Acute primary glaucoma typically presents as a painful eye with bulbar conjunctival congestion, mild general corneal oedema, a mid-dilated pupil and vision loss in the eye. Glaucoma occurs when there is an obstruction to drainage of aqueous humour from the eye leading to abnormally high intraocular pressure, pain and damage to optic nerve and retina. While most cases of glaucoma are due to ‘primary’ iridocorneal drainage angle abnormalities, some cases are ‘secondary’ to other ocular conditions such as anterior lens luxation, uveitis and intraocular tumours.
If you suspect glaucoma implement the following:
- Perform tonometry: TonoVet rebound tonometers and TonoPen applanation tonometers are the most common in veterinary practice. Normal intraocular pressure is less than 25mmHg. A prolonged pressure above 35mmHg is potentially harmful to optic nerve and retina.
- Beware restraint-induced ocular hypertension: Neck compression during restraint of wriggly dogs during tonometry can lead to intraocular pressure elevation and a false diagnosis of glaucoma. Hands off the neck and loosen that collar!
- Rule out (or treat) causes of secondary glaucoma: The presence of another ‘primary’ ocular disease causing ‘secondary’ glaucoma may require a different approach to therapy and treating the primary disease may resolve the glaucoma. Pupil dilators (mydriatics) are contraindicated for primary glaucoma as they can further compromise the drainage angle, but they can be helpful in some cases of secondary glaucoma. Anterior lens luxation triggers pressure elevation by blocking aqueous flow through the pupil and a mydriatic can relief this. Mydriatics can also help control uveitis.
- Topical Carbonic Anhydrase inhibitors are always safe: Agents such as Trusopt, Cosopt and Azopt are used to reduce aqueous humor production and can be used three times daily safely in any form of glaucoma.
- Topical Prostaglandin analogues can make some forms of glaucoma worse: Agents such as Xalatan, Xalaprost and Travatan are potent anti-glaucoma drugs which both reduce aqueous humor production and improve its drainage and can be used up to three times daily. However, they lead to pupil constriction (miosis) and are cause a degree of uveitis, so they will make glaucoma secondary to anterior lens location or uveitis worse.
- Other treatments: Include osmotic diuretics and aqueocentesis, but early referral to a specialist to determine the exact type of glaucoma and optimal management will provide the best outcome.