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Frank Schaeffel, Barbara Swiatczak; Effects of reading with different letter size and contrast polarity on short term changes of axial length. Invest. Ophthalmol. Vis. Sci. 2021;62(8):1374.
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Animal studies have shown that selective stimulation of ON and OFF pathways in the retina can induce bi-directional changes in the eye growth. Recently, it has also been found that choroidal thickness increases in young human subjects when they read text with inverted contrast but decreases when they read normal text. The effect was assumed to be associated with asymmetrical stimulation of ON vs OFF pathways but the receptive field sizes were not studied.
Ten young adult subjects (average age: 23±1 year) with a mean refraction of -0.7±1.9D (range: +1.7 to -4.2D) read text from a large screen (65”) in the dark room at 2 m distance. Four kinds of texts were tested: (1) small standard text (black letters on bright background, 0.8 cm height), (2) like 1 but contrast inverted, (3) large standard text (2 cm height), (4) like 3, but contrast inverted. The visual angle for a large text was similar as for newspaper letters read at 40 cm distance. All displays were matched in brightness (40 cd/m2) and were presented to the subjects for 30 min on two separate days (one day small text, other day large text). Changes in axial length were measured using low coherence interferometry with autopositioning system (Lenstar LS-900) before and after reading.
Averaged over all subjects, the small text did not cause any significant changes in axial length after 30 minutes of reading (standard text +0.6±7.7µm and inverted text -3.9±10.6µm, n.s.). However, large text with inverted contrast induced significant axial shortening of the eye, compared to standard large text (-11.7±8.5µm vs. -1.6±5.9µm, p=0.015). Also in myopes the large inverted text caused significant axial shortening despite the small sample size (n=3, -16.3±9.6µm vs. 0.8±5.8µm, p=0.05).
As previously described for choroidal thickness, we find that reading text with inverted contrast induces significant shortening of the eyeball. However, in this study this only worked when the visual angle of the text height was about 0.6 deg but not when it was only 0.2 degrees.
This is a 2021 ARVO Annual Meeting abstract.
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