Glaucoma is one of the most frequently encountered ocular emergencies. The accurate diagnosis and appropriate and early management of this condition is essential in preserving vision in acute cases. Differentiating those cases which are true emergencies with the opportunity to preserve vision from those in which normalizing the pressure is designed for comfort alone is the first priority.
Acute or chronic
- Pupil larger than the fellow eye
- Cornea edematous in dogs, usually not in cats
- Sclera injected; minimal in the cat
- Vision loss. This can be difficult to diagnose when the glaucoma is unilateral.
- Globe enlargement
- Secondary lens luxation, usually posteriorly
Bear in mind that these signs are all variable. Also, there are numerous potential causes (other than glaucoma) for each sign. For example, anisocoria (unequal pupil size) is often due to age-related iris degeneration (especially in the Miniature Poodle). In dogs, most of the above signs will occur concurrently.
There are numerous ocular diseases which can cause secondary glaucoma. Examples include hyphema, anterior lens luxation, and uveitis.
Evaluate pupillary light reflexes carefully. An intact consensual pupillary reflex (light directed into the affected eye causing the opposite pupil to constrict) indicates that the optic nerve is still functional and vision may be saved in this eye. Use a bright light source and dim ambient light for this test.
Acute glaucoma is an ophthalmic emergency and justifies consultation with an ophthalmologist. Call Veterinary Vision at (650) 551-1115. If needed, our voice mail system will instruct you how to leave a message for the doctor on duty for after-hour emergencies.
Chronic glaucoma (pressure elevation for greater than about one week) is rarely an emergency since vision is usually irreversibly lost. The signs of chronic glaucoma can include those listed above, as well as absent consensual light reflex, globe enlargement (buphthalmos) and perhaps posterior lens luxation/subluxation. If in doubt please contact us. These patients should be examined by an ophthalmologist within several days, and treatment is directed at relief of discomfort.
Measurement of IOP:
We strongly recommend the use of the Tonopen as a method of measuring IOP. It is both easy to use and reliable. Information on purchase can be obtained from www.danscottandassociates.com. The Schiotz tonometer is associated with a high frequency of inaccurate measurements due to difficulties in maintaining the instrument in proper working order and challenges associated with correct positioning of the animal and instrument. In the absence of an available Tonopen, the clinical signs of glaucoma should be interpreted as more reliable than Schiotz pressure readings.
Use of Tonopen:
- Instill one drop topical anesthetic (proparacaine) and measure pressure in both eyes.
- Press the top of the tonometer perpendicular to the surface of the cornea repeatedly until a reading with 5% error is given. Normal is less than 25 mmHg.
- Any pressure on the neck will occlude jugular blood flow and artificially raise intraocular pressure.
- Excessive pressure on the lids will artificially raise intraocular pressure.
Treatment of acute glaucoma:
First it is essential to evaluate systemic state, BUN (+/- creatinine) and cardiovascular status. This may bear upon which systemic medications are safe to use. These are suggestions only – your clinical judgment must prevail.
- IV catheter; send pet home with catheter since it will likely be needed the following day.
- Mannitol 25%: 5ml/kg IV.
- Dexamethasone IV _ to 1mg/kg or Solu-Medrol 30mg/kg IV.
Again, we emphasize the importance of phone consultation upon diagnosis and plans to be examined at Veterinary Vision the next day. After administration of above medications, the animal can generally be discharged with the catheter stabilized and capped and the following medications dispenses.
Medications to go home:
These medications are generally available from a human pharmacy and a prescription can be written if they are unavailable at your hospital.
- Methazolamide: 50mg tablets; 1 tablet/30 pounds BID-TID for dog; _ tablet BID for 10 pound cat. This medication can be more difficult to obtain from a human pharmacy. It is inexpensive and stable and we recommend stocking this in your pharmacy.
- Topical latanoprost (Xalatan) is most effective*, use SID-BID; dorzolamide (Trusopt), Brinzolamide (Azopt) and/or Timolol 0.5% may be used as well QID.
- Topical antibiotic/steroid combination QID.
The owner should be prepared for the likelihood that medical management alone is usually not successful in managing glaucoma on a long-term basis. Surgery (such as laser cyclophotocoagulation) is often necessary.
*Xalatan is contraindicated in cases of anterior lens luxation, and possibly with severe fibrinous uveitis. Xalatan causes extreme miosis; any material in the anterior chamber (such as the lens or large amounts of fibrin) can occlude a miotic pupil and exacerbate glaucoma.