Thermographer enables temperature measurement in screening for dry eye

Ocular surface temperature decreased more significantly in dry eyes than in healthy eyes 10 seconds after eye opening, study results show.

Masahiko Yamaguchi

A new thermographic imaging device enables clinicians to reliably measure ocular surface temperature in testing for dry eye and other ocular surface conditions, a study found.

The study authors evaluated the ocular surface thermographer (Tomey).

“The newly developed ocular surface-oriented thermography provides that anybody who is inexperienced in the device can obtain highly reliable results of ocular surface temperature easily,” Masahiko Yamaguchi, MD, PhD, said in an email interview. “Because this device is developed for eye temperature measurements, this one is more sensitive than past thermographers for the measurement of human body temperature.”

Previous studies showed that surface temperature was significantly higher in dry eyes than in healthy eyes, and that the temperature at the center of the cornea of dry eyes was lower than that of healthy eyes after sustained eye opening. However, using thermography to screen for dry eye proved difficult and time-consuming, Dr. Yamaguchi and colleagues said.

“Dry eyes have tear film instability. We think that the instability of the tear film in dry eyes increases the tear fluid evaporation, and then the heat of vaporization results in a decrease in ocular surface temperature in dry eyes,” Dr. Yamaguchi said.

The thermographer has infrared and visible-light cameras and built-in software for data analysis. The device’s optical head can be aligned with the pupil and operates at a fixed distance from the eye. Thermographic images and analytic charts, tables and graphs are displayed on a computer monitor.

“After measuring, the analysis is done automatically and the result is obtained quickly so that we can explain it to the patients on the same day,” Dr. Yamaguchi said.

The study was published in the American Journal of Ophthalmology.

Infrared and visible light

The prospective study included 30 eyes of 30 patients diagnosed with dry eye. Mean patient age was 52.9 years.

A comparator group included 30 eyes of 30 patients without dry eye, with a mean patient age of 42.7 years.

Patients with a history of atopy, allergic disorders, Stevens-Johnson syndrome, ocular or systemic disorders, previous ocular surgery, contact lens wear, or chemical, thermal or radiation injury were excluded.

Diagnosis of dry eye was based on three criteria: subjective symptoms identified during examinations or patient interviews, Schirmer 1 test results of less than 5 mm or tear breakup time of less than 5 seconds, and positive staining of the cornea and conjunctiva with fluorescein, rose bengal or lissamine green.

Control subjects had clear corneas and conjunctivae, with no signs or symptoms of dry eye or other ocular surface pathology.

Ocular surface temperature was measured in a standard examination room at a fairly consistent temperature, humidity and brightness. Temperature was measured immediately after eye opening and every second for 10 seconds of sustained eye opening.

Temperature was measured in the central cornea, nasal conjunctiva and temporal conjunctiva. The central cornea was defined as a 4-mm area at the center of the cornea. The nasal conjunctiva and temporal conjunctiva were defined as areas 2 mm in diameter.

Reliable measurements

Investigators calculated average temperatures for each region and measured body temperature after gauging ocular surface temperature.

Intraclass coefficients were calculated to determine the reliability of ocular surface temperature measurements. An intraclass coefficient greater than 0.7 denoted reliable measurement.

Investigators determined correlations between change in ocular surface temperature and tear breakup time, Schirmer 1 test values and fluorescein staining scores.

Study data showed that intraclass coefficients at 10 seconds were 0.958 for the central cornea, 0.926 for the nasal conjunctiva and 0.967 for the temporal conjunctiva. The measurements exceeded the threshold of reliability.

Promptly after eye opening, surface temperature of dry eyes did not differ markedly from that of control eyes. However, temperature decreased more significantly in dry eyes than in healthy eyes 10 seconds after eye opening. The difference was statistically significant (P < .001).

Decreased temperature of the cornea correlated strongly with tear breakup time (P < .001).

Dr. Yamaguchi said that the Tomey ocular surface thermographer may be used to measure ocular surface temperature in other clinical settings.

“There is a possibility that the device can be used to evaluate the function of a filtering bleb and the severity of ocular surface inflammation disease, such as conjunctivitis and infectious keratitis,” he said. – by Matt Hasson

Reference:

• Kamao TK, Yamaguchi M, Kawasaki S, Mizoue S, Shiraishi A, Ohashi Y. Screening for dry eye with newly developed ocular surface thermographer. Am J Ophthalmol. 2011;151(5):782-791.

• Masahiko Yamaguchi, MD, PhD, can be reached at Department of Ophthalmology, Medicine of Sensory Function, Ehime University Graduate School of Medicine, Toon, Japan; email: masahiko@m.ehime-u.ac.jp.
• Disclosure: Dr. Yamaguchi has no direct financial interest in the products discussed in this article, nor is he a paid consultant for any companies mentioned.