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L. O'Donoghue, K.J. Saunders, R.S. Anderson; Effect of Accommodation on Axial Length Measurement in Myopes and Emmetropes . Invest. Ophthalmol. Vis. Sci. 2005;46(13):5591.
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Purpose: Axial length increases with accommodation (Drexler et al, 1998). The aim of this study is to compare accommodative induced changes in axial length in myopes and emmetropes. Methods: 7 emmetropes and 6 myopes, aged 19–21 years, with no history of ocular pathology, participated in this study. The emmetropes had a mean refractive error of +0.143DS (range +0.375 to –0.125); myopes had a mean refractive error of –1.85DS (range – 0.625 to –3.50). All refractive error measurements were made using the Grand Seiko WV–500 autorefractometer. Refractive error in the myopes was corrected using soft contact lenses before testing. Axial length was measured using the Zeiss IOLMasterTM . Subjects fixated a red light within the instrument using the right eye. A semi–silvered mirror placed in front of the left eye permitted co–axial viewing of targets at different distances producing accommodative demands of 0, 4, 6 and 8 diopters. At 6m the target was a spot of light whilst at closer viewing distances letter targets (N6) were used. Five readings were taken at each target distance; the longest and shortest measures were rejected and the mean of the remaining measures used to calculate the axial length. Results: Myopic eyes were significantly longer than emmetropic eyes under all test conditions (t–test p<0.05). Emmetropes demonstrated a significant increase in axial length with increasing accommodation (ANOVA p=0.006). However, this increase was only significant for targets demanding more than 4D of accommodation. Myopes failed to demonstrate a significant change in axial length with accommodation. Conclusions: The results of the present study support previous reports that axial length increases with accommodation in emmetropic eyes. This increase is most marked at higher levels of accommodation. In contrast, myopes showed no significant changes in axial length with accommodation. These results may enhance our understanding of the relationship between accommodation and myopia.
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