Myopathy is a general term for diseases affecting the body’s voluntary muscles. When this condition targets the muscles controlling eye and eyelid movements, it is known as ocular myopathy. This involves weakness in the external muscles surrounding the eyes, which are tasked with precise movements for vision. Ocular myopathy is not a single disease but a clinical sign linked to various underlying systemic conditions, and its progression can vary depending on the cause.
Symptoms of Ocular Myopathy
The most common symptoms of ocular myopathy are ptosis, the drooping of the upper eyelids, and ophthalmoplegia, a weakness of the eye muscles. Ptosis can affect one or both eyes and may be subtle at first, becoming more apparent as the day progresses or with fatigue. Individuals may unconsciously compensate by tilting their heads back to see from under their drooping lids or by using their forehead muscles to lift the eyelids.
Ophthalmoplegia directly impacts the ability to move the eyes, leading to diplopia, or double vision. This occurs because the weakened muscles cannot keep the eyes aligned, causing two separate images to be sent to the brain. The double vision can be horizontal, vertical, or a combination and may worsen with specific eye movements. These symptoms can interfere with daily activities such as reading, driving, or navigating surroundings.
Underlying Causes and Types
Many of the underlying disorders that cause ocular myopathy are genetic. A primary cause is mitochondrial myopathy, which results from the failure of mitochondria, the energy-producing components within muscle cells. Without adequate energy, the highly active muscles that control the eyes cannot function properly. This cellular energy deficit is a hallmark of several conditions presenting with ocular symptoms.
One of the most common forms is Chronic Progressive External Ophthalmoplegia (CPEO). This condition is characterized by a slowly advancing weakness of the eye muscles and ptosis, beginning between the ages of 18 and 40. CPEO is caused by mutations in either mitochondrial DNA or the nuclear DNA that regulates mitochondrial function. In some instances, CPEO is part of a broader syndrome, like Kearns-Sayre syndrome, which also involves other body systems.
Another cause is Oculopharyngeal Muscular Dystrophy (OPMD), a genetic disorder that appears in individuals between 40 and 60 years of age. OPMD is caused by a mutation in the PABPN1 gene and is characterized by ptosis and dysphagia, or difficulty swallowing. While eye muscle weakness is prominent, OPMD can also affect muscles in the limbs over time. Double vision is less common in OPMD compared to other myopathies.
The Diagnostic Process
The diagnostic process begins with a clinical examination by a neurologist or ophthalmologist. A physician will assess eye movements, eyelid function, and look for signs of muscle fatigue. The patient’s family history is also taken into account, as many of the underlying conditions are inherited.
To investigate further, specific diagnostic tests are used. Blood tests may be ordered to screen for genetic mutations associated with conditions like OPMD or CPEO. Electromyography (EMG) is a procedure used to measure the electrical activity within muscles. During an EMG, a small needle electrode is inserted into the muscle to record its response to nerve signals, helping confirm the weakness originates in the muscle.
A muscle biopsy is sometimes necessary for a definitive diagnosis. A small sample of muscle tissue, often from the shoulder or thigh, is surgically removed and examined. For mitochondrial myopathies like CPEO, the biopsy may reveal “ragged red fibers,” which are muscle cells with an accumulation of abnormal mitochondria. For OPMD, the biopsy can show specific intranuclear inclusions within the muscle fibers.
Management and Treatment Options
Since there is no cure for many underlying conditions, treatment focuses on managing symptoms to improve quality of life. Regular monitoring by specialists, including neurologists and ophthalmologists, is an important part of long-term care.
For ptosis that interferes with vision, several non-surgical and surgical options are available. Ptosis crutches are a non-invasive option; these are small bars attached to eyeglasses that help hold the eyelids open. Surgically, a frontalis sling procedure can be performed. This surgery uses a sling to connect the eyelid to the frontalis muscle in the forehead, allowing it to help lift the eyelid.
To address diplopia, or double vision, corrective lenses containing prisms are often prescribed. These prisms bend light before it enters the eye, helping to align the two images into a single one. Patching one eye can eliminate double vision, though this impacts depth perception. For stable diplopia, surgery on the eye muscles may be considered to realign the eyes.