vertical deviation in contralateral elevation. A possible alternative procedure for the weakness in contralateral depression is a contralateral inferior rectus recession (Khawam et al. 1967). There are problems with this procedure in that the inferior rectus is attached to the lower lid by the retractors of the lid. Recession of the inferior rectus without severing of these attachments may lead to lower lid recession, which creates a poor cosmetic result. Surgery of torsion In acquired superior oblique palsy, the presence of torsion is the major complaint. If the measurement of excyclotorsion exceeds 10 degrees then it is very likely that a bilateral condition is present. If the only findings are those of the congenital type of problem then tucking is the procedure of choice. Surgical intervention in excyclotorsion is more problematical as some of these patients may have sustained a closed head injury severe enough to cause damage to the fine motor fusional areas. In these cases even if torsion is eliminated and all the vertical and horizontal deviations are corrected the patients may still not be able to use both eyes together in a coordinated fashion. In this situation the only treatment is occlusion of one eye to eliminate the symptoms. Harada Ito surgery The surgical treatment of torsion was first described by Harada and Ito (1964) and the procedure was later refined 81

4 IB Marsh by Fells (1976). In the modified form of the procedure the anterior one third of the superior oblique tendon is detached from the globe where it inserts on the lateral side of the superior rectus muscle. That part of the tendon is then advanced around the globe and is inserted back onto the sclera about 8mm behind the lateral rectus muscle insertion (Figure 3). The anterior fibres of the superior oblique, which undertake incyclorotation, are therefore strengthened by this procedure. Bilateral use of this technique can correct up to 20 degrees of excyclotorsion. In the management of acquired bilateral superior oblique palsy this surgical manoeuvre should be the first procedure as torsion cannot be corrected by prismatic therapy. Inferior Oblique Surgery The inferior oblique has now three procedures that can be performed upon it. The muscle can be weakened by either recession or performing a myectomy. Both of these procedures are performed in the presence of an overacting muscle. Perhaps the commonest situation where an overacting muscle is found is a superior oblique palsy as discussed above. The patients who are suitable for this procedure are those whose vertical deviation is maximal in elevation to the opposite side to the palsy. The inferior oblique is an elevator of the eye in adduction and so weakening of this muscle has no effect in down gaze positions. The maximal vertical correction expected in the primary position of gaze with this procedure is approximately 10 prism dioptres. The other usual indication for weakening of the inferior oblique is younger children with congenital or acquired type of squints who may develop overactions of the muscle without obvious cause. A V pattern is present in these cases. Early onset esotropia is commonly affected with the accommodative esotropias less likely. It is rare for the patient with exotropia to have this phenomenon. Inferior oblique surgery is performed through the inferior and temporal fornix. The muscle is exposed by making an incision about 5 to 8mm behind the limbus in the area between the inferior and lateral rectus. The muscle is invested in Tenons capsule and often difficult to hook by the inexperienced surgeon. Lying just posterior to it is the vortex vein as it exits from the globe. Care must be taken not to damage this, otherwise marked bleeding will occur. The insertion of the inferior oblique is close by the macula and so disinsertion of the muscle at the tendinous end is difficult. Visual function may also be disturbed by a tractional effect through the sclera on the macular area. Recession of the muscle is performed by inserting sutures as far back as possible in the tendon and then reinserting the muscle approximately 8mm behind the inferior rectus insertion. Myectomy of the inferior oblique is, literally, removal of a central section of the muscle. In this procedure, the muscle is exposed by the same technique as for recession, but the central section is removed following ligation of the blood vessels to prevent bleeding. The removed section does not need to be large, indeed only 2 to 3mm will suffice. It is very rare to see an underaction of the eye in elevation following either of these weakening procedures. The most recently described procedure on the inferior oblique muscle