The cause of glaucoma remains largely unknown. Of late, there has been a lot of interest in the relationship between glaucoma and ocular blood flow. The role of diseases of the blood vessels, and the regulation of blood flow to the optic nerve, in glaucoma pathogenesis has been extensively studies. Despite that, the exact mechanism of each of these risk factors for glaucoma development is not known.
Risk factors of Glaucoma
The risk factors known to be associated with glaucoma include:
- Elevated eye pressure (also called intraocular pressure, IOP)
- Increasing age
- Ethnicity, especially African and Hispanic for POAG, Asian and Inuit for PACG
- High myopia, for POAG, high hypermetropia for PACG
- Central corneal thickness,
- Family history,
- Sleep apnea,
- Systemic vasculopathic conditions, that is diseases of the blood vessels like diabetes, high blood pressure, migraine etc.
What is Autoregulation of Ocular Blood Flow in Glaucoma?
The human body has the ability to regulate its blood supply so that each organ gets adequate oxygen and nutrients. The eye, for example, the blood flow to the eye is maintained as normal despite changes in eye pressure and blood pressure, BP. Because of this reason, the eye withstands wide fluctuations in IOP and BP, without any damage due to ischemia, or lack of blood supply.
The blood flow to the eye depends on both, systolic and diastolic BP. Damage to blood flow may be due to both high and low BP. However, studies suggest that low blood pressure may play a more significant role in damaging the optic nerve, especially at night.
In case this mechanism of autoregulation is compromised or its regulatory range is surpassed, the optic nerve can be damaged.
In the first case, the optic nerve can be damaged despite relatively normal eye pressure and BP. In the second case, the IOP is so high or the blood flow to the eye is so less that the autoregulatory mechanism cannot cope.
What Does Glaucoma and Ocular Blood Flow Mean For You?
Diabetes
Glaucoma occurs more frequently in patients with diabetes. In fact, in diabetes, the damage to the inner lining of blood vessels is the culprit . This results in dysregulation of the blood supply to the eye.
Controlling your blood sugars, therefore is essential for glaucoma management.
Hypertension
Glaucoma is also more common in patients with high blood pressure or hypertension. Any impact on the blood supply of the eye, may disrupt ONH blood supply, and result in glaucomatous damage. Hypertension, therefore, causes an increase in the resistance to blood flow, leading to decreased blood flow, and optic nerve damage.
On the other hand, low blood pressure (BP) actually decreases the blood supply reaching the ONH, causing damage. In fact, this remains a concern in patients on anti-hypertensive medications.
Very aggressive BP control, therefore, may worsen glaucoma. This is especially true for night time low BP. Sometimes, your glaucoma doctor may advise round the clock 24 hour BP monitoring in order to detect any nocturnal dips in blood pressure.
Sleep apnea
Snoring and frequently disturbed sleep, are frequent associations of sleep apnea. This can result in decreased oxygen supply to the optic nerve. Sleep apnea, therefore, increases the glaucoma risk and also its progression.
Migraine
There is an increased prevalence of migraine in patients with glaucoma, particularly in patients with normal tension glaucoma, NTG. The mechanism of both, migraine and NTG, is supposed to be vasospastic, that is, due to a spasm of the blood vessels. This obviously compromises ocular blood flow.
In fact, sometimes migraine also results in field changes, which may mimic glaucoma.
An acute attack of migraine often has the same symptoms as acute angle closure glaucoma.
