September 2016
Volume 57, Issue 11
Open Access
Letters to the Editor  |   September 2016
Gravity Does Not Affect Accommodative Amplitude
Author Affiliations & Notes
  • Andy T. Augousti
    Faculty of Science, Engineering and Computing, Kingston University, London, United Kingdom.
  • Barbara K. Pierscionek
    Faculty of Science, Engineering and Computing, Kingston University, London, United Kingdom.
Investigative Ophthalmology & Visual Science September 2016, Vol.57, 4570. doi:10.1167/iovs.16-19827
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      Andy T. Augousti, Barbara K. Pierscionek; Gravity Does Not Affect Accommodative Amplitude. Invest. Ophthalmol. Vis. Sci. 2016;57(11):4570. doi: 10.1167/iovs.16-19827.

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      © ARVO (1962-2015); The Authors (2016-present)

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Lister et al.1 used the Lenstar LS 900 to measure the change in anterior chamber depth and lens thickness of 13 young (mean age of 20.9 years) and 10 older (mean age of 58.3 years) subjects in the upright and prone positions before and during maximum pilocarpine-stimulated accommodation. The authors state that “the main finding for the young group is that head position affected ACD for all drug states and accommodation combinations (Fig. 3c), but mean effects were small at 0.04 to 0.07 mm and much smaller than reported in the literature.” 
Given that the minimal change in anterior chamber depth following maximally pharmacologically stimulated accommodation was less than 70 μm, which translates to approximately 0.1-D increase in optical power of the average eye,2 the data indicate that any change in accommodative amplitude induced by gravity is not clinically significant. This finding confirms the reports by astronauts and pilots35 about the lack of effect of gravity on accommodative amplitude, which tends to support the measurements by Schachar.6 
In addition, the 70-μm positional change in anterior chamber depth is at or below the accuracy of the instrument. The manufacturer's specified standard deviation for the repeatability of the Lenstar LS 900 is 40 μm/s.7 The accuracy of the instrument's repeatability is 2 SD,8 which is 80 μm. Since the results are less than the accuracy of the repeatability for the Lenstar LS900, the effect of gravity may be even smaller, further confirming that any gravitational change in anterior chamber depth does not significantly affect accommodative amplitude. 
References
Lister LJ, Suheimat M, Verkicharla PK, Mallen EAH, Atchison DA. Influence of gravity on ocular lens position. Invest Ophthalmol Vis Sci. 2016; 57: 1885–1891.
Hunter JJ, Campbell MC. Potential effect on the retinoscopic reflex of scleral expansion surgery for presbyopia. Optom Vis Sci. 2006; 83: 649–656.
Vanderploeg JM. Near visual acuity measurements of space shuttle crew members. Aviat Space Environ Med. 1985; 57: 492.
Gibson CR, Mader TH, Schallhorn SC, et al. Visual stability of laser vision correction in an astronaut on a Soyuz mission to the International Space Station. J Cataract Refract Surg. 2012; 38: 1486–1491.
Schachar RA. The Mechanism of Accommodation and Presbyopia. Amsterdam, The Netherlands: Kugler Publications; 2012: 73–74.
Schachar RA, Cudmore DP. The effect of gravity on the amplitude of accommodation. Ann Ophthalmol. 1994; 26: 65– 70.
Haag-Streit Diagnostics. Biometer Lenstar LS 900. Instructions for Use. 8th ed. Koeniz, Switzerland: Haag-Streit Diagnostics; 2014: 13.
Bland JM, Altman DG. Statistical methods for assessing agreement between two methods of clinical measurement. Lancet 1986; 1: 307–310.
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