This article is for informational purposes only and does not diagnose any conditions
The signs and symptoms of glaucoma can vary, depending on the type of glaucoma you have, and in many cases, symptoms are not noticeable until the disease has progressed, while for others, the symptoms are sudden and require urgent medical attention.
What is glaucoma?
Glaucoma is disease characterized by damage to the optic nerve. The optic nerve is the nerve behind the eye that transmits light energy from the outside world into electrical energy that is processed by the brain.
Glaucoma often develops because of increased pressure inside a person’s eye (intraocular pressure – IOP). Increased intraocular pressure is often caused by a build up of excess fluid within the eye, that can lead to damage to the optic nerve. In rare cases, some people that have pressure within a normal range can also develop glaucoma (normal tension glaucoma). Also, a person with increased eye pressure (also known as ocular hypertension), will not always develop glaucoma.
Glaucoma can develop in one or both eyes. Primary open-angle is the most common type of glaucoma, followed by angle-closure glaucoma, and each have very different symptoms. The best way to detect if you have glaucoma is to have regular eye examinations by your Ophthalmologist or Optometrist. The signs and symptoms of glaucoma can vary, depending on the type of glaucoma you have, and in many cases, symptoms are not noticeable until the disease has progressed, while for others, the symptoms are sudden and require urgent medical attention.
What is considered high intraocular pressure?
Pressure within the eye that is higher than normal is referred to ocular hypertension. People with higher pressure have a greater risk of developing glaucoma and should be monitored by their eye care professional on a regular basis.
Eye pressure is measured by a test called tonometry. The measurement is recorded in millimeters of mercury (mmHg). A normal eye pressure ranges from 12-22 mmHg and any value higher than 22mmHg is considered high or elevated.
How do ophthalmologists or optometrists detect and evaluate glaucoma?
During regular eye examinations, your ophthalmologist or optometrist will conduct specific tests to determine if you have glaucoma or to assess the progression of glaucoma. These tests are relatively painless and include:
Measurement of the pressure inside your eye (tonometry)
Evaluate the drainage angle of your eye, that allows fluid to flow normally from the back to the front of your eye (gonioscopy)
Inspect your optic nerve at the back of your eye (ophthalmoscopy)
Assess your visual field to determine if any of your peripheral or central vision has been lost (perimetry)
What are the symptoms of primary open-angle glaucoma?
Primary open-angle glaucoma has few, if any, early signs or symptoms and for this reason, diagnosis is often delayed until the disease reaches a relatively late stage.
Primary open-angle glaucoma is caused by an increase in the pressure inside your eye that occurs when the canals that typically drain fluid from the eye because clogged. This increased pressure over time puts a strain on the optic nerve that can lead to significant damage.
Although difficult to detect and often not noticeable, symptoms of primary open-angle glaucoma may include:
Loss of peripheral vision – appearance of looking through a tunnel or a straw
Vision loss - often in spots or patches
Noticing more glare
Letters on a page appear dim when reading
Difficulty distinguishing colors
Primary open-angle glaucoma is often called the “the silent thief of sight” because, especially in its early stages, there are no obvious symptoms. Initially, primary open-angle glaucoma causes no pain and vision will seem normal. It develops very slowly and sometimes does not cause any noticeable changes in vision or sight loss for several years. Studies have suggested that up to 50% of people with this type of glaucoma are not aware they have it. 
Once primary open-angle glaucoma has developed and progresses, patchy blind spots will begin to appear in your peripheral (side) vision. These changes in vision have been described as “tunnel vision” or similar to, “looking through a straw”.  When glaucoma remains untreated, people can begin to miss seeing objects that are located to the side or “out of the corner of their eye” until eventually it seems like they are looking through a tunnel.
Beyond the narrowing of the visual field, people may also experience a deterioration in the overall quality of their vision.  Studies have shown that even early in the disease, people have had a deterioration of contrast sensitivity, meaning they have trouble detecting objects at different levels of light, while others have found it more challenging to distinguish colors of similar shades. [7, 4]
Many people feel fine, overall, and do not even notice the changes in their vision. Initial loss of peripheral vision is difficult to detect, especially when it occurs very gradually, and the sharpness of central vision (straight ahead vision) is usually not affected until much later in the disease, when irreversible damage has already occurred. Up to 40% of someone’s vision can be lost before it becomes noticeable to them. It can be difficult to notice the changes in vision, especially if one eye is more affected by glaucoma than the other. The least affected eye will compensate since the majority of visual activities involve the use of both eyes. Over time, central vision may also decrease until no vision remains.
In a study of 99 people with early glaucoma, most with primary open-angle glaucoma, more than half reported that they felt as though they needed more light to complete their usual tasks, and that their vision appeared slightly blurred, as though they were looking through dirty glasses.  Other symptoms reported by more than 25% of patients included seeing more glare, letters appearing faded when reading, or seeing too much light. 
Primary open-angle glaucoma can be detected at regular eye examinations and treatments that prevent further progression can be prescribed. Unfortunately, once vision loss is noticed by the patient, the disease is often quite advanced and any recovery of vision is unlikely, even with available treatments, including surgery.
Will the symptoms of glaucoma affect my daily activities?
As the disease progresses, the blind spots may make it more difficult to get around, or to do the things you might normally do. Obstacles like steps or curbs may become more difficult to see and navigate. Although central vision might seem normal when looking straight ahead, things in the side view or periphery will be missed. This can be particularly dangerous when driving, because even though the view of the street ahead may be clear, you may not be able to see the objects, people, and other vehicles to the right and left. The ability to adapt from changes in light, such as going from sunny outside to darker indoors may also become increasingly difficult and take far more time for your eyes to adjust.
