OM t of c.iii - Vision Research Coordinating Center - Washington ...

2/22/96 Chapter 9 Contact Lens Fit Assessment page 9-5
Table 9-2. Tolerances of fabrication for CLEK Study Trial Lens Set
Parameter
Tolerance
Base curve radius
0.05 mm without distortion or
warpage
Power
0.25 D
Overall diameter
0.1 mm
Optic zone diameter
0.1 mm
Center thickness
0.02 mm
Surface quality
No surface quality degradation is accept
9.3 Verification of the CLEK Trial Contact Lens Set
It is important that CLEK Study trial lenses be verified throughout the Study to
confirm parameter stability. It is also imperative that after every use, each lens is
returned to its appropriate storage case. To monitor parameter stability and lens
labeling, all trial lens base curves must be verified monthly for base curve radius,
warpage, and correct storage. The CLEK Trial Contact Lens Verification Form is used to
record these findings at each Participating Clinic. It is completed monthly and stored
on-site.
The base curve radius can be verified using a radiuscope, keratometer, or
handheld keratometer. Trial lens base curves should not be warped by more than 0.02
mm and should not be more than 0.05 mm from the targeted or labeled value (Table 9-
2). If the base curve findings fall outside these targeted parameters, contact the
Chairman’s office for a replacement lens.
The following protocol is used for verifying the order and parameter stability of
the CLEK Study Trial Lens Set on a monthly basis by Clinic personnel certified for rigid
contact lens verification.
(1) Use a radiuscope, keratometer, or handheld keratometer to analyze the base
curve radius of each lens in the CLEK Study Trial Lens Set every month. The
measurement of other lens parameters is not required.
(2) Record the base curve radius in millimeters in the column labeled Analyzed
Base Curve Radius opposite the target or labeled value on the CLEK Trial
Contact Lens Verification Form.
(3) Any lens found in the wrong case should be transferred to the appropriate
case.
(4) Any lens analyzed as at least 0.06 mm different from the target measurement
on the lens case should be replaced. Report the lens to be replaced to the
Chairman’s Office.