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MANAGING OPEN ANGLE GLAUCOMA

VALUE OF 24-HOUR AMBULATORY BLOOD PRESSURE MONITORING AND SLEEP APNEA TESTING IN
POAG MANAGEMENT
24-hour Ambulatory Blood Pressure (ABP) Monitoring
As previously noted, it is well known that there is an association between low ocular perfusion pressure and
POAG. 29,61 In clinical practice, in-office blood pressure measurement may help identify individuals who have
low blood pressure, but in isolation, a single measure does not give much insight into the individual’s dy-
namic blood pressure profile. An ambulatory blood pressure monitor is a portable blood pressure record-
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ing device that automatically measures blood pressure and generates a blood pressure profile over a defined
period, usually 24 hours. The optometrist can coordinate ordering the test with the patient’s primary care
physician, and review the results to identify instances of low diastolic blood pressure, paying particular
attention to the nocturnal time frame. Most patients have a nocturnal BP “dip” of approximately 10% com-
pared to daytime readings. This drop in BP may coincide with an increase in IOP, further exacerbating the
decrease in ocular perfusion pressure due to the low blood pressure alone. It has been suggested that this
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situation of low DOPP may be more pronounced in patients with or at risk of glaucoma. However, there is
a subset of individuals who are “extreme dippers”, dropping more than 20% at night compared to daytime
readings. It is thought this might be the case in some patients who are progressing despite what appears to
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be adequate IOP control. 86,87 Graham et al suggested that the magnitude of the nocturnal dip in individuals
with glaucoma correlates with visual field progression. Similarly, Plange et al found that those with NTG
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had greater variability of nighttime blood pressure measurements compared with controls who were “non-
dippers”, and that “extreme dippers” were more likely to progress than those who had a normal dipping pat-
tern. It has also been shown that central visual field may be affected more severely than peripheral visual
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field in NTG with higher 24-hour fluctuation of OPP. 88,89
Clinical Recommendations for 24-hour ABP study:
• Progression is noted despite what appears to be adequate IOP control
• Low blood pressure is suspected in a person at risk of NTG
• Suspicion that a person with systemic hypertension may be over-treated
• A paracentral field defect encroaching on fixation is noted in NTG

OBSTRUCTIVE SLEEP APNEA (OSA)
Obstructive sleep apnea is characterized by a complete or partial obstruction of the upper airway during sleep
that causes nocturnal hypoxia, elevated levels of CO2 in the blood, increased vascular resistance, and sympa-
thetic activation. It is associated with hypertension, metabolic syndrome and cardiovascular disease. 90,91 In
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addition to these systemic associations, there is consistent evidence that individuals with OSA are also at a
higher risk of developing POAG. The underlying etiological mechanisms for the relationship between glau-
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coma and OSA remain unclear. One hypothesis is that hypoxia leads to increased intracranial pressure during
sleep. The increased intracranial pressure subsequently decreases cerebral perfusion pressure and disturbs
blood supply to the optic nerve. Another theory is that the increased sympathetic tone observed in patients
with OSA can lead to increased blood pressure, vascular resistance and endothelial dysfunction which may
cause insufficient perfusion to the optic nerve and RNFL. 92-94 The risk of sleep apnea in the development of
glaucoma appears to be greater in younger individuals, women and those of Chinese ethnicity. OSA might be
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more strongly associated with POAG when IOPs are less than 21mmHg. 82,92 Despite the association of sleep
apnea and risk of glaucoma being confirmed in the literature, the benefit of CPAP treatment for glaucoma re-
mains unknown. There is some evidence suggesting that CPAP treatment may raise nocturnal IOP, but Liu et
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al concluded that treatment of OSA does not increase the risk of glaucoma.
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Clinical Recommendations for sleep study investigations:
• NTG is suspected or progression in glaucoma is detected despite what appear
to be controlled IOPs.
• Treatment of confirmed OSA should not be avoided in individuals with glaucoma.

CANADIAN JOURNAL of OPTOMETRY | REVUE CANADIENNE D’OPTOMÉTRIE VOL. 79 SUPPLEMENT 1, 2017 15