February 2021
Volume 62, Issue 2
Open Access
Letters to the Editor  |   February 2021
Image Registration Is Required for Experiments of Accommodation
Author Affiliations
  • Ronald A. Schachar
    Department of Physics, University of Texas at Arlington, La Jolla, California, United States. E-mail: ron@2ras.com.
Investigative Ophthalmology & Visual Science February 2021, Vol.62, 17. doi:https://doi.org/10.1167/iovs.62.2.17
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    • Get Citation

      Ronald A. Schachar; Image Registration Is Required for Experiments of Accommodation. Invest. Ophthalmol. Vis. Sci. 2021;62(2):17. doi: https://doi.org/10.1167/iovs.62.2.17.

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

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Experiments require baseline references from which to measure change. When comparing images, multiple fixed, positional reference points must be identified, and then the images must be registered with regard to these positional references before assessment of change. These basic methodological requirements are lacking in studies by Croft et al.1,2 in both the human and monkey accommodation comparisons. 
The authors state: “During ultrasound biomicroscopy (UBM) … there was minimal convergent eye movement, if any…. Thus, there was very little, if any change in angle of the transducer to the eye during accommodation.” This generalization is not a quantitative measure of the inherent stability or variability of their experimental system. Repeat UBM measurements are required without any other pertubation of the system. First, the UBM transducer itself should be moved and then, with the position of the UBM fixed, just the eye should be moved in different directions and speeds. 
The failure of the authors’ experiments is exemplified in Figure 1. The corneal lengths in the unaccommodated and accommodated images of the eyes are different. The difference in corneal lengths reflects a change in alignment between the eye and the UBM transducer. Either the eye or the transducer moved or both relative to one another so that the plane (or axis) of the image was changed. 
Figure 1.
 
Reproduction of the left-sided UBM images of Fig. 2 from Croft et al.2 with arrows and labels added for clarification. Note: the corneal lengths are different, indicating the imaging plane (axis) changed between the unaccommodated and accommodated images.
Figure 1.
 
Reproduction of the left-sided UBM images of Fig. 2 from Croft et al.2 with arrows and labels added for clarification. Note: the corneal lengths are different, indicating the imaging plane (axis) changed between the unaccommodated and accommodated images.
The authors need to ensure that images are properly registered before making their comparisons.3,4 Their invalid data obfuscate the ability to understand the actual mechanism of accommodation and presbyopia.5 
References
Croft MA, McDonald JP, Katz A, Lin TL, Luetjen-Drecoll E, Kaufman PL. Extralenticular and lenticular aspects of accommodation and presbyopia in human and monkey eyes. Invest Ophthalmol Vis Sci. 2013; 54: 5035–5048. [CrossRef] [PubMed]
Croft MA, Nork TM, McDonald JP, Katz A, Luetjen-Drecoll E, Kaufman PL. Accommodative movements of the vitreous membrane, choroid, and sclera in young and presbyopic human and nonhuman primate eyes. Invest Ophthalmol Vis Sci. 2013; 54: 5049–5058. [CrossRef] [PubMed]
Schachar RA, Tello C, Cudmore DP, Liebmann JM, Black TD, Ritch R. In vivo increase of the human lens equatorial diameter during accommodation. Am J Physiol. 1996; 271(3 Pt 2): R670–R676. [PubMed]
Schachar RA, Kamangar F. Computer image analysis of ultrasound biomicroscopy of primate accommodation. Eye. 2006; 20(2): 226–233. [CrossRef] [PubMed]
Schachar RA . The Mechanism of Accommodation and Presbyopia. Amsterdam: Amsterdam Kugler Publications; 2012.
Figure 1.
 
Reproduction of the left-sided UBM images of Fig. 2 from Croft et al.2 with arrows and labels added for clarification. Note: the corneal lengths are different, indicating the imaging plane (axis) changed between the unaccommodated and accommodated images.
Figure 1.
 
Reproduction of the left-sided UBM images of Fig. 2 from Croft et al.2 with arrows and labels added for clarification. Note: the corneal lengths are different, indicating the imaging plane (axis) changed between the unaccommodated and accommodated images.
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