What is Glaucoma?

Glaucoma is an eye disease that can result in slow painless loss of eyesight. The loss is so slow that it remains undetected till most of the vision is lost so it is known as the thief of eyesight. Peripheral (or side) vision is usually affected first, and then the total vision is lost if glaucoma is insufficiently controlled. In glaucoma there is optic nerve damage and visual field loss with or without raised pressure inside the eye (Intraocular pressure - IOP). Raised IOP is only major risk factor known till date and it is the only parameter which can be treated. Early detection of glaucoma can prevent total blindness.

How is Glaucoma Detected ?

As the side vision is lost first the disease may remain unnoticed till your eye is thoroughly examined. Just checking your central vision may not give any suggestion of Glaucoma. There are several factors that are considered in the diagnosis of glaucoma.

  Accurate measurement of the pressure in the eye (intraocular pressure) is critical. Normal and abnormal pressure values
     vary from person to person. What is considered a normal pressure for one person, may be a harmful pressure for
     another. It is best measured by an applanation tonometer. 
  Ophthalmoscopy to examine the optic nerve and retina. The appearance of the optic nerve (Optic disc) also varies from
     person to person, and abnormal changes of the optic nerves are recognizable to the doctor.

Normal Optic Disc Glaucomatous Disc

Advanced Glaucomatous Disc

  Visual field evaluation (perimetry): Perimetry measures both side vision and the central "straight-ahead" vision of the
     eyes. Sophisticated computerized visual field analyzers provide the doctor with accurate and reliable data on the
     usable vision of the right and left eyes. Often there are characteristic patterns of vision loss from glaucoma, and other
     eye diseases as well.

Normal Field Progressive loss of field as seen in Glaucoma Almost Blind Eye

  Gonioscopy: It involves placing of special lens, which contains mirror, gently on the eye. By this doctor can examine
     the angle of the eye. It helps to differentiate the type of Glaucoma and so the treatment.

More Investigations in Glaucoma

Because of complicated nature of disease causing irreversible blindness more investigations are now available for early diagnosis of Glaucoma. These are not diagnostic on their own but add to information obtained by History, Clinical examination and visual fields. These are:

  Corneal thickness or Pachymetry.
  Diurnal Intraocular Pressure (IOP) fluctuation.
  Stereo photography of Optic Disc.
  Confocal Scanning Laser Ophthalmoscopy ( Heidelberg Retinal Tomograph HRT) .
  Scanning Laser Polarimetry ( SLP)
  Optical Coherence Tomography ( OCT).

Corneal Thickness

It has become important parameter in diagnosis of Glaucoma. People with thin cornea are more prone to Glaucoma and its progression.

Diurnal IOP fluctuation

Intraocular pressure changes throughout the day and is more in morning than in evening. In case of suspicious glaucoma, patient may be admitted and his IOP should be checked every 2 hours. Large diurnal fluctuations in the normal range may also be a risk factor.

Stereo photography of Optic Disc

It helps to detect changes in Optic disc such as Cup disc ratio, color of neuroretinal rim, peripapillary zone and retinal nerve fiber layer.

Confocal Scanning Laser Ophthalmoscopy, Scanning Laser Polarimetry ( SLP ), Optical Coherence Tomography ( OCT ).

These tests detects structural changes in the optic disc and retinal nerve fiber layer.

Types of Glaucoma

Open angle glaucoma: In this, as seen by gonioscope, the angle is wide open and obstruction is considered to be in drainage channel, trabecular meshwork.

Angle Closure glaucoma: In this iris blocks the angle when pupil is dilated causing sudden rise of Intraocular pressure and severe pain along with nausea and vomiting. If the rise is not so acute it may cause symptoms like seeing rainbow halos around the light.

Normal Tension glaucoma: It is similar to open angle glaucoma with intraocular pressure in normal range that is less than 21. Management is same as open angle glaucoma.

Ocular Hypertension : In this case the intraocular pressure is above 25 with no damage to optic nerve and visual fields. These cases need observation specially in high risk cases. 

Congenital Glaucoma: Occurs in children and young adults because of structural abnormalities in angle.

Secondary Glaucoma:  
       i)    Glaucoma due to prolonged use of steroids.
       ii)   Glaucoma due to eye diseases as uveitis, mature cataract, proliferative retinopathy. 
       iii)  Glaucoma due to systemic diseases as beriberi

Who Gets Glaucoma ?

Glaucoma can occur at any age but older the person greater is the risk of glaucoma. 
Risk factors include:

  Hereditary: being related to someone with glaucoma, 
  Caucasians over 50 or African-Americans over 35,
  Being very nearsighted,
  Eye surgery or an eye injury,
  Long term steroid medication usage.

What Can Be Done ?

Once vision loss from glaucoma has occurred, it cannot be restored, but the progression of the disease can be usually halted as soon as it is detected. The intraocular pressure can normally be treated and controlled successfully by medication, laser,  surgery or a combination of these.

Disease cannot be prevented but regular check up may help to diagnose disease in early stage.

  Medical treatment:
Most medications come in the form of drops, but pills are used as well. These medications work to lower the pressure. The effect and side effect of these medications vary from person to person. The eye doctor and patient work together to tailor the best combination of efficacy and fewest side effects. Regular use of medicines is must to control intraocular pressure. 
It is better to keep eyes closed for 2 minutes and press on medial side of eyelid to occlude nasolacrimal duct to reduce side effects and increase efficacy of these drops.

Most common surgery is known as Trabeculectomy : If medications fail to control the IOP, surgery may be required. In it we make a drainage channel for excess fluid to drain out but the surgery may fail because of blockade of new channel. In these cases patient may need medication and even repeat surgery using some medication to prevent the blockade.

  Yag Iridotomy (Laser):
This is helpful in angle closure glaucoma. In this a tiny hole is made in periphery of the iris so that the fluid passes from behind the iris to the outflow passage of the eye and prevents acute attack. This is a safe procedure with few risks. The hole is too small to be noticed by naked eye and so is cosmetically acceptable.

What Can You Do?

Since there are no symptoms for glaucoma, regular eye examinations are the only way to detect this disease. Learn about your family history of eye problems and inform your doctor. As a general guideline, a comprehensive vision and eye health exam is recommended once every two years if your eyes are completely healthy. Your doctor will indicate to you how often you need to be examined. The eye tests for glaucoma are not painful, but they may not be part of the routine eye exam for glasses or contact lenses. Make sure you ask your eye doctor for a comprehensive eye examination.

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