Method for manufacturing toric contact lenses
A method of manufacturing of an astigmatic contact lens having a toric portion and a ballast portion such that said ballast portion causes the toric portion of the contact lens to properly orient in the eye of the wearer. The toric lenses are manufactured by an effective process control method for cylinder axis angle in toric lens production by modifying the target cylinder angle for mold rotation by eliminating the accumulative cylinder axis error from all previous steps including tool making, tool assembly, and molding. The amount modifying the target angle is determined by accurately determine the true cylinder axis on the corresponding mold by using a high-resolution interferometer, such as FISBA FS10M or equivalent models from Trioptics μShape® vertical series.
1. A method for manufacturing a toric contact lens, the method comprising the steps of:
a. Injection molding to form an anterior mold section and a posterior mold section, wherein the posterior mold section or the anterior mold section has a toric portion and the other mold section has a prism ballast, wherein each mold has a tab or other locating features for facilitating a determination of orientation of the mold,
b. measuring a cylinder axis angle error of the mold section having the toric portion by an interferometer apparatus, wherein the cylinder axis angle error is defined as a difference of measured cylinder axis angle by the interferometer apparatus and a reference cylinder axis angle defined by the tab position or other locating features,
c. determining an actual amount of rotation angle by subtracting the cylinder axis angle error from a target axis angle,
d. rotating one of the mold sections by the actual amount of rotation angle, while the other molding section is not rotated,
e. introducing a lens forming material into the mold section being rotated or the other mold section being not rotated after step d of rotating one of the mold sections,
f. assembling the anterior mold section and the posterior mold section to form a lens shaped cavity there between,
g. curing the lens forming material in the lens shape cavity to form the toric lens.
2. The method of claim 1 , further comprising a step of repeating the steps d to g to finish a manufacturing batch.
3. The method of claim 1 , wherein the posterior mold section has the toric portion and the anterior mold section has the prism ballast.
4. The method of claim 1 , wherein the anterior mold section has the toric portion and the posterior mold section has the prism ballast.
5. The method of claim 1 , wherein the lens forming material comprises at least one member selected from the group consisting of a hydrophilic vinylic monomer, a silicone containing vinylic monomer, a silicone-containing prepolymer, a hydrophilic prepolymer free of silicone, and combinations thereof.
6. The method of claim 1 , wherein the curing step is performed by an ultraviolet curing.
7. The method of claim 1 , wherein the curing step is performed by a thermal curing.