Referring Veterinarians

Using Your Tono-Pen or Tonovet Instruments

Intraocular pressure readings should be performed in both eyes with a Tono-Pen or TonoVet instrument. Schiotz tonometry can be accurate if done correctly but is difficult to perform on a patient with a painful glaucomatous eye.

Be familiar with your instrument and follow all the care and maintenance instructions. TonoVet instruments tend to read higher than Tono-Pens. The instruments should be calibrated daily. Tono-Pen tips should not be too loose or too tight. Store the instrument in its case and always have a tip cover in place on the instrument. Periodically use canned air to blow dust and debris off the Tono-Pen tip prior to putting on a tip cover. Use a new tip for each patient to avoid bacterial transfer. Continue to take Tono-Pen readings until you get a 5% error. Tap gently on the eye with the Tono-Pen tip positioned perpendicular to the corneal surface.

Several operator errors can result in falsely high readings. Pressure on the eyelids during IOP measurement and pressure on the jugular veins (holding the neck or pulling on a collar) will elevate the IOP by 4 to 10 points. Be sure of your technique to avoid falsely elevated pressures. If the animal is painful and squinting, give injectable pain medications prior to taking the pressures. Always take and record the pressure in both eyes. Tono-Pen instruments require you to use topical anesthetic (proparacaine) 30 seconds prior to taking pressures.

Normal intraocular pressure is < 25 mmHg.

Emergency Glaucoma Treatment

Glaucoma is an acute or chronic condition in which elevated intraocular pressure causes pain and rapid vision loss. Glaucoma occurs in patients with inherited abnormalities in the drainage angle or it can occur secondary to uveitis, lens movement and intraocular tumors. Acute glaucoma is an ophthalmic emergency since total vision loss can occur in less than 24 hours when intraocular pressures are higher than 40 mmHg. It is imperative to take intraocular pressures to accurately diagnose the condition. If your hospital doesn’t have a method of taking intraocular pressures, the patient should be referred immediately if glaucoma is suspected.

Clinical signs of acute glaucoma:

1. Dilated pupil
2. Scleral vascular injection
3. Vision loss

Clinical signs of chronic glaucoma:

1. Buphthalmic or enlarged globe
2. Secondary lens luxation
3. Vision loss

Clinical signs can be variable and not all symptoms are present in all eyes. For example, eyes with glaucoma secondary to uveitis may not present with a dilated pupil due to posterior synechia. Corneal edema occurs when the intraocular pressure is over 40 mmHg in dogs. Cats can present with high pressures and no corneal edema. If the glaucoma is chronic (buphthalmic globe and permanent vison loss), emergency treatment is not necessary. Medications to reduce intraocular pressure and pain are indicated to treat chronic glaucoma, but enucleation and histopathology examination may be the best choice for chronic glaucomatous eyes.

Referral of patients to a veterinary ophthalmologist for treatment of acute glaucoma is recommended in order to try to preserve vision and determine if the fellow eye is at risk. The drainage angle of the opposite eye should be evaluated using gonioscopy or ultrasound to determine if it is at risk of developing glaucoma. Prophylactic therapy of the opposite eye can delay the onset of glaucoma and vision loss. Prompt medical treatment to lower the pressure in the affected eye may preserve vision. Additional surgical therapy including Ahmed Drainage Valve placement and Endolaser Cyclophotocoagulation (ECP) surgery may be indicated. If your glaucoma patient is unable to see an ophthalmologist immediately, you should institute emergency therapy as follows. If you need assistance in determining whether your patient needs immediate therapy, please call us at (916) 624-4364.

Emergency medical therapy for glaucoma:

1. IV mannitol (1-2 g/kg) given over a 30 to 45 minute period or oral USP glycerin 2 ml/kg given slowly by mouth over 30 to 45 minutes. Evaluate hydration and renal function before administering either drug. Mannitol is preferable to glycerin in diabetic patients as glycerin will cause blood glucose levels to increase.
2. Topical Xalatan, Lumigan or Travatan BID. These drugs cause intense miosis so don't use in patients with a lens luxation or severe uveitis.
3. Topical Dorzolamide or Brinzolamide TID
4. Topical Steroids (Neopolydex drops or Pred acetate1% drops) TID. Check for ulceration prior to use.
5. Oral methazolamide (2-4 mg/kg) or acetazolamide (5-10 mg/kg) BID to TID.
6. DON’T FORGET PAIN MEDICATIONS. A buprenorphine (or similar) injection at presentation and Tramadol to go home is advised.

Treatment of Corneal Ulcers

Superficial ulcers

Superficial ulcers involve a loss of the corneal epithelium with no stromal loss. If they show no sign of infection then treatment with a topical antibiotic (neomycin/polymixin, gentocin or erythromycin) is appropriate as well as topical atropine and oral pain medications and non-steroidal anti-inflammatory medications. An E-collar should be used until the ulcer heals. Close examination for distichia, ectopic cilia, entropion, KCS, and foreign bodies is warranted.

Indolent ulcers

Indolent ulcers are superficial and non-infected ulcers that have not healed in seven to 10 days. They occur in older dogs with Boxers being over represented. Herpes virus keratitis is a cause of non-healing ulcers in cats. Surgical therapy is oftentimes required to stimulate healing of these ulcers in dogs. (Don’t grid corneal ulcers in cats.)

We can perform a grid keratotomy or corneal burr procedure in the exam room using topical anesthetic and systemic pain medications. In addition a bandage contact lens is often applied to reduce pain and aid healing. Over 90% of these ulcers heal in two to three days post treatment. Medical therapy with topical antibiotics and systemic anti-inflammatory and pain medications are continued. Some cases require an additional grid procedure. In rare cases, surgical keratectomy is required under general anesthesia.

NEVER PERFORM A GRID KERATOTOMY ON AN INFECTED CORNEA OR A STROMAL ULCER!

Dogs under 5 years of age should not have indolent ulcers. There is almost always something rubbing on the cornea or decreased tear production present to delay healing in young dogs.

Stromal infected ulcers

Stromal ulcers occur when bacteria are present in a superficial ulcer. The corneal stroma can digest due to bacterial and WBC enzymatic action. Clinical signs of infection include, increased corneal haze or cloudiness, increased mucopurulent discharge, loss of corneal stroma (divet), hypopyon and anterior uveitis. Any dog with corneal stromal loss has an infected ulcer.

YOU MUST USE A BROAD SPECTRUM ANTIBIOTIC EVERY HOUR TO AVOID CORNEAL RUPTURE! A good choice is ofloxacin or moxifloxacin (Vigamox). BNP and Terramycin will not be effective. In addition, topical serum can be used hourly until the infection clears and topical atropine to treat reflex uveitis and pain is indicated. Systemic pain medication and anti-inflammatory medication should be prescribed. It is wise to refer these patients before the ulcer deepens to a descemetocoele and the patient requires a conjunctival graft or in the worst case scenario, enucleation for a ruptured eye. The ulcer can rupture in less than 24 hours from the first sign of infection so these patients should be monitored daily.