- What is glaucoma?
- What is the optic nerve?
- What is the intraocular pressure?
- How is the eye affected by glaucoma?
- What are the risk factors for glaucoma?
- Which are the most common types of glaucoma?
- How the diagnosis of glaucoma is made?
- Necessary equipment for glaucoma diagnosis
- How is glaucoma treated?
- What you should do if you are under treatment for glaucoma
- What questions should I ask my doctor?
- Medical Treatment
- How glaucoma drops are used?
- Visual Fields
What is glaucoma?
With the term Glaucoma we report to a group of eye diseases, which have as common characteristic the progressive damage of the optic nerve. The commonest cause of the disease is elevated pressure within the eye (intraocular pressure).
Glaucoma initially manifests with reduction in peripheral vision and most often patients are not aware of visual loss-they start noticing it only when it has become very significant. If left undiagnosed and untreated, glaucoma can cause destructive damage of the optic nerve leading to end stage disease and blindness.
“The term glaucoma is mentioned for the first time by Aristotle and emerges from the ancient Greek word γλαυκός (light blue) and the ending –ωμα (that comes from σύμπτωμα-symptom).
What do you know about Glaucoma?
Glaucoma consists the main cause of blindness for people aged less than 65 years in the USA. Moreover, millions of people around the world are in danger of visual loss.
What is the optic nerve?
The optic nerve can be considered as an “electric cord” that starts from the back part of the eye, the retina and ends within the brain. It contains a huge number of neural fibers, approximately 1.000.000 through which the image captured from the eye is transferred to the brain. A healthy optic nerve is prerequisite for good vision.
What is the intraocular pressure?
The front part of the eye is filled by a transparent fluid (the aqueous humor), which contributes in nutrition and the maintenance of a steady intraocular pressure. The aqueous humor is produced within the eye and drained through a complex of tiny channels that looks like a sponge and they are called the trabecular meshwork.
The system of drainage channels is located in the angle created between the cornea and the peripheral iris (drainage angle).
In most people this angle is open but in other people it may be narrow or closed. When the drainage of the aqueous humor is normal, the intraocular pressure varies between 8 and 20 mm Hg.
Other factors, such as the corneal thickness may be responsible for deviations of intraocular pressure measurements from the normal range. More precisely, in somebody who has a thin cornea, the real intraocular pressure is higher than the on measured by the ophthalmologist and accordingly in somebody who has a thick cornea, the real intraocular pressure is lower.
If for any reason the drainage of aqueous humor is impaired, the intraocular pressure increases.
Increased intraocular pressure causes usually damage to the retinal nerve fibers, which initially manifests with restriction of the peripheral visual field.
In more advanced stages, the visual field is also restricted centrally, leading to complete visual loss within a period of 1 to 10 years.
It is very important to point out that the diagnosis can only be made with a comprehensive examination by an ophthalmologist.
How is the eye affected by glaucoma?
If the drainage system of the eye is blocked, then the aqueous humor cannot be drained properly. In this case, the aqueous humor is trapped in the front part of the eye, the intraocular pressure is raised and the optic nerve is affected.
This happens because the endings of the retinal nerve fibers are very sensitive to the increase of the intraocular pressure and their damage affects the transmission of the optic signal from the optic nerve to the brain.
Initially, the retinal nerve fibers responsible for the periphery of the visual field are affected, which causes the appearance of peripheral scotomas. Later on, the loss of peripheral vision is extended, leaving only a small area in the center of the visual field. This is called tunnel vision (like seeing through a tunnel). When the optic nerve is completely damaged, total blindness occurs.
What are the risk factors for glaucoma?
- Intraocular pressure
- Age. Increased prevalence in people over 60 years old
- Race because of anatomical differences (e.g. thinner cornea in Afro-Americans and people of Latin origin)
- Family History. The most common type of glaucoma (Primary Open Angle Glaucoma) is inherited
- Use of corticosteroids. Long-term use of cortisone (even in inhalers as e.g. in asthma) increases the chance of glaucoma
- Ocular trauma
- High Myopia
Which are the most common types of glaucoma?
Open Angle Glaucoma
In open angle glaucoma, the drainage system of the eye becomes defective over the years, which results in progressive increase of the intraocular pressure and possibly in progressive damage of the optic nerve. It consists the commonest type of glaucoma.
