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Ocular diagnostics (Proceedings)
The ability to accurately perform ocular diagnostics plays a crucial role in many aspects of evaluation of the ophthalmic patient. First and foremost, take the history.
"You miss more for not looking than not knowing".
The ability to accurately perform ocular diagnostics plays a crucial role in many aspects of evaluation of the ophthalmic patient.
First and foremost, take the history:
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. Not only was it burning but it created a deep hole in the cornea that required a graft to save the eye.
Ophthalmic examinations may be challenging on moving pets let alone any who really don't want anyone to stare into their eyes. Training the veterinary technician (VT) to properly restrain patients is critical in thoroughly examining the patient. 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 corner 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. If you have a suspicion of a potential biter, you may want to ask 'Has your pet ever nipped when scared? I will have my nose right up to your pet's muzzle so if there is any concern, I would like to get a soft muzzle'.
Ideally the pet will be looked at in a relaxed state before you even lay hands on them to determine if symmetry is present. I then do a quick summary neurologic examination of sensation and motor to the eyelids, ears, and globes as I am talking to the owner.
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 critical in an accurate tonometry. The pet should be held under the jaw with one hand and around the muzzle if possible with the other.
Vision testing is very important. It's not uncommon to zero in on the problem without checking to see if the patient can see! Feel comfortable doing a menace to assure you know the dog has vision out of each eye. Cover one eye with your hand that is holding the head and wave the other hand from down low, across the visual field, to above the head. Do no push toward the head and illicit a sensation response from the air movement. A basic ocular examination is best done systematically and from front to back....look at each structure (eyelid margins, conjunctiva including the third eyelid, cornea, anterior chamber especially ventrally, iris, lens especially the periphery, vitreous, and retina) every time. Again, "you miss more for not looking than not knowing". If you don't have an eye exam form in your clinic, create diagrams within your SOAP sheet to refer back to for follow-up or in order to allow another veterinarian to pick up.
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 removed from the eye 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. Always perform this test bilaterally if possible and assuming there is no deep laceration or ulceration that may lead to globe rupture. Although chronic inflammatory conditions in the cat may lead to 'dry eye', we rarely perform this test in cats due to literature that indicates normal cats are extremely variable in their STT responses.
The fluorescein stain is available in strips or multidose vials. In our hospitals where the bottles are used so frequently we go through almost one a day, the chance of bacterial or fungal contamination of the bottles has been shown to be unlikely. However, in a general practice, the use of 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 stained eye should be examined fairly quickly. If there is a question of a tear duct blockage, timing of the stain down the nasolacrimal duct can be performed with the pet's nose tipped down towards the floor [Jones Test]. This test should also be timed immediately after drop instillation. Using the cobalt blue filter can greatly enhance examination of fluorescence binding to disrupted corneal epithelial cells although white light, especially a narrowed beam, may be sufficient. Commonly seen indolent erosions may have edematous non attached cells and require careful examination of small uptake areas to determine if stain is leaking underneath the cells.
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.
Tonometry is ideally performed with a Schiotz, TonoPen, or TonoVet to evaluate indirectly the intraocular pressure. If you do not have any of these and need to determine simply if a 'red eye' is uveitis or glaucoma, try a drop of topical anesthetic, wait 5 minutes, GENTLY press a wet Q Tip to the central cornea (assuming a corneal defect is not present). The eye in comparison to the other eye will either feel and look too soft or too hard. Wait sufficient time between topical anesthetic and tonometry (other than the TonoVet which does not require it). If not complete analgesia, the pet may feel a Tono Pen, squint or pull away, altering the measurement. Commonly, the primary cause of a faulty high measurement is due to handler error. 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 a high number which doesn't correlate since the eyes are symmetrical, the dog is visual, both eyes have high pressures (a rare situation), 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 positioning.
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's 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. Assure laboratory submission forms state from where the sample is taken and if you want ocular and/or systemic sensitivities.
Cytology should certainly be taken after the instillation of anesthetic. The use of a cytobrush 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. Evaluation of cytology in the acute patient may provide not only the diagnosis but much more clarity if the case is eventually referred. Additionally, your choice of antibiotic in an acute case may depend upon gram negative or positive focus. Don't forget your in house gram stain!
Other diagnostics utilized in veterinary ophthalmology are ultrasound [US], radiography, and the electroretinogram [ERG]. Orbital disease, contrast studies for epiphora, at times Horner's Syndrome (middle ear and anterior thorax evaluation), 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.
I would like to suggest a couple of take home points you can also use in the clinic. Remind clients do not bother using 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 potentially leading to moist dermatitis medially. 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.