The Phase Focus Virtual Lens® operates in both reflection and transmission modes. For examples of optical reflection metrology applications, see Metrology.
Ophthalmic lens characterisation is an exemplar application of Virtual Lens transmission mode metrology. The benefits demonstrated for contact lens imaging are also applicable to the imaging and quality assurance of hydrogels in general.
Contact lens thickness is a critical determinant of oxygen delivery to the cornea, and is difficult to measure using conventional technologies, especially for torics. Particular challenges are faced in measuring contact lens properties in their natural hydrated state.
Very similar needs exist in the high-value intra-ocular lens markets.
The simplest optical arrangement relevant for transmission metrology consists of a coherent light source; a moveable X-Y stage; an aperture; and a detector.
Appropriate adjustments to the data acquisition parameters enable high resolution thickness measurements of lens edges, or of the whole lens.
Phase Focus Virtual Lens® benefits for ophthalmic lens metrology include:
- Non-contact
- Non-destructive
- Measurements in natural hydrated state
- Whole lens vs. high-resolution edge thickness profiling
- Thickness resolution <0.1µm
- User-selectable scan area and resolution. E.g. (typical):
- Lens edge area (1mm x 1mm) with 1µm lateral resolution
- Whole lens area with 20µm lateral resolution
- “Point-and-click” operation
- Performance is essentially operator-independent
- Straightforward integration with existing non-contact optical metrology tools
- Potential for integration as an on-line process control tool
