Glaucoma

Glaucoma is the term used for a group of eye disorders involving gradual and permanent damage to the optic nerve. Usually, this damage to the optic nerve occurs because fluid pressure within the eye (intraocular pressure) is too high; however, damage may also occur as the result of an insufficient blood supply to the optic nerve. Since the optic nerve is responsible for transmitting images from the eye's light-sensitive retina to the visual cortex of the brain, damage to the optic nerve can have serious effects on vision. In the initial stages of glaucoma, people tend to lose peripheral (side) vision; though, central vision is affected as the damage to the optic nerve progresses. NOTE: Most types of glaucoma develop slowly and subtly over time without dramatic or painful symptoms. 

There are several types of glaucoma. Even though the most common type of glaucoma cannot be cured, usually if detected and treated in the initial stages, it can be controlled to preserve vision. Since glaucoma tends to develop gradually without noticeable symptoms yet causes permanent vision loss before awareness by the patient, early detection is challenging and very important. Once diagnosed, it is essential that patients dutifully comply with treatment programs prescribed by a physician or blindness can result.

Dispelling the myths: 

• Reading in dim light, wearing contact lenses and other vision-related activities do not cause glaucoma unless they result in a traumatic injury to the eye.
• High blood pressure is a condition completely unrelated to eye pressure and does not lead to glaucoma. However, patients suffering from glaucoma should have their blood pressure under control.

Although anyone can develop glaucoma at any time in life, the following factors tend to increase the probability of its occurrence:

1. Elevated Intraocular Pressure
High internal eye pressures are a serious risk factor for glaucoma.

2. Age
Though glaucoma can develop at any time in life, the risk increases after the age of 40 years and as we age.

3. Family History
Since many types of glaucoma are hereditary, people with a family history of this eye pressure disorder should have a routine eye examination scheduled and performed by an ophthalmologist.

4. Nearsightedness
High levels of myopia (nearsightedness) increase the risk of 
developing glaucoma.

5. Diabetes Mellitus
Diabetes Mellitus increases the risk of developing glaucoma as well as other 
eye diseases.

6. Racial Background
Glaucoma is more common amongst people of African descent than other 
racial groups.

It is essential for people affected by any of these six factors to:

• Arrange for regular eye examinations to ensure healthy eye pressures and 
  good vision
  As well as 
• Learn everything they can about lifestyle changes that can minimize the risks of suffering vision damage due to glaucoma.

NOTE: Though smokers are not more likely to develop glaucoma than non-smokers, smoking does interfere with some forms of glaucoma treatment.

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Gimbel Eye Centre uses a variety of assessment tools to determine eye health and wellness in each general eye examination, including some of the tests described here. However, some testing is performed only when glaucoma is suspected (e.g., Visual Field test).

Measure the Intraocular Pressure — Instruments called tonometers or smaller hand-held TonoPens™ are used to check the fluid pressure in the eye. The surface tissues of the eye are immediately numbed by a topical anesthetic eye drop administered to the surface of the eye before the tonometer gently touches the cornea (the clear front window of the eye) and records the eye's internal fluid pressure. NOTE: If the eye's fluid pressure is measured to be high, further testing may be indicated.

Examine the Optic Nerve — Since glaucoma damages optic nerve fibres and reduces the number of nerve fibres passing through the optic nerve head, it is essential for doctors to examine the back of the eye where the optic nerve is located. In order to detect glaucoma, doctors use special lenses and instruments to observe the optic cup (the enlarged central depression in the optic nerve head) at the back of the eye.

Measure the Thickness of the Retinal Nerve Fibre Layer — Since it is believed that retinal thinning can be detected before there is visual field loss and early detection can reduce the likelihood of visual field loss, Gimbel Eye Centre employs an instrument called the GDx-VCC that uses Scanning Laser Polarimetry to measure the thickness of the nerve fibres around the optic nerve head without touching the eye. Gimbel Eye Centre uses the GDX-VCC to confirm or rule out glaucoma, establish a baseline measurement of the retinal nerve fibre layer thickness as well as evaluate the progress of the disease by repeating this test over a period 
of time.

