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Sleep apnea a potential risk factor for glaucoma, researcher says
Early studies indicate a possible correlation between the condition and the development of glaucoma.
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AUGUSTA, Ga. – A correlation between sleep apnea and glaucoma is a new concept being explored by glaucoma researchers. The mechanism of sleep apnea could affect ocular blood flow or nocturnal intraocular pressure.
Parag A. Gokhale, MD, said he began researching the relationship between sleep apnea and glaucoma at the Medical College of Georgia, where the correlation between sleep apnea and pseudotumor cerebri was being studied. In the previous studies in Augusta, researchers observed abnormalities of the retinal blood vessels in patients with pseudotumor and sleep apnea, he said.
“We saw abnormalities of the retinal blood vessels that we wouldn’t have expected in someone with pseudotumor alone, so we started looking at this and optic nerve abnormalities in sleep apnea patients, and the appearance of glaucoma seemed more common in that group,” Dr. Gokhale said.
Dr. Gokhale does a sleep review of systems in patients with certain conditions: glaucoma, branch or central retinal vein occlusion, or vessel tortuosity. If the review is positive for sleep apnea, he refers patients to the sleep laboratory at the medical college for further study.
Sleep apnea studies
Several studies have shown a possible relationship between sleep apnea and glaucoma.
Researchers in Switzerland introduced the concept of a relationship between sleep apnea and glaucoma in a study done in 1999.
In one study, 114 patients undergoing sleep studies were given comprehensive ophthalmalogic exams. Sixty-nine of the patients were diagnosed with sleep apnea, and of that 69, three were diagnosed with primary open-angle glaucoma and two more with normal-tension glaucoma, based on disc and field abnormalities.
In another study, the same group looked at the association from a different angle. They performed overnight testing on 30 consecutive patients with primary open-angle glaucoma and found that six of the patients had sleep apnea.
A study in Georgia by Dr. Dennis Marcus and others found a large proportion of normal-tension glaucoma patients also had sleep apnea.
Dr. Gokhale and colleagues in Augusta did a study evaluating patients with sleep-disordered breathing. They performed fundus and optic disc photography and found that a larger proportion than expected had glaucomatous appearing optic nerves, he said.
The mechanism of action possibly leading to glaucoma is unknown, but researchers theorize that sleep apnea may cause ischemic damage to the optic nerve stemming from hypoxia, or abnormal blood-flow autoregulation, Dr. Gokhale said.
“It is well known that patients suffer episodes of hypoxia, and there’s a large variation of oxygen and carbon dioxide blood concentration throughout the night,” he said. “This is felt to lead to abnormal blood-flow autoregulation.”
There is also documentation of cerebral hypoxemia in patients with sleep apnea. Another theory is that nocturnal elevation of intraocular pressure may cause mechanical damage. Currently, there is no measurement data to support these theories in patients with glaucoma, he said.
Additional studies are needed; however, analyzing changes in the disease in relation to sleep apnea will be difficult because of the chronic nature of glaucoma.
A clinical trial examining sleep parameters in patients with a definitive diagnosis of glaucoma is needed, Dr. Gokhale said.
Criteria
In evaluation of sleep apnea, patients undergo polysomnography, or sleep study, which involves multiple measures. Pulse oximetry, electroencephalography, electrocardiography, electromyography and measurement of airflow from the nose and mouth are recorded, Dr. Gokhale said. Respiratory effort is measured by measuring abdominal and chest wall expansion. The sleep study is evaluated by a sleep technician and a physician, usually a pulmonologist or a neurologist.
Dr. Gokhale hopes to obtain funding to conduct a larger clinical trial. He hopes to study patients with a diagnosis of glaucoma and sleep apnea with a control group of similar body weight and size to more strongly determine whether there is an association.
“I’d like to use some measure of blood flow or intraocular pressure or both to get an idea of a possible mechanism,” he said.
Studies have not been done to examine whether treatment for sleep apnea will affect glaucoma in patients with both conditions.
For Your Information:
- Parag A. Gokhale, MD, is an assistant professor of ophthalmology at the Medical College of Georgia, 1120 15th Street, Augusta, GA 30912; (706) 721-1153; fax: (706) 721-8328; e-mail: pgokhale@mail.meg.edu.