Conjunctivitis

A 69-year-old woman comes to her physician for evaluation of  “gritty,” red, itchy eyes for the past three months. The patient has also had intermittent episodes of associated blurry vision. The patient's visual acuity acutely worsens during periods of reading, driving, and watching television. She reports a past medical history of “seasonal allergies” and takes oral antihistamines without relief of symptoms. Vital signs are within normal limits. Physical examination reveals bilateral conjunctival injection. Visual acuity testing demonstrates 20/80 vision in both eyes bilaterally. Slit-lamp examination using fluorescein stain reveals “spotty” uptake. Oral examination reveals multiple dental caries and halitosis. Laboratory results are demonstrated below:  
 

Laboratory value	Result
Hemoglobin	11.3  g/dL
Hematocrit	39 %
Leukocyte count	9,100 /mm3
Platelet count	375,000/mm3
Leukocyte count	3,000/mm3
Erythrocyte sedimentation rate	5 mm/h
Antinuclear antibodies	Negative
Rheumatoid factor	Negative
Anti-dsDNA	Negative
Anti-Ro/La	Negative

Which of the following is the most likely etiology of this patient’s clinical condition?