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Management of diplopia in MS

Val Trimble, MS Specialist Orthoptist
The Walton Centre, Liverpool

Way Ahead 2008;12(3):8-9

Eye movement disorders are a commonly encountered problem in MS. However, it seems that many people with MS, and often the health professionals who work with them, lack knowledge about the potential treatment options that are available.

People with MS often show a stoical attitude to having double vision (diplopia) or oscillopsia (shaking vision caused by nystagmus). They tend to adjust their lifestyle to the eye problem rather than adjusting their eyes to relieve the problem. Equally, not all health professionals recognize the methods that can be used to reduce symptoms and restore binocular single vision.

In normal vision, the two eyes point to the same place on the visual horizon resulting in binocular single vision In normal vision, the two eyes point to the same place on the visual horizon resulting in binocular single vision

In order to understand how and why eye movement disorders occur in MS it is important to understand the physiological aspects of human vision. Each eye has six extra ocular muscles (supplied by the third, fourth and sixth cranial nerves) to move it to any given position. In MS, if there is damage to any of these nerves there will be a resultant loss of pull and the eye will drift up, down, in, or out. As the two eyes will no longer be pointing to the same place on the visual horizon, double vision will result. In MS, the onset of diplopia will usually be as part of a relapse, and there is generally a good rate of a recovery, often facilitated by the use of steroids. The main aim therefore, is to use a temporary means of giving a reasonable area of single vision until resolution.

Orthoptists and Ophthalmologists will always look to set realistic goals when devising management plans, and it will largely depend on the nature and extent of the disorder as to how well it can be managed. A number of useful tools and management strategies can be worked into management plans and may include the use of prisms (special lenses that shift images), botulinum toxin, eye muscle surgery, and occlusion (to blank out the extra image).

Diagram to show the horizontal and vertical muscles and their insertions on the eye globe Diagram to show the horizontal and vertical muscles and their insertions on the eye globe

One of the less invasive ways of managing diplopia that is symptomatic of MS is the use of temporary stick on prisms - often referred to as Fresnel Prisms. Prisms can be changed to lower strengths over several weeks or months as normal vision returns.

There may be times, perhaps during a severe relapse when several muscles are affected and oscillopsia present, that occlusion may prove to be the most practical temporary management option. Although the covering of one eye results in the loss of 3D vision, occlusion need not mean the use of a 'black pirate patch'. An alternative is the application of a fine opaque tape to one lens of the spectacles that are usually worn, or to a pair of sunglasses.

Unfortunately, not everyone will experience a full recovery from the visual disturbances and may need to consider more active interventions. Generally, the aim of any subsequent treatment or procedure will be to restore symmetry of eye position.

The use of botulinum toxin injections has proven to offer temporary and sometimes permanent symptom relief. Botox is injected (under topical anaesthesia) into an eye muscle that is over pulling against the MS damaged one. This gives the desired balanced effect and prevents possible contracture.

Where less invasive methods have failed, muscle surgery may have to be considered. The actions of the muscles can be enhanced or decreased by either shortening the body of the muscle or by moving the position of the insertions on the globe to change the mechanical pull. The aim being to achieve a vertical or horizontal balance. This surgery is normally carried out under general anaesthetic as a day case procedure.

Surgery will only be undertaken in stable cases, where no further natural recovery is possible. To ensure this is the case, repeated orthoptic measurements will be taken over several months until consistent readings are obtained. This need for stability means that those with longstanding defects are just as suitable for treatment. Surgery can also be used to overcome diplopia that has been present in an individual for many years.

A general belief held by specialist eye centres across the UK is that too few patients are referred from their neurological units. However, last year's BISA (British Isles Strabismus Association) meeting revealed that a number of special units across the country are already successfully treating Internuclear Ophthalmoplegia (a problem of horizontal gaze common in MS), but that many centres are still not getting the referrals. Eye specialists are keen for people with MS and their health professionals to become more aware of the treatments that are often possible.

While there will always be individual cases that will not respond positively to treatment, it is important that people with MS are aware of the potential treatments and, where appropriate, offered specialist assessment.

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