Glaucoma is a disease of the eye’s optic nerve, and can result in the gradual loss of peripheral vision, causing tunnel vision and ultimately blindness. Usually, the damage to the optic nerve is caused by increased pressure within the eye, which results from greater production than outflow of the fluid of the eye (the aqueous humor). The normal intraocular pressure (IOP) is about 10 to 21 mm Hg. In chronic glaucoma, the IOP is usually mildly to moderately elevated (22 to 40 mm Hg). In acute glaucoma, the IOP is greater than 40 mm Hg.
In some case,s glaucoma develops in people with normal IOP. Referred to as low-tension or normotensive glaucoma, this form accounts for approximately 25 to 30 percent of all glaucoma cases in the United States.
Causes of Normotensive Glaucoma
Since elevated IOP is not a factor in normal-tension glaucoma, other factors are responsible for the optic nerve damage. Suggested causes include:
- Reduced blood flow
- Early nerve cell death
- Nerve irritation
- Excess glutamate production
- Autoimmune disease
The condition is more common in women than in men, and affects adults with an average age of 60. A common risk factor for normal-tension glaucoma is low blood pressure.
To evaluate the effect of supplemental magnesium on ocular blood flow and perimeter vision in patients with normotensive glaucoma (NTG), researchers gave 15 patients with NTG 300 mg oral magnesium citrate for one month, while 15 patients without NTG received no treatment. In the NTG group, significant improvements were noted in visual field measurements, e.g., mean deviation improved from -3.7 at baseline to -2.5, and pattern standard deviation improved from 3.6 to 2.8. There was no change in ocular blood flow, so the exact mechanism of magnesium’s effect is not known.
Aydin B, Onol M, Hondur A, et al. The effect of oral magnesium therapy on visual field and ocular blood flow in normotensive glaucoma. Eur J Ophthalmol. 2010 Jan-Feb;20(1):131-5.