Link between glaucoma, sleep apnea unclear

"I do believe that sleep apnea is a risk factor for glaucoma," said Dr. Gokhale, a cataract and glaucoma specialist at Virginia Mason Medical Center, Seattle. "In my glaucoma patients, I take a brief sleep history and refer these patients for sleep studies if symptoms are positive."

Larger clinical trials with age- and weight-matched controls are required to obtain a definitive answer about the association between sleep apnea and glaucoma, he added. Features of such trials should include a carefully chosen definition of glaucoma, IOP measurements taken both diurnally and nocturnally, and perhaps measurements of ocular blood flow, he recommended.

Sleep apnea defined

Sleep apnea syndrome is defined as repeated episodes of cessation of airflow with sleep, often defined with a respiratory disturbance incidence (RDI) being greater than 5 or 10. Hypopnea, a reduction in airflow with oxygen desaturation but no apnea, also is important in defining this disease.

"It's important to realize that sleep apnea is very common," Dr. Gokhale said. "It can have serious systemic sequelae with great morbidity and some mortality."

In one study, he said, sleep apnea was found in 4% of women and 2% of men aged 30 to 60 years.

Formal diagnosis of sleep apnea or other sleep disorders requires a sleep history. If the history is positive, then it is followed by polysomnography, an overnight sleep study that usually looks at sleep stages, time in stages, oxygenation, CO₂ levels, time spent in less than 90% O₂ saturation, and RDI.

"Sleep apnea has been associated with multiple ophthalmic conditions, including external conditions such as floppy eyelid syndrome and keratoconus, as well as intraocular conditions affecting the retina and the optic nerve," Dr. Gokhale said. "In particular, recent studies have suggested an association between sleep apnea and glaucoma."

Many studies

Mojon et al., in several studies, have explored this association in several ways. When they looked at patients with sleep apnea, they found a greater proportion with glaucoma than would be expected in the general population. They also examined the association from the opposite perspective, administering sleep studies to patients with glaucoma and finding a high proportion of sleep apnea.

Marcus et al. administered a sleep questionnaire to patients with normal-tension glaucoma, patients with suspected normal-tension glaucoma, and controls (patients with cataract). Those with positive sleep histories then underwent polysomnography, which showed a high proportion of sleep disorders among both the patients with normal-tension glaucoma and those with suspected glaucoma.

In a study conducted in China, Tsang et al. evaluated visual fields and the optic nerve in patients with moderate to severe obstructive sleep apnea as well as in age-matched controls.

"Again, they found a statistically significant higher percentage of suspected glaucoma by studying discs in this group, as well as abnormal or worse visual field indices," Dr. Gokhale said.

Taking another approach, Kargi et al. assessed patients referred for sleep studies and used patients with a negative result as controls.

The investigators excluded patients with diagnosed glaucoma and looked at the retinal nerve fiber layer (RNFL) in the remaining individuals. Statistically significant thinner RNFL measurements were found in the group with sleep apnea than among controls.

Contradictory findings