Neurodegenerative conditions: When AMD, Parkinson’s, and Alzheimer’s affect the eyes
January 26, 2022
By John Hulleman, Ph.D.
The eyes are figuratively the windows to the soul – but they also can literally be windows to the brain. Aside from traditional age- and genetics-related vision conditions, such as macular degeneration, central nervous system conditions including Parkinson’s disease and Alzheimer’s disease can affect patients’ vision. These diseases can cause direct or retrograde degenerations of the optic nerve, retinal cells, and surrounding visual structures. While not often obvious, these conditions affect coordination, mobility, and visual perception, resulting in increased risks of falls and related injuries.
The UT Southwestern Department of Ophthalmology is on the leading edge of diagnostics and treatment. With a suite of advanced tools, techniques, and ongoing research studies, we collaborate with researchers in UTSW's Peter O'Donnell Jr. Brain Institute and community physicians to translate our expertise and data into active, effective therapies to diagnose, treat, and even prevent degenerative eye conditions in patients in North Texas and around the world.
Neurodegenerative conditions that affect the eyes
Macular degeneration
Age-related macular degeneration (AMD) damages the macula, prohibiting patients from performing everyday tasks that require central vision, such as reading, watching television, and recognizing faces. In the U.S., about 11 million people have AMD. Symptoms can include fuzzy, blurry, or distorted vision. Dry AMD, the early stage of the condition, accounts for about 90 percent of cases; if the disease progresses into wet AMD, bleeding, swelling, or fluid buildup can occur in the eye.
Certain patients with dry AMD can receive therapy to decrease the likelihood of developing vision loss associated with advanced disease. UT Southwestern ophthalmologists participated in the Age-Related Eye Diseases Study (AREDS), in which more than 4,000 patients were treated with either a vitamin formula containing antioxidants and zinc, a fish oil formula, or a placebo. Researchers discovered that the AREDS or AREDS2 vitamin formula cannot stop or reverse AMD, but it can slow the development to advanced disease by approximately 25 percent. Patients with wet AMD can undergo more advanced treatments, such as laser therapy and intraocular injections. These treatments often are very effective in managing wet AMD.
Parkinson’s disease
Each year, about 60,000 people are diagnosed with Parkinson’s disease, which involves the loss of specific neurons in a part of the brain called the substantia nigra. While Parkinson’s is primarily characterized by tremors, rigidity, and postural instability, vague visual symptoms such as blurred and double vision, uncontrolled eye movements, light sensitivity, eye strain, and difficulty reading are common.
Mild ocular motor abnormalities occur in as many as 75 percent of patients with idiopathic Parkinson’s disease but often are left untreated. Yet because these symptoms can further reduce a patient’s already jeopardized quality of life and functionality, they warrant specialized treatment.
Alzheimer’s disease
Alzheimer’s disease is the most common form of dementia, and it is characterized by destroyed and damaged connections between neural cells. These injuries occur due to abnormal accumulations of β-amyloid protein (Ab) in the form of amyloid plaques and/or neurofibrillary tangles composed of aggregated tau protein.
Ocular degeneration in Alzheimer’s disease occurs as the retinal nerve fiber layer thins. Neurons responsible for visual processing tend to be damaged more than primary vision neurons, resulting in ambiguous vision symptoms in the early stages of the disease. Deficits in recognizing objects, seeing colors, and processing visual motion can occur at any stage, increasing the risk of accidents such as falls, lacerations, and burns.
Ongoing research to further treatment
UT Southwestern researchers and ophthalmologists regularly participate in national clinical trials as well as international research projects. For example, Vinod Mootha, M.D., a member of our research team, traveled to an area of India in which inbreeding is common. Data retrieved were analyzed in order to identify, characterize, and model genetic variations and mutations that alter specific genes and cause hereditary degenerative diseases that affect the eyes. Using this information and our relevant systems, we are working to identify prevention methods to reduce incidences of eye-related neurodegeneration symptoms around the world.
Among the most exciting accomplishments in vision research is gene therapy for the treatment of Leber congenital amaurosis (LCA), a rare retinal degenerative condition characterized by severe vision loss starting at birth. Today, using a benign adeno-associated virus (AAV), researchers can replace the defective copy of the gene that causes LCA with a fully functional copy, preventing the disease from progressing. Alternatively, in certain instances, harmful genes linked to ocular disorders can be reduced or “silenced” by the injection of antisense oligonucleotides (ASOs) into the eye.
Within the Department of Ophthalmology, we also perform AAV/ASO gene therapy studies in mouse models of eye diseases to assess their preventive and therapeutic effectiveness. In some instances, we are able to gauge the effectiveness of such therapies nearly immediately after introduction into the eye using noninvasive functional tests – a benefit of ophthalmology that many other areas of medicine do not enjoy.”
Advanced technology for ocular degeneration care
Technology is key in advancing our understanding of neurodegenerative eye diseases at a tissue and cellular level. For example, by using noninvasive, high-resolution optical coherence tomography (OCT), we can evaluate the structural changes of the retina in mice and assess how the retina changes along the continuum of the disease and treatment. Early research indicates that OCT measurements can serve as biomarkers for the early recognition and progression of neurological conditions, though further research is needed before such techniques can be fully utilized in a clinical setting.
The UT Southwestern ophthalmology research labs are well-equipped with the cutting-edge instrumentation necessary for elucidating the cause of disease and identifying potential treatments. Our department’s instrumentation includes multi-laser flow cytometers with cell-sorting technology for enrichment/analysis studies, focal and full field electroretinography for noninvasive inner/outer retina health measurements, optokinetic reflex monitoring for visual acuity determination, and mass spectrometers for analysis of complex lipid and protein samples.
Today’s researchers are at an apex of science. We have an increased understanding of the causes and progression of neurodegenerative conditions, as well as an array of advanced therapies to prevent and treat ocular symptoms. Thus, with continued research, we can improve upon today’s therapies to potentially assuage degenerative eye symptoms and related health risks in a greater number of patients in the future.
To discuss your condition with one of our ophthalmology providers, please call 214-645-2020 or request an appointment.