is an anterior transposition (Burke et al. 1993). In this situation, the inferior oblique is approached through the same incision as for the weakening procedure. The muscle has sutures inserted, as if a recession were to be performed, but the muscle is now placed adjacent to the inferior rectus at its insertion. In this procedure, the direction of action of the inferior oblique has been changed. The muscle is no longer an elevator of the globe but has become a depressor. In practice there is no active rotation of the eye downwards but a restriction of upgaze. The indication for this procedure is limited to the little understood condition of dissociated vertical deviation (DVD). Previously, this has been called alternating hypertropia or alternating circumduction. DVD usually occurs in early onset esotropias in association with an abnormal response to opticokinetic nystagmus (OKN). The patient has a disordered smooth pursuit and saccadic response to OKN drum stripes presented monocularly in a nasal to temporal direction. In DVD, the patient or relatives notice a slow drift of the non-fixing eye into elevation and often abduction when the patient is tired or not concentrating. Drawing the patients attention to the defect often will cause them to control the eye but the problem may be very frequent and cosmetically worrying. It is not often manifest until the patient is in their teenage years, although the OKN changes are present from the age of 3 months. Surgery for DVD includes superior rectus recession, superior rectus Faden sutures or inferior oblique anterior transposition. All of these operations should be performed bilaterally as the condition is bilateral but asymmetrical. The number of patients requiring surgery is small and the condition is not cured but the manifest hyper deviation of the eye lessens in frequency, duration and size. 82

5 Optometry in Practice Muscle suture passing through scleral tunnel Muscle Suture tied in loop around muscle stitches (boy scout s woggle) suture inserted in it. In this procedure the suture from each end of the muscle is passed through the sclera usually at the original muscular insertion. The stitches pass forward at an angle of 45 degrees to the insertion to exit the sclera adjacent to each other. At this point a piece of the suture material is tied tightly around the stitch ends to form a tie somewhat similar to a Boy Scouts woggle (Figure 4). This tie then holds the muscle at the place determined by the surgeon. Once the patient has recovered from the anaesthetic then adjustment of the eye position can be undertaken. Advancement of the recessed muscle or further recession can be undertaken until the patient is happy with the ocular position or diplopia is eliminated. Indications Figure 4. Adjustable suture placement As there is more than one operation described for DVD it is obvious that no procedure is better than the other. The indication for the use of anterior transposition surgery is in the patient who has a combination of both inferior oblique overaction and DVD. In this situation the two problems are treated by the same procedure. Strengthening procedures of the inferior oblique are not usually undertaken. Adjustable Strabismus Surgery The idea of being able to change the eye position postoperatively was suggested early in the twentieth century. The technique was popularised by Jampolsky (1978) in the 1970s who described the surgical manoeuvres required. Fells (1984) also described his modification of the procedure. The operation is now described in terms of one or two stages. In the one stage procedure, as described by Fells, the operation is performed under topical local anaesthesia. Regional anaesthesia in the form of peribulbar and retrobulbar cannot be undertaken. The patient is taken to theatre and the operation is performed. Before the sutures are finally tied the patient is sat up and the angle of deviation measured. The ocular position can be altered and fine-tuned before the suture is completed. The adjustable suture is placed on the recessed muscle. In the two stage procedure as described by Jampolsky the initial part of the procedure is performed under general anaesthesia. The recessed muscle again has the adjustable The ability to produce accurate ocular alignment is very desirable in a number of conditions. There is some degree of drift away from the position left at the end of the adjustment with time, so degrading the final outcome. The patients who demonstrate this phenomenon tend to have poor binocular function of both motor and sensory type. It is likely that these would have drifted in due course even if surgery had been undertaken in a conventional