A question and answer session with Mr Jay Self, , a nystagmus specialist

What is nystagmus?

Nystagmus is a disorder of the eyes where they move uncontrollably in a to-and-fro motion. Some types of nystagmus are normal (for example if you take your eyes to an extreme gaze they will often get nystagmus) but most forms are not. It can occur from birth (usually actually appearing after a few months) or as an ‘acquired’ form later in life. When it appears in young children it is usually caused by either problems with the eye/visual system or problems with the parts of the brain that control eye movement. If it appears at a young age, children don’t tend to see the world moving (Oscillopsia) but when it appears later in life, they often do.

How does it affect children that have it?

If it appears at a young age, children don’t tend to see the world moving (Oscillopsia) but when it appears later in life, they often do. Symptoms can vary widely depending on the underlying cause. For children with CASK mutations, the eye is often very healthy and so many children will see quite well, they won’t have Oscillopsia but the nystagmus will impact on the speed of seeing (imagine trying to quickly find a face in a crowd) and the perception of moving objects and complex visual scenes. It is not well understood how the brain interprets the visual information that comes into it in people with CASK related disorders. It is likely that some degree of cerebral visual impairment (CVI) is also present in some cases meaning that their visual experience is somewhat atypical and this is likely to be bespoke in each case. This means that learning what works for each person is key.  

Why is it more common in CASK related disorders?

Nystagmus is caused by an interruption to a very complex system of nerves and reflexes in the back of the eye and the brain. These are multiple, overlapping reflexes that have evolved one on top of the other (some of them have their origins in fish!). Due to the complexity of these systems, the specific underlying mechanism in most forms of nystagmus is still debated. However, we do have some clues when it comes to CASK. The CASK gene is responsible for making the CASK protein and this protein is known to interact with other proteins and help build some of the complex circuitry in the eye and brain. Therefore, it is thought that mutations in the CASK gene cause these circuits to be incorrectly built and so the eyes find it hard to fix on a target and instead drift away from it and then drift (or flick) back. This is nystagmus.

Are there any treatments for the condition?

There are medical, surgical and optical treatments for the various forms of nystagmus but these vary with the type of nystagmus, the symptoms it is causing, the age of the patient and various other factors. For some conditions which cause nystagmus there are some developing therapies for the underlying condition (such as gene therapy for retinal diseases etc.) but for the vast majority treatments are limited to reducing the impact of the various symptoms.

Are there any treatments for nystagmus in people with CASK disorders?

Currently, the treatments available are to help with some of the symptoms and secondary problems, rather than to rescue the eye movement itself. For example, needing to wear glasses is much more common in children with nystagmus and so this should be checked regularly in people with CASK mutations and nystagmus. The eye condition in children is often associated with a direction of gaze where the nystagmus reduces to some degree (often a ‘null zone’). Some children will then adopt a head posture so that they can benefit from this improvement in vision and this might be a head posture in any direction depending on where the nystagmus reduces. In some cases, eye muscle surgery can be used to move this position to the middle, reducing extreme head postures and aiming to give people their best vision more of the time. It is also important that children with nystagmus (and many with CASK mutations) are given visual support and often this is facilitated in the UK by the child be registered as having a visual impairment (CVI registration).

Is the nystagmus likely to get worse?

The nystagmus in CASK disorders tends to appear in the first few months of life, will often be quite chaotic and then settle into a more consistent pattern. After this period, there will be periods of worsening and improvement during the day, weeks, months and even years but broadly, most people will have nystagmus which we do not expect to consistently worsen over their lifetime. Many people with the condition note that it tends to vary with stress, tiredness, illness and many other factors and so short term fluctuations in both the size and the speed of the nystagmus are common.

Mr Jay Self, BM FRCOphth PhD, is a UK Nystagmus Specialist at the University of Southampton

See Nystagmus Network UK for more information