Ординатура / Офтальмология / Английские материалы / Manual of Squint_Ahuja_2008

Forced Duction Test

This test is performed by anesthetizing the conjunctiva over the insertion of the muscle to be tested. Grasp the insertion of the muscle with a toothed forceps and attempt to rotate the eye in the field of action of weak muscle.

This is of great value in deciding whether the anomaly of ocular motility is caused by mechanical factor such as contracture or fibrosis of a muscle, tightness of muscle following excessive resection, and shrinkage and scarring of the conjunctiva or Tenon’s capsule.

Estimation of Generated Muscle Force

This test is helpful to judge the residual function of an apparently paretic muscle. The active force generate by muscle can be estimated by stabilizing the eye with a forceps while the patient moves his eyes against the resistance. The tug that examiner feels on the forceps is a sign of residual function. Absence of the tug is a sign of complete paralysis.

Exaggerated Force Duction Test

It is to estimate the tightness of oblique muscle. For this test eye must be put in the orbit (retroplace the globe) as it is then rocked back and forth by extorting and moving the globe around the tendon to check the tight oblique muscle now.

Differential Intraocular Pressure

The generated muscle could be estimated by comparing into ocular pressure in various positions of gazes and pressure increases as may be as high as 50 mm kg in case of restrictive elements.

Eye Movement Velocity

It may be useful only as an auxiliary diagnostic method, in evaluating the paralytic squint the eyes are capable of morning saccades/first eye movements upto the velocity of 200–5000/sec. In cases of paralysis slow drifting eye movement, restriction squints have normal saccadic velocity till the restriction comes into effect.

Electromyography

Electromyography is useful procedure to test the function of each muscle separately and follow-up study will indicates whether the muscle is in the process of recovery or not.

Other Investigations

a.Investigations for systemic diseases like diabetes, hypertension, syphilis, etc.

b.X-ray skull

c.X-ray sinus and orbit

d.X-ray chest

e.Complete hemogram

f.CT scanning to ultrasonography

g.Carotid angiography

h.Orbital venography.

TYPES OF PARALYSIS

Depending on the involvement of individual muscles or group of muscles there can be many form of paralysis.

The main are as follows:

IIIrd Nerve Palsy

a.Complete third nerve palsy — Here only spared muscles are lateral rectus and superior oblique. The eye will be depressed, abducted and intorted. LPS paralysis, causes ptosis as well. In complete IIIrd nerve palsy the intrinsic muscles are also involved causing dilatation of pupil and loss of accommodation.

b.Isolated paralysis of individual muscle, i.e. SR, MR, IR or IO do occur, though rarely.

IVth Nerve Palsy

The movement affected are adduction and depression, superior oblique being the muscle paralyzed. The eye may be hypertropic due to over action of the antagonist. Head will be tilted to the normal side and chin will be depressed. Patients with bilateral SO palsy will have right hypertropia in left gaze and left hypertropia in right gaze, which increases on tilting the head on either sides.

VIth Nerve Palsy

Adduction will be affected, lateral rectus being the muscle paralyzed. The palpebral fissure may be widened on looking to the side of paralysis (adduction), due to maximal innervational effort. Esotropia may be present in the primary position. Head is turned over the affected shoulder.

Pseudograefe Sign

During the recovery of the IIIrd nerve palsy, nerve fibers originally connected with inferior ractus grow into the sheath of nerves fibers

supplying the levator muscle so that impulse to look down increase the tonus of the levator, hence there will be retraction of the upper lid in downward gaze, it may be accompanied by contraction of the pupil.

MANAGEMENT

Treatment of paralytic squint is always difficult and must depend on casual conditions. Every case of paralytic squint should be managed initially on conservations lines.

The Indications for Therapy

1.Presence of diplopia in the practical field of fixation

2.Inability to maintain binocular single vision without anomalous head posture.

Prisms are effective in treating deviations less than 10. for larger

deviations prisms are not usually tolerated for prolonged periods and in such cases surgery becomes unavoidable. Fresnel prisms are tried, but it should be kept in mind that the prisms take away whatever stimulus left to control strabisms and this may eventually lead to an increase in the extent of residual deviation.

Treatment of Diplopia

Management of diplopia in a case awaiting spontaneous recovery or surgery is important.

If the patient does not have BSV in any position of gaze simple eye shields are given to cover each eye alternately.

If the patient enjoys BSV in certain gazes the occlusion need not be complete, but it may be so arranged that BSV may be exercised in a limited area, i.e. occlude part of the field of one eye only.

Orthoptic treatment to maintain simultaneous binocular vision, and prevention of suppression is of almost importance.

Surgical Correction

The aim of the surgery in a case of paralytic squint is to abolish diplopia and to regain comfortable binocular vision in all directions of gaze as well as to produce a good cosmetic look. Operation is delayed until 6 months since the onset of deviation in order to allow spontaneous recovery and to stabilize the squint.