Angle Closure Glaucoma
It happens mostly in hypermetropes due to anatomic predisposition (eyes smaller than the normal) where the drainage angle of the eye can close completely. This can present acutely and consists the acute angle closure glaucoma. Symptoms include:
- Severe pain
- Halos around lights
- Hard eye (on palpation)
- Nausea and vomiting
If you have any of the above symptoms, you should consult immediately your ophthalmologist, as this is an ophthalmic emergency. If not treated urgently, the acute angle closure glaucoma can lead to blindness.
Normal Tension Glaucoma
In this type of glaucoma, the intraocular pressure is within the normal range. Patients suffering this type of glaucoma may have unusually vulnerable optic nerves or reduced blood flow in the optic nerve (e.g arrhythmias, systemic hypotension, vasospasm). It is more common in women and Japanese people and also in people who suffer severe hypotension (e.g. faint easily).
It normally follows trauma or severe intraocular inflammation (e.g. uveitis).
It is caused by anatomic abnormalities of the eye; mostly in first-born boys in families with glaucoma history and it can be present in birth or manifest within the first months of life.
How the diagnosis of glaucoma is made?
As glaucoma does not give any symptoms at the beginning, the diagnosis can only be made by a complete ophthalmic examination using the following tests:
- Measurement of intraocular pressure (tonometry).
- Measurement of corneal thickness (pachymetry), to evaluate accurately the level of intraocular pressure.
- Examination of the drainage angle of the eye (gonioscopy).
- Evaluation of the optic nerve head (ophthalmoscopy).
In the case of suspicion of glaucoma, the following more specialized tests must be performed:
- Visual field test (perimetry).
- Optic nerve tomography, analysis of the retinal fiber layer and ganglion cells (OCT & HRT II).
Necessary equipment for glaucoma diagnosis
a. Goldmann Applanation Tonometry
The intraocular pressure is measured during the examination by the ophthalmologist at the slit lamp (corneal thickness is taken into account).
It is mostly used in more sensitive eyes
2. Visual Field- Humphrey VF
In this examination, the sensitivity to a flashing light of varying size and brightness is recorded which helps to diagnose glaucomatous damage even in early stages when the central vision is completely unaffected and the patient asymptomatic. A visual field defect becomes apparent when 30-40% of the retinal nerve fibers are damaged.
3. Optical Coherence Tomography (OCT)
The technology of this machine can diagnose glaucoma at a very early stage from the morphology of the retinal nerve fibers and gaglion cells around the optic nerve as well as from the 3 dimensional morphology of the optic nerve. It contributes to the early diagnosis of glaucoma (before visual field loss becomes apparent).
4. Heidelberg Retinal Tomography (HRT II)
It involves a laser confocal scanning system that allows the analysis of three-dimensional images of the posterior segment of the eye. It is useful in the evaluation of the thickness of retinal nerve fibers and the monitoring of changes that may occur due to glaucoma.
How is glaucoma treated?
The reduction/loss of vision due to glaucoma cannot be repaired, as the damage caused is irreversible. However, the early diagnosis is of paramount importance as the progression of the disease can be delayed with treatment that can include:
- Laser trabeculoplasty (ALT or SLT)
- Laser iridotomy or iridoplasty
- Traditional drainage surgery (trabeculectomy)
- Cataract surgery (can be helpful in certain cases)
- Insertion of glaucoma drainage device
- Combination of the above
The above treatments can preserve the remaining vision but cannot restore visual loss that has already happened.
What you should do if you are under treatment for glaucoma
- Be compliant with the care of your eyes and install the medications provided by your ophthalmologist.
- Have regular check-ups by your ophthalmologist, at least every 6 months.
- Encourage your children to have a complete ophthalmic examination, at least every 2 years.
Keep in mind that reduction of the intraocular pressures in the early stages of glaucoma delays the progression of the disease and helps in the long-term preservation of useful vision.
What questions should I ask my doctor?
- What is the diagnosis?
- What has caused the disease?
- Can the condition be treated?
- How this condition will affect my vision now and in the future?
- Do I need to watch out for specific symptoms and contact you if I experience them?
- Do I need to change my lifestyle?
- Which is the appropriate treatment for my condition?
- When will the treatment start and how long will it last for?
