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O. A. Candia, C.-W. M. Kong, R. Gerometta; Changes in Rabbit and Cow Lens Shape and Volume under Anisotonic Conditions. Invest. Ophthalmol. Vis. Sci. 2009;50(13):4390.
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© ARVO (1962-2015); The Authors (2016-present)
To determine if a range of anisotonic conditions could simulate lens shape changes in accommodation. In vivo, human lenses accommodate over the course of decades at least 106 times, a process involving completely reversible changes in shape, and possibly volume. We recently reported that lens volume could be calculated from lateral photographs. In this work, we characterized tonicity-evoked changes in lens shape and volume. Earlier work measuring lens hydration incubated lenses under anisotonic conditions for hours, and the altered hydration state was irreversible.
Based on lens topology, we developed an approach that allows volume determination from the lens cross-sectional area (CSA). The CSA was obtained from photographs taken perpendicularly to the anterior-posterior (A-P) axis and computed with software. From the same digital images, the A-P length between the polar surfaces and the equatorial diameter (ED) were also measured. This approach was described in detail in Gerometta et al. (AJP, 2007).
The A-P length of isolated rabbit and cow lenses increased under hypotonic conditions (-40 to -100 mOsM), with less extensive, or no change, in ED. The effects of hypertonic conditions (+50 to +100 mOsM) were tested on rabbit lenses, which primarily exhibited a reduction in ED, while the A-P length was only marginally reduced. Under hypotonic conditions, rabbit lenses increased their volume from 352 ± 3.2 mm3 (n= 8) to 358 ± 4.4 at -40 mOsM (P< 0.05, as paired data), and increased to 367 ± 4.4 mm3 (P< 0.05) when the media was sequentially reduced to -100 mOsM from the control tonicity. These volumes were measured 20 min after the tonicity shift. The volume reverted to 362 ± 4.5 mm3, 20 min after the control bath was restored. Similar proportional changes were obtained with 5 cow lenses. Under hypertonic conditions (+50 and +100 mOsM), lens volumes declined by 1% and 3% respectively from the control value (372 ± 6.5 mm3, n= 8, P< 0.01). The shrunken lenses did not recover their volume when measured 20 min after restoring the control tonicity. All osmotically elicited effects included irreversible changes in lens shape; lenses characteristically became more "circular".
Using methods developed for determining rapid changes in lens shape and volume, small changes in volume were measured minutes after a tonicity shift. However, the shifts used were too large to obtain volume and shape recoveries within the time frame of the present experiments. This underlines the small range under which lens shape can be reversibly changed. It appears likely that reversible volume changes may be obtained with shorter exposure to the external forces.
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