manner. The indications for adjustable suture surgery are still not completely agreed within the ophthalmology world. Some surgeons would advocate using the technique for all adult strabismus surgery regardless of motor or sensory function. Others reserve the use for patients who have had multiple surgical procedures in the past where tables of muscle movement for degree of angle change are probably not useful. Another group would advocate its use in patients who have both motor and sensory function, but who require very accurate ocular alignment to prevent diplopia. Finally there are a group of ophthalmic surgeons who would never advocate the use of adjustable sutures. In view of this, there are no absolute indications for the use of adjustable sutures. It is probably important to list the contraindications. The patient who is deemed to be unlikely to cooperate with the adjustment or surgery under local anaesthesia is an absolute contraindication. It can be difficult to decide this prior to undertaking surgery but some surgeons advocate attempting a forced duction test in the clinic to assess patient compliance. If the patient is happy to undertake this procedure then adjustment is likely to be trouble free. Most children under the age of 15 years are probably unsuitable but anecdotally surgeons have discussed this type of surgery in children below this age. 83

6 IB Marsh Probably the commonest indications are previous multiple surgery, risk of diplopia postoperatively, mechanical restrictions and some neurogenic forms of strabismus. In primary strabismus where no previous surgery has been undertaken all of the standard texts publish surgical tables correlating millimetres of muscle movement of the rectus muscles with angle change achieved. As a general rule of thumb these work very well in practice and can be personalized by experience by the operating surgeon. Once the muscles have been affected by surgery or a disease process then the tables are difficult to interpret. In the commonest mechanical restriction seen in clinical practice (thyroid eye disease) the tightness of the inferior or medial recti found at surgery can cause large unpredictable changes in angle of deviation postoperatively. In this situation the addition of an adjustable suture allows postoperative change to be undertaken if a large under or over correction is present. Some patients pre-operatively exhibit the possibility of diplopia if the angle of deviation is corrected or over corrected. In this situation, it is desirable to leave the patient without diplopia at the end of the surgical intervention. The use of adjustable sutures allows that flexibility. Neurogenic forms of strabismus have abnormal or absent innervation to one or more of the extra ocular musculature. The commonest type of condition that would be amenable to the use of adjustable surgery would be a sixth nerve palsy. This cranial nerve supplies the lateral rectus muscle and paralysis of this muscle causes an esodeviation mainly manifest in the distance and in the direction of horizontal gaze ipsilateral to the affected muscle. The abnormal innervation means that the surgical outcome from a recession and resection procedure is not predictable. Adjustable surgery is useful here. Complications Complications are possible while undertaking the technique. The ideal timing of performing the adjustment postoperatively is not known if the two-stage procedure is used. The adjustment can be on the same day or the following day. If left longer than this the muscle may prove difficult or impossible to move. Surgery under local anaesthesia may not be possible if multiple procedures have been undertaken in the one stage technique. One of the worst complications is suture breakage during the adjustment period. In this situation, the patient must be returned to theatre promptly to secure the extra-ocular muscle and prevent its loss. Faden Procedures Cuppers (1976) first described the Faden operation and as such it is often called the Cuppers operation. It is also called the posterior fixation suture or a retro-equatorial myopexy. Perhaps this last term is the one to use as it describes the operation in its entirety. In some clinical situations the eyes are parallel and function together in the primary position of gaze without diplopia. However when they move away from this position the excursions are not equal. Either an excessive contraction occurs in one or both eyes or an underaction is present in one eye. In the childhood age group the condition of convergence excess esotropia fits into the excessive contraction group. Convergence excess is an esotropia that occurs around the age of 3 years. The