Just as everything can look like a nail when you have a new hammer, every bulgy eye can look like a potential glaucoma case when you have a fancy new TonoVET or TonoPEN tonometer.
The trap is that in less experienced hands it is very easy to get a falsely high intraocular pressure reading with these instruments. This typically occurs with restraint of less co-operative patients, leading to neck compression. This results in reduced blood drainage from the head and subsequent increased scleral venous plexus pressure resulting in reduced aqueous humor drainage from inside the globe and iatrogenic temporary elevation of intraocular pressure.
So, the next time a wriggly patient with bulgy eyes is lined up for tonometry, remember the following tips:
• Beware ‘false positive’ pressure readings
• Neck/jugular compression artificially elevates intraocular pressure
• Remove collars, E-collars
• Use minimal light restraint around shoulders, under muzzle, at back of the head – NOT a choke hold!
• Use central cornea but avoid areas of pathology
• Have instrument tip perpendicular to cornea
• Hold tonometer in dominant hand, gently part eyelids with non-dominant hand
• Use non-dominant hand or patient’s head as a rest or stand-off for dominant hand
• Look for consistent readings
Remember these tips and you may save your clients time and money by avoiding a referral to VOR. Also, don’t forget plenty of our canine and some of our feline patients have been selectively bred to be bug-eyed without a hint of glaucoma!