Normal Tension Glaucoma

Definition:

Normal-tension glaucoma, also called as low-tension glaucoma is a unique condition in which optic nerve damage and vision loss have occurred despite a normal pressure inside the eye. The angle formed by iris and cornea is open and appears normal similar to primary open-angle glaucoma. Optic nerve damage and vision loss caused by normal-tension glaucoma are permanent.

Risk factor of Normal-tension glaucoma

Individuals who are at higher risk of developing normal-tension glaucoma include the following:

• Family history
• Women
• Age above 60 years
• Japanese & Korean ancestry
• Systemic heart disease such as irregular heart rhythm
• Nocturnal hypotension
• Eye trauma

Normal-Tension Glaucoma Causes

Although the main cause of normal-tension glaucoma is not known, but following factors may be the cause of optic nerve damage in the absence of raised intra-ocular pressure:

• Inherited fragile optic nerve
• Autoimmune disorders
• Sleep apnea (decreases oxygen saturation)
• Decreased blood flow to the optic nerve due to:
  • Vascular diseases
  • Peripheral vasospasms due to Raynaud syndrome, Migraine headaches
  • Ischemia

Symptoms of Normal-Tension Glaucoma

Normal-tension glaucoma is silent in nature and patient generally does not experience any warning signs or symptoms of the disorder. Only in the later or advanced stage of the disease, patient experiences vision loss because of optic nerve damage.

Screening of Normal-tension glaucoma

As with all glaucoma’s, regular eye examinations with an ophthalmologist is most important as there are no early symptoms of the diseases. Moreover, in this type of glaucoma, the eye pressure is also normal which makes it all the more difficult as well as required to get diagnosed as early as possible. Patient usually has no visual complaints until late in the course of the disease and by that time, irreparable damage to vision and optic nerve would have already occurred. So early diagnosis and prompt treatment is the key to preserve vision for all individuals who are at risk of developing any kind of glaucoma.

Diagnosis of Normal-Tension Glaucoma

Diagnosis of normal-tension glaucoma requires thorough eye examination, along with other tests like:

• A slit lamp examination to examine cornea, anterior chamber, iris, and lens
• Tonometry to measure the pressure inside the eye to rule out ocular hypertension and early Primary Open-Angle Glaucoma
• Pachymetry to assess central corneal thickness
• Gonioscopy to check the drainage angle of eye
• Visual field test to check for any areas of sight loss
• Ophthalmoscope examination to look through the pupil and examine the shape and color of the optic nerve for any damage

Normal-Tension Glaucoma Treatment

Treatment of normal-tension glaucoma includes use of medications to lower or stabilize the eye pressure to avoid any worsening of the condition.

Medication : Topical eye drops are prescribed to maintain the intra ocular pressure. It may include any of the following:

• Prostaglandin analogs
• Beta-blockers
• Alpha2 agonists
• Carbonic anhydrase inhibitors
• Miotics

Surgical intervention :

• Trabeculoplasty is performed using a laser beam to create an alternative pathway in the eye.
  • Argon laser trabeculoplasty (ALT)
  • Selective laser trabeculoplasty (SLT)
• Trabeculectomy is performed in cases where medical therapy is ineffective.

Follow-up for Normal-Tension Glaucoma

It is a very fragile condition that needs to be managed accurately with regular follow-up visits to monitor the progression of disease. Follow-up visits are typically scheduled every 3-6 months.