Understanding Glaucoma

Glaucoma is a group of eye diseases that gradually steal sight without warning. Glaucoma is characterized by gradual destruction of the nerve of the eye (Optic Nerve). This eventually results in irreversible loss of vision if not treated. Optic nerve is like a wire which connects the eye to the brain. It transmits the electrical signals from the retina (light sensitive tissue at the back of the eye) to the brain allowing us to ‘see’. It consists of millions of ‘nerve fibres’ with each fibre carrying information about different parts of the image. It is the gradual loss of these fibres which ultimately leads to loss of vision in glaucoma.

In the early stages of the disease, there may be no symptoms. It is estimated that half of the people affected by glaucoma may not know they have it.

It was once thought that high pressure within the eye, also known as intraocular pressure or IOP, is the main cause of this optic nerve damage. Although IOP is clearly a risk factor, we now know that other factors must also be involved because even people with “normal” levels of pressure can experience vision loss from glaucoma.

Cause of Increase in IOP (Intraocular Pressure):

A watery fluid known as aqueous humour fills the spaces in the front one-third area of the eye. This fluid nourishes the cornea and the lens and gives the front of the eye its form and shape. The aqueous humour is continually produced by the ciliary body and drains through channels located in the trabecular spaces of the angle of the eye. In a normal eye the rate of production should be balanced by an equal rate of drainage. This keeps the pressure inside the eye (intraocular pressure) stable. In some individuals, with advancing age, these channels get blocked; disrupting the outflow of this fluid. This results in raised pressure within the eye. This raised pressure may then start damaging the optic nerve.

Co-Relation of IOP with Glaucoma: Normal pressure for an eye is one which does not cause any damage to the optic nerve. In most normal people the eye pressure is around 17 to 20 mm of mercury. Some people have higher pressure than this, but that does not cause damage to the nerve for years. However, such patients need careful monitoring so that damage to the nerve is detected at its earliest stage. On the other hand, some patients have a much lower eye pressure, say 12- or 14-mm Hg, but this low pressure is not tolerated by the eye and the nerve is damaged. This is a special type of glaucoma and needs more careful monitoring and treatment.

Different Types of Glaucoma:

• Open-angle glaucoma
  With this most common type of glaucoma, the fluid that normally flows through the pupil into the anterior chamber of the eye cannot get through the filtration area to the drainage canals, causing a build-up of pressure in the eye. Nearly 3 million Americans – half of whom do not know they have the disease – are affected by glaucoma each year.
• Low-tension or normal-tension glaucoma
  While normal intraocular pressure ranges between 12 to 21 mm Hg, an individual may have glaucoma even if the pressure is within this range. This type of glaucoma presents optic nerve damage and narrowed side vision.
• Angle-closure glaucoma
  In angle-closure glaucoma, the fluid at the front of the eye cannot reach the angle and leave the eye, because the angle becomes blocked by part of the iris. This results in a sudden increase in pressure and is generally a medical emergency, requiring immediate treatment to improve the flow of fluid.
• Childhood glaucoma
  Childhood glaucoma is a rare form of glaucoma that often develops in infancy, early childhood, or adolescence. Prompt medical treatment is important in preventing blindness.
• Congenital glaucoma
  Congenital glaucoma, a type of childhood glaucoma, occurs in children born with defects in the angle of the eye that slow the normal drainage of fluid. Prompt medical treatment is important in preventing blindness.
• Primary glaucoma
  Both open-angle and angle-closure glaucoma can be classified as primary or secondary. Primary glaucoma cannot be contributed to any known cause or risk factor.
• Secondary glaucoma
  Both open-angle and angle-closure glaucoma can be classified as primary or secondary. Secondary glaucoma develops as a complication of another medical condition or injury. In rare cases, secondary glaucoma is a complication following another type of eye surgery.

