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Norberto Lopez-Gil, Sofia Peixoto-de-Matos, Larry N. Thibos, Jose Manuel Gonzalez-Meijome; The Importance Of Stimulus Configuration For Explaining Night Myopia. Invest. Ophthalmol. Vis. Sci. 2012;53(14):1360.
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© ARVO (1962-2015); The Authors (2016-present)
Many researchers have examined the myopic shift in refractive error experienced at night (i.e. night myopia) but current explanations do not take into account the large differences of size, luminance, and contrast polarity between typical daytime and nighttime objects. Our study assessed the importance of these differences in stimulus configuration for measuring refractive error.
Subjective refraction of 19 eyes (mean and SD of 21.9±4.6 years) were obtained with a custom made Badal optometer under two conditions: using a diffusely reflective letter-chart (black letters on a white background of 200 cd/m^2) under standard room light conditions, or using a self-luminous object consisting of a small white LED (subtending 0.86 arcmin and a intensity of 70 mcd) on a black background in a dark room. Objective paraxial refraction and pupil size were measured with the WAM5500 open-field autorefractometer (Grand Seiko, Japan) simultaneously with subjective refraction. Wavefront errors were measured with the irx3 aberrometer (Imagine Eyes, France) at the end of the experiment.
For all subjects, subjective refractive errors for the LED stimulus were more myopic than for the letter-chart (mean value and SD of 0.91±0.52 D). Objective measurements with the autorefractormeter indicated that 0.41±0.34 D of this increased myopia manifest for the LED stimulus was caused by accommodation. The pupil diameter when observing the LED (mean and SD of 5.65±0.81 mm) was nearly the same as when viewing letters (6.08±0.70 mm), which eliminates pupil size as a major contributing factor to the measured change in refractive error.
Subjective refractive error is influenced by stimulus configuration. Stimuli typically encountered at night leave the eye in a more myopic state compared to daytime targets. Approximately half of the manifest increase in myopia for the nighttime stimulus was due to increased accommodation. The remaining half represents changes in refractive state that affect the balancing of higher order aberrations with defocus to optimize retinal image quality.
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