Oculomotor apraxia is the inability to perform horizontal eye movements voluntarily or under verbal command.
It was described by Cogan in 1952 and its etiology is unknown today. Let’s see, in more detail, what this congenital disease consists of.
What is oculomotor apraxia?
Oculomotor apraxia or apraxia of the gaze can occur in both acquired and congenital forms . The second form is an inherited disorder that affects the eye and is usually present from birth.
It consists of an alteration of brain function characterized by the inability to perform horizontal eye movements voluntarily or on the verbal command of another person.
It is a condition, of still unknown causes, generally considered to be a sporadic disorder, although cases with autosomal dominant inheritance (when only one copy of the gene allele is sufficient for the disease to be expressed) have been described.
The patient suffering from oculomotor apraxia cannot voluntarily change the direction of his gaze towards the sides, nor does he present the rapid phase of the vestibulo-ocular or optokinetic reflexes (responsible for stabilizing the gaze to obtain clear images).
Although the causes responsible for the appearance of a condition such as oculomotor apraxia in newborn children have not yet been identified, it has been suggested that most of them could have developed Joubert’s syndrome , a genetically transmitted disorder.
This syndrome would cause partial metabolic alterations or defects in neurological development, such as hypoplasia (incomplete development) of the cerebellar vermix, aplasia (lack of development) of the corpus callosum, heterotopias of the grey substance, Kallman syndrome or chromosomal alterations.
In order to establish an accurate diagnosis of oculomotor apraxia , other causes must be ruled out, such as fixation defects and abnormal head movements : visual deficits due to eye problems, alterations in mobility, spasms or psychomotor retardation.
In addition, the patient should maintain vertical saccadic movements (both voluntary and in the vestibulo-ocular and optokinetic reflexes). However, it should be noted that in acquired oculomotor apraxia, secondary to other central nervous system injuries, vertical movements are also affected.
Cogan identified several fundamental aspects characteristic of congenital oculomotor apraxia.
First, there is a sharp turn of the head in the direction of the object of fixation , followed by a slow movement of the eyes towards the desired place.
There are also occasional spasms in the fixation of the gaze , and a movement of the head towards the object of fixation while the gaze remains fixed in the first position, followed by a closing of the eyelids and a subsequent slow movement of the eyes towards the new place of fixation.
On the other hand, there is preservation of spontaneous eye movements and gaze on the vertical plane .
Finally, the alteration of the movements of attraction and, sometimes, of the movements of following the look, stands out.
Type 2 oculomotor apraxia
One of the most studied oculomotor apraxias is type 2, caused by a mutation in the SETX gene . This apraxia is usually accompanied by ataxia, which is the lack of muscle control or coordination of voluntary movements.
This type of apraxia is a characteristic symptom of Gaucher disease , a rare and degenerative condition resulting from the accumulation of certain fatty substances in organs such as the spleen or liver.
This disease usually causes early death in children who suffer from it, although in recent years an enzymatic treatment is being carried out to replace the inactive enzymes with new ones to try to stop its progression. In the most severe cases, bone marrow transplantation is often needed.
Some health professionals recommend vision therapy to deal with a condition such as oculomotor apraxia and the consequences that result from it.
In this type of therapy , non-surgical visual exercises are performed, personalized and prepared by a behavioral optometrist , always under the supervision of an ophthalmologist specialized in the field.
There seems to be evidence that the problem improves over the years if the exercises are executed correctly and for the specified time.
However, it has also been suggested that this disease has no cure and that the only solution is to adopt compensatory measures for the person to adapt to his/her new situation of disability.
Other types of apraxia
Oculomotor apraxia is a specific type of apraxia that involves difficulties in eye movement, but there are other types of apraxia with symptoms that generate another set of complications of a similar nature. We will see, below, what they are:
Ideomotor apraxia is the most common apraxia of all and is characterised by the fact that people who suffer from it cannot copy movements or make everyday gestures , such as waving or nodding.
Patients suffering from ideomotor apraxia are able to describe the steps to follow to perform a specific action, but have severe difficulties in performing that action or imagining that they are performing it.
2. Construction apraxia
This type of apraxia is the second most common. People who suffer from construction apraxia are unable to carry out motor actions involving spatial organization ; for example, they cannot draw a picture, figure with blocks or make a face.
3. Ideational apraxia
Ideational apraxia is a type of apraxia characterized by the difficulty of performing complex actions that require some kind of planning , such as sending an email or making a meal.
Patients with ideological apraxia usually produce incoherent, inappropriate and disorganized gestures.
4. Apraxia of speech
Apraxia of speech is characterized by the inability to reproduce necessary motor sequences with the mouth in order to speak intelligibly. This apraxia can be suffered by both adults and children of learning to speak , although in children this disorder is often called dyspraxia.
5. Limb kinetic apraxia
People who suffer from this type of apraxia have a deficit in the fluid movement of the extremities, both upper and lower. They also suffer a loss of dexterity or ability to perform both fine and precise movements with the hands and fingers (fine motor) and movements with the arms and legs (gross motor).
6. Buccofacial apraxia
In the buccofacial apraxia there is a manifest inability to correctly control the muscles of the face, tongue and throat , and therefore, problems with chewing, swallowing, sticking out the tongue, etc.
This inability manifests itself when the person performs voluntary and purposeful – and not involuntary – movements, i.e. it only occurs when a movement is executed after prior thought and planning.
- Gulias-Cañizo, R., Sánchez-Huerta, V., Rubio-Lezama, M. (2005). Congenital oculomotor apraxia: a case report. Rev Mex Oftalmol.