Sudden onset of light sensitivity in dogs is extremely unusual and I am not aware of this being a symptom of any allergic reaction (other than a reaction that is possible from some toxins). In addition, allergies will generally cause a clear discharge. Your dog needs a thorough veterinary examination immediately as the underlying cause of these symptoms could potentially cause the loss of sight if untreated.

Light sensitivity accompanied by eye discharge could be the result of several conditions. My first thought was that your dog may be suffering from damage to her cornea (the clear outermost layer of the eye), which is known as an abrasion or ulcer depending on the severity. However, it would be very unusual for this to occur to both eyes, since it is nearly always the result of some trauma to the facial area. In severe cases this is a very serious condition which can cause total collapse of the eye structure. Treatment of this condition will depend on whether your dog has a corneal abrasion or a corneal ulcer. Another theory is that she has eaten something which has actually impacted into the soft tissue at the back of the mouth and has migrated to a position behind the eye, causing an abscess which interferes with nervous tissue. I have witnessed this being the cause of light sensitivity. In such cases surgery might be necessary.

Finally, has your dog been vaccinated against Canine Distemper? Distemper often leads to problems in both eyes but there would be other symptoms, such as loss of appetite and a high temperature. Keep a close eye on your dog for any other symptom if she has not been vaccinated.

For now, let’s assume that your dog has not developed sensitivity to light, but is simply feeling mild discomfort in bright light. The most common reason for pussy eye discharge in dogs is conjunctivitis, which an occur in both eyes simultaneously. This is an inflammation or infection of the conjunctiva, which is the tissue lining the eyelids and attaching to the eyeball near the cornea. This is the most common ailment affecting the eye of the dog, and can be caused by allergies or infections. Both allergies and infections cause a severe red appearance of the conjunctiva. This is caused by fluid build-up and an increase in the size and number of blood vessels within the tissue. Infections caused by bacteria or fungus typically create a thick yellow or greenish discharge, and the eyelids may actually stick together when held shut, which might explain why he constantly blinking.