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

2/1/99 Chapter 1 Background page 1-7
information on role limitations that cannot be inferred from other clinical measures.
Several instruments for measuring quality of life were considered, including the
Sickness Impact Profile and the Index of Well-Being, in addition to the Medical
Outcomes Study Short Form (MOS SF-36). Furthermore, specific depression scales like
the Beck Depression Scale and the Community Epidemiological Study Depression Scale
(CES-D) were considered because of the widely held belief that keratoconus patients are
at higher risk of depression and anxiety. (Mannis et al., 1987; Swartz et al., 1990;
Besançon et al., 1980). 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 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 since large degrees
of impairment are likely to be rare. (3) The instrument needs to measure several
dimensions of well-being. We considered using the CES-Depression scale in addition to
the SF-36; however, results using the CES-Depression scale that were administered at
the same time as the SF-36 in the CLEK pilot study showed absolutely no trend for
increased risk of depression in the total score for the CES-D or in the mental health and
emotional role functioning scale of the SF-36. Thus, the measurement of emotional
functioning does not justify a separate instrument like the CES-D. (4) We desire a scale
that could be self-administered without compromising reliability. (5) We desire an
instrument with strong psychometric properties including good factor structure, high
internal consistency reliability, high test-retest reliability, and good external validity.
For these reasons, the Medical Outcomes Short Form with 36 items (SF-36) was selected.
In addition to the SF-36 scale, the vision specific scale will be administered.
Vision specific scales developed by the following investigators were reviewed: (1)
Haase and Bryant (1973); (2) Bernth-Peterson (1981); (3) Javitt et al. (1993); (4) Mangione
et al. (1992); (5) Sloane et al. (1992). The Javitt Visual Function Questionnaire (Javitt,
1993) was selected because the format of questions resembles the SF-36, which reduces
response errors, and because it has high test-retest reliability.
The National Eye Institute Visual Function Questionnaire is administered
beginning in the first year of follow-up in the CLEK Study (Mangione et al., 1998).
1.2 Specific Aims of the Collaborative Longitudinal Evaluation of Keratoconus
(CLEK) Study
This multi-center observational study, the Collaborative Longitudinal Evaluation