Risk factors for Glaucoma:

Although anyone can develop glaucoma, some people are at higher risk than others. The following are suggested as risk factors for glaucoma:

• Race:Glaucoma is the leading cause of blindness for African-Americans.
• Age: Glaucoma is much more common among older people. You are six times more likely to get glaucoma if you are over 40 years old.
• Family History Of Glaucoma: The most common type of glaucoma, primary open angle glaucoma, is hereditary. If members of your immediate family have glaucoma, you are at a much higher risk than the rest of the population. Family history of glaucoma increases the risk of glaucoma four to nine times.
• High intraocular pressure
  People with an elevated (greater than 21 mm Hg) intraocular pressure (IOP) are at an increased risk.
• Indiscriminate use of Steroids: Studies indicate Steroids increase intraocular pressure. These could be in the form of Oral medications, Steroid Inhalers and Steroid Eye Drops used for long periods of time. Patients who are on long term steroid therapy for other diseases such as asthma, arthritis etc.
• Injury to Eye: Injury to the eye may cause secondary open angle glaucoma. This type of glaucoma can occur immediately after the injury or years later.
• Diabetes: Some diseases that impact the entire body, such as diabetes, anaemia, or hardening of the arteries, increase the risk of the condition. Persons who do not actually have diabetes, but have a strong family history of the problem, should have their eyes checked frequently for early development of the disease.

Other possible risk factors:

• People having high minus or plus numbered glasses
• Hypertension
• Central corneal thickness less than 500 microns.
• People who have undergone any kind of eye surgery.
• People with thyroid gland related ailments.
• People with over – mature cataracts.

Symptoms of Glaucoma:

Glaucoma in early stages generally does not show noticeable symptoms or is associated with very mild symptoms which the patient often tends to ignore. It is possible for a person suffering from chronic glaucoma to be completely unaware of the disease. The early symptoms associated with chronic open angle glaucoma (the most common form of the disease) are usually unnoticed. In most cases, the initial build-up of pressure is gradual, without any discomfort or pain. Most people do not detect any change in their vision until substantial loss of sight has occurred. Certain parts of peripheral vision are affected first, with the top, sides and bottom of the field of vision becoming affected. Later, central vision becomes affected. As optic nerve fibres are damaged by glaucoma, small blind spots may begin to develop, usually in the side or peripheral vision. Many people do not notice the blind spots until significant optic nerve damage has already occurred. If the entire nerve is destroyed, blindness results.

Chronic Glaucoma generally progresses too slowly to get noticed. Some common symptoms of chronic glaucoma could be:

• Inability to adjust the eyes to darkened rooms such as theatres.
• Frequent changes in near (reading) eyeglass prescription.
• Gradual loss of peripheral vision.
• Blurred vision.
• Mild eye ache or headache towards the evening after a day’s work.
• Poor night vision
• In advanced cases, there is a loss of side vision, while the central vision remains good. The patient becomes more prone to accidents as he/she is unable to see vehicles coming from the sides.

Acute Glaucoma: One type of glaucoma, acute angle-closure glaucoma, does produce noticeable symptoms because there is a rapid build-up of pressure in the eye. The following are the most common symptoms of this type of glaucoma. However, each individual may experience symptoms differently. Symptoms may include:

• Blurred or narrowed field of vision
• Severe pain in the eye(s)
• Haloes (which may appear as rainbows) around lights
• Seeing rainbow coloured halos around lights.
• Severe eye pain, facial pain
• Red eye.
• Cloudy vision with halos around light.
• Nausea
• Vomiting
• Headache

The symptoms of acute angle-closure glaucoma may resemble other eye conditions. Consult a physician for diagnosis immediately if you notice symptoms, as this type of glaucoma is considered a medical emergency requiring prompt medical attention to prevent blindness. These attacks usually resolve without any treatment within a few hours and can be missed by the patient. Treatment at this stage is very easy and can prevent a full-blown attack and need for lifelong medications or surgery.

Congenital glaucoma presents noticeable symptoms in infants, including enlarged eyes, cloudy cornea, sensitivity to light and excessive tearing.

Glaucoma Screening

The American Academy of Ophthalmology’s recommended intervals for eye exams are:

• Age 20-29: Individuals of African descent or with a family history of glaucoma should have an eye examination every three to five years. Others should have an eye exam at least once during this period.
•  Age 30-39: Individuals of African descent or with a family history of glaucoma should have an eye examination every two to four years. Others should have an eye exam at least twice during this period.
• Age 40-64: Individuals should have an eye examination every two to four years.
• Age 65 or older: Individuals should have an eye examination every one to two years.

Early detection is vital to stopping the progress of this sight threatening disease.

Since glaucoma cannot be prevented, the next best measure to protect sight is early detection and treatment before optic nerve fibres have been destroyed. This can be accomplished only through regular comprehensive eye health examinations, because glaucoma often is symptomless.

Everyone over the age of 35 should be tested for glaucoma every 1-2 years or whenever problems arise. Get an Eye Check up routinely above the age of 40 years.

