Ophthalmic optics — Contact lenses — Part 6: Mechanical properties test methods
1 Scope
GB/T 11417.6 specifies the test methods for mechanical properties of contact lenses including sizes.
This part is applicable to the test for mechanical properties of contact lenses.
2 Normative references
The following referenced documents are indispensable for the application of this document. For dated references, only the edition cited applies. For undated references, the latest edition (including any amendments) applies.
GB/T 2411-2008 Plastics and ebonite—Determination of indentation hardness by means of a durometer (shore hardness)
GB/T 11417.1-2012 Ophthalmic optics—Contact lenses—Part 1: Vocabulary, classification system and recommendations for labeling specifications
GB 11417.2-2012 Ophthalmic optics—Contact lenses—Part 2: Rigid contact lenses specification
GB 11417.3-2012 Ophthalmic optics—Contact lenses—Part 3: Soft contact lenses
GB/T 11417.4-2012 Ophthalmic optics—Contact lenses—Part 4:Saline solution for contact lens testing
3 Terms and definitions
For the purposes of this document, the terms and definitions given in GB/T 11417.1-2012 apply.
4 Determination of radius of curvature
4.1 General
There are two generally accepted instruments for determining the radius of curvature of rigid contact lens surfaces. These are the optical microspherometer (see 4.2) and the ophthalmometer with contact lens attachment (see 4.3).
The ophthalmometer method (see 4.3) measures the reflected image size of a target placed a known distance in front of a lens surface, and the relationship between curvature and magnification of the reflected image is then used to determine the back optic zone radius.
Note: The ophthalmometer may also be used for measurement of hydrogel contact lenses, see Table 1.
Ultrasonic, mechanical, and optical measurements of sagittal depth are applicable to hydrogel contact lens surfaces (see 4.4 and Table 1), but are generally not recommended instead of radius measurement for rigid spherical surfaces. Sagittal depth of rigid aspheric surfaces can be useful, however, as indicated in 4.2.4.
Table 1 Test methods, application and reproducibility
4.2 Optical microspherometer
4.2.1 Principle
The optical microspherometer locates the surface vertex and the aerial image (centre of curvature) with the Drysdale principle, as described below. The distance between these two points is the radius of curvature for a spherical surface, and is known as the apical radius of curvature for an aspheric surface derived from a conic section. The optical microspherometer can be used to measure radii of the two primary meridians of a rigid toric surface, and with a special tilting attachment, eccentric radii can be measured as found in the toric periphery of a rigid aspheric surface.
The optical microspherometer consists essentially of a microscope fitted with a vertical illuminator. Light from the target T (Figure 1) is reflected down the microscope tube by the semi-silvered mirror M and passes through the microscope objective to form an image of the target at T′. If the focus coincides with the lens surface, then light is reflected back along the diametrically opposite path to form images at T and T′′. The image at T′′ coincides with the first principle focus of the eyepiece when a sharp image is seen by the observer [Figure 1 a)]. This is referred to as the “vertex surface image”.
Foreword i
1 Scope
2 Normative references
3 Terms and definitions
4 Determination of radius of curvature
5 Diameter and widths
6 Thickness
7 Inspection of edges, inclusions and surface imperfections
8 Rigid lens flexural deformation and rupture
9 Hardness
