To study the effects of pulsed microwaves and the interaction of opthalmologic drugs (Timolol and Xalatan) on corneal endothelial damage in four adult Rhesus monkeys under anesthesia in order to confirm the results of previous studies (Kues et al. 1985 and Kues et al. 1992) reporting a microwave-induced corneal endothelial damage at a low threshold (2.6 W/kg). Additionally, previous studies reported that vasoactive ophthalmologic medications lowered the threshold by a factor of 10 to 0.26 W/kg.
A nine-exposure regimen was selected for experiment I. Drug sensitization of microwave-induced corneal endothelial injury in experiment II (one year later) followed the three-exposure regimen of Kues et al. (Kues et al. 1992).
In Experiment I, ophthalmologic examinations were conducted before and 7, 30, 90, and 180 days after exposures. In Experiment II, ophthalmologic examinations were done 7, 30, 90, and 180 days after exposures.
| Exposure | Parameters |
|---|---|
|
Exposure 1:
2.8 GHz
Modulation type:
pulsed
Exposure duration:
continuous for 4 hr/day, 3 days/week for 3 weeks
experiment 1
|
|
|
Exposure 2:
2.8 GHz
Modulation type:
pulsed
Exposure duration:
continuous for 4 hr/day on 3 or 7 days
experiment 2
|
|
Experiment 2 was executed one year after experiment 1. In experiment 2 subjects were pretreated with 0.5 % Timolol maleate and 0.005 % Xalatan(R) before exposure to pulsed microwaves
| Frequency | 2.8 GHz |
|---|---|
| Type | |
| Charakteristic | |
| Exposure duration | continuous for 4 hr/day, 3 days/week for 3 weeks |
| Additional info | experiment 1 |
| Modulation type | pulsed |
|---|---|
| Pulse width | 1.5 µs |
| Repetition frequency | 34 Hz |
| Exposure source | |
|---|---|
| Setup | rectangular waveguide connected to a 2.44 m x 3.66 m x 2.44 m anechoic chamber, lined with 15 cm Eccosorb cones; aluminum-flanged WR284 waveguide and a pressure plate located at the end of the microwave transmission line were used as an open-ended waveguide antenna; surface of the subject's eyes centerd in the boresight of the open-ended waveguide antenna at a distance of 20 cm |
| Measurand | Value | Type | Method | Mass | Remarks |
|---|---|---|---|---|---|
| power | 29 W | average over time | measured | - | - |
| power density | 13 mW/cm² | average over time | measured | - | - |
| power density | 464 mW/cm² | peak value | measured | - | - |
| power density | 14.2 mW/cm² | average over time | measured | - | at 20 cm from the pressure plate |
| Frequency | 2.8 GHz |
|---|---|
| Type | |
| Charakteristic | |
| Exposure duration | continuous for 4 hr/day on 3 or 7 days |
| Additional info | experiment 2 |
| Modulation type | pulsed |
|---|---|
| Pulse width | 1.5 µs |
| Repetition frequency | 34 Hz |
| Exposure source |
|
|---|
| Measurand | Value | Type | Method | Mass | Remarks |
|---|---|---|---|---|---|
| power | 29 W | average over time | measured | - | - |
| power density | 13 mW/cm² | average over time | measured | - | - |
| power density | 464 mW/cm² | peak value | measured | - | - |
| power density | 14.2 mW/cm² | average over time | measured | - | at 20 cm from the pressure plate |
The microwave exposure resulted in a 1.0-1.2°C increase in eyelid temperature, but the absolute temperature never exceeded 38°C, a level well below the known damage threshold. Pulsed microwave exposure did not cause alterations in corneal endothelial cell density and corneal thickness with or without ophthalmologic drugs.
Therefore, the authors conclude that previously reported changes in the cornea exposed to pulsed microwaves were not confirmed at exposure levels that are more than an order of magnitude higher.
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