Exophoria may be a risk factor for developing three-dimensional asthenopia, which may be induced by viewing 3-D television, according to a study.
“Although more frequent relaxation periods may be advisable for achievement of reduced symptomatology, there is currently no evidence to show that these 3-D asthenopic symptoms are harmful to the visual system,” the study authors said.
The study included 115 patients aged 18 to 55 years who were shown 3-D images for 90 minutes on a 3-D high-definition television. The 14 patients who experienced ocular or nonocular pain, dizziness, or image blurring while viewing the 3-D television were placed in an asthenopia group. A control group contained 22 patients who did not experience asthenopia symptoms.
Both groups were evaluated for visual acuity, refractive errors, interpupillary distance, IOP, tear breakup time, near point of accommodation, presence of strabismus, stereoacuity and retinal abnormalities.
The presence of strabismus was the only statistically significant difference observed between the two groups (P = .08). The six patients with strabismus in the asthenopia group had exophoria of less than 10 ∆D without suppression.
According to the study authors, patients with exophoria usually have normal stereopsis, enabling them to perceive 3-D images well.
“Because patients with exophoria maintain normal ocular alignment by fusional vergence, additional vergence may be required while viewing 3-D images, which means that patients with exophoria require more vergence than normal people when watching 3-D television,” the authors said. “This explains why subjects in our study who had exophoria showed more 3-D symptoms, because they had not been previously aware of the symptoms of eyestrain.”