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

2/1/99 Chapter 2 Study Design page 2-10
to visual acuity loss (Yackels, 1991; Burger, 1990). Elevated corneal scars and associated
abrasions can prohibit the comfortable, long-term wear of rigid contact lenses
(Moodaley, 1991; Rosenthal, 1993). Corneal scars that either limit visual acuity or
decrease contact lens comfort can provide the rationale for surgical intervention (Sharif
and Casey, 1991).
The CLEK Photography Reading Center performs an independent, masked,
standardized assessment of the presence or absence of corneal scarring at every CLEK
Study Visit. It also maintains hard copy documentation that can be reviewed and reevaluated
when needed. In addition, photodocumentation of corneal scarring permits
monitoring of CLEK Study personnel to ensure that the protocol is being adhered to in a
standardized fashion. In the absence of photographic documentation, it would be
difficult to determine whether differences between Clinics in the rate of scarring
observed could be attributable to subtle shifts or differences in the criteria used by
Clinicians to assess scarring or to true differences in scarring rates.
2.5.4 Biomicroscopic Signs
Vogt’s striae and Fleischer’s ring have been poorly documented in keratoconus
(Lass et al., 1990). The significance of these pathognomonic signs of the disease in terms
of disease staging or disease prognosis has never been determined. Although the
presence of one of these signs and/or corneal scarring in at least one eye is a CLEK
Study entry criterion, many eyes will not have one or more of these signs and will
enable us to evaluate their importance longitudinally.
Corneal staining may be an indicator of compromised corneal epithelium
integrity in keratoconus, especially in contact lens wearers (Maguen, 1983; Korb, 1982).
Many eyes in this study will show some degree of corneal staining, and the type and the
severity of corneal staining is assessed by the Clinician with slit lamp biomicroscopy at
each CLEK Study Visit. The Executive Committee felt that independent, photographic
assessment of corneal staining would not have been feasible. Indeed, corneal fluorescein
photography of CLEK pilot study patients revealed much variability of photograph
quality.
2.5.5 Quality of Life
We selected the MOS SF-36 and decided against the inclusion of an instrument
specific to depression. There are several reasons for these two decisions. (1)
Keratoconus is a chronic disease that does not severely compromise health status,
although keratoconus might result in impaired social and physical role functioning.
Results from the CLEK pilot study suggest that instruments that focus only on activities
of daily living that reflect physical functioning are insensitive to the role of the visual
impairment associated with keratoconus. The results from the CLEK pilot study
demonstrate the utility of assessing “role functioning” independently from “activities of
daily living.” (2) The instrument needs to be sensitive to small degrees of impairment