Identification

• The ophthalmoscope will help the eye doctor visualize the dog's eye.ophthalmoscope image by JASON WINTER from Fotolia.com
  
  Initially, the eye is carefully examined with an ophthalmoscope in order to confirm the presence of glaucoma and if possible, determine if it is a case of primary or secondary glaucoma. Primary glaucoma is an inherited condition, occurring mainly in predisposed breeds, whereas secondary glaucoma occurs when other eye disorders contribute to the decreased drainage of fluids, according to Animal Eye Care LLC. The level of damage to the optic nerve and retina can be also assessed upon examining the eye. Often, a referral to a veterinary ophthalmologist is required for a more in depth examination, such as a tonometry test.
  
  

Function

• The function of a tonometry test is to measure the level of pressure within the eye in order to determine the presence of glaucoma. The eye specialist will apply a local anesthetic eye drop to the dog's eye in order to numb the eyeball. Sedation is not required. Normal intra-ocular pressure values in dogs may vary depending on breed and the technique used to measure them; however, the normal range appears to be between 11 and 22 mm Hg, according to Petplace veterinarians.
  
  

Values

• Generally, a tonometry reading greater than 25 mm Hg is sufficient to confirm the presence of glaucoma. Many ophthalmologists have a "30-30 rule". If the eye pressure is above 30 mm Hg and stays so for about 30 hours, very likely the dog will lose vision in the eye. Intra-ocular pressure readings of 50 mm Hg are known to be sufficiently high to permanently damage the dog's optic nerve and retina; therefore, with a reading of 50 mm Hg or more, vision loss has permanently occurred or is very near to occur, according to Dr. Ron Hines, DVM.
  
  

Considerations

• If the tonometry test turns out to be inconclusive, the eye specialist may use gonioscopy in order to evaluate the dog's drainage system using specialized instrumentation. The ophthalmologist instills in the dog's eye a local anesthetic eye drop and, with the use of a goniolens, performs a visual examination of the eye's iridocorneal angle. If the affected dog's eye appears to be too cloudy to be visualized in depth, an ultrasonography test may help reveal damage to the optic nerve, according to Dr. Jennifer Welser.
  
  

Warning

• Because glaucoma is a devastating eye disorder that progresses quickly, it is imperative that owners have their dog tested for glaucoma as soon as possible. This is a condition that cannot wait for the end of a week-end or be delayed for a day or two because of holidays. Prompt, immediate intervention is required for dogs exhibiting suspicious eye symptoms or dogs who have already lost an eye to glaucoma and are again exhibiting familiar symptoms of glaucoma in the other good eye, according to Dr. Jennifer Welser.