Method and apparatus for the measurement of the refraction index of a hydrogel contact lens
The invention is generally directed to an apparatus and a method for measuring a refractive index of a soft contact lens under a consistent pressure.
1. A method for measuring a refractive index of a hydrogel contact lens using a critical-angle refractometer comprising a flat prism interface surface, a light source that radiates light to the interface surface and a photoelectric sensor for receiving light reflected from the interface surface, the method comprising:
a) adding a solution to a cavity, wherein the cavity is located on the top surface of the refractometer, concavely shaped and contains the flat prism interface at the bottom, and the prism has a small effective detection area,
b) placing the hydrogel contact lens on the top of a flat zone of a contact lens arm fixture which is pivotally connected to the refractometer,
c) pivotally turning the hydrogel contact lens arm fixture toward the cavity to contact the hydrogel contact lens with the liquid and the flat prism interface in the cavity, wherein the hydrogel contact lens maintains at saturating state by the liquid,
d) applying a predetermined pressure on the hydrogel contact lens arm fixture to contact the hydrogel contact lens with the flat prism interface under the pressure,
e) activating the critical-angle refractometer to measure the refractive index of the hydrogel contact lens after the step of d).
2. The method of claim 1 , wherein the solution is saline.
3. The method of claim 2 , wherein the predetermined pressure is from 1 PSI to 20 PSI.
4. An apparatus for measuring a refractive index of a hydrogel contact lens comprising:
a refractometer, wherein the refractometer having a cavity to hold a solution and the hydrogel contact lens, wherein the cavity is concavely shaped to hold a liquid, temperature controlled, and contains a flat prism interface,
a refractometer fixture configured to be connected to the refractometer,
wherein the refractometer fixture comprising:
a fixture stage plate connected to the refractometer,
a fixture arm pivotally connected to the fixture stage plate which is adjustable X, Y, and Z positions,
a hydrogel contact lens fixture connected to the fixture arm and is pivotally moveable to apply a predetermined pressure to the hydrogel contact lens against the prism.
5. The apparatus of claim 4 , wherein the solution is saline.
6. The apparatus of claim 5 , wherein the predetermined pressure is from 1 PSI to 20 PSI.