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Am J Physiol Cell Physiol 293: C1727-C1728, 2007; doi:10.1152/ajpcell.00266.2007
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LETTERS TO THE EDITOR

Ocular lens does not change volume during accommodation

TO THE EDITOR: Using the change in half of the cross-sectional area (CSA) of profile photographs of in vitro bovine lenses, Gerometta et al. (5) calculated the change in volume of the lenses in response to equatorial traction. For this calculation the authors used the theorem of Pappus (7):

Formula 1(1)
where d is the distance between the center of masses of the two symmetrical halves of the CSAs. Critical to the use of this theorem is the determination of the exact center of mass of each CSA (6, 7). The authors did not specify how the center of mass was determined nor the accuracy, precision, and variation of this measurement in the bovine lens.

There are additional significant deficiencies with the design and execution of the authors’ study. First, to support the bovine lens the authors used cyanoacrylate glue to attach the iris and ciliary body to a rubber washer. The authors did not control for the effects of the fumes generated by the cyanoacrylate glue (3) on the shape and permeability of the bovine lens capsule.

Second, they state: "the visual axis of the photographic camera was on a perpendicular plane with respect to the A-P axis of the lens; validated by determining that the two CSAs were symmetrically identical and that each CSA was a minimum." The fallacy in this approach can be appreciated by noting that simple rotation of the lens around its equatorial axis would cause the CSA to minify and remain symmetrically identical. Three-dimensional, positional references are needed to provide a reliable way of ensuring that the lens did not rotate between photographs.

Third, since the ciliary body and expandable ring were completely intact around the entire circumference of the bovine lens equator, it is not apparent how the authors were able to image the complete profile of the lens through just the aperture of the supporting aluminum plate (see Fig. 3 in Gerometta et al.). Did the authors interpolate the position of the bovine lens equator where its edge was blocked by the ciliary body and the expandable ring?

Fourth, the cross-sectional profile of the relaxed (accommodated) in vitro bovine lens shown in their Fig. 4 (reproduced herein in as Fig. 1) does not demonstrate the flattening of the peripheral anterior surface of the lens that has been observed during human in vivo accommodation by the reflection of light from the anterior surface of the lens (4, 14), Scheimflug photography (2), and optical coherence tomography (OCT) (9). The authors images actually demonstrate the opposite of the in vivo observations (Fig. 3 in Ref. 5), confirming that their experiments are not representative of in vivo accommodation.


Figure 1
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  		Fig. 1. Reproduction of Gerometta et al.'s (5) Fig. 4 with notes and arrows for emphasis. Note that unlike the flattening of the peripheral curvature that occurs during in vivo human accommodation, the anterior peripheral curvature of the relaxed bovine lens is steeper than the anterior peripheral curvature of the stretched lens; i.e., opposite the in vivo observations.

 
Fifth, the authors’ used dimensional data given by Rosen et al. (10) to predict volume changes of in vitro human lenses. A subsequent study by members of this same group (1) demonstrated that Rosen's et al. (10) data were unreliable. They indicated that to assess whether measurements of in vitro lenses are correct, it is necessary "to determine if swelling has taken place before acceptance of data" (1). Gerometta et al. (5) did not meet this prerequisite for their bovine lens study and used Rosen's et al. (10) faulty human lens data.

Finally, the authors used the magnetic resonance imaging studies of Strenk et al. (12, 13) to support their calculations. The Strenk et al. (12, 13) studies failed to incorporate the essential positional references required to demonstrate image correspondence before making their measurements (8), and their calculations of lenticular CSA were, consequentially, unreliable (6, 11).

Because of the above deficiencies, the authors’ study does not provide any reliable information concerning volume change of the lens with accommodation. Conclusions concerning the mechanism of accommodation cannot be based on this study.

FOOTNOTES


Address for reprint requests and other correspondence: R. A. Schachar, PO Box 601149, Dallas, TX 75360 (e-mail: ron{at}2ras.com)

REFERENCES

1. Augusteyn RC, Rosen AM, Borja D, Ziebarth NM, Parel JM. Biometry of primate lenses during immersion in preservation media. Mol Vis 12: 740–747, 2006.[Web of Science][Medline]

2. Dubbelman M, Van der Heijde GL, Weeber HA. Change in shape of the aging human crystalline lens with accommodation. Vision Res 45: 117–132, 2005.[CrossRef][Web of Science][Medline]

3. Edwards HGM, Day JS. Fourier transform Raman spectroscopic studies of the curing of cyanoacrylate glue. J Raman Spectr 35: 555–560, 2004.[CrossRef]

4. Fincham EF. Mechanism of accommodation, Br J Ophthalmol 8, Suppl: 2–80, 1937.

5. Gerometta R, Zamudio AC, Escobar DP, Candia OA. Volume change of the ocular lens during accommodation. Am J Physiol Cell Physiol 293: C797–C804, 2007.[Abstract/Free Full Text]

6. Judge SJ. The MRI data of Strenk et al. do not suggest lens compression in the unaccommodated state (eLetter). Invest Ophthal Vis Sci (http://www.iovs.org/cgi/eletters/45/2/539#149, May 6, 2004).

7. Leithold L. The Calculus With Analytic Geometry (2nd ed). New York: Harper & Row, 1972.

8. Levy N. Comparing MRIs with movement artifact (eLetter). Invest Ophthal Vis Sci (http://www.iovs.org/cgi/eletters/40/6/1162#7, Dec 28, 1999).

9. Li Y, Chalta MR, Huang D. Measurement of lens curvature change during accommodation with high-speed optical coherence tomography (e-Abstract). Invest Ophthalmol Vis Sci 46: 2554, 2005.

10. Rosen AM, Denham DB, Fernandez V, Borja D, Ho A, Manns F, Parel JM, Augusteyn RC. In vitro dimensions and curvatures of human lenses. Vision Res 46: 1002–1009, 2006.[CrossRef][Web of Science][Medline]

11. Schachar RA. Change in intralenticular pressure during accommodation (eLetter). Invest Ophthal Vis Sci (http://www.iovs.org/cgi/eletters/45/2/539#213, Jan 3, 2005).

12. Strenk SA, Semmlow JL, Strenk LM, Munoz P, Gronlund-Jacob, DeMarco JK J. Age-related changes in human ciliary muscle and lens: a magnetic resonance imaging study. Invest Ophthalmol Vis Sci 40: 1162–1169, 1999.[Abstract/Free Full Text]

13. Strenk SA, Strenk LM, Semmlow JL, DeMarco JK. Magnetic resonance imaging study of the effects of age and accommodation on the human lens cross sectional area. Invest Ophthalmol Vis Sci 45: 539–545, 2004.[Abstract/Free Full Text]

14. Tscherning M. Physiological Optics (2nd ed). Keyston: Philadelphia, PA, 1904.


Ronald A. Schachar1
Guojun G. Liao2
 1Department of Physics and 2Department of Mathematics
University of Texas at Arlington
Arlington
Texas





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