Several million Americans have neurologic diseases and disorders that affect vision, causing ocular symptoms that can range from dry eye to double vision to legal blindness.
Neurologic disorders specific to the eye include optic neuritis, ischemic optic neuropathy and primary glaucomatous optic nerve disease, while systemic neurologic diseases such as Parkinson’s and Alzheimer’s diseases have ocular manifestations related to deterioration of the brain. Patients after stroke also often have visual problems stemming from neurologic damage.
Steven Feldon, MD, Ocular Surgery News Neuro-Sciences Section Member, said many neurologic diseases manifest with ocular symptoms because so much of the human brain is involved in vision and visual processing.
“Since about one-third of our brain deals with processing vision in one way or another, almost any diffuse disease of the brain is going to affect vision,” Dr. Feldon said.
Optic neuritis, one of the most common neuro-ophthalmic conditions, is an inflammation of the optic nerve. According to Dr. Feldon, it is associated with demyelinating diseases, which case a loss of the protective myelin layer around the nerve. The disease most commonly associated with optic neuritis is multiple sclerosis, he said. About one-third of cases of multiple sclerosis first present as optic neuritis, he stated, and up to 50% of patients with multiple sclerosis develop optic neuritis at some point. Multiple sclerosis affects about 500,000 people in the United States.
Symptoms of optic neuritis include a dimming of vision that occurs over hours or days and painful eye movements, usually in one eye, Dr. Feldon said. It rarely occurs in both eyes. Optic neuritis recovers spontaneously, with symptoms typically improving after a period of 3 to 5 weeks, Dr. Feldon said. He said in about 85% of cases, visual acuity recovers close to the previous normal level. In about 15% of cases, there is substantial visual loss.
Optic neuritis occurs most commonly in young white women. It is diagnosed clinically by history and by the presence of an afferent pupillary defect, a decrease in visual acuity, a change in the visual field and a swelling of the optic nerve, Dr. Feldon said.
Treatment can include prescription of immunomodulatory agents for multiple sclerosis, such as Avonex (interferon beta-1a, Biogen Idec), Betaseron (interferon beta-1b, Berlex) or Copaxone (glatiramer acetate injection, Teva Pharmaceuticals).
“They go on therapy right away, and it reduces the number and severity of episodes that cumulatively cause permanent damage to the brain tissue,” Dr. Feldon said.
Ischemic optic neuropathy
When the optic nerve does not receive a constant and sufficient flow of blood, ischemic optic neuropathy can occur.
“Diagnosis of ischemic optic neuropathy is typically made on the basis of acute visual loss associated with an afferent pupillary defect in the affected eye, evidence of optic disc edema and visual field loss,” said Anthony C. Arnold, MD, an Ocular Surgery News Neuro-Sciences Section Member.
The disease can be divided into two categories, that which is related to temporal arteritis and that which is unrelated to temporal arteritis.
In ischemic optic neuropathy related to temporal arteritis, a serious condition that typically occurs in patients over 70 years old, there is a rapid onset of severe visual loss, according to Dr. Arnold. This form of the disease is often associated with the systemic symptoms of temporal arteritis, which include severe headache, scalp tenderness, jaw pain, joint and muscle pain and weakness, fever, and unexplained weight loss, he said.
In the form that is not related to temporal arteritis, the nonarteritic form, there typically are no associated symptoms aside from the painless rapid onset of visual loss in the affected eye, commonly in the inferior field of vision, Dr. Arnold said.
Patients with nonarteritic ischemic optic neuropathy are typically 60 years old or more and may have vasculopathic risk factors including hypertension, diabetes, hyperlipidemia and smoking, Dr. Arnold said.
“In both forms of the disease, the affected eye tends to suffer permanent visual loss with varying severity, the arteritic form more commonly being severe,” Dr. Arnold said. “The arteritic form also is more likely to affect both eyes sequentially and result in permanent blindness, while the nonarteritic form most frequently affects one eye only, although that eye may suffer significant permanent visual loss.”
Primary glaucomatous optic nerve disease
Primary open-angle glaucoma is an optic neuropathy that occurs across all age groups, genders and ethnicities, and it typically does not produce symptoms until later states of the disease, Dr. Arnold said.
“Glaucomatous optic nerve damage produces insidious loss of peripheral vision with eventual blindness in more severe cases that have gone untreated,” Dr. Arnold said. “Central detail vision often is spared until the very latest stages, but peripheral impairment may affect patients’ ability to maneuver in their environment.”
