Ocular diagnostics (Proceedings)

The veterinary technician [VT] plays a crucial role in many aspects of evaluation of the ophthalmic patient in our hospital. First and foremost the VT takes the history. This is not as simple as it sounds as you have the job of obtaining only the ophthalmology pertinent history or systemic history related to the eyes. As you know, people often want to tell you what the pet had for breakfast 3 weeks ago, how he ate it, and what came out the other end. We want to focus on a few points:

1. Which eye is the problem?

2. How long has it been going on for?

3. Have you used any medication for this problem? People often use medications from other pets or themselves or over the counter.

4. When was the last time you medicated?

5. Does your pet have any problems seeing?

6. Is your pet exhibiting signs of pain with squinting, tearing, redness or itchiness?

7. Has this ever happened before?

8. Is your pet otherwise healthy?

9. Is your pet on any medication or supplements?

I always recommend when owners are coming into the hospital that they bring with them any medication that they are using or have previously used for this condition. I had one owner come in who was using a Gentocin product on the eye that was prescribed for her other dog. The problem was that it was Gentocin OTIC. Ear medications CAN NOT go in the eye. Not only was it burning the poor little dog but it created a deep hole in the cornea that required a graft to save the eye.

In our hospitals where we do complete ophthalmic examinations, the VT also performs many of the diagnostic tests before the ophthalmologist comes in the room. Unless an ulceration is suspected, the VT will perform the Schirmer's Tear Test [STT], perform tonometry (a glaucoma test), and drop fluorescein dye in the eye. Your veterinarian may want to examine the pet first to determine which tests are necessary.

Ophthalmic examinations may be challenging on moving pets let alone any who really don't want anyone to stare into their eyes. The VT job is critical here in holding the pet properly. I will talk about this in particular and show videos of how we examine dogs and cats. We place big dogs on the floor backed into a cornea with a VT standing behind and reaching forward to hold the chin. Small dogs under about 40 pounds or those close to the ground like a big Basset are placed on the table. Cats are also examined up on a table and may be gently wrapped up in a towel to isolate the head. We do not do examinations under anesthesia as even most aggressive pets can be examined with proper handling techniques and anesthesia affects our results significantly.[ The exception is if pets are very painful from a physical trauma.] As you may well know, owners are often reluctant to express a concern about their pet biting until it is too late. If you have a suspicion from your initial meeting of the pet, you may want to ask 'Has your pet ever nipped when scared? The veterinarian will have her nose right up to your pet's muzzle so if there is any concern, I would like to get a soft muzzle'. Most people will value the vet's nose if there is any question.

It is important that the pet is held in spinal alignment. Head, neck, spine, tail should all be in one direction pointing towards the examiner. Not only does this allow evaluation of symmetry of the face, eyelids, pupils, responses, and reflexes, but this is important in an accurate tonometry. The pet should be held under the jaw with one hand and around the muzzle if possible with the other.

Schirmer's Tear Test must come first before any topical anesthetic or stain and preferably, hours after any topical ointment. The tear test strip is standardized to read a certain amount after 60 seconds. It provides much less valuable information if it is taken out before then. Even if a case appears to be staining the test strip abnormally high, do not be tempted to remove it. Abnormally high values are also of help with disease interpretation.

