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What is Glaucoma?

Glaucoma is a group of diseases in which a progressive loss of retinal ganglion cells is characterized by a specific pattern of both optic nerve head excavation (glaucomatous optic neuropathy) and visual functional loss (glaucomatous visual field defect). Intraocular pressure is its most frequent causative risk factor and presently the only factor that is controllable.

It is the second most common cause of bilateral blindness worldwide.

  • About 9.1 million people globally are blind because of this disease.
  • About 90.8 million of world’s population suffers from this disease and this number is increasing.
  • In most of cases it is blamed as “The Silent Killer of Sight”

Intraocular Pressure (IOP)

It is the pressure inside the eye needed to maintain the shape of the globe, as well as the normal function of the eyeball.

It is maintained by the balance between formation and drainage of an intraocular fluid called aqueous humor. It is formed by the ciliary processes in the posterior chamber, passes between the iris and lens to enter the anterior chamber, and leaves the eye through the trabecular meshwork and Schlemm’s canal.

Normal IOP About 10-21 mm of Hg, but varies considerably from individual to individual. Glaucoma may occur with IOP within the so called normal range or persons with high IOP may not have glaucoma (ocular hypertension).

Types of Glaucomas:

  • Primary open angle glaucoma:

    An increase in resistance to the outflow through the trabecular meshwork in the angle of the anterior chamber causes a rise in the IOP. This type develops slowly and the symptoms may not be obvious till the damage to the optic nerve has occurred. The patient may lose peripheral vision, leaving only central or tunnel vision.

  • Primary angle closure glaucoma:

    It is caused due to acute, sub acute, creeping or chronic closure of the anterior chamber angle, blocking outflow of aqueous fluid through the trabecular meshwork. In the rarer acute cases, the symptoms are dramatic and may include severe pain in the eye, headache, nausea, reduced vision, and seeing rainbow colored rings around lights.

    Primary Open-Angle Glaucoma & Angle-Closure Glaucoma

  • Developmental glaucoma:

    It may be further divided into congenital glaucoma (in infants from birth) and juvenile glaucoma (in children and young adults). It is characterized by improper development of the eye’s aqueous outflow system.

    • a) congenital glaucoma

      Congenital glaucoma is evident either at birth or within the first few years of life. This condition is caused by abnormalities in anterior chamber angle development that obstruct aqueous outflow in the absence of systemic anomalies.

    • b) Juvenile Glaucoma

      Juvenile glaucoma has been used to describe open-angle glaucoma in children, adolescents and young adults. It is a rare juvenile-onset open-angle glaucoma (JOAG) often found associated with myopia that shows autosomal dominant transmission.

 

Causes and symptoms

Causes

 

The cause of vision loss in all forms of glaucoma is optic nerve damage. There are many underlying causes and forms of glaucoma. Most causes of glaucoma are not known, but it is clear that a number of different processes are involved, and a malfunction in any one of them could cause glaucoma. For example, trauma to the eye could result in the angle becoming blocked, or, as a person ages, the lens becomes larger and may push the iris forward. The cause of optic nerve damage in normal-tension glaucoma is also unknown, but there is speculation that the optic nerves of these patients are susceptible to damage at lower pressures than what is usually considered to be abnormally high.

It is probable that most glaucoma is inherited. At least ten defective genes that cause glaucoma have been identified.

Secondary : Common causes

  • Iridocyclitis,
  • Trauma,
  • Cataract,
  • Neo-vascular glaucoma Following CRVO or proliferative diabetic retinopathy.
  • Drugs – Steroids etc.

Risk Factors for developing Glaucoma

  • Family History – Parent or sibling,
  • Age above forty
  • Myopia
  • Diabetes mellitus
  • Hypertension, hypothyroidism
  • Ocular inflammation, trauma, neglected cataract
  • Long term use of steroids

Symptoms

At first, chronic open-angle glaucoma is without noticeable symptoms. The pressure build-up is gradual and there is no discomfort. Moreover, the vision loss is too gradual to be noticed and each eye fills-in the image where its partner has a blind spot. However, if it is not treated, vision loss becomes evident, and the condition can be very painful.

