Can I have glaucoma if my eye pressure is low or within the normal range?
If you’ve ever been told your eye pressure is normal, you might assume your risk of glaucoma is low. But for many people, glaucoma can still develop despite having “normal” intraocular pressure readings.
‘Normal tension glaucoma’ is a type of glaucoma where damage to the optic nerve occurs even though a person’s eye pressure sits within the normal range. It highlights that this condition is primarily a disease of the optic nerve, rather than simply a disorder caused by elevated eye pressure.
The reasons for this are not always fully understood. Some people appear to have optic nerves that are more vulnerable to damage, even at lower eye pressure readings. Factors such as reduced blood flow to the optic nerve, migraines, sleep apnoea, Raynaud’s disease, genetic predisposition, to name a few, may also contribute. What is clear, however, is that normal eye pressure does not exclude the possibility of glaucoma.
Population data reinforces this point. In this scientific journal for glaucoma research, Specsavers’ Australian data showed 66% of individuals who were referred from their optometrist to an eye specialist with suspected glaucoma, had an intraocular pressure below 22 mmHg.
This is why regular eye examinations are so important, even if your eye pressure has always been described as “normal”.
How is normal-tension glaucoma detected?
Detecting normal tension glaucoma requires a detailed assessment of both the structure and function of the eye.
Optometrists examine the optic nerve for early signs of damage and use imaging technology, such as optical coherence tomography (OCT), to identify thinning of the retinal nerve fibre layer (RNFL). These structural assessments can be complemented by visual field testing, which evaluates peripheral vision and identifies functional vision loss.
Almost a decade ago, Specsavers introduced OCT scanning as part of every eye examination at no additional cost, significantly improving the early detection of conditions such as normal tension glaucoma. By providing detailed imaging of the optic nerve and the retinal nerve fibre layer, OCT supports earlier identification of glaucomatous changes and more informed referral decisions.
If you’re at risk of glaucoma, it is highly recommended that you have an OCT scan with every routine eye exam.
If I’m referred to an ophthalmologist, does that mean I have normal-tension glaucoma?
A referral to an ophthalmologist for further glaucoma assessment does not necessarily confirm a glaucoma diagnosis, but rather aims to determine whether suspicious findings truly do indicate glaucoma or represent normal variations.
Glaucoma can be difficult to identify in its early stages, and optometrists are trained to refer patients to an ophthalmologist whenever there are signs that warrant further investigation. This cautious approach prioritises patient safety and early detection.
Why is this important?
Normal tension glaucoma highlights an important message that eye pressure is only one piece of the puzzle.
Glaucoma is often called the “silent thief of sight” because it develops slowly and without symptoms in its early stages. If you’ve been told your eye pressure is normal, that’s reassuring, but it doesn’t replace regular eye checks.
Regular, comprehensive eye examinations remain the most effective way to detect glaucoma early and preserve vision. Even when eye pressure is within the normal range, ongoing monitoring of the optic nerve and visual function is essential.
As optometrists, our role is to bring together all the key pieces of information – including eye pressure, the structures of the eye, and how it functions – to provide the most accurate and comprehensive assessment of your eye health.
Many thanks to Head of Professional Development Cindy Nguyen, and Duchesne Markham at Specsavers for preparing this article.