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

2/22/96 Chapter 6 Vision Assessment page 6-8
At each Study Visit a sphero-cylindrical over-refraction is performed on all CLEK
Study patients who wear contact lenses. The over-refraction procedure is exactly the
same as in Sections 6.2 or 6.3 above. If the over-refraction is plano, it is recorded on the
CLEK Examination Form as 00.00. Plano trial lenses (or +0.12 D and –0.12 D) are
inserted into the trial frame, and visual acuity is measured according to protocol.
In non-rigid contact lens wearing CLEK Study patients, a sphero-cylindrical
over-refraction is also performed (Sections 6.2 and 6.3 above). This sphero-cylindrical
over-refraction must be over a contact lens from the CLEK Study Trial Lens Set equal in
base curve to the steep keratometric meridian. If a referring corneal surgeon requests
that no rigid contact lenses be placed on a grafted eye, that request must be honored.
However, it is optimal to perform all required CLEK Study procedures on all eyes of all
patients.
For non-rigid contact lens wearers only, keratometry is performed to select the
appropriate contact lens (with base curve equal to the steep keratometric reading) for
over-refraction and best-corrected visual acuity measurement.
Note: The lens used for the steep keratometry/visual acuity measurement is also
the first lens used in the First Definite Apical Clearance Lens protocol (Chapter 9), and
its central and peripheral fluorescein patterns can be assessed at the same time.