Hello, my name is***** and I have over 20 years of experience as a veterinarian. I am sorry to hear that Darby has been stumbling a bit only within the last hour.
Cats that have had cataracts for a period of time adjust quite well to their change in ability to see and we rarely see them stumble. They use their other senses and memorize their home such that a person that didn't know that they were visually challenged probably wouldn't be able to tell just by watching them get around.
External ear infections should not change their ability to balance, although if she is shaking her head a lot that could put her off balance. And if an ear infection progresses into the inner ear that can cause a disturbance in the balance system (vestibular system) and those kitties will definitely be off balance.
Is her head tilted to one side consistently?
When she tries to walk is she circling or leaning more to one side or seeming to walk with a very wide based, slow motion?
Does she have rhythmic back and forth or circular eye movement? (like this: https://www.youtube.com/watch?v=ojM-5ftYUAs )
Is her appetite off such that she is not eating well?
Does she have signs of an ear infection (red ears, increased waxy debris)?
There can be several causes of vestibular disease. They range from very benign causes such as idiopathic (meaning we don't know the cause but they resolve on their own with supportive care) to middle ear infections or polyps, brain infections (bacterial, fungal or viral) or even a primary brain lesion such as a blood clot, bleeding or a tumor.
If we cannot identify a cause then we will often treat the patient symptomatically (antinausea drugs, anti-inflammatories and antibiotics) as most cats do get better with supportive care. Prognosis if this is caused by a lesion outside the brain is very good in most cases. We will check bloodwork to make sure organ failure or low thyroid hormone are not the cause of her symptoms.
At home if she has signs of vestibular disease you can give Gravol also known as Dramamine (dimenhydranate) to control nausea and help with balance. This drug is also used for carsickness. The dose is 4mg to 8mg per pound of body weight every 8 hours. Side effects are mild sleepiness and dry mouth.
Or you can try Benedryl (diphenhydramine) at 1mg per pound of body weight orally every 8 hours. Side effects are sedation and dry mouth as well.
To stimulate her appetite start a bland diet of 2/3 boiled white skinless chicken, mixed with 1/3 boiled, plain white rice. Feed several small meals a day.
If after a week’s time there is no improvement in her vestibular disease symptoms or she is worse then she needs further diagnostics to try and identify the cause. Serious central nervous system (the brain) causes are more likely and thus prognosis is much more guarded.
Things such as an MRI or spinal tap are indicated at that point.
If she is not improving a referral to a neurologist is best as they can perform this advanced testing.
Please see this link if you would like to read more about vestibular disease: http://www.petside.com/condition/dog/vestibular-disease-canine
Other possible reasons for stumbling include poor oxygenation due to anemia or heart disease, so please check her gum color. It should be a nice bubblegum pink.
Increased levels of metabolic wastes, very high or low blood sugar and changes in blood levels of organ wastes can affect brain and muscle function, and thus if she isn't showing signs of vestibular disease then a visit to her veterinarian for diagnostic testing is best.
Please let me know if you have any further questions.