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Hello, I am Dr RB and I am a small animal veterinarian. Can you describe the amount of swelling that is present? One eye or both eye? Is the color of the discharge clear and very thin (like tears) or thick, yellow/green color (like mucus). If both of Tinkerbell's eyes are red but she is not squinting them/holding them closed and the discharge is completely clear, this is what is known as "allergic conjunctivitis" which is usually caused by an environmental irritant. The only medication I would recommend over the counter is an anti-histamine known as Chlorpheniramine (all tablets come in 4 mg) and an average sized (e.g. 8-10 lb) cat can take 1/2 tablet every 24 hours.
However, if she is holding one or both eyes mostly shut, the third eyelid is swollen and covering the lower portion of the eye, or if thick, colored discharge is present then this is more serious and a bacterial or viral conjunctivitis. This may or may not be complicated by a secondary corneal ulcer from irritation or rubbing at the eye. In this case, she would need to see her veterinarian right away so he could examine her eyes and apply a stain to determine if an ulceration may be present. Based on this, the right medication could be dispensed for her.
I hope this advice is helpful to you! However, let me me know if you need any clarification on anything. If my response was helpful, please take the time to rate my answer today. Let me know if I can help further with this:)