The disease is diagnosed based on glaucomatous excavation of the optic nerve head and typical visual field tests, most often — but not always — in the presence of elevated IOP, Dr. Arnold said.
“We now realize that IOP is only part of the etiology and maybe only part of the therapy,” he said. “The emphasis is shifting to the optic nerve damage and how to manage it, in addition to controlling the IOP.”
Early optic neuritis. Blurred disk margins and visual loss occurred.
Normal fundus in a patient with unilateral optic neuritis.
Left eye of the patient in Figure 2, which shows blurred disk margins and an absence of the physiologic cup.
Images: The Atlas of Ophthalmology Photo CD, SLACK Incorporated.
Both Parkinson’s and Alzheimer’s diseases can have effects on the eye and vision, Dr. Feldon said.
Parkinson’s disease is a chronic progressive movement disorder marked by degeneration of dopamine-producing brain nerve cells. It affects about 1.5 million people in the United States. The disorder occurs in all races, but is somewhat more prevalent among whites. Men are affected slightly more often than women.
Patients with Parkinson’s disease have difficulty correcting for slight drifts of the two eyes, according to Dr. Feldon. Patients’ most common ocular complaint is double vision, which is difficult to correct, he said.
“A lot of people have a tendency for their eyes to drift either inwards and outwards, but most of us can correct for it because we have fine motor control of our eye muscles. So as soon as our vision sees that the eyes are not aligned, a signal is sent out to the brain to move things into alignment,” Dr. Feldon said. “But the fine motor control for Parkinson’s patients is not there, so they tend to have more trouble with double vision.”
Patients with Parkinson’s also have problems with lack of blinking, causing dry eye and blurred vision, he said.
Alzheimer’s disease is a progressive neurologic disorder marked by deterioration of brain neurons. About 4.5 million America have Alzheimer’s disease, and the prevalence of the disease doubles with every 5 years of age beyond age 65 for both sexes.
Patients with Alzheimer’s often complain of poor visual acuity. The visual effects of the disease are difficult to treat, Dr. Feldon said.
It is unknown whether the problem resides in patients’ optic nerves or in their brain’s inability to interpret what they are seeing, he said.
“Probably, there’s some element of both going on. There probably is some cortical degeneration in the brain, which prevents the vision that does come from the eyes being properly interpreted, and probably there is some decrease in the actual signal coming through the optic nerves,” he said.
Patients sometimes lose vision after the occurrence of a stroke, according to Dr. Feldon. He said it is common for patients to lose half of their vision, a functional defect referred to as hemianopia.
In addition to the functional defect, he said, “sometimes patients, even though they’re blind in those visual fields, can see things that aren’t there.”
That phenomenon is called palinopsia, or the reappearance of images in the blind visual field. This phenomenon can be mistaken for monocular double vision. Patients may either see things that are not in the field, or an image in the left visual hemifield can be repeated in the right, he said.
Toxic optic nerve disease
Toxic optic nerve injuries are typically insidious and progress gradually over several months, resulting in impaired acuity, central visual field and color vision symmetrically, according to Dr. Arnold.
“This disease does not preferentially affect specific segments of the population and relates to exposure to toxic agents, often medications, although toxicity may be potentiated by concomitant medical problems including impaired clearance of a drug related to liver or renal insufficiency,” he said.
Toxic effects from medications such as ethambutol are often suspected in the etiology of this disease, he said. A complete clinical evaluation is called for.
“Clinical findings often include impaired acuity, color vision, central visual field and optic nerve appearance, which may range from normal initially to mildly edematous or atrophic in a symmetric pattern,” Dr. Arnold said. “Patients with toxic optic neuropathy tend to have significant difficulty with detailed central vision including reading at both distance and near, and discriminating colors. In severe cases this may lead to legal blindness.”
For more information:
- Steven Feldon, MD, can be reached at 601 Elmwood Ave., Box 659, Rochester, NY 14642; 585-275-1126; 585-273-1043; e-mail: firstname.lastname@example.org.
- Anothony C. Arnold, MD, can be reached at Jules Stein Eye Institute/UCLA, 100 Stein Plaza, Los Angeles, CA 90095-7005; 310-825-4344; fax: 310-267-1918; e-mail: email@example.com.
- Erin L. Boyle and Daniele Cruz are OSN Staff Writers who cover all aspects of ophthalmology.