patient may or may not have a refractive error. They show normal binocularity at distance fixation with no manifest deviation but for near they have a marked eso deviation for an accommodative target. They may be straight to a light used as a target. This is present even with their refractive correction in place. Measurement of the AC/A ratio is important. The AC/A is a ratio that relates the amount of convergence produce in response to an accommodative stimulus. The normal ration has not been fully described but often these children have one greater than 5:1. Using a near addition the eyes may be straightened and binocularity demonstrated. Spectacle wear with bifocals using an e-line (executive) segment that bisects the pupil are used in some centres to control the near deviation. This treatment modality is popular in the United States. In the United Kingdom treatment is often surgical and bilateral medial rectus recessions or bilateral medial rectus Faden (Leitch et al. 1990) sutures are used. Sometimes both treatments are necessary to realign the eyes. In the condition of DVD, which has been described before, a Faden suture is used in the superior rectus muscle to aid control. In adult strabismus practice, a Faden suture is sometimes used on the vertical recti muscle in restrictive or neurogenic strabismus. In a blow out fracture of the orbital floor, the inferior rectus may become weak in depression but have caused no manifest deviation in primary position. In this situation insertion of a Faden suture into the opposite inferior rectus muscle may match the depression defect and increase the area of binocular single vision. It is often difficult 84

7 Optometry in Practice Globe Equator Muscle Botulinum Toxin Injections For many years ophthalmologists have been seeking a way of altering eye position without resorting to surgery. A number of chemicals have been tried including local anaesthetic and cobra toxin. Either the side effects had been unacceptable or the duration of action too short until Alan Scott started experimenting with botulinum toxin. His initial results were with monkeys but human work (Scott 1980) soon followed. Figure 5. Faden suture placement Non absorbable sutures Botulinum toxin (BTA) is a neurotoxin, which is produced by the bacterium Clostridium botulinum. The toxin is produced in eight different immunological types denoted as A to E. It is an exotoxin, which means that the bacterium produces it within its cell membrane and then excretes it into the surrounding medium. Types A,B and E are those, which are associated with human toxicity. The type used in medicine is type A. to persuade the patient to have a surgical procedure performed on what is considered to be the unaffected eye. In a unilateral superior oblique palsy, inferior rectus Faden suture on the contralateral eye can be useful to expand the field of single vision. The Faden procedure works by progressively weakening the muscle action as it moves into its field of action (Scott 1977). The reason for this is the position of the suture placed within the muscle. The material utilized in the stitch is of a non-absorbable type to ensure the effect does not degrade with time. The suture is positioned at a point behind the equator of the globe (Figure 5). The surface marking of this structure varies according to which muscle is being operated upon. In the normal situation the muscle lifts away from the globe as the eye rotates in the direction of muscular pull. The Faden suture prevents this happening. By geometrical analysis this continued contact of muscle with globe behind the equator causes a reduction of force. The procedure is usually irreversible and causes globe movement restrictions. The surgical technique is testing as the equator is difficult to expose and visualise accurately. Because of the distance back from the limbus the oblique muscles may obstruct the surgery if this is performed on the superior or inferior recti. One complication of the procedure is lack of effect, some patients may have a larger field of single vision postoperatively but still not be happy. The second possible complication may be perforation of the globe as needle control so deep in the surgical field can be difficult. Method of action Botulinum toxin causes an irreversible paralysis of nerve endings that contain acetylcholine. Nerve conduction in the human takes place at nerve to nerve, nerve to muscle and nerve to end organ (i.e. sweat or salivary gland etc.). Some of these connections are mediated by acetylcholine. In these connections the neural impulse arrives at the nerve ending which then causes a release of acetylcholine. This then diffuses across