Download New Diagnostic Modalities for Dry Eye Syndrome

COVER STORY
New Diagnostic
Modalities for
Dry Eye Syndrome
A look at novel and precise methods for assessing dry eye.
BY PAUL M. KARPECKI, OD
T
raditionally, one of the most difficult ocular
conditions to diagnose is dry eye syndrome.
Although beneficial, much of the standard testing that eye care specialists have employed over
the years (such as the Schirmer’s test, corneal staining,
and the tear film breakup time test) have a specificity of
less than 30% in accurately diagnosing dry eye.1,2
Symptom questionnaires are the most common assessment tests,3 but unfortunately, studies have shown
them to be a relatively unreliable measure of dry eye
syndrome owing to a very poor relationship between
these tests and symptoms.4 For example, in one study,
quality-of-life scores of patients with dry eye either
showed no correlation to dry eye signs or appeared to
disagree.5 Some researchers hypothesize that, in dry eye
syndrome, the cornea may become neurotrophic, which
affects symptoms. Additional factors are downregulation and the overlap of dry eye symptoms with those of
other entities such as lid disease, allergy, and even
asthenopia.
Fortunately, new and more accurate diagnostic tests are
available to help in the assessment of dry eye syndrome.
OSMOLARITY CALCULATOR
Osmolarity is the gold standard for diagnosing dry eye
disease.6 Osmolarity is essentially the balance of solutes
to solution in the tear film and is likely the first indicator
of dry eye disease.7 Until recently, however, eye care specialists had no way to consistently measure this parameter. The TearLab Osmolarity System (TearLab
Corporation, San Diego, CA) is a nanotechnology-based,
point-of-care diagnostic instrument that can measure
osmolarity noninvasively in about 10 to 20 seconds.
In one study, this lab-on-a-chip technology measured
osmolarity at a 95% correlation to the more complex,
gold standard osmometers.8 It also has a positive predic42 ADVANCED OCULAR CARE OCTOBER 2010
“Readily implemented in refractive
and cataract practices, topography
is not often used as a tool for
assessing dry eye disease.”
tive value of disease severity in the 90% range (94%
specificity) versus 30% and under for other commonly
used dry eye tests, as mentioned earlier.9 The TearLab
Osmolarity System test is much easier on the patient
and requires only 50 nL of tear fluid—a volume hundreds of times smaller than used in standard laboratory
osmometers. Thus, even a patient with Sjögren’s syndrome and a severe aqueous deficiency will have sufficient tears for an osmolarity measurement.
Testing can be conducted by the doctor or a technician. As a reference, normal osmolarity measurements
on healthy eyes are less than 308 mOsm/L and tend to
show consistent readings between the patient’s two
eyes (ie, a difference of no more than 15 mOsm/L
between eyes). Readings over the 308 mOsm/L range
are significant for mild-to-moderate dry eye, and readings higher than 325 mOsm/L indicate severe dry eye
disease. When patients have symptoms but osmolarity
readings of less than 308 mOsm/L, they may have allergies, inflammatory ocular conditions, infections, or even
asthenopia rather than dry eye syndrome.
TOPOGRAPHY CALCULATOR
Readily implemented in refractive and cataract practices, topography is not often used as a tool for assessing dry eye disease. Most technicians tell patients, “Blink
and then hold your eyes open.” Consistently making this
recommendation allows for a relatively accurate diag-
nostic test, because in essence, a tear film breakup test is being performed.
If within those few seconds the mires on the Placido ring’s reflection begin
to blur or become distorted, the pattern will appear on the topographic
image. Systems with significant sensitivity such as the iTrace (Tracey
Technologies, Houston, TX), Pentacam Comprehensive Eye Scanner
(Oculus, Inc., Lynnwood, WA), and Orbscan (Bausch + Lomb, Rochester,
NY) appear to capture these images well. Because the iTrace’s ray-tracing
technology gives very accurate wavefront aberrometry measurements and
refractive images, and because it can separate corneal from lenticular aberrations, cornea-specific distortions can be readily identified. Irregularities in
the pattern indicate a poor-quality tear film or poor ocular coverage.
Some companies have used imaging technology specifically to obtain dry
eye measurements. For example, the Oculus Keratograph (Oculus, Inc.) has
scanning software for noninvasively assessing the tear film. Changes in the
projected Placido rings show where the tear film is breaking up, within a
certain number of seconds of a blink, and the data are produced in an
image showing the areas of tear film instability or dry spots. The device
also measures the height of the tear meniscus. Normative data suggest
that the height in a normal eye is greater than 0.2 mm. That measurement
combined with the noninvasive tear breakup scan can point to dry eye
syndrome.
CONCLUSION
Anterior segment optical coherence tomography (Visante OCT; Carl Zeiss
Meditec, Inc., Dublin, CA) also appears to have the ability to measure the
height of the tear film meniscus and may in the future give eye care specialists an indication of the tear film’s quantity and quality. Other technologies
in development include infrared imaging of the meibomian glands for plugging and atrophy.
New diagnostic modalities such as osmolarity testing and imaging technology are greatly increasing the accuracy of dry eye diagnosis. Because the
ocular surface is key to accurate refractions and successful outcomes after
cataract and refractive surgery, more accurate early diagnoses of dry eye
syndrome will lead to prompt treatment and happier patients. ■
Paul M. Karpecki, OD, is the clinical director of the Ocular Surface
Disease Center at Koffler Vision Center in Lexington, Kentucky. He is
a paid consultant to Bausch + Lomb, he serves on TearLab
Corporation’s Board of Directors, and he is on the speakers’ bureau
for Oculus, Inc., and Carl Zeiss Meditec, Inc. He stated that he holds
no financial interest in the products mentioned herein. Dr. Karpecki may be
reached at [email protected].
1. Bell AJ,Sejnowski TJ.The “independent components”of natural scenes are edge filters. Vision Res.1997;37(23):3327-3338.
2. Nichols KK,Nichols JJ,Zadnik K.Frequency of dry eye diagnostic test procedures used in various modes of ophthalmic practice. Cornea.2000;19(4):
477-482.
3. Nichols KK,Nichols JJ,Mitchell GL.The lack of association between signs and symptoms in patients with dry eye disease. Cornea.2004;23(8):762-770.
4. Mizuno Y,Yamada M,Miyake Y.Association between clinical diagnostic tests and health-related quality of life surveys in patients with dry eye syndrome.
Jpn J Ophthalmol.2010;54(4):259-265.
5. The definition and classification of dry eye disease:report of the Definition and Classification Subcommittee of the International Dry Eye Workshop (2007).
Ocul Surf.2007;5(2):75-92.
6. Sullivan BD,Whitmer D,Nichols KK.An objective approach to dry eye disease severity. Invest Ophthalmol Vis Sci.2010.
http://www.iovs.org/cgi/rapidpdf/iovs.10-5390v1.Accessed August 31,2010.
7. Yildiz Eh,Fan VC,Banday H,et al.Evaluation of a new tear osmometer for repeatability and accuracy,using 0.5-microL (500-nanoliter) samples. Cornea.
2009;28(6):677-680.
8. Tomlinson A,Khanal S,Ramaesh K,et al.Tear film osmolarity:determination of a referent for dry eye diagnosis. Invest Ophthalmol Vis Sci.2006;47(10):
4309-4315.
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