I recall from my years in clinical practice the emotional upset expressed by owners - specifically because their pets went suddenly blind or that their pet had a poor prognosis for retaining vision over time. For some, a diagnosis of “blind” or “will go blind” was devastating. In many instances, a window of opportunity for helping a pet had passed; they had waited too long to see the specialist or their veterinarian had not referred the case early enough to institute treatment for the condition. As with any disease or condition, early recognition of a problem and prompt referral for intervention by a specialist gives us the upper hand and stands to benefit our patients.
Some of the more common reasons that prompt pet owners to seek an evaluation of their pet (for possible vision loss) are that the pet:
- Bumps into household objects
- Has difficulty catching toys
- Is relunctant to walk in certain environments
- Freezes in place
- Has changes in behavior (e.g. anxiety or increased vocalization)
Pets can have are varying degrees of vision loss and there are many possible causes for reduced vision. Obtaining a careful and thorough history is essential, and clinicians must avoid leading owners toward certain answers. Clinicians, however, often face a significant limitation: there simply aren’t many reliable tools to quantify a dog’s visual ability in the clinical setting. Hearing owners' observations and perspectives is important, but determination of a dog's ability to see or the quality of its vision is not always straightforward.
Although it’s intuitive to ask whether or not a pet bumps into things, the weight we give to observations (which can be subjective) or our assessment of a pet's performance of rudimentary maze navigation testing is questionable. There is more value in using scientifically validated questions - those found to reliably assess vision. Validated owner questionnaires exist for evaluating quality of life in dogs with cancer or behavior problems; we also have another instrument that can be helpful in assessing vision. The Canine Visual Function Instrument (CVFI)1 - is a validated and reliable pet owner-directed questionnaire that can be helpful for revealing deteriorating quality of vision in dogs. One application for this instrument is in assessing treatment outcomes of therapies used in clinical research trials, however 12 of the questions in this CVFI are helpful to both clinicians and pet owners for identifying reduced quality of vision in dogs.
The questionnaire is designed to quantify a dog’s visual ability based on how their vision impacts daily activities. The CVFI consists of four major sections: basic signalment and health information, details about the dog’s visual diagnosis and severity, the owner’s feelings about the dog’s vision, and finally 12 targeted questions addressing how vision affects normal daily activities. These questions are the most informative and form the core of the instrument. The questions explore:
- Whether their vision impairs of prevents normal daily activities
- Their ability to go in and out of the house
- Whether they bump into objects when those objects are moved (e.g. a piece of furniture that the pet was always familiar with but is now in a new location)
- Their difficulty navigating unfamiliar environments - a common issue for dogs that slowly lose vision and learn to compensate at home, but don't do well in unfamiliar surroundings
- Changes in the dog’s ability to take food or a snack from the owner's hand
- Changes in the ability to catch treats when tossed
- Changes in their ability to jump onto or off furniture
- Ability to track toys when thrown
- Ability to recognize people at a distance
- Interest to look out windows
- Ability to transition from bright to dim lighting
- Ability to transition from dim to bright lighting
For each question, owners choose from five response options: "not at all," "infrequently / on occasion," "sometimes," "quite often," and "almost all of the time.
The CVFI is simple, low-effort, validated, and useful for quantifying visual function in dogs and maximizing the value of the pet's history. As noted in Kirk & Gelatt’s textbook on Veterinary Ophthalmology, history should never replace a complete exam but rather complement it. With respect to vision loss, it’s important to consider a broad list of differential diagnoses. First, consider that not all vision problems are ocular in origin. Some dogs with long facial hair, for example, may be visually impaired simply because they cannot see through their bangs! Part of their initial evaluation should include pulling the hair back out of their face and watching the dog navigate the exam room. These dogs are easily cured by simply keeping the hair trimmed or pulled back and secured away out of their line of sight. Eye problems that can result in reduced or loss of vision include a variety of different conditions, and some of the more obvious ones can be diagnosed during the course of an eye exam including:
- Anterior segment problems - corneal scarring, pigmentary keratitis, hyphema (blood in the anterior chamber) or anterior chamber disease, and lenticular abnormalities like advanced cataracts.
- Posterior segment diseases - vitreous changes, retinal degeneration or inflammation, and optic nerve disorders such as papillitis or optic neuritis.
In patients with normal exam findings, blindness can be caused by a problem outside of the eye (e.g. retrobulbar optic nerve disease) or beyond the eye (e.g. intracranial / brain disease).
The information provided by the CVFI and ophthalmic examination can guide decision-making about referral to a veterinary ophthalmologist - for determining or confirming the cause of vision loss. As with any problem, early detection and intervention generally leads to better outcomes compared with a “wait and see” approach. As was evidenced in this study1 - 56-61% of owners expressed concern or were upset about their dog’s quality of vision; client concerns or requests to seek a specialist’s opinion should be respected. As caregivers, we should always empower owners in the care and understanding of their pet's problems.
Reference:
[1] Development and validation of the canine visual function instrument. Vet Ophth 2018; 21:586-594. https://doi.org/10.1111/vop.12656
Contributed by Sheri L. Berger, DVM, DACVO
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