the space between nerve and the next structure. It then stimulates the cell membrane of that structure to undertake its action. In the case of a muscle, this will then contract. The eye muscles contain this arrangement. Botulinum toxin when injected will bind to the terminal nerve ending, break it down and become internalised into the cell. The toxic effect of the botulinum then destroys the vesicles containing the transmitter, acetylcholine. The muscle is therefore paralysed. The function will recover in due course by a process of neural budding. In this process the nerve to muscle connections are reformed by growth of new endings from the original nerve to reactivate the muscle. The muscular paralysis in humans takes effect within two to three days, becomes maximal at about two to three weeks and lasts for up to three months. Once injected there are no antidotes available, however any undesirable effects will wear off in time along with the paralysis. There has been an increase in botulinum toxin treatment over recent years, not only in ophthalmology, but also other medical disciplines. The initial indication in ophthalmology were blepharospasm and hemifacial spasm, but Scott soon went on to report its use in strabismus. The toxin is injected under electromyographic 85

8 IB Marsh control directly into the belly of the extra ocular muscle where the vast majority of the motor end plates are found. It can be administered under topical anaesthesia or in children using ketamine general anaesthesia. Ketamine is avoided in adults because of its propensity for severe hallucinatory effects. In strabismus the use of toxin can be conveniently divided into therapeutic and diagnostic (Lee 1988). Therapeutic BTA Therapeutic BTA is used in four situations. The first is following surgery where an overcorrection has occurred and the patient has strong fusion potential (Dawson et al. 1999). BTA injected early in the postoperative course can realign the eyes permanently. The usual situation that this is necessary is consecutive esotropia following surgery for exotropia. Rarely do esotropias have strong binocular potential. The second therapeutic use is maintenance therapy (Horgan et al. 1998). In this situation the patient may have had multiple surgical procedures and become disillusioned with the results. Often there is no fusion potential and alignment is the only desire by the patient. Repeat injections of BTA at three monthly intervals will give the patient the desired effect and can be continued permanently. There is no reported accumulation of toxin effect with time. Some patients may also undergo maintenance therapy while on the waiting list for definitive surgery. Use of BTA in children has been reported and there is some evidence that long-term alignment can occur without surgery. The two types of childhood strabismus that may respond in this way are early onset esotropia and intermittent exotropia (Spencer et al. 1997). The final reported therapeutic BTA use is in acquired nystagmus (Helveston et al. 1988). Those patients who respond well have to continue with long-term maintenance treatment. Acquired nystagmus can occur in a variety of neurological situations but often the commonest cause is multiple sclerosis. Constant ocular movement with the nystagmus causes the illusion that the world is moving. This symptom is called oscillopsia and is very disabling. No drug treatment is possible to relieve this. The injection of BTA into the retrobulbar space will reduce the degree of oscillopsia and symptoms. Occlusion of the opposite eye is mandatory as diplopia is the inevitable result. Not all patients are suitable for this treatment and the ideal patient will be wheelchair bound with potentially good vision in the eye to be treated and willing to wear occlusion. Some patients with neurologically degenerative conditions may have had optic nerve disease and will not respond well. Restrictions of ocular movement in the injected eye and the risk of ptosis limit its usefulness. Diagnostic BTA BTA is used diagnostically in two situations. Postoperative diplopia testing is performed in the outpatient clinic in patients who are thought to have the risk of developing double vision. These types of patients have had often a previous intervention for squint as a child followed by recurrence of the same or different deviation. Visual acuity can be virtually the same in each eye or marked amblyopia may be present in one eye. The usual test is to neutralise the deviation with a prism and enquire about whether diplopia is present or not. If present often patients are advised against surgery. BTA injection in these cases can be beneficial to cause