Glaucoma is a group of diseases that are characterized by resulting damage to the optic nerve, which impairs its ability to relay visual information to the brain. Glaucoma often has no early symptoms, but if left untreated, it may lead to permanent vision loss or blindness. Therefore, early detection of glaucoma is important.
It is usually detected by checking the eye’s intraocular pressure during ophthalmic examinations. Glaucoma cannot be cured, but it is medically and surgically treated to delay and inhibit vision loss.
Forms of Glaucoma
The two most common forms of glaucoma are primary open-angle and angle-closure. Primary open-angle glaucoma begins within the anterior chamber, which is the space between the iris and cornea. The anterior chamber is filled with a clear fluid called aqueous humor. When aqueous humor drains very slowly out of the anterior chamber through the trabecular meshwork, the pressure within the space increases.
This gradually pushes on the lens and the vitreous chamber. The vitreous chamber is the space between the lens and eye’s posterior wall, and houses many blood vessels and optic nerve cells. As the anterior chamber exerts pressure on the vitreous chamber, the eye’s intraocular pressure increases, and optic nerve cells within the vitreous chamber become compressed and damaged.
This process leads to peripheral vision loss and eventually blindness. Primary open-angle glaucoma is normally painless and may go undetected until an individual loses vision. It is therefore a chronic condition. It is referred as “open-angle” because the angle between the iris and cornea is large enough to permit steady but slow drainage of aqueous humor out of the anterior chamber through the trabecular meshwork.
Angle-closure is an acute and rarer form of glaucoma. It occurs when the angle between the iris and cornea becomes small enough to completely block aqueous humor drainage out of the trabecular meshwork. This causes the anterior chamber to swell, and leads to a rapid intraocular pressure increase. The rapid pressure increase quickly damages the optic nerve.
Patients with angle-closure will lose vision rapidly compared to those with primary open-angle glaucoma. Angle-closure is therefore an emergency and requires immediate medical attention.
Screening and Detection
Glaucoma is usually detected by measuring a patient’s intraocular pressure. During ophthalmic examinations, Dr. Jacobson uses a tonometer for pressure checks.
First, he uses an anesthetic drop to numb the eye, and then places a flat blue-lit prism on the cornea. The tonometer measures the force required to flatten a small area of the cornea. The more force required to flatten the cornea denotes a higher intraocular pressure. When high intraocular pressure is suspected, other tests help Dr. Jacobson come to a diagnosis and monitor its progression.
Fundus photos are pictures that allow him to examine the health of blood vessels and the optic nerve. A visual field test maps a patient’s peripheral vision, since peripheral vision loss is an earlier symptom of glaucoma. Additionally, optic coherence tomography (OCT) analyzes the different layers of the optic nerve as well as previous cell damage. Repeating these tests allow Dr. Jacobson to investigate intraocular changes over time.
When glaucoma is detected, it is treated, but it cannot be cured. Once optic nerve cells are damaged and vision is lost, they cannot be restored. Modern treatment regulates intraocular pressure to prevent further damage to optic nerve cells and surrounding blood vessels.
There are now a variety of oral and eye drop medications that use different pathways to reduce intraocular pressure. Some including beta-blockers and carbonic anhydrase inhibitors decrease aqueous humor production. Others including cholinergics and prostaglandin analogs increase drainage through the trabecular meshwork. There are even a number including adrenergic agonists and combined medications that both decrease aqueous humor production and increase drainage.
When a medication is prescribed, it is important to adhere to the prescribed regimen. This both allows the results to be more accurately monitored and provide better outcomes.
When an acute form of glaucoma is detected or medications are not sufficient, surgery may be required to slow vision loss. For those with angle-closure glaucoma or its precursor, narrow-angles, a laser iridotomy is performed. This procedure creates a small hole on the outer rim of the iris that allows aqueous humor to flow from the anterior chamber into the posterior chamber. The posterior chamber is the space surrounding the lens.
For those with open-angle glaucoma, an iStent® Trabecular Micro-Bypass can be performed during cataract surgery to create a permanent opening in the trabecular meshwork to promote drainage and lower intraocular pressure.
Another conventional surgery is a trabeculectomy which bypasses the trabecular meshwork by creating a new drainage site called a bleb. Choosing the best treatment depends on many factors and can be very complex. Dr. Jacobson listens and works with each of his patients so that their medical or surgical treatments match their desired outcome and future quality-of-life.
Patients receive the best results from glaucoma treatment before symptoms manifest. Once vision is lost, it cannot be recovered. At the Eye Specialists of Santa Barbara, Dr. Jacobson checks intraocular pressure during new patient and follow-up visits. When a patient shows signs of glaucoma, he will use modern tests and treatments to prevent future damage to their vision. This ensures that his patients continue enjoying excellent vision later in life. For more information about glaucoma detection and management, please visit http://eyessb.com/glaucoma/.