A-HA!! That has been very helpful!
What you are describing in your dog sounds like it might be conjunctivitis, which means an inflammation of the conjunctiva (mucous membranes in the lower and upper eyelids).
Conjunctivitis in a dog is generally allergic (to pollens, dust, etc) or bacterial (from swimming in dirty pond water), viral or due to parasites.
In a dog of this age allergic conjuncitivitis is most likely.
Dogs are notoriously curious creatures and like to put their faces into dusty corners, under bushes and in the sand. All of that dust, pollen and sand can get trapped under the eyelid and cause irritation. At this time of year, ragweed is a big allergen in many states, and perhaps it is where you are, too? I see lots of dogs coming in every day with allergic conjunctivitis in Fall in Ontario, Canada!
Often, this needs some prescription medication containing anti-inflammatories to treat it.
However, you could try a couple of things at home first if you would like to see if you can help her before considering a vet.
1. Try to limit her play in the dusty areas.
2. If she does play under the trampoline, rinse her eyes out afterwards.
What I would suggest is that you go to the contact lens section of your local drugstore/pharmacy and look for sterile ophthalmic saline solution (eyewash). There should be nothing else in it except sterile saline!
Ask the pharmacist if you are not sure.
After your girl plays in the dust, rinse her eyes by having her sit with her bum in a corner, and you standing over her with your back in the corner, and her head between your knees.
Hold her with your legs, and tilt her head so her nose points to the ceiling. Now, squirt the sterile saline into the lower lids to really flush them! You need to use 1-2 tablespoons of solution per eye to do this. A towel under you both is helpful.
3. Wipe her eyes gently with a soft facecloth dipped in warm water to remove any dust around them after she plays outside.
Thus, less will end up in her eyes!
4. Benadryl (diphenhydramine) can be helpful if this is due to allergies. Many times, people really under-dose dogs with this medication as they take much higher doses than humans. I'm not sure if this is what you have tried?
If you try it, do please MAKE SURE IT IS PLAIN BENADRYL WITH NO OTHER INGREDIENTS.
The dose that one generally gives is 1mg/lb. Is she about 30lbs? It comes as 25 mg tablets, and if she is 30lbs, her dose would be ONE TABLET. This can be repeated every 8 hours for 24-36h. You would need to give the full dose every 8 hours for 2 days to really see much improvement. It might make her sleepy.
Here is more about Benadryl:
5. If she continues to rub at her eyes or hold them closed, or has green mucoid discharge from them, then seek immediate veterinary care.
Here is more information about conjunctivitis:
I hope that this helps!
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The above is given for information only. Although I am a licensed veterinarian, I cannot legally prescribe medicines or diagnose your pet's condition without performing a physical exam. If you have concerns about your pet I would strongly advise contacting your regular veterinarian.