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M. Fukuda, H. Sasaki, N. Takahashi, M. Yoshikawa, M. Kojima, K. Kitagawa, Y. Sakamoto, K. Sasaki; Evaluation of Corneal Injury by the Contact Lens Electrodes. Invest. Ophthalmol. Vis. Sci. 2009;50(13):911. doi: https://doi.org/.
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© ARVO (1962-2015); The Authors (2016-present)
To evaluate the corneal resistance (CR) and the correlation between topical timoptol concentration in the aqueous humor and CR by the newly developed contact lens electrodes.
A contact lens electrode was used to measure the CR in albino rabbits. Two concentric gold wire electrodes were attached to the inner surface of a contact lens and served as bipolar electrodes (Mayo Corporation; Aichi, Japan). The electrodes delivered electrical pulses to the cornea, and also measured the resistance between the electrodes. The electrical current was generated by an electronic pulse generator and was delivered through a constant current isolator (BSI-2; BAK Electronics, INC. USA). The parameters of the current were; frequency=1000 Hz, waveform=biphasic square wave pulses, duration=5 ms, and current= ± 50 µA. In Experiment 1, 0.5% timoptol ophthalmic solution with 0, 0.125, and, 0.5 mg/ml benzalkonium chloride (BAK) was applied to the rabbit cornea 3 times at 15-minute intervals. The change in the relative CR (CR at test time/CR before BAK) was measured as the corneal injury recovered in real time. The CR at 2, 30, and 60 min after the final instillation was determined. The changes in the corneal epithelium were confirmed by fluorescein staining of the cornea by slit-lamp biomicroscopy. In Experiment 2, 0.5% timoptol ophthalmic solution with 0 or 0.125 mg/ml BAK was dropped on the cornea of rabbit eyes 3 times at 15-min intervals. The timoptol concentration in the aqueous was measured at 60 min by high performance liquid chromatography (HPLC).
Experiment I. The relative CR in the eyes with topical 0.5% timoptol solution with 0, 0.125 and 0.5 mg/ml BAK were 99.9%, 99.0% and 61.8% at 2 min, 99.6%, 92.0% and 81.8% at 30 min, and 100%, 95.0% and 100% at 60 min, respectively. The slight corneal fluorecein staining in the corneal epithelial was observed only in the eyes with topical 0.5% timoptol solution with 0.5 mg/ml BAK at 2 min. Experiment 2. After applying 0.5 mg/ml of BAK to the cornea, the timoptol concentration in the aqueous humor was 5.6±2.9 µg/ml which was significantly higher than the 3.7±1.3 µg/ml after 0 mg/ml of BAK (n=12; P<0.005).
The result of the timoptol concentration in the aqueous humor was correlated with results of the relative CR obtained by this instrument. The contact lens electrode is useful for measuring the function of the corneal epithelium with very slight damage by eye drops.
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