Daily axial length and choroidal thickness variations in young adults: Associations with light exposure and longitudinal axial length and choroid changes.

Evidence from animal studies suggests that the eye's natural diurnal rhythms can be disrupted by altering the light/dark cycle or during refractive error development. Although diurnal variations in axial length (AL) and choroidal thickness are well documented in human eyes, the relationship between ambient light exposure, refractive error progression and diurnal AL and choroidal thickness variations is not well understood. Therefore we examined the association between objective ambient light exposure and daily variations in AL and subfoveal choroidal thickness (SFCT), along with longer-term changes in AL and SFCT over 12 months. Thirty-four young adult emmetropes and myopes had their daily variations (measurements ~ every 3 h from 9 a.m. to 9 p.m.) in AL and SFCT assessed on a weekday and weekend in winter and then six months later in summer. Participants then returned six months later for a single measurement session to determine the longer-term change in AL and SFCT. Personal ambient light exposure was captured in winter and summer using wrist-worn light sensors (Actiwatch-2) worn for 14 days over the same period of time when the diurnal measurements were collected. Linear mixed model analyses revealed significant daily variations in AL and SFCT (each p < 0.05). The mean daily peak to trough difference (amplitude) in AL was significantly greater in myopes (0.020 mm; 95% CI: 0.014-0.026 mm) compared to emmetropes (0.010 mm; 95% CI: 0.005-0.015 mm) (p < 0.01), but the SFCT variations were not significantly different between the refractive groups (p = 0.45). Daily variations in AL were negatively associated with the daily SFCT variations (r = -0.603, p < 0.001). Correlation analyses indicated that the amplitude of daily AL variations was negatively associated with the daily time exposed to bright light (r = -0.511, p = 0.002) and positively associated with the longitudinal AL changes over 12 months (r = 0.381, p = 0.04). There was an inverse association between the longer-term changes in AL and SFCT (r = -0.352, p = 0.002). The daily ocular diurnal variations were not significantly different between weekdays and weekends, or between summer and winter (each p > 0.05). In summary, diurnal variations in AL were higher in amplitude in myopes compared to emmetropes and were also associated with longitudinal changes in AL. These findings suggest that diurnal variations may be associated with longer-term axial eye growth. Time spent in bright light also significantly influenced the amplitude of daily AL variations, with more time exposed to bright light associated with a smaller amplitude of diurnal AL change. Choroidal thickness exhibited an inverse association with the AL changes, implying a potential role for the choroid in eye growth.

Measurement Duration and Frequency Impact Objective Light Exposure Measures.

PURPOSE: To determine the measurement duration and frequency required to reliably quantify the typical personal light exposure patterns of children and young adults. METHODS: Ambient light exposure data were obtained from 31 young adults and 30 children using a wrist-worn light sensor configured to measure ambient light exposure every 30 seconds for 14 days. To examine the influence of measurement duration upon light exposure, the daily time exposed to outdoor light levels (>1000 lux) was initially calculated based upon data from all 14 days and then recalculated from 12, 10, 8, 6, 4, and 2 randomly selected days. To examine the influence of measurement frequency, the outdoor exposure time was calculated for a 30-second sampling rate and again after resampling at 1-, 2-, 3-, 4-, 5-, and 10-minute sampling rates. RESULTS: Children spent significantly greater time outdoors (44 minutes higher [95% CI: 26, 62]) compared to adults (P = .001). Children spent more time outdoors during the weekdays (13 minutes higher [-7, 32]) and adults spent more time outdoors during the weekends (24 minutes higher [7, 40]) (P = .005). Calculating light exposure using a lower number of days and coarser sampling frequencies did not significantly alter the group mean light exposure (P > .05). However, a significant increase in measurement variability occurred for outdoor light exposure derived from less than 8 days and 3 minutes or coarser measurement frequencies in adults, and from less than 8 days and 4 minutes or coarser frequencies in children (all P < .05). Reducing measurement duration seemed to have a greater impact upon measurement variability than reducing the measurement frequency. CONCLUSIONS: These findings suggest that a measurement duration of at least 1 week and a measurement frequency of 2 minutes or finer provides the most reliable estimates of personal outdoor light exposure measures in children and young adults.

Influence of seasons upon personal light exposure and longitudinal axial length changes in young adults.

PURPOSE: To investigate the association between objectively measured ambient light exposure and longitudinal axial length changes (and their seasonal variations) over a period of 12 months in young adults. METHODS: This prospective longitudinal observational study included 43 healthy young adult university students (21 emmetropes and 22 myopes) aged between 18 and 30 years. Three axial length measurements were collected at 6-month intervals (i.e. at baseline, 6 and 12 months), in summer and winter to determine the axial eye growth. Personal ambient light exposure data were measured in winter and summer months with wearable sensors, from which the mean daily time exposed to bright (outdoor) light levels (>1000 lux) was derived. RESULTS: Greater daily bright light exposure was associated with less axial eye growth (ß = -0.002, p = 0.006) over 12 months. In summer, myopes exhibited significantly greater changes in axial length (mean change 0.04 ± 0.05 mm) compared to emmetropes (-0.01 ± 0.05 mm) (p = 0.001), but there was no significant difference between refractive groups in winter. Emmetropes also spent significantly greater time in outdoor light levels in summer compared to winter (p < 0.0001), while myopes spent similar time outdoors during both seasons (p = 0.12). Differences in light exposure between summer and winter were also associated with seasonal differences in axial eye growth (p = 0.026). CONCLUSION: In young adults, greater time spent in bright light was associated with slower longitudinal axial eye growth. Seasonal light exposure and axial length changes were dependent on refractive error in this population and also exhibited an inverse relationship.

Plateau Iris Configuration and Dark-Light Changes in Anterior Segment Optical Coherence Tomography.

The angle opening distance (AOD) was analyzed using anterior segment optical coherence tomography (ASOCT) in dark-light conditions in 14 convex iris configuration (CIC) and 12 plateau iris configuration (PIC) patients. AOD500 measured in dark and bright conditions in nasal quadrants were 0.156 +/- 0.072 mum; 0.186 +/- 0.084 mum for CIC (P = .025) and 0.177 +/- 0.121 mum; 0.186 +/- 0.116 mum for PIC (P = .38). AOD750 in dark and bright conditions in nasal quadrants were 0.235 +/- 0.082 mum; 0.280 +/- 0.097 mum for CIC (P = .000) and 0.294 +/- 0.181 mum; 0.306 +/- 0.172 mum for PIC. PIC showed no significant difference in the dynamic changes, whereas the nasal quadrant in CIC showed significant changes. The AOD parameters from ASOCT can be used to analyze the dark-light changes of the anterior chamber angle to differentiate between CIC and PICs.