September 2016
Volume 57, Issue 11
Open Access
Letters to the Editor  |   September 2016
Author Response: Gravity Affects Amplitude of Accommodation
Author Affiliations & Notes
  • David A. Atchison
    Institute of Health and Biomedical Innovation & School of Optometry and Vision Science Queensland University of Technology, Australia; and the
  • Lucas L. Lister
    Institute of Health and Biomedical Innovation & School of Optometry and Vision Science Queensland University of Technology, Australia; and the
  • Marwan Suheimat
    Institute of Health and Biomedical Innovation & School of Optometry and Vision Science Queensland University of Technology, Australia; and the
  • Pavan K. Verkicharla
    Institute of Health and Biomedical Innovation & School of Optometry and Vision Science Queensland University of Technology, Australia; and the
  • Edward A. H. Mallen
    School of Optometry and Vision Science, University of Bradford, Bradford, United Kingdom.
Investigative Ophthalmology & Visual Science September 2016, Vol.57, 4571. doi:10.1167/iovs.16-20069
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      David A. Atchison, Lucas L. Lister, Marwan Suheimat, Pavan K. Verkicharla, Edward A. H. Mallen; Author Response: Gravity Affects Amplitude of Accommodation. Invest. Ophthalmol. Vis. Sci. 2016;57(11):4571. doi: 10.1167/iovs.16-20069.

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

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  • Supplements
Our paper1 referred to by the Augousti and Pierscionek letter2 did not investigate the effect of gravity on amplitude of accommodation. Nevertheless, it is a logical conclusion of our results that gravity affects amplitude. The effect would be small, with a mean reduction in anterior chamber depth of 0.07 mm for the young group for the drug/maximum accommodation condition corresponding to 0.14 D if applied to the 10.9 D accommodating form of the Gullstrand exact eye. Stating “any change in accommodative amplitude induced by gravity is not clinically significant” is true but not relevant. Also not relevant is the claim about lack of effect of gravity being found in pilots and astronauts—one referenced study did not involve accommodation3 and two referenced studies involved astronauts4,5 who, from their ages, would have had real amplitudes less than 4 D.6 
Augousti and Pierscionek argue that the Lenstar repeatability (given as twice the standard deviation of repeated measurements) is bigger than the effects we obtained, referencing the instrument manual as giving a standard deviation for repeatability of 0.04 mm.7 This is an intrasession repeatability, rather than an intersession repeatability, which is the relevant repeatability when considering whether the effects found by us are real. Buckhurst et al.8 found an intrasession standard deviation for anterior chamber depth of 0.051 mm, similar to that given in the manual, but a much smaller intersession standard deviation of 0.013 mm, which is small compared with the effects we found. Also relevant here is the point in our other author reply9 that our results were always in the direction supporting the effect of gravity on anterior chamber depth. 
While giving references that are intended to help refute our results, Augousti and Pierscionek disregard studies referenced by us that support the effect of gravity on amplitude of accommodation. 
In summary, our study indicates that there should be small effects of gravity on amplitude of accommodation. It provides yet more support for the Helmholtz theory that accommodation is produced by ciliary muscle contraction relaxing zonular tension and enabling the lens to reduce in diameter and take up a more rounded form. 
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.
Augousti AT, Pierscionek BK. Gravity does not affect accommodative amplitude. Invest Ophthalmol Vis Sci. 2016; 57: 4570.
Vanderploeg JM. Near visual acuity measurements of space shuttle crew members. Aviat Space Environ Med. 1985; 57: 492.
Schachar RA. The Mechanism of Accommodation and Presbyopia. Amsterdam, The Netherlands: Kugler Publications; 2012: 73–74.
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.
Adnan, Efron NE, Mathur A, et al. Amplitude of accommodation in type 1 diabetes. Invest Ophthalmol Vis Sci. 2014; 55: 7014–7018.
Haag-Streit Diagnostics. Biometer Lenstar LS 900. Instructions for Use. 10th ed. Koeniz, Switzerland: Haag-Streit Diagnostics; 2015–2016.
Buckhurst PJ, Wolffsohn JS, Shah S, Naroo SA, Davies LN, Berrow EJ. A new optical low coherence reflectometry device for ocular biometry in cataract patients. Br J Ophthalmol. 2009; 93: 949–953.
Atchison DA, Lister LJ, Suheimat M, Verkicharla PK, Mallen EAH. Author response: gravity affects lens position during accommodation. Invest Ophthalmol Vis Sci. 2016; 57: 4568–4569.
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