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Sandra Wagner, Frank Schaeffel, Eberhart Zrenner, Torsten Strasser; Does close work affect the ciliary muscle morphology?. Invest. Ophthalmol. Vis. Sci. 2019;60(9):1399.
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© ARVO (1962-2015); The Authors (2016-present)
There is ample evidence for a possible relationship between myopia development and near vision. We have studied whether sustained nearwork may have an effect on ciliary muscle (CM) morphology and accommodation and whether there are differences between emmetropes and myopes.
17 emmetropic and 18 myopic students (19-25 yr; spherical equivalent right eye 0.05±0.29D and -2.50±1.09D, respectively) were included. Accommodation and CM morphology were assessed at far (0D) and near vision (4D) before and after a 30-min reading task at 25 cm. Accommodation response was recorded to a step pulse of 0D–4D–0D with a target presentation of 15 sec using eccentric infrared photorefraction. The right eye’s temporal CM was imaged via anterior-segment optical coherence tomography. A custom-developed semi-automatic algorithm was used to determine CM thickness (CMT) profiles and CM dimensions in the perpendicular axis. Accommodation dynamics were assessed using a 4-parameter logistic fit. Pre- to post-task changes were analyzed by means of a univariate ANOVA with relative values (△pre-post).
On average, CM was thinner after reading, predominantly at 0.0 to 1.4 mm posterior to the scleral spur in emmetropes, and in a narrower region of 1.0 to 1.8 mm in myopes (Figure 1). The perpendicular axis was significantly reduced after nearwork (F1,66=25.942, p<0.001), however without a significant impact of refractive error (F1,66=1.870, p=0.176) or target distance (F1,66=0.019, p=0.891). Accommodation responses for targets at infinity differed significantly before and after nearwork (F1,32=7.775, p=0.009). There was also a significant effect of refractive error (F1,32=11.310, p=0.002): While myopes exhibited a mean myopic shift of 0.20±0.21D, emmetropes showed little change after nearwork (-0.02±0.16D). No changes were seen in the velocity of accommodation.
Sustained nearwork caused thinning of the CM in both emmetropic and myopic eyes. In myopes, CMT changes are associated with a significant sustained increase in lens power. Sharing features of striated muscles, CMT was expected to rather increase after prolonged contraction but the opposite was found here. Further studies are necessary to understand possible influences of sympathetic innervation which is activated during intense nearwork.
This abstract was presented at the 2019 ARVO Annual Meeting, held in Vancouver, Canada, April 28 - May 2, 2019.
CMT profiles for far (left) and near vision (right) of emmetropes (top) and myopes (bottom) before (blue) vs. after 30 min of nearwork (red).
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