Evidence for axial eye shortening in response to a reading text with inverted contrast polarity was previously found by Aleman et al.,
12 although, in their study choroidal thickness was measured rather than axial length. However, because thicker choroids cause a shorter axial length, both measures should at least partially reflect the same intraocular changes. A difference to the work by Aleman et al.
12 was that bidirectional changes in choroidal thickness were found after 60 minutes of reading, whereas in the current study only contrast-inverted text elicited significant changes in axial length after 30 minutes. Possible explanations include (1) choroidal thinning was too small to be reliably detected by low coherence interferometry, (2) reading tasks lasted too short time or, that, (3) in the current study, screen luminance was higher (82 cd/m²) than in the previous experiments (35 cd/m²). Different luminance may partially explain the different outcomes, although it was shown that looking at an empty screen at three different screen luminance (35, 48, and 62 cd/m²) did not influence on axial length change.
12 In line with the previous study is that “choroidal thickening with ON stimulation was not correlated with refractive errors,” we also found that the effects of reading text with inverted contrast were not dependent of refractive error (
Fig. 4). Recently, Hoseini-Yazdi et al. found that reading text with standard contrast, stimulating predominantly the OFF pathways, caused choroidal thinning that was additive to the choroidal thinning induced by accommodation (Hoseini-Yazdi H RS, et al. ARVO Abstract. 2021;2021).
40 Again, there was no correlation noted with refractive error, in line with our findings and findings by Aleman et al.
12 Also, recently, Hogue and Taylor found that the individual sensitivity to ON or OFF stimuli is variable and, interestingly, it was related to axial length as well (Hogue WTC, et al.
IOVS. 2021;2021:ARVO Abstract).
41