When blood pressure dips at night, risk for normal-tension glaucoma rises, study says

For over a decade, researchers have investigated what happens when people with glaucoma sleep at night.

When asleep, blood pressure (BP) naturally decreases in most cases, yet intraocular pressure increases. These imbalances have been linked to the progression of glaucoma. Further, vascular dysregulation (disrupted blood flow) has been attributed to glaucoma progression, despite normal intraocular pressure.

A recent report underscores the connection between BP fluctuations and glaucoma progression. It also hints at the role doctors of optometry can play in the detection of systemic diseases with ocular manifestations, one AOA-member doctor of optometry says. 

The study appeared in the April issue of the American Journal of Ophthalmology. Over a minimum of three years, about 375 study participants were followed to evaluate the link between normal-tension glaucoma (NTG) and BP. 

Participants were broken into three groups: 

• Dippers, whose BP dropped between 10% and 20% compared to their daytime BP readings.
• Nondippers, whose BP dropped minimally (less than 10%) compared to their daytime readings.
• Overdippers, whose BP dropped excessively (greater than 20%) compared to their daytime readings.  

The research's purpose was "to investigate the effect of nocturnal blood pressure dips on the occurrence of optic disc hemorrhage (ODH) in NTG patients and determine whether ODH is associated with greater likelihood of visual field progression (VFP)." 

Among the key findings: ODH was linked to IOP-independent risk factors and vascular mechanisms can play a part in the development of ODH in some glaucoma patients. To a lesser extent, according to the study, nondippers appeared to be at risk, too. 

"Being an overdipper is a significant risk factor for ODH in NTG eyes," study authors concluded. "The detection of ODH during follow up is a potent predictor of future VFP." 

Overall, ODH was found in 15.3% of eyes and VFP in 8.6% of eyes. Among the three groups, the rates of VFP were: dippers, 6%; nondippers, 7%; and overdippers, 24%. 

"Eyes with ODH were associated with greater likelihoods of subsequent VFP than those without," the study says. "VFP occurred only in eyes with ODH." 

The role of doctors of optometry  

Leo Semes, O.D., is a retired professor at the University of Alabama - Birmingham School of Optometry. Dr. Semes also was principal author of the AOA's clinical practice guideline,  Care of the Patient with Ocular Surface Disorders in 2010; a panel member for the clinical practice guideline,  Care of the Patient with Retinal Detachment and Related Peripheral Vitreoretinal Disease; and a founding member of the Optometric Glaucoma Society and Optometric Retina Society. 

Dr. Semes praised the study's design and execution. "This study confirms earlier works that associated ODH with increased risk for progression," he says. 

The research also offers up some interesting findings, Dr. Semes says. "It also highlights the importance of the association between BP behavior and NTG, emphasizing the vascular dysregulation component of NTG," he says. "The significance of optic disc hemorrhaging, despite its fleeting nature, was confirmed as a risk for progression in glaucoma, especially when the underlying cause is vascular dysregulation. Vascular dysregulation is emerging as the key to what we call and treat as NTG.  

"It's a little bit of a wake-up call for us," Dr. Semes says. 

In optometry school, students are trained to take BP measurements. It's also part of their national boards licensing examination. As primary eye care providers, they are expected to educate their patients about their BP and how it can affect their health, including their eyes. Random BP measures, such as an in-office intraocular pressure reading, provide only a snapshot in a 24-hour profile. 

For many patients—depending on their risk factors—their doctors of optometry will take their measurements as they screen, for instance, for systemic hypertension, which has ocular manifestations. That link has been well-established, Dr. Semes says. 

In cases of progression in NTG or glaucoma at target pressure, Dr. Semes says, "it would be ideal to seek monitoring of a patient's BP for a 24-hour period. Over that period, you could detect fluctuations, rather than get just a snapshot," he adds, "in co-management with a patient's primary care physicians or ophthalmologists.

"It certainly would be beneficial to patients," Dr. Semes says. "But it can be difficult—time-consuming and not cost-effective."