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Vision at the End of the Tunnel

By: Marc Evans M. Abat, MD, FPCP, FPCGMVision at the End of the Tunnel

You glare at something with those steely eyes, as if your sight needs to penetrate that object.  Your vision tunnels around you and it becomes painful just looking at anything.  Your eyes are bloodshot, as if ready to bleed out.  Sadly, this is not Clint Eastwood staring down at something through the sight of his gun – it can be anybody with glaucoma!

Glaucoma is often mistakenly interchanged with cataracts, another common condition in older patients.  The latter is the thickening of the lens of the eye, which can be easily treated by removing the thick opaque lens and replacing it with a clear synthetic one.  Glaucoma, on the other hand, can be serious because it causes permanent damage progressively to the optic nerve (the nerve that conducts the impulses from the eye to brain), which translates to eventual loss of vision.

The main culprit in this disease is eye pressure.  There is a space called the anterior chamber in the front of the eye that is filled with a fluid called aqueous humor.  This fluid drains through a trabecular meshwork near the angle between the iris (the colored part of the eye) and the cornea (the clear covering over the front of the eye).  Any problem that may prevent proper movement or circulation of the fluid through the meshwork causes increased eye pressure and hence, glaucoma.

Those aged over 40 can become at risk of having glaucoma.  This can happen especially to those with a family history of glaucoma, although it is a bit difficult to explain clearly how genetics come into play.  Those with particular diseases like diabetes can also have an increased risk for glaucoma.  Any blunt trauma or chemical injury to the eyes or any infection or inflammation that involved the eye may lead to glaucoma.  Even the occasional eye surgery can have glaucoma as an unwanted and unexpected complication. 

The most common types of glaucoma are open-angle glaucoma and angle-closure or narrow-angle glaucoma.  Open-angle glaucoma is the most common type – think of it as the eye having what seems to be normal structures but the aqueous humor cannot seem to flow properly through the trabecular meshwork, leading to an increased eye pressure.  The less common type, angle-closure or narrow-angle glaucoma, is when the drainage of the aqueous humor is narrow or suddenly closes, sometimes leading to a rapid increase in eye pressure.  There are other less common types like congenital glaucoma or secondary glaucoma from trauma or surgical complications.

So how do you know whether or not you have glaucoma?  Some people can actually go on for some time without feeling any symptoms.  That is why it is important for you to see your ophthalmologist or eye doctor on a regular basis especially after the age of 40, maybe every one to two years, for a regular eye exam. The peripheral vision then starts to decline, which means the outer areas of your field of vision start to become dim or totally disappear.  This manifests as tunnel vision in progressive cases, as if you are looking through a tube or a tunnel.  You may also have eye pain, headaches, eye redness, halos around light, and nausea.  Eventually, as your optic nerve gets progressively damaged, your visual field progressively tunnels out until you become blind.

The eye examination will usually start with a visual acuity test to assess your eye sight.  This may be followed by a visual field test, wherein the eye doctor will try to assess whether or not there are areas in your field of vision that you cannot see already.  The visual field defects are commonly in the peripheral or outer areas.  Afterwards, the doctor will try to measure your eye pressure.  An anaesthetic drop will be put on your eyes, then a tonometer (a small instrument resembling an inverted scale) will be placed on your cornea to measure the eye pressure.  Other procedures that the ophthalmologist may do include examining your eye using a slit lamp and looking at your retina and optic disk (the part of your retina that is continuous with your optic nerve) and cup (the central portion of the optic disk) using an ophthalmoscope.  What they will look for is an increasing size of the optic cup relative to the size of the disk.

How is glaucoma treated?  Management of glaucoma can be through medications or through surgery.  It is important to detect glaucoma early since late treatment cannot restore any vision that is already lost from damage to the optic nerve.  Medications can either be eye drops or oral tablets.  In both situations, they either decrease the formation of aqueous humor or increase its drainage of the eye’s anterior chamber.  These are especially helpful in the early stages, but they have to be taken on a regular basis even if the patient is not feeling any symptoms so that the eye pressure can be maintained at low levels.  However, like other medicines, they may have side effects like eye stinging, redness or systemic side effects like effects on the heart.  Various medications are available so the doctor may switch from one medication to another to achieve the best results or minimize side effects.  It is also important to mention to the eye doctor any medications you are taking that may worsen your glaucoma.

Surgery takes several forms:

  • Laser trabeculoplasty uses a laser to ‘repair’ the trabecular meshwork, increasing the draining holes for better flow of aqueous humor. 
  • Iridotomy involves making a hole in the iris to improve flow of the aqueous humor.
  • Microsurgery, particularly trabeculectomy, involves removing a small piece of tissue to create drainage for the aqueous humor. 

In all cases, medications for glaucoma, together with antibiotics or anti-inflammatory agents, may have to be given after the procedures to prevent complications.

Glaucoma cannot be prevented, so it is important to have early detection and treatment to prevent permanent visual loss.

There is light beyond the tunnel!  Get your eyes checked now before the tunnel closes!

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