A C T A O P H T H A L M O L O G I C A VOL. 5 3 1 9 7 5

The Ophthalmological Department, (Head: Professor T . L. Thomassen), Univeristy o f Oslo, Rikshospitalet, Norway

IN

CORNEAL TEMPERATURE NORMAL SUBJECTS AND ARTERIAL OCCLUSIVE DISEASE BY

WAR HBRVEN

A direct, thermo-electrical method of corneal temperature recording is presented. The corneal temperature averaged 33.7OC in normal subjects, with no side difference and no difference between the sexes. The various parameters which may influence the corneal temperature are discussed. The technique was applied to groups of patients suffering from either polymyalgia rheumatica, central retinal artery embolism or temporal arteritis. In the latter group of patients a marked drop in corneal temperature was demonstrated in the affected. or most affected, eye. Corneal temperature measurements are therefore presented as an easy and effective diagnostic approach in temporal arteritis. Key words: age - arterial occlusive disease - arteritis temporalis - central retinal artery embolism - corneal temperature - ocular temperature oral temperature - temperature - thermistor probe.

In 1900 Hertel observed a 0.78OC drop in ocular temperature in rabbits following a 3 min compression of the ipsilateral common carotid artery, thus demonstrating that the temperature, at least in the anteriqr part of the eye, is dependent upon the ocular blood supply. Colle et al. (1931) found a 2-4OC decrease in anterior chamber temperature following ipsilateral internal carotid artery occlusion in cats and dogs. When they applied compression over the abdominal aorta, Received September 27, 1975.

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Ivar Horven

thus forcing. more blood to the animal's head, a corresponding increase in ocular temperature was noted. In four patients with monolateral carotid artery stenosis, Mapstone (1968a) demonstrated lower corneal temperatures on the affected side. The decrease averaged 1.0"C (0.8-1.2). These studies indicate that accurate recording of corneal temperature may be used as a valuable clinical approach to the diagnosis of the arterial occlusive diseases affecting the ocular blood supply. In order to proclaim pathological results, a proper knowledge of the corneal temperature pattern in normal subjects is mandatory. A control group is therefore included in the present study.

Instrumentation The corneal temperature was recorded by a specially constructed thermistor probe (Harven & Larsen 1975) and a Brush Mark 220 recorder. T he equipment yielded an output of 13.6 mV per "C. With a recorder sensitivity setting of either 5 or 2 mV per paper division, the temperature tracings could be read with an accuracy of 0.ZoC, or less than 0 . l o C , respectively (Harven & Larsen 1975).

Methods Allowing proper time to equilibrate in the room in which the temperature was kept between 21.5-24.5"C, the subject was placed in the supine position and given two drops of oxibuprocain 0.40/0in each eye. A reference temperature was recorded by placing the thermistor probe in water with known temperature. Afterwards, the water remaining on the probe tip was removed. T he subject was asked to blink, and a recording was performed first on the central part

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Fig. 1. Corneal temperature measurement in a normal subject. Sensitivity setting: 2 mV per paper division.

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Corneal Temflcrature in Arterial Diseases

of the right cornea, then on the left. Another reference temperature was recorded, the probe tip cleaned and, following blinking, the corneal temperature measurements were performed in reversed order. Then subsequent reference temperatures were recorded, and the probe tip cleaned with ethanol. T he oral temperature was measured by the use of a mercury thermometer.

Material Control material. Forty normal subjects were examined, eight in each of the 10-year age groups between 20 and 70 years. There were 22 women and 18 men. Polymyalgia rheumatica. Nine consecutive patients with polymyalgia, elevated erythrocyte sedimentation rate but without ocular symptoms were included. The average age was 66.1 years (52-86). Central retinal artery (CRA) embolism. Eight consecutive patients with a fresh, monolateral retinal artery embolism were measured. Two of the patients had a branch occlusion, the others had a complete CRA-occlusion. The average age was 65.3 years (54-75). Temporal arteritis. Seven consecutive patients with a biopsy-proven temporal arteritis were included, four had bilateral and three monolateral eye involvement. Two of the patients were examined 4 years after steroid treatment had started, at a time when the ocular blood supply had returned to fairly normal levels as judged by the dynamic tonometry results (Hsrven 1973). The corneal indentation pulse amplitudes, which initially were low, had at this time improved to almost a normal level. The other five patients had an active disease. The average age was 74.5 years (68-78).

Results Control material. All of the normal subjects were examined with a recorder sensitivity setting of 2 mV per paper division, as seen in Fig. 1 . The average corneal temperature on the right side was 33.74OC (32.25-34.9) and on the left side 33.67"C (32.0-34.9). The difference in average temperature between the two eyes was 0.07"C, which was not statistically significant as judged by the statistical method of paired comparison (t = 0.463). T he standard deviation (s. d.) of the side difference was 0.23"C, indicating that a side difference above 2.58 . 0.23OC = 0.59"C will normally be found in less than one out of a hundred 865 Acta ophthal. 53, G

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Ivar Hsrven

subjects. A repeated side difference between the two eyes of 0.6"c or more is therefore accepted as pathological. T he average corneal temperature was 33.67"c in women and 33.83OC in men, the difference was not statistically significant (Student's t-test, t = 0.828). As demonstrated by Braendstrup (1952), measuring corneal temperature on one eye initiates an increase in the recorded corneal temperature of the other eye. She suggested the term "reflectory increase" for this temperature rise, although its origin is obscure. A similar temperature rise was found in the present study, as seen in Table I and Fig. 1 . In the first sequence, the average corneal temperature of the second, left eye was 0.295"c higher than that of the first recorded eye. Dilring the time required for reference temperature recording, the recorded temperature of the left eye dropped to the value first recorded in the right eye. However, an increase occurred in the right eye too, when this eye was recorded last in the second sequence. This increase averaged 0.435OC. Therefore, in order to minimize the influence of this temperature rise, the procedure suggested in the present study, to record the average values of two sequences of which the second is performed in reversed order, should be followed. In order to test the possible relationship between corneal temperature, age and environmental factors, the results from the 40 right eyes were used, as seen in Fig. 2. The oral temperature averaged 36.67"C (36.1-37.3) and the room temperature 23.13"C (21.5-24.5). A positive correlation was demonstrated both between corneal and oral temperature and between corneal and room temperature, as seen in Fig. 2. Age. A negative correlation was found between age and corneal temperature, significant at the 0.1 O/o level, as seen in Fig. 2. Table I1 offers the results from the various 10-year periods. The decrease in corneal temperature with age is

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Fig. 2. Positive correlation between cornea (y) and room (x) temperature: y = 0 . 3 7 2 ~+ 25.13 (r = 0.431, P 0.01). Positive correlation between corneal (y) and oral (x) temperature: y = 0 . 9 3 2 ~- 0.45 ( r = 0.399, P 0.02). Negative correlation between oral temperature (y) and age (x): y = - 0 . 0 0 6 1 ~+ 36.94 (r = - 0.324, P < 0.05). Negative correlation between corneal temperature (y) and age (x): y = - 0 . 0 2 3 ~+ 34.74 (r = - 0.523, P 0.001).

Corneal temperature in normal subjects and arterial occlusive disease.

A direct, thermo-electrical method of corneal temperature recording is presented. The corneal temperature averaged 33.7 degrees C in normal subjects, ...
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