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Time of day influences ocular response to defocus
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Researchers found that ocular response to optical defocus varied significantly depending on the time of day.
Ranjay Chakraborty, PhD, and colleagues reported at the Association for Research in Vision and Ophthalmology meeting that they measured the axial length and anterior chamber depth (ACD) of 13 emmetropic young adults (mean age 23 years) over 3 consecutive days with the IOLMaster 500 (Zeiss).
According to the study abstract, on day 1, they measured baseline axial length in the morning and in the evening. On day 2, researchers evaluated ocular parameters when seven subjects wore a +3 DS and six wore a -3 DS spectacle lens over the right eye in the morning. On day 3, subjects were evaluated after subjects wore those lenses in the evening. The left eye was used as the control.
On day 1, axial length was significantly shorter in the evening than in the morning in both eyes, according to the abstract, with a mean change of +2.43 + 2.70 um in the evening compared to a mean change of +11.01 + 2.14 um in the morning.
The monocular myopic defocus that was induced in the evening caused a significantly greater reduction in axial length (-13.33 + 8.25 um) compared to that induced in the morning (+3.94 + 2.76 um), while the hyperopic defocus induced in the evening caused a much smaller increase in axial length (+3.26 + 2.84) than that induced in the morning (+20.00 + 7.57 um), according to the study.
The left eye experienced a significant reduction of axial length (24.50 + 3.42 um) resulting from hyperopic defocus being reduced in the evening. On the day with no induced defocus, ACD decreased significantly in the morning (-23.93 + 5.81 um) and increased in the evening (+19.87 + 8.49 um).
“Our results show that changes in the length of the eye in response to visual blur, which causes myopia, are dependent on the time of day,” Chakraborty said in an ARVO press release. “As a result, scheduling intensive reading activities in the evening, along with frequent breaks for distance viewing, may prevent the development of myopia in school children, particularly the ones that are at risk of developing myopia due to excessive near work.” – by Nancy Hemphill, ELS, FAAO
Reference:
Chakraborty R, et al. Time of day influences the response to optical defocus in human eyes. Presented at: Association for Research in Vision and Ophthalmology; Honolulu; April 29-May 3, 2018.
Disclosures: Chakraborty and colleagues report no relevant financial disclosures.