Monocular hyperopic defocus and diurnal variations in axial length and choroidal thickness

Purpose: To investigate the influence of monocular hyperopic defocus on the normal diurnal rhythms in axial length and choroidal thickness. Methods: Axial length and choroidal thickness measurements were collected approximately every 3 hours for 15 emmetropic young adults over three consecutive days, with the first measurement at ~9am and final measurement at ~9pm on each day. The natural diurnal rhythms with no defocus (Day 1 and 3) and with monocular hyperopic defocus (Day 2, -2.00 DS spectacle lens over the right eye) were examined. Results: Both axial length and choroidal thickness underwent significant diurnal changes on each of the three days (p<0.0001). The introduction of monocular hyperopic defocus on day 2, resulted in significant changes in the diurnal rhythms of both parameters (p<0.05). A significant increase in the amplitude (peak to trough) of change in axial length (mean increase, 0.016±0.004 mm) and choroidal thickness (mean increase, 0.012±0.003 mm) was observed with hyperopic defocus compared to the two ‘no defocus’ days. At the second measurement (mean time 12:10 pm) on the defocus day, the eye was significantly longer by 0.013±0.002 mm compared to the other two days (p<0.05). No significant difference was observed in the average timing of the peaks of diurnal rhythms in axial length (peak at 12:12 pm) and choroidal thickness (21:02 pm) over the three days. Conclusion: Diurnal changes in axial length and choroidal thickness in human eyes were significantly altered by monocular hyperopic defocus, but returned to normal upon removal of the defocus.