discovering dry eye
The
Ups and Downs of Clinical Grading
BY JASON J. NICHOLS,
OD, MPH, PHD
Clinical grading of contact lens complications
can prove difficult at times — especially when more than one practitioner
is involved — because of the subjective nature of most clinical grading. Further
complicating the issue is the tremendous variability in the presentation of lens-related
complications and tear film abnormalities, added to the fact that practitioners
vary in training and expertise relative to these outcomes. Finally, we see many
different facets or presentations of contact lens complications and tear film disorders
that we need to assess as they all relate to the severity, treatment and prognosis
of the condition. For example, we can grade corneal fluorescein staining in terms
of its
extent as well as of its depth, type and location.
Statistically Speaking
It's important to think
about subjective clinical grading in somewhat of a statistical sense to make improvements.
For example, you can sum up clinical grading or measurements as a "true value" plus
an "error" term. You can further break down this error term into systematic error
(bias) and non-systematic error (random noise). It's important that we limit error
associated with the true value, which ultimately makes our estimate more precise (closer to the
true value).
For an individual grader who is
consistent, most of the error associated with his grading results from random noise,
or human variability. But, when we compare two or more graders (between-examiner
reliability), more error occurs because of noise and bias between examiners.
Improving Reliability
We can improve the reliability
of clinical grading in several ways. We could attempt to objectify clinical measurements.
For instance, many studies and techniques have objectified traditionally subjective
measurements such as bulbar hyperemia and tear breakup time. We could also train
examiners, which often occurs during a practitioner's clinical training or at the
outset of a new study. Lastly, we could use grading scales, which provide some standardization
to the clinical grades, especially between examiners. Table 1 shows some of the
grading scales available.
Note that some grading scales use
photographic images, while others use artistic renditions. It's important
that practices employ only one grading scale for clinical practice, as
consistency in this regard is extremely important.
Dr. Nichols is
assistant professor of optometry and vision science at The Ohio State University
College of Optometry.
Contact Lens Spectrum, Issue: July 2005