Differential Diagnosis for Unilateral Conjunctivitis
Single Most Likely Diagnosis
- Allergic conjunctivitis: This is the most likely diagnosis given the unilateral presentation during spring, which is a common time for allergic reactions due to increased pollen counts. The acute onset also supports an allergic cause.
Other Likely Diagnoses
- Viral conjunctivitis: Although it can be bilateral, viral conjunctivitis can start unilaterally and is highly contagious. The patient's age and the acute onset are consistent with this diagnosis.
- Bacterial conjunctivitis: This can also present unilaterally and is characterized by a purulent discharge. The patient's age and the acute onset could fit this diagnosis, although it's less likely than allergic or viral causes given the seasonal context.
- Irritant conjunctivitis: Exposure to an irritant could cause unilateral conjunctivitis. Given the patient's age and the potential for exposure to various substances, this remains a plausible diagnosis.
Do Not Miss Diagnoses
- Acute angle-closure glaucoma: Although rare, this condition is an emergency and can present with unilateral conjunctival injection, severe eye pain, and decreased vision. It's crucial to rule out this diagnosis due to its potential for permanent vision loss if not promptly treated.
- Herpes zoster ophthalmicus: This condition can cause unilateral conjunctivitis along with a rash on the forehead and is a significant concern due to the potential for serious complications, including vision loss.
Rare Diagnoses
- Giant papillary conjunctivitis: Typically associated with contact lens use, this condition can cause unilateral conjunctivitis but is less likely in a 65-year-old female without a history of contact lens use.
- Parasitic conjunctivitis: Caused by parasites such as phthiriasis palpebrarum or loa loa, this is extremely rare and usually associated with travel to endemic areas or specific exposures.