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Glaucoma

Overview

Glaucoma is a group of eye diseases usually due to intraocular hypertension (increased pressure in the eye) due to the building- up of aqueous humor. The increased pressure damages the optic nerve, which is a nerve that carries visual information from the eye to the brain. If treatment is not done, it can even lead to blindness.

Causes

The fluid inside our eye is called aqueous humor. It usually flows out of our eye through a mesh-like channel. If this channel gets blocked or the eye produces too much fluid, the liquid builds up, causing the eye pressure to increase. Sometimes the cause of the blockage is unknown; It may be inherited, which means passed from parents to children. Less commonly because of trauma, chemical injury, severe eye infection, blocked blood vessels inside the eye, or rarely in some cases due to eye surgery 

Following are the causes of glaucoma;

Congenital Causes

  • Infantile / Buphthalmos 

Associated with congenital abnormalities such as 

  • late infantile glaucoma 
  • Pigmentary glaucoma 
  • Aniridia 
  • Axenfelds syndrome 
  • Sturge weber syndrome 
  • Marfans syndrome 
  • Neurofibromatosis 
  • Lowes syndrome 

Acquired Causes

  • Primary 
  • open-angle glaucoma 
  • Angle-closure glaucoma 
  • Secondary 
  • Uveal tract related inflammation such as in the case of heterochromia iridium, pigment dispersion, essential iris atrophy, malignant melanoma 
  • Trauma in case of angle recession, hemorrhage, contusion injury
  • Lens related in case of dislocation, phacogenic, occulo-cerebral renal syndrome
  •  Exfoliative syndrome
  • Ciliary body tumor
  • Corticosteroids induced 
  • Thyrotropic, exophthalmos 
  • Anterior displacement of the lens/ iris /diaphragm,
  • A pupillary block occurs when there is inflammatory adhesion in the iris or vitreous body. 

Types

Among the several types of glaucoma, the main three categories are;

  • Open-angle glaucoma is the most common type. It has its name because the angle between the cornea and the iris is open. In this type, the drainage system slowly gets clogged over time, so there is a gradual increase in pressure on the optic nerve. This increase in pressure initially causes atrophy of the outer rim of the nerve, so the peripheral vision is decreased at first. Later as that pressure increases more, there is continued damage to the optic nerve, which eventually leads to a loss of central vision.
  • Closed-angle glaucoma is also known as angle-closure or narrow-angle glaucoma. This is because the angle between the iris and the cornea is too small, so the passageway for aqueous humor outflow is too narrow. It can be a result of the lens being pushed against the iris resulting in the blockage of the drainage system. This causes a rapid build-up pressure within the eye, causing abrupt onset eye pain, eye redness, blurry vision, headaches, nausea, and visual halos.
  • Normal-tension glaucoma or low tension glaucoma happens when the pressure is normal in the eye. The cause of normal-tension glaucoma is unknown. It is believed that the optic nerve is damaged due to hypo-perfusion or poor blood flow or potentially genetic hypersensitivity to pressures that are even in the normal range 

Risk Factors

Following are the risk factors of glaucoma:

  • Having high internal eye pressure (intraocular pressure)
  • Old age that is being over age 60
  • Being black, Asian, Hispanic, Russian, Japanese, Inuit, or of Scandinavian decent
  • Having a family history of glaucoma
  • Having diseases or medical conditions, such as diabetes, heart disease, high blood pressure, and sickle cell anemia
  • Having thin corneas 
  • Being extremely nearsighted or farsighted
  • Trauma to the  eye or certain types of eye surgery
  • Taking corticosteroids, such as those in  eyedrops, for a long time 
  • Taking certain medications for bladder control or seizures or certain over-the-counter cold medication. 

Epidemiology

Glaucoma is considered one of the most common causes of irreversible blindness in the United States. It often affects adults over 40, but young adults, children, and even infants can be affected. More than 3 million Americans have glaucoma. It is estimated that by 2050, that number may rise to 6.3 million. 

Signs And Symptoms

Open-angle glaucoma develops gradually over time, so you may not feel significant symptoms except gradual vision loss. Since it has no warning signs, the condition may not be noticed until later in the advanced stages. You must consult your ophthalmologist if you have risk factors for glaucoma and monitor changes in your vision.

In the case of Acute angle-closure glaucoma, you may have;

  • severe headache, 
  • eye pain, 
  • nausea vomiting, 
  • blurred vision, 
  • eye redness, 
  • photophobia (sensitivity to bright indoor light or the sun)

Differential Diagnosis

Several other conditions can present as glaucoma like;

  • Ischemic optic neuropathy
  • optic atrophy
  • Compressive tumors
  • trauma
  • non-glaucomatous optic neuropathy
  • optic neuritis

Treatment

Glaucoma is not curable, but it can be slowed down with treatment. If the underlying issue is intraocular hypertension, it can be managed by taking medication to lower pressure in the eye either by decreasing the production of aqueous humor (with medications such as beta-adrenergic receptor antagonist and carbonic anhydrase inhibitors ) or by increasing the outflow of aqueous humor (by taking prostaglandin analogs) or by taking medication that does both (such as alpha-adrenergic agonists). Morphine is given as a sedative and pain killer.

Medications

  • Beta-blocker: timolol, betaxolol, and levobunolol 
  • Carbonic anhydrase inhibitor: dorzolamide, acetazolamide, and brinzolamide
  • Prostaglandin analog:  latanoprost, travoprost and bimatoprost
  • Alpha adrenergic agonist: apraclonidine, brimonidine

Procedures

In addition to medications, laser treatments are also available for example,

  • Trabeculoplasty: It is a procedure in which laser is used to open the trabecular meshwork, which helps in open- glaucoma. 
  • Iridotomy: In this procedure, a laser is used to punch a tiny dot or hole in the iris, which helps treat closed-angle glaucoma.
  • Some lasers destroy humor-producing cells, which reduce the production of the fluid 
  • A laser can also be used to create a new channel through which the aqueous humor can be drained out 
  • Sometimes, implants can be used to shunt fluid out of the anterior chamber by bypassing the trabecular meshwork and collecting system.

Diagnosis

Your physician will ask you questions regarding your symptoms and examine you with special emphasis on head and eye examination to make the diagnosis. Following investigations may help in confirming the diagnosis;

  • Tonometry: It is a test that is used to calculate the intraocular pressure
  • Visual field testing 
  • Imaging like MRI scan of the eyeball