Visual complaints seen with neurodegenerative diseases

August 15, 2005

St. Louis—Neurodegenerative diseases, such as Alzheimer's disease, Parkinson's disease, and progressive supranuclear palsy, are characterized by visual complaints, which must be assessed carefully to establish the correct diagnosis.

Sophia M. Chung, MD, described the various eye movement disorders that are associated with these neurodegenerative disorders. She is associate professor, department of ophthalmology, Saint Louis University Eye Institute, and the department of neurology, Saint Louis University School of Medicine, St. Louis, MO.

Dr. Chung presented the case of a 72-year-old woman with short-term memory loss. The patient's chief complaint was difficulty seeing and reading. Examination revealed bilateral distance visual acuity of 20/20, J1+ at near, and a normal examination except for motility. The motility examination revealed slowed saccades and pursuits, limited upgaze, and convergence paresis.

The finding of note in this patient was that she could not name common objects, could not read type on a page although she could write words when they were dictated to her, could not walk without bumping into objects, and could not reach accurately for Dr. Chung's pen. Alzheimer's disease was diagnosed, the number-one neurodegenerative disease. In most patients, Alzheimer's disease is manifested by loss of intellect in daily life with normal consciousness, she said.

"Patients with Alzheimer's disease can present with a variety of visual complaints, including blurry vision, difficulty reading, and mild to severe inability to see. Yet, their eight-point examination is typically normal. Later in disease development, electrophysiology findings, color vision, and contrast sensitivity may be impaired," she said. "However, the visual association cortex is primarily involved and it is the visuospatial tasks and the visual agnosia that plague the patients and their families."

The eye movements in Alzheimer's disease are not particularly striking, with saccades delayed and hypermetric. Fixation stability and square-wave jerks interfere with patient examinations, but they are usually asymptomatic. The anti-saccade test (the patient is instructed to look away from a target) is impaired, which reflects the frontal lobe disease, according to Dr. Chung.

"One of the most striking eye movement abnormalities associated with Alzheimer's disease is a Balint's-like syndrome, characterized by the triad of simultanagnosia, defined as the inability to perceive more than one visual target; optic ataxia, the inability to reach for objects of interest; and psychic paralysis of gaze, which is similar to the oculomotor apraxia of childhood," she said.

Parkinson's disease

Parkinson's disease is the second most frequently occurring neurodegenerative disease. A loss of dopaminergic neurons in the substantia nigra is responsible for the signs and symptoms of the disease. Tremor, bradykinesia, rigidity, and postural instability are the manifestations.

"Patients with Parkinson's disease also complain of blurred vision, distortion, and sometimes visual hallucinations. Unfortunately, most complaints are passed over because their objective examination is often normal," she said. "However, we recognize that there are dopamine pathways in the retina and in the occipital cortex, thereby giving the patients a pathophysiologic basis for their complaints."

Dr. Chung added that 75% of patients with Parkinson's disease have eye movement abnormalities (square-wave jerks, cogwheeling pursuits, and hypometric saccades).

Upgaze paralysis is seen commonly in aging individuals, but it develops far more frequently in patients with Parkinson's disease.

Convergence paresis, however, may be the most disabling problem for these patients, who will complain of blurred vision or diplopia on near visual tasks, according to Dr. Chung. Addition of prism to spectacles results in good management, but in some cases monocular occlusion is needed.