A 12 year-old patient is seen at your office complaining of distance blur. The cover test reveals 4 prism diopters of exophoria at near. The subjective refraction reveals -2.25 DS OU. Four weeks later, the patient reports clear distance vision with glasses but experiences fatigue and frontal headaches when reading. What is the MOST likely etiology of her headaches while reading?

The most likely etiology of the patient's headaches while reading is resultant esophoria at near induced by her glasses.

In this scenario, the patient initially presented with 4 prism diopters of exophoria at near, which indicates that her eyes tended to drift outward when converging for near tasks. However, after being fitted with glasses to correct her distance vision, the dynamics of her binocular vision changed. With the introduction of the lenses, particularly if they were non-presbyopic spherical lenses, she may have shifted from exophoria to esophoria at near due to the additional convergence demand created by the glasses. This change can lead to increased effort in eye muscle coordination and can explain the fatigue and headaches the patient is experiencing while engaging in near tasks like reading.

While other factors like the optical center being measured improperly, glasses being too tight, or pantoscopic tilt could certainly contribute to discomfort, the clear connection between the change in her phoria status from exophoria to esophoria due to the refractive correction is a direct and plausible explanation for her symptoms. This emphasizes how changes in visual demands and the need for proper convergence can impact comfort and lead to symptoms such as headaches in patients, especially children whose visual systems are still developing