No abstract

In this study, we investigated whether the objective depth-of-focus (DOF) is different from the subjective DOF and whether it correlates to accommodative microfluctuations (AMF). The objective DOF and subjective DOF at 1.5 D accommodative stimulus (AS) level were compared in the same group of subjects. The objective DOF and magnitude of AMF were measured at 5 AS levels from 0 D to 4 D. Results showed that there was a significant difference and no correlation between the objective DOF and the subjective DOF. The objective DOF was correlated to the magnitude of AMF. The results suggest that objective DOF and subjective DOF represent the blur sensitivity of two different systems. AMF are correlated with the blur sensitivity of the accommodative system.

In order to elucidate the role of optical defocus in the development of late-onset myopia (LOM), we employed both theoretical and experimental approaches. In the theoretical study, which has been reported previously, we suggested a model in which an accommodative sensory operator was added to simulate the sensory part of the accommodation system. Results derived from the model showed that the sensory part might increase the system's threshold to the accommodative error (or defocus) signal. In this study, we measured the perceptual depth-of-focus and the system's threshold to the defocus signal for three refractive error groups: emmetropic (Emm), stable myopic (S.M.), and progressing myopic (P.M.). Results show that there are no significant differences in the perceptual depth-of-focus among the three groups. However, the defocus threshold values of the P.M. group are significantly higher than the values of the other two groups. This result in combination with our previous findings, leads us to suggest that individuals susceptible of developing myopia from sustained near-work have a specific oculomotor risk profile. Although we are still trying to determine the specific sequence of changes among dark-focus, AC/A ratio, the accommodative system's defocus threshold, and refractive error, we are convinced that the changes of oculomotor parameters underlie the type of myopia associated with near-work.

The results suggest that when the effects of near addition lenses on the accommodative and vergence systems are both considered, the optimal dioptric power of the near addition lens is in a range between +0.20 D and +1.28 D for the three viewing distances. Using progressive lenses to delay the progression of myopia may have promising results if each subject's prescription is customized based on establishing a balance between the accommodative and vergence systems. Formulas derived from this study provide a basis for such considerations.