Eye movement disorders involve irregularities in how the eyes move or align. Nystagmus and strabismus are two distinct conditions in this category, sometimes leading to confusion due to their shared involvement of eye movement irregularities. While both can affect eye alignment or movement, their manifestations and underlying mechanisms differ considerably.
Understanding Nystagmus
Nystagmus is characterized by involuntary, repetitive, and uncontrolled eye movements. These appear as rapid oscillations, often side-to-side, but can also be up-and-down or circular. They vary in intensity and duration, affecting one or both eyes, though typically both are involved. It is sometimes called “dancing eyes” due to its rhythmic nature.
Nystagmus can be present from birth, known as congenital or infantile nystagmus, often appearing between 6 weeks and 3 months of age. In some cases, it develops later in life, termed acquired nystagmus, which is more common in adults. Acquired nystagmus often stems from issues affecting the brain, inner ear, or central nervous system. Causes include neurological disorders like multiple sclerosis, stroke, brain tumors, head injuries, inner ear problems, albinism, or certain medications.
Understanding Strabismus
Strabismus is a condition where the eyes are misaligned and do not look in the same direction simultaneously. This occurs when the six muscles controlling eye movement do not work together effectively. One eye may turn inward (esotropia), outward (exotropia), upward (hypertropia), or downward (hypotropia).
This misalignment can be constant or intermittent, affecting one eye or alternating. Strabismus often arises from an imbalance in the extraocular eye muscles or issues with their controlling nerves. It can be congenital or acquired later in life due to factors like stroke, head injury, or certain medical conditions.
Distinguishing the Conditions
The primary difference between nystagmus and strabismus is the nature of eye movement. Nystagmus involves involuntary eye movement, where the eyes oscillate. Strabismus is a misalignment where one eye points in a different direction. With nystagmus, eyes rapidly shake or twitch. With strabismus, one eye is visibly turned inward, outward, upward, or downward while the other remains straight.
The impact on vision also differs. Nystagmus can cause blurry or shaky vision, a sensation of the world constantly in motion (oscillopsia), or light sensitivity. Strabismus often leads to double vision (diplopia) in adults, as the brain receives two disparate images. In children, the brain may suppress the image from the misaligned eye, resulting in reduced vision in that eye, known as amblyopia or “lazy eye”.
Underlying causes also diverge. Nystagmus originates from neurological issues affecting brain-eye communication or problems within the inner ear’s vestibular system. Strabismus stems from muscle dysfunction, nerve control issues, or refractive errors like farsightedness that strain the eyes. Individuals with nystagmus may tilt their head to find a “null position” where movements are minimized. Adults with strabismus might report double vision, while children may close one eye to avoid confusion.
Diagnosis and Management
Diagnosing both nystagmus and strabismus involves a comprehensive eye examination performed by an eye care professional. For nystagmus, diagnosis includes observing involuntary eye movements and may involve neurological testing or imaging like MRI or CT scans to identify any underlying conditions, especially for acquired types. Strabismus diagnosis often utilizes tests like the cover test or the Hirschberg test, which assess eye alignment by observing light reflections on the pupils.
Management strategies are tailored to each condition. For nystagmus, treatment focuses on reducing symptoms and improving vision, as there is often no cure for the eye movement itself. Options include corrective lenses (glasses or contact lenses), prism glasses to stabilize images, or medications such as gabapentin or baclofen to reduce eye movements. Surgical intervention, such as eye muscle surgery, might be considered to adjust eye muscle positions, aiming to reduce abnormal head postures or decrease eye movement amplitude.
For strabismus, management aims to correct eye alignment and prevent vision loss. It often begins with corrective glasses or contact lenses, particularly if refractive errors are a cause. Patching the stronger eye is a common approach for children with amblyopia to encourage the weaker, misaligned eye to develop better vision. Vision therapy, a structured program of eye exercises, can help improve eye coordination and focusing. Surgical correction of the eye muscles is a common treatment, adjusting muscle length or position to achieve proper alignment.