CHRONIC OPEN ANGLE GLAUCOMA 

The most common type of glaucoma is Chronic Open Angle Glaucoma, which develops when the fluid within the eye does not drain properly. The eye's ciliary body produces a continuous supply of clear fluid, called aqueous humor, which circulates through the front portion of the eye to nourish the eye's tissues and provide the pressure necessary to maintain the eye's rounded shape.  Normally, as this fluid is secreted, it flows between the lens (clear front window of the eye) and the iris (pigmented tissue that gives colour to the eye and controls the amount of light entering the eye), through the pupil (circular opening at the centre of the iris) into the front portion of the eye. The aqueous humor flows out of the eye by seeping through the spongy filter of the Trabecular meshwork (the mechanism that controls the rate of aqueous humor leaving the eye).  After filtering through the Trabecular meshwork, aqueous humor flows into a drainage canal that passes the fluid into the bloodstream through small blood vessels near the outer surface of the eye. If the aqueous humor does not drain properly, internal eye pressure rises and damages the delicate tissues of the optic nerve.

Usually, Chronic Open Angle Glaucoma does not have any noticeable symptoms. People with this type of glaucoma are unlikely to feel pain or notice anything unusual until their field of vision begins to narrow, creating a visual disorder known as tunnel vision. Unfortunately, visual field damage is irreversible; though, early detection and prompt treatment may conserve the remaining central vision.

Typically, medication is the first line of treatment for glaucoma. Medications in the form of eye drops or oral tablets are used to either limit the production of fluid and/or increase the drainage capabilities of the eye. Since these medications can have side effects, the goal is to use the smallest possible dose required to achieve the desired effect. While monitoring the effects of treatment, it is common for a doctor to change the amounts and types of medication used. Even though the medications may be somewhat unpleasant or inconvenient to use or even appear to produce no apparent improvement, dutiful compliance to the treatment schedule is essential for the control of internal eye pressure and preservation of the remaining vision. NOTE: If medications are not taken as prescribed and eye pressure remains uncontrolled, blindness will result.

In some cases of Chronic Open Angle Glaucoma, medication does not produce a sufficient reduction in fluid pressure and surgery may be necessary. Surgery does not cure glaucoma nor does it improve vision, but it can help to control the eye's internal fluid pressure and preserve the remaining vision. NOTE: The eye is always anesthetized before glaucoma surgery, making the experience relatively comfortable for the patient.

 

NORMAL TENSION GLAUCOMA 

In some cases, patients begin to suffer optic nerve damage even though their internal eye pressure is found to be within the normal range. This condition is called Normal Tension or Low Tension Glaucoma and it continues to perplex researchers. Recent studies suggest the problem may be related to the blood supply to the optic nerves. Using medications to lower eye pressure below normal, exercising regularly and following a diet low in fat seem to be the best ways to control this type of glaucoma. If these measures are ineffective, surgery may be performed to lower fluid pressure by improving fluid drainage, thereby allowing blood to circulate into the eye and the optic nerve more freely.

 

CONGENITAL GLAUCOMA 

Some babies are born with a defective drainage system in their eyes, referred to as congenital glaucoma. When this occurs, a trabeculotomy procedure is performed to preserve vision by surgically opening the obstructed passages so that fluid may drain out of the eye more readily.

 

SECONDARY GLAUCOMA 

Injuries to the eye, some pharmaceutical drugs, tumors, inflammation as well as other factors can block the eye's drainage canals, creating a build-up of fluid pressure within the eye. If the cause of the blockage cannot be identified and treated, medication or surgery may be necessary.

