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I have for years, especially lately I have had patients wearing aspheric lenses complain of protien accumulations, fatique and sensation late in the day, more awareness of lenses than they had in spherical lenses. More sensation of foriegn bodies under lens. Increased allergy sensation. I have also noticed this in many aspheric soft lenses.
Now when I say the below it has been many years since I have manufactured contact lenses.
However I have noticed that in every case I can find very fine unpolished lathe marks in the anterior periphery of the lenses. This can also be a problem in molded lenses if the moud is not perfect. While these are very fine and only observable undermagnification with the proper lighting angles, they are there.
In the days when I did manufacture lenses this was caused by:
1: Polishing pads being too flat (causing the lens to be polished from the inside out as opposed to from the outside in.
2: Using polishing pads that are too soft (includes all foam pads).
3: Polishing pads that are too small and therefore not covering the periphery as well as the intermediate and central area.
4: Too short of a polishing time.
5: In adequate oscellation of polishing pads.
6: Lathe feed time too fast (should be much slower toward periphery of lens).
7: Lathe tool too dull (or sometimes lathe operator too dull).
If your patient has a problem, look for this. It's a good idea to include this in your inspection of the lens when you recieve it long before it is placed on an eye.
Chip
Now when I say the below it has been many years since I have manufactured contact lenses.
However I have noticed that in every case I can find very fine unpolished lathe marks in the anterior periphery of the lenses. This can also be a problem in molded lenses if the moud is not perfect. While these are very fine and only observable undermagnification with the proper lighting angles, they are there.
In the days when I did manufacture lenses this was caused by:
1: Polishing pads being too flat (causing the lens to be polished from the inside out as opposed to from the outside in.
2: Using polishing pads that are too soft (includes all foam pads).
3: Polishing pads that are too small and therefore not covering the periphery as well as the intermediate and central area.
4: Too short of a polishing time.
5: In adequate oscellation of polishing pads.
6: Lathe feed time too fast (should be much slower toward periphery of lens).
7: Lathe tool too dull (or sometimes lathe operator too dull).
If your patient has a problem, look for this. It's a good idea to include this in your inspection of the lens when you recieve it long before it is placed on an eye.
Chip
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