Abstract
Purpose :
Diurnal variations in ocular parameters have been reported previously. The present study reports the effects of short-term optical defocus on central and peripheral eye length and choroidal thickness as observed during the day (7-11 a.m. [morning] and 5-8 p.m. [evening]).
Methods :
Healthy young subjects aged 18 - 25 years were exposed to 30 min of continuous myopic (+3.00D), hyperopic (-3.00D) and multifocal defocus (Plano/+2.50D addition) lenses in the right eye only (n=10). Eye length and choroidal thickness were measured at central and peripheral locations out to 20° field angles. For each scheduled visit, two baseline assessments were conducted 30 min apart. Thereafter, the defocus lens was introduced and a measurement conducted after 30 min. Between measurements, subjects watched a movie at 4 m distance under normal indoor lighting conditions. Each participant attended six visits. Repeated measures ANOVA was used to determine the change from baseline with the time of day and lens as within-subject factors. Statistical significance was maintained at p<0.05.
Results :
Between the two baseline measurements, there were no statistically significant changes.
Exposure of central and peripheral eye length to defocus showed statistically significant changes in the evening only. Centrally, there was a significant difference between lens types (p=0.002) and between the time of day (p=0.001). Myopic and multifocal defocus led to a significant decrease in the evening (-25±13 and -21±9 µm) as compared to the morning (-7±11 and -7±16 µm). Myopic and multifocal defocus significantly decreased (-16±8 and -14±10 µm) compared to hyperopic defocus (1±10 µm). Peripheral locations also showed some statistically significant changes at temporal 10°, nasal 10° and inferior 20°.
For choroidal thickness, there was a statistically significant change between defocus irrespective to the time of the day (p=0.041). At the center, only myopic defocus had a significant decrease (-14±18 µm) compared to hyperopic (+4±13 µm) and multifocal defocus (+6±13 µm). Peripherally, there were some statistically significant changes at nasal 10°.
Conclusions :
Our preliminary data support the trend for diurnal changes in eye length. Interestingly, the effects of optical defocus could be modulated based on the time of the day. These findings, if consistent for a larger sample, have implications on the use of myopia control strategies.
This is a 2020 ARVO Annual Meeting abstract.