On the other hand, acute closed-angle glaucoma is obvious from the beginning of an attack. The symptoms are, blurred vision, severe pain, sensitivity to light, nausea, and halos around lights. The normally clear corneas may be hazy. This is an ocular emergency and needs to be treated immediately.

Similarly, congenital glaucoma is evident at birth. Symptoms are bulging eyes, cloudy corneas, excessive tearing, and sensitivity to light.

Diagnosis

Intraocular pressure, visual field defects, the angle in the eye where the iris meets the cornea, and the appearance of the optic nerve are all considered in the diagnosis of glaucoma. IOP is measured with an instrument known as a tonometer. One type of tonometer involves numbing the eye with an eyedrop that has a yellow coloring in it and touching the cornea with a small probe. This quick test is a routine part of an eye examination and is usually included without extra charge in the cost of a visit to an ophthalmologist or optometrist.

Ophthalmoscopes, hand-held instruments with a light source, are used to detect optic nerve damage by looking through the pupil. The optic nerve is examined for changes; the remainder of the back of the eye can be examined as well. Other types of lenses that can be used to examine the back of the eye may also be used. A slit lamp will allow the doctor to examine the front of the eye (i.e., cornea, iris, and lens).

Visual field tests (perimetry) can detect blind spots in a patient's field of vision before the patient is aware of them. Certain defects may indicate glaucoma.

Another test, gonioscopy, can distinguish between narrow-angle and open-angle glaucoma. A gonioscope, which is a hand-held contact lens with a mirror, allows visualization of the angle between the iris and the cornea.

Intraocular pressure can vary throughout the day. For that reason, the doctor may have a patient return for several visits to measure the IOP at different times of the day.

Direct Gonioscopy

Indirect Gonioscopy

Treatment:

  • Medications

    When glaucoma is diagnosed, drugs, typically given as eye drops, are usually tried before surgery. Several classes of medications are effective at lowering IOP and thus preventing optic nerve damage in chronic and neonatal glaucoma. Beta blockers, like Timoptic; carbonic anhydrase inhibitors, like acetazolamide; and alpha-2 agonists, such as Alphagan, inhibit the production of aqueous humor. Miotics, like pilocarpine, and prostaglandin analogues, like Xalatan, increase the outflow of aqueous humor. Cosopt is the first eyedrop that is a combined beta blocker (Timoptic) and carbonic anhydrase inhibitor and may be helpful for patients required to take more than one glaucoma medication each day. It is important for patients to tell their doctors about any conditions they have or medications they are taking. Certain drugs used to treat glaucoma should not be prescribed for patients with pre-existing conditions. Some of these drugs mentioned have side effects, so patients taking them should be monitored closely, especially for cardiovascular, pulmonary, and behavioral symptoms. Different medications lower IOP by different amounts, and a combination of medications may be necessary. It is important that patients take their medications and that their regimens are monitored regularly, to be sure that the IOP is lowered sufficiently. IOP should be measured three to four times per year.

    Normal-tension glaucoma is treated in the same way as chronic high-intraocular-pressure glaucoma. This reduces IOP to less-than-normal levels, on the theory that overly susceptible optic nerves are less likely to be damaged at lower pressures. Research underway may point to better treatments for this form of glaucoma.

    Attacks of acute closed-angle glaucoma are medical emergencies. IOP is rapidly lowered by successive deployment of acetazolamide, hyperosmotic agents, a topical beta-blocker, and pilocarpine. Epinephrine should not be used because it exacerbates angle closure.

  • Surgery

    There are several types of laser surgery used to treat glaucoma. Laser peripheral iridotomy makes an opening in the iris allowing the fluid to drain, argon laser trabeculoplasty is aimed at the fluid channel opening to help the drainage system function and laser cyclophotocoagulation is used to decrease the amount of fluid made. Microsurgery, also called "filtering surgery" has been used in many different types of glaucoma. A new opening is created in the sclera allowing the intraocular fluid to bypass the blocked drainage canals. The tissue over this opening forms a little blister or bleb on the clear conjuctiva that Doctors monitor ensuring that fluid is draining. These surgeries are usually successful, but the effects often last less than a year. Nevertheless, they are an effective treatment for patients whose IOP is not sufficiently lowered by drugs and for those who can't tolerate the drugs. Because all surgeries have risks, patients should speak to their doctors about the procedure being performed.