Screening for glaucoma is done by an ophthalmologist (eye doctor) and involves the following tests.

Detection of Glaucoma:

Unfortunately, glaucoma is a disease, which cannot be seen or felt by the patients in the early stages.  It is usually spotted during the course of a routine eye check-up done by an Eye Surgeon, when he detects presence of risk factors as discussed above or when high IOP is suspected and more detailed test is conducted. A surgeon may also suspect Glaucoma when he finds on examination increased cup:disc ratio with or without raised IOP.  The mistake that most people commonly make is getting only their glass numbers checked by an Optician ignoring the need for a detailed eye check-up.

Sometimes the patient discovers it and come to the Doctor with complaints of mild headache, fuzzy vision in morning or seeing rainbow colours around lights. These all should lead to suspicion of raised IOP and warrant further detailed testing for Glaucoma.

In addition to a complete medical history and eye examination, your eye care professional may perform the following tests to diagnose glaucoma:

• Tonometry – This determines the pressure in the eye by checking the firmness of the eye ball. Several types of tonometer are available for this test, the most common being the ‘Applanation tonometer’. After the eye has been numbed with anaesthetic eye drops, the tonometer’s sensor is placed on the eye and pressure measured. Other newer tonometers are also available which does not involve touching the eye (Noncontact tonometer). These are good and safe for screening purposes but have lesser accuracy compared to applanation tonometer.
• Pachymetry: Measurement of the eye pressure (IOP) can be affected by the thickness of the cornea (transparent front part of the eye). Pachymetry is the measurement of the corneal thickness so as to provide the corrected IOP. Similar to tonometry, the eye is numbed with anaesthetic eye drops and the pachymeter tip is touched on the eye. Within a few seconds the machine gives the reading.
• Gonioscopy: This test is done in patients with narrow angles who are at a higher risk of ‘Angle Closure Glaucoma’. The test involves numbing the eye with anaesthetic drops and placing a special type of thick contact lens on the eye. The lens enables the doctor to view the interior angle and the drainage of the eye. The doctor can evaluate the type and severity of blockade of the eye drainage.
• Pupil dilation and Ophthalmoscopy – the pupil is widened with eye drops to allow a close-up examination of the eye’s retina. This is an examination in which the doctor looks directly into the eye to examine the optic nerve(seen as the optic disc) at the back of the eye. Damage to the optic nerve due to glaucoma is seen as cupping of the disc. Due to the loss of nerve fibres, the disc develops enlarged craters or cups which is seen during ophthalmoscopy. Special cameras can be used to take photographs of the optic nerve to compare changes over time.
• Visual Field (Perimetry): It is a functional test of the optic nerve which actually maps the visual fields to detect any signs of damage to the optic nerve. It is typically done by a computerized assessment. For this procedure, one eye is covered and the patient places his or her chin in a bowl-shaped machine. The machine shows small dots of light of varying intensities and at different locations. The patient is supposed to press a button whenever he perceives the light. The computer produces a computer-generated map of the visual field based on the response by the patient.
• GDx VCC Retinal Nerve Fibre Layer Analyzer / HRT / OCT: These special tests measure the thickness of the nerve fibre layer and helps your doctor detect glaucoma at a very early stage
• Vision testing: Since glaucoma more often affects the side vision, the central vision may be retained till a very advanced stage. It is important to remember that a good central (straight ahead) vision test may mislead a glaucoma patient about the severity of glaucoma and the extent of damage to the optic nerve.

Treatment of Glaucoma:

Glaucoma cannot be cured. Lost vision is impossible to restore. As damage to nerve caused by glaucoma cannot be reversed, the aim of the treatment is to prevent or reduce further damage to the optic nerve and to preserve the highest possible level of vision. If detected early, however, a combination of laser treatment, eye drops and medication can be used to treat it. Reduction of eye pressure can be achieved with eye drops, pills (rarely), laser, surgery or a combination of these

Specific treatment for glaucoma will be determined by your physician based on:

• Your age, overall health, and medical history
• Extent of the disease
• Your tolerance for specific medications, procedures, or therapies
• Expectations for the course of the disease
• Your opinion or preference

The first step to do that is to lower the eye pressure. The three modalities of treatment are: –