Surgical Procedures

Surgery for VIth Nerve Palsy

Sixth nerve palsy can be unilateral or bilateral. It can be aparesis or paralysis.

In unilateral palsy

1.See whether contracture is fully developed or not.

2.Assess the deviation for near and distance.

i.If the muscle sequent has fully developed, the angle of deviation is same on dextroversion and on levoversion. In such cases you will have to do a resection of LR along with recession of the ipsilateral MR. However if the angle of deviation is small resection of LR alone may be sufficient.

ii.If the muscle sequelae is partially developed, i.e. there is no contracture of the MR but there is over action of the contralateral MR in such cases you will have to do LR resection along with recession of the contralateral MR or alternately a Faden operation:

1.Here the rectus muscle is first recessed and muscle belly is anchored to the sclera by one or more circumferentially placed mattress sutures. The muscle is then reinserted in its original position.

2.The muscle remain inserted. The edges of the muscle are attached to the globe. The appropriate distance of posterior fixation sutures behind the normal muscle insertion is MR 11-13 mm.

In this procedure the power of the muscle is decreased although its primary position is not altered.

iii.In the case of VIth nerve palsy and the eye is not moving even

upto midline, see whether it is a case o MR contracture or complete loss of function of LR.

This is feasible by:

(i)Forced duction test

(ii)Forced generation test

(iii)EMG

(iv)EOG, etc.

If there is MR contracture with LR function, in such cases, do resection of the LR along with recession of MR.

In case of contracture of MR with no LR function recess MR at least 7 mm with recession of overlying conjunctiva. A transposition operation (reverse Jensens) is also indicated.

In bilateral palsy: It is usual to operate first on the nonfixing eye followed by surgey on the fixing eye at a second stage some weeks later.

In the case of both VIth and IIIrd nerve palsy the VIth nerve palsy should be treated first (as outlined in Table 11.1).

IVth Nerve Palsy

In IVth nerve palsy the choice of surgery depends on:

1.Whether the palsy is unilateral or bilateral

2.Whether the sequelae have developed particularly whether there is overaction of the inferior oblique

3.The presence and amount of extorsion and whether this is superable.

In unilateral palsy: The surgery is usually performed and on overacting muscle, not on the superior oblique itself, because of technical difficulties, and plication on the vertical component is unpredictable as compared to the effect on cyclodeviation. There is also likelihood of inducing Brown’s syndrome.

If the muscle sequelae has fully developed, there will be overaction of the contralateral inferior rectus, contracture of the inferior oblique and secondary underaction of the superior rectus. Vertical deviation will be same on contralateral up gaze and down gaze. Weakening of IO is the operation of choice.

If torsion is insuperable, recession of IR is contraindicated and a Harada procedure on the affected superior oblique should be performed as a first stage.

According to Payman the surgery to the VIth nerve palsy depends on the degree of abduction possible (Table 11.1).

Divergence paralysis: May be difficult to differentiate from unilateral or bilateral VIth nerve palsy, but this condition is usually comitant. The esotropia is unchanged or may decrease on lateroversion, unlike without a VIth nerve palsy, fusional divergence amplitudes are either severally reduced or absent, causes are head trauma intracranial space occupying lesions and cerebrovascular accidents.

Harada procedure: The anterior half of the superior oblique tendon is disinserted and split from the posterior portion along the line of its

fibers for some 10mm. The mobilized portion is then reattached 8 mm. Posterior to LR insertion and just above the LR muscles upper margin.

Once the torsion has been reduce, the vertical deviation can be reassessed and contralateral inferior rectus recessed.

In bilateral SO palsy, i.e. when there is:

1.Insuperable torsion – (torsional diplopia)

2.The head posture is mainly one of chin depression

3.Only a small vertical deviation in primary position.

Here bilateral Harada operation is the most effective procedure to overcome torsional deviation. If the palsy is asymmetrical maximum amount is performed on the more affected side and a smaller amount of the other eye. Further surgery may be necessary to correct a residual vertical deviation.

If there is marked contracture of both IO. Bilateral weakening surgery on the muscles is the first choice. Further surgery depends on the effect on cyclodeviation.

The ‘V’ pattern if marked need to be considered, either during vertical muscle surgery at a later stage.

Complete paralysis: In a case of complete IIIrd nerve palsy with contracture of the two remaining active muscles, i.e. SO and LR weakening procedures are adopted.

1.LR recession by 10mm with recession of the overlying conjunctiva.

2.SO tenectomy—this helps to avoid mechanically induced hypotropia.

Strengthening procedures—A superomaximal (up to 8 mm) resection of

MR.

Alternatively—Muscle transportion procedures like Jenson’s procedure are also indicated.

