And YES – I know you hate it, but the air puff test is still very important!
I always tell my glaucoma-suspect patients to imagine the optic nerve as a bundle of a million nerve fibers connecting the eye to the brain. Now imagine if you were to lose those nerve fibers one by one slowly over the years until you go blind. That is essentially the typical process of glaucoma. It is usually caused by high internal fluid pressure inside the eye, but it often occurs in patients with normal pressures.
There are several types of glaucoma and low (or normal) -tension glaucoma makes up about 30% of the glaucoma patients in our practie. The exact cause is unknown but it is probably due do poor oxygen delivery to the optic nerve. This can be caused by type 2 diabetes, low blood pressure, chronic migraines etc.
You may be wondering; how do eye doctors detect glaucoma if someone’s pressures read normal? A thorough eye exam will typically reveal an optic nerve that has a thin appearance. Then, I consider a patients other risk factors such as family histroy, systemic desease, age, race etc. For example, 60 year-old female migraine sufferers are classic low-tension glaucoma suspects.
In other cases, a patient may have low eye pressure during the daytime, and a very high pressure at night. Most peoples’ eye pressures are highest at night. Lets say someone has a VERY high pressure at night. That day-to-night fluctuation by itself could eventually damage the optic nerve. Now, lets add another factor in; the patient takes their blood pressure medications before bedtime. Now we have low blood pressure at night, and therefore low oxygen perfusion to the optic nerve. Couple that with high internal eye pressure physically exerting force on the nerve, and voila! You have normal pressures at the eye doctor’s office by day, glaucoma damage by night.
Normal-Tension Glaucoma can be at times difficult to diagnose. However, with proper testing, the disease can be detected, treated and stabilized just the same as high pressure glaucoma. Whatever your age, be sure to have your comprehensive eye examinations on a regular basis.