Design considerations for liquid crystal contact lenses

Abstract

Switchable liquid crystal contact lenses with electrically controllable focal powers have previously been investigated as an alternative to bifocal contact lenses and spectacles for the correction of presbyopia. The simplest lens design uses a meniscus shaped cavity within the lens to contain the liquid crystal. The design of such a lens is considered in detail, including the nematic alignment and electrodes materials. The organic transparent conductor PEDOT:PSS was used as both electrode and planar alignment. Four different configurations are considered, using both planar and homeotropic orientations with either homogenous or axial alignment. Controllable switching of the focal power was demonstrated for each mode and focal power changes of up to ΔP=3.3 ± 0.2 D achieved. Such lens designs offer significant potential for a novel form of correction for this common visual problem.

Switchable Liquid Crystal Contact Lenses for the Correction of Presbyopia

“…Equation (4) can be used to calculate the minimum gap within the LC layer ΔY, assuming that the refractive index is switching between ne and no. The plot in Figure 8 [38,42] shows the required ΔY (with an aperture radius x = 2.5 mm and an inner radius r1 = 7.8 mm) with respect to Δn' to enable ±1.5D, ±2.0D and ±2.5D changes in focal power. This demonstrates that the lens cavity spacing can be made lower if a LC with a larger Δn is used, which is the intuitive result.…”

“…Most lenses have been designed with alignment applied linearly, but axial and radial configurations have also been considered [37,38]. This arrangement reduces field-induced defects within the lens that cause unwanted scattering, by allowing the director to follow the circular symmetry of the alignment layers throughout the switching [38].…”

“…This arrangement reduces field-induced defects within the lens that cause unwanted scattering, by allowing the director to follow the circular symmetry of the alignment layers throughout the switching [38]. However, it is the most challenging alignment mode to manufacture.…”

“…Figure 6 illustrates how the shape and dielectric anisotropy of the LC layer must be considered when designing the device [38]. Figure 6a,b shows an LC layer with a positive meniscus, whereas (c) and (d) illustrate negative meniscus systems.…”

“…The dielectric anisotropy of the LC used and the shape of its lens cavity will predetermine how the device functions in the switched OFF state, V = 0; and ON, V >> VC, where VC is the Fréedericksz threshold dictated by the LC elastic constants and dielectric anisotropy and, importantly, is independent of cell gap. Figure 6 illustrates how the shape and dielectric anisotropy of the LC layer must be considered when designing the device [38]. Figure 6a,b shows an LC layer with a positive meniscus, whereas (c) and (d) illustrate negative meniscus systems.…”