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2/22/96 Chapter 9 Contact Lens Fit Assessment page 9-1
Chapter 9
Assessment of Habitual Contact Lenses and First Definite Apical Clearance Lens
(FDACL) Determination
9.1 Introduction
At each CLEK Study Visit, the Clinician will apply a series of CLEK Study trial
lenses, beginning with the lens with base curve equal to the steep keratometric reading,
until the first definite apical clearance fluorescein pattern is observed. This lens
represents the flattest lens that shows apical clearance—our so-called First Definite
Apical Clearance Lens or FDACL. This fluorescein pattern will be photographed, as will
the lens that is 0.2 mm flatter than the first apical clearance lens. This measurement
provides an estimate of corneal curvature as well as a measure of how flat or steep the
patient’s current lenses are and better defines the current standard of rigid contact lens
care in the CLEK Study sample.
The First Definite Apical Clearance Lens (FDACL) determination is made on all
CLEK Study patients, even those who do not currently wear rigid contact lenses.
FDACL is not required on eyes of CLEK Study eligible patients with corneal grafts. The
FDACL protocol should be followed on the non-grafted eye of these patients.
It is desirable to obtain data summarizing how the eye care community optically
manages its keratoconus patients. The most common method of managing keratoconus
is to fit the patient with rigid gas permeable contact lenses. Although many approaches
have been advocated in the literature, a standardized fitting method has not been
universally utilized. Screening results from a CLEK pilot study indicate that 75% of
keratoconus patients are wearing rigid contact lenses fitted flat or with apical touch.
Although we know that the majority of keratoconus patients are currently being fitted
flat, there are no data indicating the degree of apical touch. Also, there have been
various suggestions in reports in the literature as to the potential relationship between
certain fitting methods and corneal scarring. Therefore, to properly characterize the
habitual contact lens treatment of CLEK Study patients an assessment of the degree of
apical touch or apical clearance must be performed.
Data on habitual rigid lenses are obtained for all patients wearing rigid gas
permeable contact lenses at the time they are enrolled into the CLEK Study and at each
CLEK Study Visit. If the patient is fitted into rigid gas permeable contact lenses during
the course of his or her participation in the study, these data are collected at every
CLEK Study Visit after they are fitted. Enrolled CLEK Study patients who are not
habitual rigid contact lens wearers, eg, spectacle-only or soft contact lens wearers,
obviously are not assessed.