Effect of Text Type on Near Work–Induced Contrast Adaptation in Myopic and Emmetropic Young Adults

Abstract

PURPOSE. Contrast adaptation has been speculated to be an error signal for emmetropization. Myopic children exhibit higher contrast adaptation than emmetropic children. This study aimed to determine whether contrast adaptation varies with the type of text viewed by emmetropic and myopic young adults.METHODS. Baseline contrast sensitivity was determined in 25 emmetropic and 25 spectacle-corrected myopic young adults for 0.5, 1.2, 2.7, 4.4, and 6.2 cycles per degree (cpd) horizontal sine wave gratings. The adults spent periods looking at a 6.2 cpd high-contrast horizontal grating and reading lines of English and Chinese text (these texts comprised 1.2 cpd row and 6 cpd stroke frequencies). The effects of these near tasks on contrast sensitivity were determined, with decreases in sensitivity indicating contrast adaptation.RESULTS. Contrast adaptation was affected by the near task (F 2,672 ¼ 43.0; P < 0.001). Adaptation was greater for the grating task (0.13 6 0.17 log unit, averaged across all frequencies) than reading tasks, but there was no significant difference between the two reading tasks (English 0.05 6 0.13 log unit versus Chinese 0.04 6 0.13 log unit). The myopic group showed significantly greater adaptation (by 0.04, 0.04, and 0.05 log units for English, Chinese, and grating tasks, respectively) than the emmetropic group (F 1,48 ¼ 5.0; P ¼ 0.03).CONCLUSIONS. In young adults, reading Chinese text induced similar contrast adaptation as reading English text. Myopes exhibited greater contrast adaptation than emmetropes. Contrast adaptation, independent of text type, might be associated with myopia development. (Invest Ophthalmol Vis Sci.

Accommodation response to Chinese and Latin characters in Chinese‐illiterate young adults

“…Thus, there was no need to interpret or attach meaning to the symbols. Under these circumstances, accommodation to Chinese and Latin characters showed no significant differences over the stimulus range zero to 5.00 D. This implies that any differences in accommodation caused by the differing cognitive demands of the two types of text in the reading tasks used by Yeo, Atchison and Schmid must be small. A key point in both studies is that there is no evidence that lags of accommodation are greater with Chinese compared to Latin characters, so that it seems unlikely that the greater levels of myopia observed among ethnic Chinese are related to differences in accommodative lags associated with the form of characters of the reading texts used in childhood.…”

“…In the only comparable study, using a larger number of subjects (n = 83), Yeo, Atchison and Schmid found that mean accommodative lags (around 1.00 D) in both emmetropic and myopic Chinese children during binocular reading tasks at stimulus levels of 3.00 and 4.00 D were lower for Chinese characters, when compared to those for Latin characters by modest amounts (less than 0.05 D), which were statistically but not clinically, significant. For these stimuli, the present data gave overall mean lags of 1.00 ± 0.63 D for Chinese characters and 1.05 ± 0.62 D for Latin characters.…”

“…Yeo, Atchison and Schmid suggested that the small mean response differences (less than 0.05 D) that they found in Chinese‐literate children may arise because reading Chinese characters demands closer scrutiny of the symbols, which in turn elicits a more accurate accommodation response. In contrast, in the present study, adult Chinese‐illiterate subjects were used, with monocular accommodation being assessed during the viewing of single‐character targets rather than during reading of a text.…”

“…Yeo, Atchison and Schmid found that in both emmetropic and progressive‐myopic Chinese‐literate children, accommodative lags at 25 and 33 cm were very slightly (less than 0.05 D on average) lower when binocularly reading Chinese text than when reading Latin characters with similar stroke frequency (around five cycles/degree at 33 cm) . Clearly, these findings do not support the idea that enhanced myopic progression in some Chinese readers is associated with the existence of larger lags of accommodation when Chinese characters are read.…”

“…Clearly, these findings do not support the idea that enhanced myopic progression in some Chinese readers is associated with the existence of larger lags of accommodation when Chinese characters are read. Although the difference in lags for Chinese and Latin texts was not large enough to be clinically significant, Yeo, Atchison and Schmid offered the interesting speculation that, since the Chinese characters demanded more careful scrutiny for their interpretation, they elicited more accurate accommodation. Cognitive demand and mental effort are known to affect accommodation, mainly as a result of changes in autonomic function .…”