1. Medical (Eye drops and tablets) 
2. Laser treatment
3. Surgery

1. 1. Medical treatment : –Your doctor will prescribe you certain medication (Eye drops and tablets) so as to lower your eye pressure. These are the most common form of treatment to lower IOP. These are used once or several times a day depending upon the type and stage of glaucoma. The drops work either by reducing the production of the aqueous fluid or by increasing the drainage of the fluid out of the eye. In severe cases of glaucoma,. medications may also be given orally or intravenously along with the eye drops for adequate control of IOP. You must use the medicines regularly as directed by your ophthalmologist. You should not stop medicines even if you do not have symptoms. A regular follow up, as advised by your doctor, is mandatory.
   2. Laser treatment : –

      Laser -. If done early enough, the laser may prevent an acute attack of glaucoma and need for lifelong medications and surgery.If glaucoma is not controlled with the help of medicines, if the side effects of the medicines are not well tolerated and the patient is non-compliant, or cannot afford the cost of the medicines, the second option is LASER TREATMENT. There are various types of lasers that are used in the treatment of glaucoma.

      1. 1. 1. Trabeculoplasty

               In this, most common type of laser surgery to treat open-angle glaucoma, a laser is used to place “spot welds” in the drainage area of the eye (known as the trabecular meshwork) which allows fluid to drain more freely.

            2. YAG Laser Peripheral Iridotomy

               In ‘Angle Closure Glaucoma’, the most common treatment used is laser. The laser (YAG Laser) is used to create small holes (Peripheral Iridotomy) in iris (the part of the eye which gives it the colour). The holes form alternate channels for flow of aqueous fluid and prevents closure of the angle and the drainage of the eye. A small opening is made in the iris so that the stagnant fluid finds a way to the anterior chamber, the front portion of the eye, and subsequently drained off. This is an OPD procedure, done under local anaesthetic drops and takes only a few minutes to be completed. After the laser, you can wash your eye with water and can lead a normal life.<?p>

            3. Selective Laser Trabeculoplasty (SLT)

               This is a new type of laser, which does not cause any thermal burn in the eye and may be called “COLD LASER”. It stimulates the autoimmune system of the eye to clear the block in the drainage area without damaging the surrounding delicate tissues. SLT is a painless OPD procedure, which takes a few minutes to be completed. One can resume normal activities immediately after the laser. If necessary, it can be safely repeated without damaging the eye.

            4. Argon Laser Trabeculoplasty

               When applied at the drainage area, the laser causes small burns, which contract to open up the block.

            5. Diode Laser Cycloablation (Cyclophotocoagulation) Cilioablative Therapy

               This therapy is used in severe cases of glaucoma in whom the medications are not working and surgery is not an option. A procedure that uses a laser beam to freeze selected areas of the ciliary body – the part of the eye that produces aqueous humour – to reduce the production of fluid. It can be used if the IOP is too high and is intractable. The ciliary ablation can be done using laser or cryo (cold) therapy.

         Your treating doctor will decide which laser is suitable for you.

   3. Operative procedures (Glaucoma Filtering Microsurgery or “By-pass” surgery of eye)

      Operation for glaucoma is the only option left for patients in whom the eye pressure is not controlled with medication or laser. It is also the treatment of choice in non-compliant patients, and in infants and children with glaucoma. A surgery called Trabeculectomy is performed to control glaucoma. Filtering microsurgery involves creating a drainage hole with the use of a small surgical tool, to bypass the blockage in the eye’s trabecular meshwork (the eye’s drainage system). This opening helps increase the flow of fluid out of the eye and thereby reduce the eye pressure.

Tube shunt
This implantable drainage device creates an artificial pathway in the eye. It is made from a miniature, stainless steel tube, and can be implanted in less than five minutes. A tube shunt is usually selected after it is determined that a patient cannot benefit from conventional surgical treatments.

REMEMBER: Glaucoma cannot be cured. But it can be controlled and further damage to the optic nerve can be slowed down or halted. This control can only be sustained through very disciplined and regular treatment as advised by a glaucoma specialist. It is a lifelong process. Medication usually must continue for life and must be taken regularly to effectively reduce eye pressure.

Follow-up after treatment – Treatment for glaucoma is usually lifelong and requires frequent monitoring. Check-ups are planned every few months to check for adequate reduction in eye pressure and if the reduced pressure is good enough to halt optic nerve damage. In case glaucoma continues to advance inspite of lowered pressure, further medications may be added or surgical treatment may be planned to further lower the IOP.

In some cases, a single surgical procedure is not effective in halting the progress the glaucoma, and repeat surgery and/or continued treatment with medications may be necessary.