In paresis—It is advisable to correct the horizontal angle initially by resection of MR and recession of LR residual deviation can be treated conservatively with prisms or by surgery to strengthen the SR or IR.

COMPLETE PARALYSIS OR PARESIS

a.Medial rectus—Resection of MR with ipsilateral or contralateral LR recession.

b.Inferior rectus palsy—Resection of IR and ipsilateral SR recession.

c.Superior rectus palsy—Resection of SR weakening of the IR and IO

d.Inferior oblique palsy—Intrasheath tenotomy of ipsilateral SO, a recession of the contralateral SR depending whether the hypotropia is more marked in down gaze and on the amount of torsional deviation.

Weakening Operation

Recession (Rectus muscle weakening operation).

Hang back recession—In this method muscle is disinserted and reattached to its original insertion.

BLOWOUT FRACTURE

A blunt injury to the eye causes increased orbital pressure, and the orbit tends to give way at its weakest point, the orbital floor. As a result, the ligament of Lockwood drops down and the inferior rectus and occasionally the inferior oblique are trapped in the fracture. Limitation of action of the superior and inferior rectus muscles and occasionally

the inferior ethmoidal area may cause simultaneous limitation of lateral rotation. There may also be a relative enophthalmos, or this may develop later as the edema surrounding the fracture subsides or as the orbital fat atrophies. Damage to the infraorbital nerve with anesthesia of the lower lid and cheek can occur. The eyes be straight in the primary position, or the patient may have a hypotropia with diplopia in the up and down positions because of the superior and inferior rectus muscles restrictions.

Ocular Myopathy

This is a progressive external ophthalmoplegia. There is limitation of extraocular movement and progressive ptosis ultimately the patient ends up with a total ophthalmoplegia (it is not usually necessary to perform surgery on the extraocular muscles because the patient’s eyes are straight in the primary position).

Myasthenia Gravis

Myasthenia gravis is a disease characterized by fatigue and weakness of striated muscles within the body. This is due to blockage at the neuromuscular end plate, symptoms of ocular myasthenia gravis include diplopia and ptosis symptoms of myasthenia gravis are less in the morning and they are worse towards the end of the day when patient become fatigued. Diagnosis is confirmed in most cases by the administration of tensilon intravenously see if there is any improvement in clinical signs or symptoms, tonography is useful on making the diagnosis.

Painful Ophthalmoplegia

Refer to the involvement of one of more of the ocular motor nerves by a chronic granulomatous or nongranulomatous inflammation, usually at the orbital apex, in the superior orbital tissues, or in the cavernosus sinus patient experience pain and involvement of IIIrd, IVth and VIth nerve. If the orbital apex is involved, there may be visual loss from involvement of the optic nerve ESR is usually high. Many terms have been used to describe the syndrome, including the orbital apex syndrome, superior orbital fissure syndrome and Tolosa Hunt syndrome.

DOUBLE ELEVATOR PALSY

Double elevator palsy is a common of hyperdeviation. There is a parises of the superior rectus and inferior oblique muscles in the same eye. The

inferior oblique shows more restriction than superior rectus. Ptosis and occasionally Marcus Gunn (Jaw winking) may also be associated. The patient will generally walk with the head elevating slightly in order to maintain binocular vision just below the midline and in the inferior field of gaze.

Double elevator palsy probably results from some type of congenital nuclear lesion, because in the orbit the superior rectus and medial rectus.

Marcus Gunn phenomenon is apparently caused by misdirected nerve pathway. In cases with ptosis, surgery for have a risk of exposure Bell’s phenomenon.

Treatment

Surgery is the main stay of treatment in such cases. However, no surgery is indicated if the patient has binocular vision in a straight ahead position, deviation showing only on locking up and there is no backward head tilt in the primary position.

The surgical approach depends upon the amount of elevation achieved in the affected eye can be elevated above the midline the procedure of choice is to weaken yoke muscles, that is, the superior rectus and inferior oblique muscle in the normal eye. The superior rectus 4-5 mm and the inferior oblique 8- mm. In cases where the eye cannot be brought above the midtime recession of IR and resection SR muscle in the affected eye is required. In some of the patient who had undergone surgery on MR for esotropia, the eye develop a market esotropia and the patient tries to elevate the eye. In the down gaze, the same patient has a large esotropia. The eye cannot be elevated to midtime in either the adducted or abducted position. Because if this limitation, the condition has been called “congenital fibroses syndrome. Such eyes require recession of IR and congenital, the SR is reseated 4-5 mm.

Differential Diagnosis of Ocular vs Congenital Torticollis (Tables 11.2 and 11.3)

The cause of congenital (nonocular) torticollis include:

a.Congenital bony malformations of Atlas (Atlas = Ist vertebra), cervical vertebrae and ribs.

b.Malformation of sternomastoid muscles.