 

ACUTE ANGLE CLOSURE GLAUCOMA 

Acute Angle Closure Glaucoma is a sudden and rapid build-up of internal eye pressure that occurs when the iris blocks the Trabecular meshwork, preventing aqueous humor from leaving the eye. In some eyes, there is an abnormally narrow space between the lens and iris through which the aqueous humor must flow before passing through the pupil, into the front portion of the eye and then draining out of the eye through the Trabecular meshwork. Certain factors such as small eyes, high levels of hyperopia (farsightedness), a mature cataract or increasing pupil size in dim illumination can minimize the space between the lens and the iris. When this passage into the front chamber of the eye is restricted, fluid builds up behind the iris very quickly and causes the iris to bulge forward and block the Trabecular meshwork, preventing the fluid from draining out of the eye.

The result of this blockage is an immediate and dangerous rise in internal eye pressure that causes symptoms such as nausea, vomiting, severe pain, blurred vision and rainbow-coloured halos around lights. This condition requires immediate medical treatment (receiving treatment within a few hours) to prevent irreparable damage to vision. As part of the emergency treatment or performed at a later date, laser surgery may be necessary to create alternative openings in the iris and restore normal fluid circulation. This laser treatment creates a small opening, called a Peripheral Iridotomy, in the outer portion of the iris to enable the fluid to flow more effectively into the front portion of the eye. If internal eye pressure is reduced quickly and the underlying problem is resolved, vision tends to be preserved and another episode is unlikely. NOTE: If one eye suffers acute angle closure glaucoma, peripheral iridotomies are performed in both eyes due to the increased risk of secondary glaucoma in the fellow eye.

The surgeon may choose to perform one or more of the following surgical treatments:

FILTERING DRAINAGE TREATMENTS: Reducing internal eye pressure by draining excess aqueous humor

• Laser Trabeculoplasty — A laser light is focused onto the Trabecular meshwork to open the channels and allow the aqueous humor to flow out of the eye and into the drainage canal more easily.
  
  
• Trabeculotomy — A small instrument is inserted into the drainage canal to create an opening through the Trabecular meshwork into the front chamber of the eye. It is through this newly created opening that fluid can drain out more readily. Typically, this technique is used in the treatment of children with 
  uncontrolled glaucoma.
  
  
• Trabeculectomy — A small flap is created in the sclera (the white wall of the eye) and an opening is made into the eye to form a new drainage canal that will allow fluid to drain more easily into the bloodstream. When the procedure is successful, the conjunctiva (clear membrane covering iner lids and outer eyeball, excluding the cornea) expands directly over the location where the tissue was opened. This bulge of conjunctiva, known as a filtering bleb, indicates fluid is draining out of the eye and into the bloodstream.
  
  
• Viscocanalostomy — The viscocanalostomy, currently under clinical investigation, involves creating two flaps in the sclera — with a smaller inner scleral flap located underneath a larger outer scleral flap. The advantage of this procedure is that it does not penetrate the eye, which eliminates post-operative complications such as extremely low intraocular fluid pressures and hemorrhages that may occur after a trabeculectomy procedure. The long-term results of the viscocanalostomy procedure are under investigation.  
  
  
• Seton Insertion — When all other glaucoma treatment options have been explored, the surgeon may elect to insert a small valve system, called a seton, into the wall of the eye. Like a trabeculectomy, this procedure involves creating a filtering bleb in order to allow the intraocular fluid to drain more easily. NOTE: Typically, the filtering bleb is located out of view, covered by the eyelid.

Most of these procedures can easily be combined with cataract surgery — requiring a minor alteration of the cataract incision. It is important to note, in many cases, the cataract procedure alone can help to reduce intraocular fluid pressure.

NON-FILTERING DRAINAGE TREATMENT: Decreasing the amount of aqueous humor production

• Endoscopic Cyclophotocoagulation (ECP) — This new procedure uses an infrared laser to cauterize the ciliary body. During this non-filtering treatment, a microprobe is inserted into the eye through a small incision; if performed at the time of a cataract procedure, the same incision may be used. This microprobe emits a focused beam of intense light energy to sear the ciliary tissues, resulting in reduced production of aqueous humor and a decrease in internal 
  eye pressure.

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