What is Glaucoma?
Glaucoma is a condition with elevated pressure within the eye affecting the optic nerve which is responsible for transmitting perceived images from the retina to the brain (figure 1). If not treated, damage to the optic nerve will cause blind spots which are undetectable in the early stages. If the disease progresses without treatment, it can lead to loss of side vision followed by loss of central vision and even blindness.
Figure 1 showing elevated pressure within the eye causing pressure (arrows) affecting the optic nerve
Glaucoma is a leading cause of blindness in the United States among adults. However, this can be prevented with early detection and treatment. In many instances there are no symptoms. Optic nerve damage is irreversible when it occurs. For these reasons, it is very important for all adults to have regular eye examinations in order to be screened for this condition.
How Does Glaucoma Cause Optic Nerve Damage?
A clear fluid called the aqueous humor, which is produced in the front part of the eye, circulates in a space called the anterior chamber and drains from an area where the cornea and iris meet called the angle (figures 2 and 3). When the fluid drains too slowly through the trabecular meshwork of the angle or is blocked, it builds up in the eye causing elevated pressure. Most cases of optic nerve damage from glaucoma are due to elevated eye pressure but some cases can develop in the presence of a normal eye pressure, due to poor blood flow to the optic nerve.
Glaucoma Risk Factors
The most common risk factors include age, elevated eye pressure, family history of glaucoma/anatomic predisposition, African or Hispanic heritage, vascular conditions such as diabetes and/or hypertension, nearsightedness, farsightedness, previous eye injuries and a cornea that is thinner than normal.
Types of Glaucoma?
Primary open angle glaucoma is the most common form of glaucoma and is usually due to the drainage angle of the eye becoming less efficient (figure 3).
Angle closure glaucoma occurs when the angle between the iris and the cornea is very narrow especially in farsighted and short eyes. This usually leads to complete blockage or closure of the drainage angle (figure 3) leading to a rapid buildup of eye pressure causing an acute episode of blurred vision, severe eye pain with redness, headache, halos around lights, nausea and vomiting. This is a medical emergency as the acute and severe rise in eye pressure can lead to blindness. If you are experiencing any of these symptoms, you need to call an ophthalmologist immediately as prompt treatment with eye medications followed by laser surgery can relieve the blockage, lower the eye pressure and protect vision.
How is Glaucoma Detected?
The only definitive way to detect glaucoma is through a comprehensive glaucoma evaluation, including central visual acuity testing, intraocular pressure measurement (tonometry), examination of the drainage angle (gonioscopy), examination of the optic nerve, peripheral vision testing known as Visual Field Perimetry, scanning of the optic nerve structure called Optical Coherence Tomography (OCT) and measurement of the corneal thickness (pachymetry).
Glaucoma Treatment Options
Daily medication eyedrops which lower eye pressure are usually given. The goal of treatment is to lower the pressure to a normal level of 20 or below. In cases where eye drops are not effective or they are causing side effects, laser treatment can be performed. In open angle glaucoma, multiple laser spots are applied to increase the fluid drainage through the trabecular meshwork. This procedure, called trabeculoplasty, can decrease eye pressure and dependence on eyedrops (figure 4).
In closed angle glaucoma, the laser makes a hole through the iris called iridotomy, thus relieving and bypassing the fluid blockage in the drainage angle (see figure 5 C and D).
In cases where neither medication eye drops nor laser treatment are effective, glaucoma surgery is performed to create a new filter or drainage channel for the fluid to leave the anterior chamber. This procedure is called trabeculectomy.
If you have glaucoma and would like to find out more about the different treatments available, contact us to set up an appointment with Dr. George Khouri.