The fluorescein stain is available in strips or multidose vials. In hospitals were the bottles are used so frequently we go through almost one a day, the chance of bacterial or fungal contamination of the bottles is unlikely. However, in a general practice the strips would be recommended. A drop of saline is dropped onto the strip above the impregnated fluorescein area. Tip it down over the pet's eye and let it fall onto the cornea. Do not touch the cornea with the strip. These are not designed to touch the cornea and may cause abrasions if they do so. The veterinarian will want to look at the stained eye fairly quickly. If there is a question of a tear duct blockage, you may want to wait to do the stain until the doctor is in the room and timing of the stain down the nasolacrimal duct can be performed [Jones Test]. A drop of proparacaine or topical ophthalmic anesthetic can now be applied. Keep in mind with any drops that 1. You should be about 1" away from the eye to assure contamination of the bottle does not occur. 2. One drop is 50uL, the eye can only usually hold about 20uL. If you give more than one drop it is a waste. If you have a Tono Vet it does not require topical anesthesia. A Tono Pen does. Wait at least 5-10 minutes after giving the drop to take the pressure. If not completely numb, the pet may feel the Tono Pen, squint or pull away, altering the measurement. The number one faulty measurement is too high due to handler error. As we spoke about with handling, the pet should be aligned directly towards the examiner. Any pressure at all on the neck from the technician's hands or a nervous dog looking to see the owner off to the side or a cat pulling his neck into his body to hide can dramatically elevate the intraocular pressure [IOP]. If you have high number and don't suspect them because the eyes are symmetrical, the dog is visual, both eyes are elevated, re-evaluate your holding technique. Sometimes with very nervous dogs, we will give them a 5 minutes break and come back to it. We rarely have owners hold their pets for a tonometry test due to the sensitivity of the position. Tonometry would not be recommended if a deep ulcer was first noted.

Culture and sensitivity may be taken after the instillation of topical anesthetic. It was thought that this may alter the ability to culture organisms but the anesthetic affect has found to be, for the most part, insignificant and it use will greatly improve comfort and ability to accurately sample the correct area. Aerobic culture is the most common test required in veterinary ophthalmology although retrobulbar abscess may be associated with anaerobic organisms.

Cytology should certainly be taken after the instillation of anesthetic. The use of the cytobrush, however, allows for minimal interference with a high cellular yield. It is important when filling out laboratory submission forms to state from where the sample was taken. Cellular variation between cornea and conjunctiva for example can be significant.

Other diagnostics utilized in veterinary ophthalmology involving the veterinary technician are ultrasound [US], radiography, and the electroretinogram [ERG]. Although I feel that real time ocular ultrasound should be evaluated by the veterinarian, the technicians in our hospital play a critical role in the computer set up of the ultrasound machine, the probe set up and connection, file formation of the specific case, and data storing in the US computer as well as transfer to the patient's medical record. Holding the pet properly is also important as we often perform US on awake patients.

Orbital disease, contrast studies for epiphora, at times Horner's Syndrome, and periocular foreign body investigation are a few of the reasons we would perform radiographs in an ophthalmology hospital. For best accuracy, these studies should be done under general anesthesia. Radio-opaque object identification of the orbit may be beneficial in reading films. Eyelid speculums or a carefully bent paper clip may be placed in the eyelids as an aid.

The electroreitnogram [ERG] summates the electrical activity of the retina and is used for both diagnostic (ie. does the dog have sudden acquired retinal degeneration SARD?) and predictive purposes (ie. is the retinal healthy behind the cataract prior to surgery?). The technician sets up the computer and ERG machine for that patient, attaches electrodes to the machine, and with a second technician holding the pet, performs the test. The technician then evaluates the wave forms by placement of numbers within the ERG program to determine the overall height and latency of the ERG peak. Although all the previous diagnostics are all performed on horses, pocket pets, and zoo animals, the ERG is a little more complicated but can be done.

The technician role in client communication in our hospital is enormous and although not associated with diagnostics I would like to suggest a couple of take home points you can also use in the clinic. Remind clients do not bother recommending more than one drop into the eye. The eye can hold 20uL, most drops are 50uL. It is just wasting their money and running down the face. If prescribing 2 different drops make sure the owners wait FIVE minutes in between instillation so that they don't dilute out each one. If using two ointments, then wait about 20 minutes in between ointments. Use only about a pea sized amount of ointment; more is a waste. Recommend owners wash their hands after instillation of potentially immune modulating drugs like cyclosporin, tacrolimus, or chloramphenicol.