||Andrew G. Lee, MD, Chairman, Department of Ophthalmology, The Methodist Hospital, Houston, TX, Professor of Ophthalmology, Weill Cornell Medicine; Rohit Gupta, Baylor College of Medicine, Class of 2022
||Summary: • Hypotension impacts the perfusion pressure of the optic nerve; o; Perfusion pressure of the optic nerve equals the mean arterial pressure minus the intraocular pressure (PP = MAP - IOP) o Anything that lowers MAP or raises IOP could cause ischemia to the optic nerve • Nocturnal hypotension is thought to be the cause of acute phase non-arteritic anterior ischemic optic neuropathy (NAION) via decreased MAP o Although not proven, advising patients to avoid agents that could lower the blood pressure at night may be helpful o Also, obstructive sleep apnea alters the blood pressure and the hemodynamics to the optic nerve • Acute angle closure glaucoma can increase IOP and produce ischemic optic neuropathy o Normal-tension glaucoma in the setting of low mean arterial pressure could lead to a similar decrease in perfusion pressure, leading to ischemic optic neuropathy -This optic neuropathy is likely a chronic form resulting from long-term low-grade ischemia, and lacks the disk swelling and low cup-to-disk ratio seen in NAION. o Some studies suggest that both obstructive sleep apnea and nocturnal dips of blood pressure at night on 24-hour ambulatory blood pressure measurements can cause progression of both normal-tension and primary open angle glaucoma • Cardiac and lumbar spinal surgeries often result in hypotension resulting in NAION or posterior ischemic optic neuropathy (PION) o Marked by disk swelling post-surgically [Transcript of video] "So, we've been talking in the past about hypertension, and today we are going to be talking about hypotension, which is low blood pressure, in neuro-ophthalmology. So, one of the key things we need to know is that the perfusion pressure of the optic nerve equals the mean arterial pressure minus the intraocular pressure. And so, anything that lowers the mean arterial pressure or raises the interocular pressure could affect the perfusion pressure to the optic nerve and produce either a chronic or acute ischemic optic neuropathy. So, in the acute phase, non-arteritic anterior ischemic optic neuropathy, some people believe that nocturnal hypotension is the cause of the disorder that we call non-arteritic anterior ischemic optic neuropathy (NAION). And there have been several of studies that have looked at blood pressure, including 24 hour blood pressure measurements and it still remains controversial and so it is still not known what the cause of NAION is, but for me I try to tell the patients to avoid nocturnal hypotension as well as avoid agents that could lower the blood pressure at night, including agents that are not being used for their blood pressure like recreational alcohol use, sedatives, sleeping pills. In addition, we know that things like obstructive sleep apnea can occur at night and can alter the blood pressure and the hemodynamics to the optic nerve, so those are the two things that could occur from nocturnal hypotension. Finally, on the intraocular pressure side, we are worried about acute angle closure glaucoma, which could produce ischemic optic neuropathy from angle closure, but just normal-tension glaucoma in the setting of low mean arterial pressure could lead to something that decreases the perfusion pressure. So just like the acute form, non-arteritic anterior ischemic optic neuropathy, which is acute, there is probably a chronic form of low grade ischemia and it's controversial as well whether or not this is the cause of patients who have progression of normotension glaucoma or primary open angle glaucoma despite adequate medical treatment who have progressive cupping. So as opposed to NAION where it is an acute thing where the disk is swollen and we have the small cup-to-disk ratio in the eye, in the chronic form it can look like glaucoma and in patients with normal-tension glaucoma, just like in NAION, 24 hour blood pressure measurements have been done and there are some studies that suggests that both obstructive sleep apnea and nocturnal dips of blood pressure at night on 24 hour ambulatory blood pressure measurements can cause progression of both normal-tension and primary open angle glaucoma. However, in the chronic form, as opposed to NAION, we are going to be seeing the big cup-to-disk ratio and not the small cup-to-disk ratio, and so both the acute and the chronic forms could be related to underlaying hypotension. And then finally, we have surgical causes of hypotension. The two most common surgeries that we encounter that produce non-arteritic anterior ischemic optic neuropathy or the retrobulbar form, posterior ischemic optic neuropathy, are related to hypotension that occur at the time of surgery. The two most common types of surgeries that we see are cardiac surgery and lumbar spine surgery, especially in the prone position. So we see patients who have acute unilateral or bilateral loss of vision after either cardiac or spine surgery, we are going to be looking for swelling in the disk, either a post-surgical non-arteritic anterior ischemic optic neuropathy, or a posterior ischemic optic neuropathy (PION), that occurs from hypotension, and that is directly related to perfusion pressure where the mean arterial pressure is low. So, you should know that both hypertension and hypotension can produce neuro-ophthalmic disorders, including ischemic optic neuropathy both acutely and chronic."