Variation in Accommodative Aftereffect Due to Age of Onset of Myopia
We have reported that adult early-onset myopia (EOM) (n = 18) (mean age 26.3 years) has a lesser accommodative aftereffect than emmetropia (EMM) (n = 18) (mean age 24.4 years). Late-onset myopia (LOM) (n = 15) (mean age 23.6 years) has a more severe aftereffect than EMM. In the present study, we similarly examined 48 younger subjects (age less than 20 years), including 24 EOMs (mean age 13.7 years), 16 EMMs (9.9 years), and 8 LOMs (16.4 years). The task was to view the target at 4D above the subject’s far point for 2 min. Pre- and post-task accommodative responses to the extremely blurred target were recorded for 1 and 5 min, respectively, using an infrared optometer. The accommodative aftereffect was calculated as the difference between the pre- and post-task accommodative responses. The results showed that: (1) a larger aftereffect was seen in adult LOMs and young LOMs; (2) the aftereffect was significantly increased during the posttask recording and was maximum 5 min after the task in both adult and young LOMs; (3) EOMs at an early stage (whose duration after onset was less than 10 years) showed aftereffects almost identical to those in the LOMs. These findings suggest that a similar mechanism of accommodative aftereffect was involved in the LOM eyes and the young EOM eyes.