A 24-year old female patient has red eyes and bilateral diffuse superficial punctate keratitis. What is the most likely etiology of her condition?

The presence of red eyes combined with bilateral diffuse superficial punctate keratitis is strongly suggestive of a viral etiology, particularly due to the commonality of viral conjunctivitis. Viral conjunctivitis often presents with symptoms such as redness, tearing, and the sensation of foreign body presence in the eyes. The diffuse superficial punctate keratitis observed on examination reflects the irritation and inflammation of the corneal epithelium that frequently accompanies viral infections.

In contrast, the other potential causes such as dry eyes generally lead to different symptoms, including a sandy or gritty feeling and discomfort, rather than bilateral diffuse punctate keratitis. Foreign bodies would typically present with localized symptoms related to the specific area of involvement and may cause acute pain or vision changes rather than diffuse keratitis. Bacterial infections often result in purulent discharge and localized conjunctival injection, in addition to keratitis, but not typically with the same pattern of punctate keratitis as seen with viral infections.

Thus, the characteristics of the patient's symptoms and the type of keratitis point towards a viral etiology as being the most likely cause.