Abstract
Purpose :
The current commercially available phoropter that is used in clinic is bulky and is not user friendly (cannot be operated by the subject). The measurement is not accurate enough either as the increment power of the individual lenses is 0.25D (diopter). It would be attractive to develop a compact photopter with continuously tunable power which can be operated by the subject himself/herself. Such a compact lens with continuously tunable power from positive to negative values can also be used for various vision corrections, including presbyopia, myopia, hyperoper, and low vision. Here we present a demonstration of the adaptive Alvarez lens that is made in our lab and meets these requirements.
Methods :
Alvarez lens is a type of varifocal composite lens that is based on lateral shift of two transmissive refractive plates, each having a plano surface and a surface shaped in a two-dimensional cubic profile. The two cubic surfaces are conjugate, rotationally asymmetric, and aspheric. They are made and mounted to be the inverse of each other, so that when both plates are placed with their vertices on the optical axis, the induced phase variations cancel out and there is no power. However, a relative lateral translation of one plate results in a quadratic phase profile—or, in other words, optical power. In this first demonstration, tunable spherical power is considered and the cubic profile was selected as z(x,y)=A(xy2+x3/3), where A = 0.004 mm-2. For 20 mm aperture, the peak-to-valley difference in z direction across this area is 0.3771 mm. The two plates were fabricated in house using a diamond turning machine.
Results :
In this example, the power of the overlapped area is equal to 0.8δx diopter, where δx is the offset between the two plates. This indicates that, when the offset between the two plates is changed from -10mm to 10 mm, the power can be continuously tuned from -8D to +8D. An optical testing setup with fine mechanics was built to mount and test the Alvarez lens. For the lens with 20 mm aperture, linear power change has been observed for the offset range [-3 mm, +3 mm]. Larger offset range will be applied to lenses with larger aperture in the near future. Visual acuity testing experiments will be performed using a model eye.
Conclusions :
The adaptive Alvarez lens with 20 mm aperture and continuously tunable power has been designed, fabricated, and tested. It is promising for visual assessment and correction.
This is an abstract that was submitted for the 2017 ARVO Annual Meeting, held in Baltimore, MD, May 7-11, 2017.