Ординатура / Офтальмология / Английские материалы / Eye Essentials Binocular Vision_Evans_2005

What do I do?

Etiology ● Congenital restrictive anomaly affecting abduction and/or adduction of one or both eye(s)

Symptoms ● Usually, there are no symptoms since the patient compensates with a head turn and/or there is suppression when the person looks in the field of action of the affected muscle

Clinical signs ● Head turn

●On motility testing, it is as if one eye is “tethered”:

●the eye does not move (or barely moves) beyond the horizontal in abduction and/or adduction

●there may be up-shoots: an eye aberrantly moves upwards when trying to look to one side

●usually, globe retraction is present causing the palpebral aperture to narrow on adduction

●There are three types depending on whether abduction, adduction or both are affected. Confusingly, there are two different classifications so it is best to describe the features rather than worrying about the label

●Even when the adduction is normal, the near point of convergence is often remote

Management ● If long-standing: no management is usually necessary

●If detected in a child and has not been previously investigated: then referral is advisable since there can (rarely) be other associated ocular and/or systemic abnormalities

Incomitant deviations

Table 6.12 Typical features of Brown’s syndrome

98Feature Detail

Etiology ● Usually congenital, but can be acquired

●Restrictive (mechanical) incomitancy caused by abnormality of the superior oblique tendon sheath which prevents this muscle from feeding out through the trochlea

Symptoms ● Usually there are no symptoms

Clinical signs ● Inability to elevate the eye when adducted

●In mild cases, this is only apparent when the eye looks up

●In more marked cases, the affected eye is also hypotropic when attempting adduction without elevation

●The main challenge is to differentially diagnose the condition from an inferior oblique palsy, which is much rarer. In inferior oblique palsy, there is usually:

●an overaction of the superior oblique muscle

●a positive Parks 3-steps (or Lindblom’s) test

●a compensatory head tilt

Management ● If recent onset: urgent referral

● If long-standing: usually, no treatment is indicated

of gaze, then this binocularity should be preserved or decompensation could occur. For example, it is probably not advisable to fit these cases with monovision contact lenses.

Nystagmus

100 What is nystagmus?

Nystagmus is a regular, repetitive, involuntary movement of the eyes whose direction, amplitude and frequency is variable. It is rare and most commonly has an onset in the first six months of life.The classification of nystagmus is made complicated by various synonyms for the different types, and these are included in parentheses in Figure 7.1.

The two most common types of nystagmus are early-onset nystagmus and latent nystagmus. Early-onset nystagmus occurs in the first six months of life. It may occur secondary to a sensory visual defect (e.g., congenital cataracts, albinism), or

Figure 7.1 Classification of nystagmus

How do I investigate?

How do I investigate?

There are two main aspects to the investigation of nystagmus.

First, determine the type of nystagmus and second make a note of the characteristics so that any future change can be detected. The key features of the main types of nystagmus are summarized

Nystagmus

Table 7.1 Problems in the evaluation of nystagmus

1021. Nystagmus is not a condition, but a sign. Many different ocular anomalies can cause nystagmus, or nystagmus can be idiopathic, with no apparent cause

2.Attempts to classify the type of nystagmoid eye movement by simply watching the patient’s eye movements often do not agree with the results of objective eye movement analysis

3.The pattern of nystagmoid eye movements cannot be used with certainty to predict the etiology of the nystagmus. Some general rules exist (e.g., early-onset nystagmus is usually horizontal), but there are exceptions

4.The same patient may exhibit different types of nystagmoid eye movements on different occasions

5.Nystagmus is often worse when the patient is under stress or tries hard to see

6.The level of visual acuity in nystagmus is only loosely correlated with the type or amplitude of nystagmoid eye movements

in Table 7.2. Early-onset nystagmus is often associated with a null zone: a direction of gaze in which the nystagmus is minimized and the vision optimized. Patients typically adopt a head position to cause them to look in this direction of gaze.

It is important to describe the characteristics of the nystagmus in clinical records, but this is difficult because it is hard to describe a form of movement in words, and the characteristics may change from one moment to another. Nonetheless, an attempt should be made and Table 7.3 describes the key features of nystagmus that can be described in clinical records.

When do I need to do something?

Most cases of nystagmus seen in primary eyecare practice are long-standing, unchanging and require no action.Any cases in which the nystagmus is of recent onset or changing require referral.

When do I need to do something?

Table 7.2 Differential diagnosis of the main types of nystagmus

(continued)

Nystagmus

What do I do?

For the new or changing cases described above, the management is referral.The urgency of the referral depends on a variety of factors, most significantly the speed of onset. If a patient reports nystagmus and oscillopsia for the first time today, then very urgent referral is indicated. If their long-standing nystagmus appears to be gradually worsening over a period of several months, then non-urgent referral is indicated. It is also important to take account of the patient’s general health. If this is poor, or there are other neurological signs (e.g., headache, unsteady gait), then the referral becomes more urgent.

One or two things need to be borne in mind in dealing with patients with long-standing and stable nystagmus. If they have a null position, then do not do anything to make it harder for them to use this zone. For example, if they have a null zone in upgaze and they use this when reading then bifocal or varifocal spectacles are contra-indicated. If there is a latent component (worse with monocular viewing) then monovision may be contraindicated.

Many cases of long-standing nystagmus have quite high refractive errors and careful correction of these can help the

What do I do?

patient to make the most of the vision that they have. If there is a latent component to the nystagmus then it is better not to occlude during the refraction. Instead, the Humphriss Immediate Contrast method can be used.There is some evidence that contact lenses, particularly gas-permeable rigid contact lenses, might help the patient to subconsciously control the nystagmus a little better.

Every now and then vision therapies or surgical treatments for nystagmus are advocated. So far, none of these has been supported by randomized controlled trials.There is a very good support group for people with nystagmus: the Nystagmus Network (www.nystagmusnet.org).