short-term ocular alignment and allow the patient to see if they can cope with the diplopia produced. Often the diplopia although present is not intrusive and surgery can be undertaken. The patients whose double vision is troublesome can then be treated with occlusion until the toxin effect wears off. Surgery is not contemplated in these individuals. Some patients after experiencing the effect of BTA injections opt to continue with this form of therapy rather than having surgical intervention. Diagnostic BTA can also be used to explore the state of ocular muscle function and prevent contracture. In a sixth nerve palsy the medial rectus muscle may undergo shortening despite recovery of lateral rectus function. Injection of BTA into the ipsilateral medial rectus will diagnose the state of recovery of the lateral rectus, and also prevent contraction of the medial rectus. In thyroid eye disease the patient has inflammation within the extra ocular muscle, which causes restriction of eye movements. BTA in this situation can unlock the contraction in the short term, diagnose the stage of shortening and relieve the patients symptoms. Introduction of BTA has probably been one of the most exciting innovations in strabismus management in recent years. Summary Until recent times, strabismus surgery had not really advanced from its first introduction. Improvements in suture materials, understanding of anatomy, modern anaesthetic techniques and lack of fear on operating on 86

9 Optometry in Practice oblique muscles have contributed to the improvement in ocular realignment. In combination with better understanding of ocular physiology and the ability to change ocular position without surgery, the treatment of patients with strabismus has changed radically. In the future, we may look forward to newer types of injectable treatments that may have a more permanent effect than BTA, and perhaps a better way of treating amblyopia than the current regime of patching treatment. In view of the fact that heredity plays a role in strabismus and refractive error, perhaps the way forwards in the future will be at a cellular and genetic level. References Adams F, trans (1946). The genuine works of Hippocrates; translated from the Greek with a preliminary discourse and annotations. With an introduction by Emerson Crosby Kelly. Huntington, NY: R.E. Kreiger Publishing Co. Burke JP, Scott WE, Kutsche PJ (1993) Anterior transposition of the inferior oblique muscle for Dissociated Vertical Deviation. Ophthalmology 100 (2), Cuppers C (1976) The so-called faden operation Transactions of the Second Congress of the International Strabismological Association. Dawson EL, Marshman WE, Lee JP (1999) Role of botulinum toxin A in surgically overcorrected exotropia. JAAPOS 3(5), Ebbell B, trans (1937) The papyrus Ebers: the greatest Egyptian medical document. London: Oxford University Press Fells P (1976) Surgical management of extorsion. Int Opht. Clinics 16, Fells P (1984) Strabismus surgery under local anaesthesia: onestage technique using adjustable sutures. Transactions of the Fifth International Orthoptic Congress Fink WH (1951) Surgery of the Oblique Muscles of the Eye CV Mosby Co. St Louis Harada M and Ito Y (1964) Surgical correction of cyclotropia. Japanese J Ophth 8, Helveston EM (1984) oblique strengthening procedures. Am Orthop J 34, Helveston EM, Pogrebniak AE (1998) Treatment of acquired nystagmus with botulinum A toxin. AJO 106, Helveston E (1993) Surgical Management of Strabismus 4th Ed. Mosby-Year Book, Inc. Horgan SE, Lee JP, Bunce C (1998) The long-term use of botulinum toxin for adult strabismus. J Pediatr Ophthalmol Strabismus 35, 9-16 Jampolsky A (1978) Adjustable strabismus surgical procedures. Symposium on Strabismus, Transactions of the New Orleans Academy of Ophthalmology CV Mosby Co., St Louis Khawam E, Scott AB and Jampolsky A (1967) Acquired superior oblique palsy: Diagnosis and management. Arch Ophthalmol 77, Lee JP (1988) Botulinum toxin therapy for squint. Eye 2, 24-8 Leitch RJ, Burke JP, Strachan IM (1990) Convergence excess esotropia treated surgically with the fadenoperation and medial rectus recessions, Br J Ophthamol 74(5), McLean JM (1948) Direct surgery of the underacting oblique muscles. Trans Am Ophthalmol Soc 46, Saunders RA and Tomlinson E (1985) Quantitated superior oblique tendon tuck in the treatment of superior oblique muscle palsy. Am Ortho J 35, 81-9 Scott AB (1977) The faden operation: mechanical effects. Am Orthop J 27, 44-7 Scott AB (1980) Botulinum toxin injection into extra ocular muscles as an alternative to strabismus surgery. Ophthalmology 87, Spencer RF, Tucker MG, Choi RY and McNeer KW (1997) Botulinum toxin management of childhood intermittent exotropia. Ophthalmology 104, Multiple Choice Questions This paper is reference C4076b. Two College credits are available. Please use the inserted answer sheet. Copies can be obtained from Optometry in Practice Administration, PO Box 6, Skelmersdale, Lancashire WN8 9FW. There is only one correct answer for each question. 