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):

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.

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.