What are the symptoms of angle-closure glaucoma?
Angle-closure glaucoma, also called narrow angle glaucoma or closed-angle glaucoma, can occur suddenly (acute angle-closure glaucoma) or more gradually. Angle closure glaucoma occurs when the normal flow of fluid within the eye becomes blocked and the pressure inside the eye increases.
Typically, fluid flows from the back part of the eye, where it is produced, through the pupil and into the front part of the eye behind the lens, the clear part at the front of the eye. In angle closure glaucoma this flow of fluid becomes blocked due to contact between the lens and the iris, the colored part of the eye. This blockage leads to an accumulation or build-up of fluid in the back of the eye which causes pressure to increase. As pressure increases, the iris is pushed farther forward and the angle between the structures at the front of the eye closes.
Acute angle-closure glaucoma should be considered a medical emergency and must be treated immediately or blindness could occur within days. Angle-closure glaucoma can cause several symptoms that can occur all at once and over a short period of time. 
These can include:
Blurred or hazy vision – a decrease in sharpness of vision
Sudden loss of vision in one or both eyes - a blind spot, decrease in sharpness of vision or reduction of peripheral vision
Appearance of halos or rainbows around lights – most obvious at night, particularly around streetlights or oncoming headlights when driving.
Flashes of light or appearance of dark spots in vision
Eye pain or pressure – a generalized feeling of pressure (similar to sinus infection) or a sharp or dull pain in the eye
Intense eye pain, in or around eyes - may increase when going from a light to dark environment – severe and sudden eye pain requires immediate attention.
Eye redness – redness that persists over many days
Sensitivity to light
Severe headache, often at the front of your head
Nausea and/or vomiting – most often occurs with one or more of the other listed symptoms
What causes so many different types of symptoms?
Patients with acute angle closure glaucoma can experience a sudden onset of pain in the eye and head from the pressure increase inside their eye. Blurred vision and rainbow-colored halos that appear around lights are caused by swelling of the cornea (clear structure at the very front of the eye) due to the increased pressure.  The sensitivity to normal or bright light (photophobia) experienced in angle closure glaucoma occurs because the pupils are often more dilated or open wider, which means that they allow more light to enter the eye, which can be very uncomfortable. Nausea and vomiting occur as a result of the changes in the eye stimulating the nervous system.
How serious are the symptoms of acute angle-closure glaucoma?
The symptoms of acute angle-closure glaucoma should be taken very seriously. Symptoms are very noticeable and damage to the structures in your eye can occur very quickly. If left untreated, blindness will occur. If you experience the symptoms listed above, seek immediate care from an ophthalmologist.
What are the symptoms of normal tension glaucoma?
Even though people with normal tension glaucoma have eye pressure that is within normal ranges, they can still experience some of the signs of glaucoma, similar to primary open angle glaucoma, such as patchy blind spots in their field of vision and damage to their optic nerve.
With or without symptoms, who should be checked for glaucoma?
Approximately 4% of everyone over 40 years of age have elevated eye pressure (intraocular pressure) but only 10% of them will develop vision loss.  Even before noticing symptoms, some people may be at higher risk for developing glaucoma and may want to be checked regularly by the eye care professional. Your ophthalmologist will consider all your symptoms, risk factors and results of a careful eye examination to determine if you have glaucoma or your risk for developing it.
Some important risk factors for developing glaucoma include:
Elevated eye pressure
Use of some medications – Steroid use (prednisone) or medications that dilate the pupil have the potential to cause acute angle-closure glaucoma.
Age – most often detected over 50 years of age
African or Asian ancestry
Family history of glaucoma
Past injuries to the eyes
History of severe anemia or shock
 Castaneda-Diez R, Mayorquin-Ruiz M, Esponda-Lamoglia C, Albis-Donado O. Current Diagnosis and Management of Angle-Closure Glaucoma. Glaucoma – Current Clinical and Research Aspects. November 2011. https://www.intechopen.com/books/glaucoma-current-clinical-and-research-aspects/current-diagnosis-and-management-of-angle-closure-glaucoma
 Friedman DS, Wolfs RC, O'Colmain BJ, Klein BE, Taylor HR, West S, Leske MC, Mitchell P, Congdon N, Kempen J; Eye Diseases Prevalence Research Group. Prevalence of open-angle glaucoma among adults in the United States. Arch Ophthalmol. 2004 Apr;122(4):532-8. https://www.ncbi.nlm.nih.gov/pubmed/15078671
 Glaucoma Research Foundation, January is Glaucoma Awareness Month, http://www.glaucoma.org/news/glaucoma-awareness-month.php
 Hawkins AS, Szlyk JP, Ardickas Z, et al. Comparison of contrast sensitivity, visual acuity, and Humphrey visual field testing in patients with glaucoma. J Glaucoma 2003;12:134–8. https://www.ncbi.nlm.nih.gov/pubmed/12671468
 Hu CX, Zangalli C, Hsieh M, Gupta L, Williams AL, Richman J, Spaeth GL. What do patients with glaucoma see? Visual symptoms reported by patients with glaucoma. Am J Med Sci. 2014 Nov;348(5):403-9. https://www.ncbi.nlm.nih.gov/pubmed/24992392
 Informed Health Online. Cologne, Germany: Institute for Quality and Efficiency in Health Care (IQWiG); 2006-. Glaucoma: Overview. https://www.ncbi.nlm.nih.gov/books/NBK367579/
 Pacheco-Cutillas M, Edgar DF, Sahraie A. Acquired color vision defects in glaucoma—their detection and clinical significance. Br J Ophthalmol 1999;83:1396–402. https://www.ncbi.nlm.nih.gov/pmc/articles/PMC1722892/
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