- What will be the benefits of the treatment and what is its success rate?
- What are the risks and the side effects from the treatment?
- Are there any foods, medications or activities that I should avoid during this treatment?
- If the treatment includes medications, what should I do if I miss one dosage?
- Are there any other treatments available?
- Which tests will I need to have?
- What I should expect out of these tests?
- When will I know the results?
- Do I need to prepare myself for these tests?
- Are there any risks or side effects associated with these tests?
- Will I need to have more tests in the future?
Glaucoma can usually be treated with drops of one or more preparations. These drops reduce the intraocular pressure, either by reduction of the production of aqueous humor or by enhancement of the drainage or both.
The more common anti-glaucoma medications are prostaglandins, b-blockers, a2- agonists, and carbon anhydrase inhibitors and less commonly used nowadays are the miotics. In some cases, treatment with pills is necessary (acetazolamide).
For the glaucoma treatment to be effective the patient must be compliant. Medical treatment requires harmonious cooperation between doctor and patient. Your ophthalmologist can prescribe you the anti-glaucoma treatment but only you can be responsible for being compliant with it.
You should never change or stop the medications unless you communicate with your doctor. The frequent follow-up examinations are crucial for monitoring of potential changes in your vision.
You should inform your doctor immediately if you present:
- Burning sensation
- Red eyes
- Blurred vision
- Changes in your heart beat (bradycardia)
- Difficulties in breathing (asthma) from use of b-blockers
- Tingling sensation of fingers or toes
- Abnormalities in the gastrointestinal tract
- Kidney stones
The simplest treatment method with laser is trabeculoplasty (ALT, SLT), which can reduce the intraocular pressure from 4 to 8 mm Hg in certain eyes. It lasts from 2 to 5 years.
In open angle glaucoma, the drainage itself is treated. The laser is used to broaden the drainage opening and to help with the control of the intraocular pressure.
In angle closure glaucoma, when immediate treatment is required, the laser creates a small hole in the iris (iridotomy) in order to improve the flow of the aqueous humor from a collateral drainage pathway.
When the above-mentioned treatment options are not adequate to stop the progression of the disease, then surgical treatment is recommended. Usually, the first surgical intervention is the trabeculectomy. The new drainage pathway that is created helps the aqueous humor to escape the front part of the eye, which results in reduction of the intraocular pressure and halts the progression of the disease.
Alternatively, the control of the intraocular pressure can be achieved by the insertion of a small valve (small silicone tube), which helps in the drainage of aqueous humor.
The most popular in our country is the valve PF7 that has been used over the last decades with great success.
Our scientific group, since February 2014, is the first one to commence the use of the new model of the valve, the M4, which is of bigger size and of different material (more porous material) and is more effective in lowering the intraocular pressure.
After the above-mentioned interventions, the patient should receive antibiotic and anti-inflammatory drops for one month.
How glaucoma drops are used?
If you have been prescribed glaucoma drops you should follow the instructions given by your ophthalmologist.
The right use of glaucoma drops can improve the effectiveness and reduce potential side effects.
For the right use of the glaucoma drops, please follow the instructions:
- Wash your hands.
- Keep the bottle upside down. Lean you head backwards. Take the bottle in one hand and keep it 5-10 cm above the eye.
- With your other hand pull down the lower eyelid. This will create a pocket (cul de sac). Squeeze at least one drop within this pocket of the eyelid.
- If you have to use more than one bottle of drops make sure that you wait 5 minutes before the installation of the second one.
- Close your eyes or press on the inner corner of the eyelids with your finger for 1-2 minutes (this reduces significantly the amount of medication that goes through the nose and thus the sensation of “bitter” taste that you may feel if the medication passes to your throat.
The visual field test consists the commonest test in glaucoma patients. It lasts 8-10 minutes and requires good patient’s cooperation. Light stimulus is projected at different locations in the space and its intensity is progressively reduced. The patient remains concentrated at a point in the center of his visual field and whenever perceives the light, even very faint, presses a button that holds in his hand. In this way, the peripheral vision of the patient is being recorded and areas of reduced sensitivity are revealed (scotomas). The visual field test is used for the diagnosis and progression of glaucoma and it should be repeated every 6 months. It is also necessary in the diagnosis of neurological disorders as well as in the monitoring of the optic nerve after use of specific medications.