1. Resection of the superior oblique muscle may not the option of choice because: a) It has shown to be ineffective for myopia and asthenopia. b) The tendon at its insertion is relatively thin and narrow. c) It needs to be carried out rapidly with minimal analgesia and anaesthesia. d) Inferior oblique surgery is the more attractive option e) Complete tucking or advancement of part of the muscle offers a better alternative. 2. A superior oblique tuck may be indicated where there is maximal vertical diplopia; a) In the right eye on dextro depression. b) In the right eye on laevo depression. c) With inferior rectus overaction (in absence of other sequelae). d) With inferior oblique overaction (in the absence of other sequelae). e) With superior rectus weakness (in the absence of other sequelae). 87

10 IB Marsh 3. Congenital superior oblique weakness: a) Is usually accompanied by torsion or tilting of the double images. b) Is often associated with whiplash type injuries. c) Is rarely associated with longstanding abnormal head posture. d) Is almost always unilateral. e) Will be accompanied by a tilt of the head to the same side as the muscle weakness. 4. With acquired superior oblique weakness; a) The symptom of vertical diplopia is less prominent than that of torsion. b) Cranial nerve IV is usually implicated because it exits from the brain anteriorly. c) The affected eye is usually unable to elevate in the abducted position. d) Scanning is mandatory to exclude closed head trauma. e) It is usually preceded by episodes of intermittent problems. 5. Which of the following statements is true? a) In Brown s syndrome the affected eye cannot elevate in the abducted position. b) A superior oblique tuck can be augmented by contralateral inferior oblique weakening. c) Bilateral acquired superior oblique palsy is likely to be present if excyclotorsion exceeds 10 degrees. d) The post-operative forced abduction test prevents acquired Brown s syndrome. e) Occlusion is the procedure of choice if torsion is the major complaint. 6. Which of the following statements about inferior oblique surgery is true? a) Anterior transposition is the procedure of choice for an overacting inferior oblique. b) The aim in myectomy surgery is to remove about 5 to 8mm of muscle. c) Recession of the muscle is performed as close to the limbus as possible. d) A vertical correction of 10 prism dioptres is the maximum expected in the primary gaze position with muscle weakening surgery. e) All of the above. 8. Which is the indicated surgical procedure for the muscular manifestation of sixth nerve palsy? a) Anterior transposition of the inferior oblique. b) Myectomy of the superior rectus. c) oblique tuck. d) Adjustable strabismus surgery. e) Recession of the inferior rectus. 9. Which of the following statements is true? a) In two-stage adjustable strabismus surgery, the adjustment is made 1 week after surgery. b) The AC/A ratio for convergence excess is normally 1:5. c) Adjustable surgery is normally only performed on children under the age of 7. d) Insertion of superior rectus Faden sutures is the only procedure indicated for DVD. e) Suture position is the reason that retro equatorial myopexy works. 10. Complications possible with Faden procedures include: a) Lack of effect. b) Suture breakage during the adjustment. c) Excessive tightening of the muscle. d) Lower lid recession. e) Bleeding as a result of damage to the vortex vein. 11. Type A Botulinum toxin: a) Is safe to use in strabismus treatment because it is not toxic in humans. b) Is of limited duration because the paralysis of nerve endings containing ACh is reversible. c) Produces a maximal muscular paralysis in humans after three months. d) When injected binds to the terminal nerve ending. e) When injected can only be reversed slowly by use of antidotes. 12. Which of the following uses of BTA is most common diagnostically? a) For realignment of the eyes where surgery has resulted in an overcorrection. b) For postoperative diplopia testing. c) For acquired nystagmus. d) For early onset esotropia. e) All of the above. 7. Which of the following are likely indications for adjustable strabismus surgery? a) Risk of post-operative diplopia. b) Certain neurogenic forms of squint. c) History of previous multiple surgery. d) Mechanical restrictions. e) All of the above. 88