The eyes of my baby are shaking… NYSTAGMUS! What is it?
Nystagmus is a rapid, involuntary and rhythmic eye movement. These trembling, shaking and “dancing” movements usually occur in horizontal or vertical directions.
Are there different types of nystagmus?
There are congenital and acquired types of nystagmus. The latter presents several subcategories.
Congenital nystagmus usually occurs between 6 weeks and 6 months of age. From then on, it is considered acquired nystagmus and may demand complementary exams according to your clinical standard. Congenital nystagmus tends to be divided into two groups with clearly different evolution and treatment needs: children with abnormal vision (sensorial nystagmus) and children with normal vision (motor nystagmus).
- Eyes of children with normal vision cannot (for different reasons) send sharp images into the brain: in turn, when brain does not obtain such fundamental visual feedback for its development, it is not able to keep eyes fixed on a stable way. Possible associated diseases to this type of nystagmus include congenital cataract, optic nerve hypoplasia, Leber congenital amaurosois, achromatopsia, oculocutaneous albinism, aniridia, choroidal coloboma and severe refractive errors, among others. Moderated to severe visual impairment is the common factor to all these conditions emerging in both eyes since birth. It is sometimes called “sensorial nystagmus” and refers to eyes having a damaged capacity to “capture” vision. This type of nystagmus tends to start around 2 to 3 months of age and continues during life according to the underlying disease evolution.
- The other type of children’s nystagmus occurs in children with normal or almost normal vision, but where brain has a damaged ocular stability motor control. For that reason, this nystagmus type is often referred as “congenital or idiopathic motor nystagmus” and usually has no other signs or symptoms. This is the most common type of nystagmus (35% of all children nystagmus), but often has no traceable cause.
This means that if a child manifests nystagmus during his/her fist months of life, it is then fundamental to develop clinical evaluation with an experienced Paediatric Ophthalmologist who can evaluate all visual anatomical elements, thus excluding other associated pathologies (like listed above ones) and assuring visual function health.
Acquired nystagmus comes a bit later, around 6 months, but it may also occur anytime after that. It may have many etiologies – structural and functional brain anomalies, medication side effects, neoplasms, genetic and metabolic disorders among others. Acquired nystagmus may be associated to severe medical conditions and usually demands an extra evaluation with imaging exams – such as magnetic resonance imaging – and auxiliary analytical exams to define a potential cause as well as interdisciplinary supervision like Paediatric Neurology and other medical specialties.
Is nystagmus a hereditary condition?
It usually happens spontaneously in a child, meaning it was not present in none of the parents. Nevertheless, there are families who have several nystagmus-affected members, which helps us identifying possible relations between genes and nystagmus – that may have several inheritance forms: dominant, recessive and X-linked. It may also manifest in several ways between family members, meaning they are not absolutely similar between people.
How does it affect a child’s visual development? What is the prognosis?
Answer differs according to the type of nystagmus! Therefore, clinical evaluation is primordial. If a child suffers from congenital sensorial nystagmus, vision will be damaged and will probably become poor, but not necessarily because of nystagmus: because of the underlying cause that may be (for instance) related to the retina or the optical nerve. Example: a child with bilateral optic nerve hypoplasia (or abnormal optic nerves’ development) will mainly be visually impaired due to the abnormality of optic nerves and not because of subsequent nystagmus. For a child suffering from congenital or idiopathic motor nystagmus, vision may be very good once eyes are healthy and normal.
What are the symptoms?
Children suffering from nystagmus often see the world in a similar way to other children. It depends on how old they were when disease started. In congenital nystagmus, the world does not seem like “shaking” due to the high neural adaptation ability of brain – the child was always like this… In contrast, when it emerges later or as an acquired nystagmus, patients often relate feeling of movement and oscillopsia, an experience characterised by the instability of images captured by visual field.
Some people with nystagmus often turn their head! Why is that?
Amplitude and speed of an eye movement may vary according to gaze direction. This means that a child suffering from nystagmus may perceive that his/her eyes move more when looking to the right side and less when looking to the left side (for example). Therefore, once the decreasing of eye movement or trembling is directly related to an improvement in vision stability, that child will turn his/her head right to allow an easier look to the left side. This is called the “null point”. Not all nystagmus cases have a null point.
If there is a vicious head position because of this null point, it means child has identified a way of improving vision. Therefore child should not be encouraged or forced to turn head into the opposite direction once it will only decrease visual capacity. You should communicate this fact to your Paediatric Ophthalmologist.
Is it possible to choose surgery?
In most cases, surgery aim is to help relieving a significant abnormal head position or to decrease nystagmus amplitude when there is a null point. In such cases, surgery is recommended once it may improve visual capacity.
What are the available treatments?
Firstly, it depends on the underlying cause of nystagmus (if there is one) and its treatment. For example, if a child has a refractive error, then eyeglasses prescription is fundamental. If a child suffers from congenital cataract, surgery is recommended. Botolinum Toxin may be useful for some individuals suffering from severe and untreatable oscillopsia.
Associação americana de oftalmologia pediatrica e estrabismo – https://aapos.org/glossary/nystagmus;
academia americana de oftalmologia – https://www.aao.org/eye-health/diseases/what-is-nystagmus
Pode ler mais em:
American Nystamus Network – http://nystagmus.org/new/