Mississippi has one veterinary college, at Mississippi State in Starkville, roughly a hundred and twenty-five miles from Jackson — call it two hours in good conditions. For most of what a dog will ever need that is irrelevant, because Jackson's own practices handle it. For an eye that has gone painful and hazy on a Saturday night, two hours is the entire question.
The practical answer is not to memorise the route. It is to know what happens before the route. A general practice can measure intraocular pressure with a handheld tonometer in a couple of minutes, and that measurement is what separates a red, weepy eye from an emergency. Ask your regular veterinarian whether they keep one and whether they can see an eye urgently. If the answer is yes, you have converted a two-hour gamble into a five-minute triage.
The signs worth acting on immediately are a suddenly cloudy or bluish cornea, a pupil that stays wide and does not respond, obvious pain — squinting, pawing at the face, a dog that will not let you near it — and a visibly reddened eye. The expensive mistake in a city two hours from specialist care is not the drive. It is the night spent deciding whether the drive is warranted.