The conjunctiva refers to the pink tissue surrounding the eye, third eyelid, and lining the upper and lower lids. This tissue contains numerous structures, called follicles, which are important for the local immune system. In some dogs, the conjunctiva can mount an exuberant reaction to environmental allergens, such as dust and grass, leading to follicular conjunctivitis. This condition is most commonly seen in juvenile dogs up to 18 months of age, as their immune system is still developing.
The most obvious clinical symptoms include eye discharge and an increase in redness of the conjunctival tissue. On closer examination, small semi-transparent, raised follicles are seen, most commonly underneath the third eyelid. They can also be present in the surrounding conjunctiva. These follicles are normally not readily visible to the naked eye. However, in this condition, they become enlarged due to chronic stimulation of the local immune system. This chronic stimulation is often associated with environmental irritants, such as plant matter, and is therefore more common in large breeds with more exposure of their conjunctiva. If large enough, these follicles can also be irritating to the surrounding tissue. Diagnosis of this condition is most commonly made by clinical appearance, although it can be confirmed by sampling the follicles and examining the cells under the microscope.
Treatment usually involves flushing the area with eye wash to remove antigens and debris. In addition, application of a topical steroid solution will help decrease local inflammation. In cases non-responsive to topical therapy, mechanical debridement of the follicles may help to stimulate resolution. Follicular conjunctivitis is typically self-limiting and usually improves once dogs grow older and their immune system matures.