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LETTERS TO THE EDITOR
General comments. The number of experiments was not 7; it was a total of 20 divided in 3 sets: 7 relaxed-stretched, 6 relaxed-stretched-relaxed (see Table 1 in Ref. 2), and 7 under oil (see Table 2 in Ref. 2).
We thank Drs. Schachar and Liao for pointing out the theorem of Pappus. We did not know about this theorem. Candia developed this property of certain bodies independently. Its application to the lens is novel. There was no attempt to ignore this reference and it should have been included in the paper.
Under the title "Calibration for Conversion of Pixels into Millimeters and Volume Determination" we said: "The needed dimensions and surfaces of the whole lens and its symmetrical halves, in both accommodative states, were obtained with ImageJ software (http://rsb.info.nih.gov/ij/) in pixels ...". This software gives the cross-sectional area (CSA) and the center of mass. To ascertain that equal CSAs were obtained from the same lens profile by the software, we indicated that "if the error was larger than 0.5%, the half lens would be disregarded and a new half lens outline would be cut, until it fell within the error set as standard", i.e., 0.5%. Clearly, we did indicate how the center of mass was determined and the possible error of the measurements. Thus the general comments of Drs. Schachar and Liao are baseless.
Specific answers. First, a thin circle of cyanoacrylate adhesive was applied over the rubber washer and the "stromal side of the iris-ciliary body". Thus the glue was relatively isolated from the lens capsule. Furthermore, we used the slow-setting (low solvent) gel form of the glue, not the liquid type. If solvent fumes reached the capsule, lens transparency would have been affected. However, the lenses were totally clear and transparent.
Second, Drs. Schachar and Liao seem to have misinterpreted our statement. We are not sure what they mean by the "equatorial axis". Let's be clear. First, we define a plane X, perpendicular to the A-P axis, that separates the anterior and posterior sides of the lens at its maximum equatorial distance. The A-P axis is a line that crosses the anterior and posterior poles of the lens. The optical axis of the camera is a line on the X plane. Now let's define plane Y as a plane perpendicular to plane X. If we rotate the lens around its A-P axis, the image on the camera will not change. The image would not change by rotating the optical axis of the camera around the lens without leaving plane X. We now find the intersection of planes X and Y and place the optical axis of the camera at that point. Rotating the optical axis on the Y plane changes the image. It will increase as the optical axis separates from the X plane and will reach a maximum when the camera is right on top of the lens. Continuing the rotation the image will decrease to a minimum when the optical axis is on the X plane. That is how we find the proper perspective for the optical axis. The lens did not rotate between photographs. There is no fallacy in our approach.
Third, Drs. Schachar and Liao are correct. There was about 1 mm (thickness of the rubber washer and ciliary body) that obstructed the view of the CSA close to the equator. However, we knew the length of the equatorial distance in millimeters (by using the plastic washer) and by the millimeters per pixels conversion factor. Thus, by interpolation, the profile could be accurately completed. This correction did not affect the equatorial length and the A-P length. These values may have an experimental error of 
1%. This was determined in preliminary experiments in which the totally isolated lens was photographed in a fixed position without any visual interruption. A second photograph was taken with the lens and camera in the same position after a ring was placed around the lens that obstructed its profile as in an actual experiment. Operators were asked to complete the profile. This completed profile matched within 1%, the view of the unobstructed lens.
Fourth, Drs. Schachar and Liao are using human lens data to predict bovine lens accommodation and conclude again that our experiments are not representative of in vivo accommodation. Fiber ends at the sutures in human and bovine lenses seem to be different (3), and this will affect how the lens deforms during accommodation. We clearly indicate in the paper that we are not concerned with accommodation, per se, but with possible changes in volume when the lens deforms in a manner that simulates accommodation.
Fifth, we used dimensions obtained by Rosen et al. (4) on in vitro human lenses to model our accommodated human lens. We could not find any validity in the allegation that the paper by Augusteyn et al. (1) "demonstrated" that the data acquired by Rosen et al. was "unreliable". Rather, Augusteyn and colleagues in their studies on the different bathing media in post mortem lenses "recommend that lenses be assessed to determine if swelling has taken place ...". Furthermore, Rosen et al. emphasized that "Lens capsule integrity was visually inspected using the optical comparator ..." and continued, "... if cataractous changes were present, the lens was excluded from the study." In the bovine lens, we determined that the lens recovered its initial dimensions and volume after stretching and relaxation (see Table 1 of Ref. 2). Dr. Schachar and Dr Liao's comments on these points are inaccurate.
Finally, we did not use the studies of Strenk et al. (6) to support our calculations. We pointed out that, just like us, they determined a clear change in CSA. They suggested that the volume also changed. Their contention that "the lens CSA increased with accommodation" and that "these accommodative changes in CSA reflect accommodative changes in lens volume" cannot be ascertained without a third dimension that required the determination of the center of mass, which we did.
If Drs. Schachar and Liao cannot accept that there is a volume change, they are implying that during lens deformation, only the capsular surface changes. Although it is commonly assumed that only the surface changes at constant volume, there is no experimental data that has demonstrated such assumption. Since Drs. Schachar and Liao seem to be expert mathematicians and proficient in how experiments should be performed, we ask them to suggest a viable method to measure the capsular surface of the lens in its accommodative and nonaccommodative states.
FOOTNOTES
Address for reprint requests: O. A. Candia, Dept. of Ophthalmology, Mount Sinai School Of Medicine, New York, NY 10029 (e-mail: oscar.candia{at}mssm.edu)
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.[ISI][Medline]
2. 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.
3. Kuszak JR, Mazurkiewicz M, Jison L, Madurski A, Ngando A, Zoltoski RK. Quantitative analysis of animal model lens anatomy: accommodative range is related to fiber structure and organization. Vet Ophthalmol 9: 266–280, 2006.[CrossRef][ISI][Medline]
4. 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][ISI][Medline]
5. Schachar RA, Liao GG. The ocular lens does not change volume during accommodation (Letter to the editor). Am J Physiol Cell Physiol 293: C797–C804, 2007.
6. 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.
Oscar A. Candia
Department of Ophthalmology
Mount Sinai School Of Medicine
New York
New York
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