The Ocular Hazards of Sleep Apnea

This article is from May 2010 and may contain outdated material.

Obstructive sleep apnea affects an estimated 12 million Americans, according to the National Heart, Lung and Blood Institute. And that is of consequence to ophthalmologists because a simple dilated retinal examination may indicate that obstructive sleep apnea syndrome (OSAS) is affecting a patient’s ocular and overall health.

A patchwork of studies have suggested that obstructive sleep apnea syndrome plays a role in causing a wide variety of eye abnormalities, including retinal microaneurysms, impaired retinal blood flow, hypertensive retinopathy and intraocular production of post-ischemic molecules associated with neovascularization, apoptosis and macular edema.

Doubters on dozers. The verdict is not unanimous, however. The first large U.S. study to look for a link between sleep apnea and retinal abnormalities failed to find any “notable relation” between the two. But the researchers in this post hoc look at data originally collected for the Sleep Heart Health Study (n = 2,927) called for further studies.¹

Erring on the safe side. Meanwhile, some retina subspecialists believe it is prudent to consider obstructive sleep apnea as a comorbidity in ischemia-related eye diseases, and they urge their colleagues with comprehensive eye practices to screen selected patients for sleep apnea (see “Profiles of Apnea”).

Acting on Apnea

A comprehensive ophthalmologist familiar with a validated questionnaire such as the Epworth Sleepiness Scale can confirm suspicions of OSAS quite quickly.² A patient who scores 10 or above should be referred for a polysomnography and possible treatment with a continuous positive airway pressure (CPAP) mask at night (see “Slumber Has a Number”).

“Many of these patients have never had a physician suggest to them that obstructive sleep apnea might be harming their overall health or their vision,” said Nancy M. Holekamp, MD, associate professor of clinical ophthalmology and visual sciences at Washington University in St. Louis. After treatment, the patients usually are amazed by the difference it has made in their lives, she said. “The patients come back into my office later, telling me that I’m a genius,” she said with a laugh.

Not breathing has consequences. But apnea is really no laughing matter, added Dr. Holekamp. “Let me give you an example: I noticed cotton-wool spots in a diabetic patient of mine. The pattern and number of cotton-wool spots were characteristic of obstructive sleep apnea syndrome. I recommended a sleep study. The formal study revealed that my patient stopped breathing 80 times an hour while sleeping. With CPAP, his cotton-wool spots went away altogether. More than that, this patient’s diabetes and blood pressure came under much better control and he was able to stop one diabetic medication and two hypertensive medications.”

Stephen H. Sinclair, MD, agrees that it is important for ophthalmologists to be alert to obstructive sleep apnea as an aggravating factor in chronic eye disease. He coauthored a case-control study, published last year, suggesting that obstructive sleep apnea in diabetics is associated with retinopathy of a more aggressive course.² “Sleep apnea is an under-the-radar problem that accelerates and aggravates diabetes and its accompanying vascular effects,” said Dr. Sinclair, adjunct professor of ophthalmology at Drexel University.

The O₂ Roller Coaster

“More and more, we ophthalmologists are seeing diabetics who have very good hemoglobin A1c readings but very bad, progressing diabetic retinopathy,” Dr. Sinclair said. The explanation for this paradox, Dr. Sinclair believes, lies in the physiologic system for protecting the retina and other organs from hypoxic damage. Usually in undisturbed sleep, systemic blood pressure drops slowly and the retinal vessels dilate to match blood flow to metabolic demands. But during an apneic episode the oxygen concentration can fall 30 points or more within seconds, he said. “When the oxygen saturation falls from 98 percent to 70 percent, this is equivalent to suddenly being thrust up onto Mount Everest 100 to 200 times a night.”

The arterioles within the retina react to apnea by dilating maximally to prevent the retina from becoming ischemic. However, when the brain is subjected to the drop in oxygen, it responds with an outpouring of norepinephrine and adrenalin. This rouses the sleeper out of the deepest levels of REM sleep repeatedly during the night, preventing adequate rest. It also results in blood pressure spikes during each reprise, often 20 to 40 points or more, which hit the retinal vessels at a point when they already are dilated.

“The blood pressure plummets and spikes like a jackhammer, all night long, while the baseline blood pressure gradually rises,” Dr. Sinclair said. When he asked some of his diabetic patients to record their supine pressure at bedtime and in the morning, they reported that the morning readings were elevated by as much as 40 points.

Retinal insults without hyperglycemia. The repeated hypertensive crises explain the nests of microinfarcts in retinal capillaries, which is what ophthalmologists sometimes see in diabetics’ eyes despite good glycemic control, Dr. Sinclair said. Similarly, retinal hypoxia might trigger the release of cytokines and growth factors that lead to conditions such as macular edema or damage the eye’s neurosensory cells.

Recommendations for Care

For these reasons, Dr. Sinclair recommends questioning patients about their sleep patterns if they have refractory hypertension. “These patients often are on three or more medications for hypertension. When you see a patient like that, you simply must think ‘sleep apnea-related hypertension,’” he said.

During an overnight sleep study, a diagnosis of sleep apnea usually requires that the patient experience at least five episodes of apnea per hour. If the airway obstruction during sleep is partial, the sleeper will snore. If it is complete, breathing stops for 10 to 20 seconds, until the brain triggers an alarm response and the blocked pharynx is forced open with a snorting or choking sound.

Gatekeeping and adherence. Most medical insurers make the primary care physician the gatekeeper for the expensive (~$2,000) sleep study and the $1,000+ CPAP device. Consequently, with each referral, the ophthalmologist must be emphatic and persistent with both the patient and the primary physician about the importance of the polysomnography, Dr. Sinclair said. “After the patient has had a CPAP for a while and you see more lesions in the eye, then there might be a patient compliance issue.” He estimates that 30 to 50 percent of people who have a CPAP device fail to use it because of improper fit of the mask. “If the mask doesn’t fit right, it will produce pressure, pain, even bruises across the bridge of nose. I hear this from patients all the time.”

Dr. Sinclair added that commonly a lack of training and inadequate follow-up by medical equipment suppliers contribute to patients’ problems. “It is often the retinopathy, as evidenced by ongoing fresh cotton-wool infarcts, that is the tip-off the treatment is not working.”

___________________________

1 Boland, L. L, et al. Sleep 2004;27(3):467–473.

2 Unver, Y. B., et al. Open Sleep J 2009;2:11–19.