Nonuniform Exposure to the Cornea from Millimeter Waves

Health physics · 2021 · Harm · Low evidence

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HarmLow evidencePaper 1183

Study snapshot

PublicationHealth physics · 2021

Study typeexposure_assessment

Reported directionHarm

Evidence ratingLow

Abstract

Nonuniform Exposure to the Cornea from Millimeter Waves Kenneth R Foster, Ilkka Laakso, Steven Chalfin. Nonuniform Exposure to the Cornea from Millimeter Waves. Health Phys. 2021 May 1;120(5):525-531. doi: 10.1097/HP.0000000000001376. Abstract This study examines the nonuniform exposure to the cornea from incident millimeter waves at 94-100 GHz. Two previous studies measured temperature increases in the rhesus cornea exposed to brief (1-6 s) pulses of high- fluence millimeter waves (94 GHz), one of which also estimated thresholds for corneal damage (reported as ED50, the dose resulting in a visible lesion 50% of the time). Both studies noted large variations in the temperature increase across the surface of the cornea due to wave interference effects. This study examines this variability using high-resolution simulations of mm-wave absorption and temperature increase in the human cornea from exposures to plane wave energy at 100 GHz. Calculations are based on an earlier study. The simulations show that the peak temperature increases in the cornea from short exposures (up to 10 s) to high- intensity mm-wave pulses are 1.7-2.8 times the median increase depending on the polarization of the incident energy. A simple one-dimensional "baseline" model provides a good estimate of the median temperature increase in the cornea. Two different estimates are presented for the thresholds for producing thermal lesions, expressed in terms of the minimum fluence of incident 100 GHz pulses. The first estimate is based on thresholds for thermal damage from pulsed infrared energy, and the second is based on a thermal damage model. The mm- wave pulses presently considered far exceed current IEEE or ICNIRP exposure limits but may be produced by some nonlethal weapons systems. Interference effects due to wave reflections from structures in and near the eye result in highly localized variations in energy absorbed in the cornea and surrounding facial tissues and are important to consider in a hazard analysis for exposures to intense pulsed millimeter waves. pubmed.ncbi.nlm.nih.gov Discussion Both IEEE C95.1-2019 and ICNIRP (2020) specifically limit the fluence of brief, high intensity mm-wave pulses to avoid excessive temperature rises. The limits discussed below refer to power densities measured outside the body, which are defined in ICNIRP 2020 as “reference levels” and in IEEE as “exposure reference levels.” For 2-s pulses of mm-waves, IEEE C95.1-2019 (IEEE 2019) has fluence limits of 0.28 and 1.4 kJ m−2 for persons in unrestricted or restricted environments (equivalent to general public and occupational limits). The corresponding limits in ICNIRP (2020) (for 100 GHz pulses) are 1.7 and 8.6 kJ m−2 for general public and occupational exposures, respectively. All of the exposures in Table 2 far exceed these limits. Exposures summarized in Table 2 would be acutely painful (Beuerman and Talenian 1979) and would trigger blink reflexes in most (but perhaps not all) awake subjects that would protect them from corneal damage. However, interference effects will also cause nonuniform absorption patterns away from the cornea, which is apparent in Fig. 1. In their corneal damage studies on rabbits, Kojima et al. (2009) noted significant thermal damage to the eyelids as well, to the extent that the eyelids had to be held open with tape during exposure to obtain reproducible corneal damage data. When analyzing potential hazards from the Active Denial nonlethal weapons system or other sources of intense mm-wave exposures, local enhancements in exposure due to interference effects over an appropriate range of subjects and exposure parameters would need to be considered.

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AI evidence extraction

Structured fields below were generated from the paper’s abstract and metadata to make the evidence easier to inspect. Automated extraction may be incomplete or incorrect; verify important details against the original paper.

Study typeexposure_assessment

Effect directionharm

PopulationHuman cornea (simulations); prior animal studies referenced (rhesus cornea; rabbits)

Sample sizeNot supplied

ExposuremmWave · 100000 MHz · short exposures (up to 10 s); brief (1–6 s) pulses referenced

Evidence strengthLowConfidence: 74% · Peer reviewed: yes

Main findings

High-resolution simulations at 100 GHz indicated that for short, high-intensity pulses (up to 10 s), peak corneal temperature increases were 1.7–2.8 times the median increase depending on polarization. The paper presents two estimates of minimum incident-pulse fluence thresholds for producing thermal lesions and notes that the pulses considered far exceed current IEEE C95.1-2019 and ICNIRP (2020) limits; interference/reflection effects can create highly localized absorption variations relevant for hazard analysis.

Outcomes measured

Simulated spatial variability of mm-wave absorption in cornea
Simulated corneal temperature increase distribution (peak vs median)
Estimated fluence thresholds for thermal lesions in cornea
Comparison of considered pulse exposures to IEEE/ICNIRP fluence limits

Limitations

Simulation-based analysis; empirical validation in humans not described in the abstract
Threshold estimates are derived from pulsed infrared damage thresholds and from a thermal damage model (model-based)
Details of exposure parameters and results tables are not provided in the abstract

View raw extracted JSON

{
  "study_type": "exposure_assessment",
  "exposure": {
    "band": "mmWave",
    "source": "nonlethal weapons systems",
    "frequency_mhz": 100000,
    "sar_wkg": null,
    "duration": "short exposures (up to 10 s); brief (1–6 s) pulses referenced"
  },
  "population": "Human cornea (simulations); prior animal studies referenced (rhesus cornea; rabbits)",
  "sample_size": null,
  "outcomes": [
    "Simulated spatial variability of mm-wave absorption in cornea",
    "Simulated corneal temperature increase distribution (peak vs median)",
    "Estimated fluence thresholds for thermal lesions in cornea",
    "Comparison of considered pulse exposures to IEEE/ICNIRP fluence limits"
  ],
  "main_findings": "High-resolution simulations at 100 GHz indicated that for short, high-intensity pulses (up to 10 s), peak corneal temperature increases were 1.7–2.8 times the median increase depending on polarization. The paper presents two estimates of minimum incident-pulse fluence thresholds for producing thermal lesions and notes that the pulses considered far exceed current IEEE C95.1-2019 and ICNIRP (2020) limits; interference/reflection effects can create highly localized absorption variations relevant for hazard analysis.",
  "effect_direction": "harm",
  "limitations": [
    "Simulation-based analysis; empirical validation in humans not described in the abstract",
    "Threshold estimates are derived from pulsed infrared damage thresholds and from a thermal damage model (model-based)",
    "Details of exposure parameters and results tables are not provided in the abstract"
  ],
  "evidence_strength": "low",
  "confidence": 0.74,
  "peer_reviewed_likely": "yes",
  "keywords": [
    "millimeter waves",
    "mm-wave",
    "cornea",
    "100 GHz",
    "94 GHz",
    "fluence",
    "pulsed exposure",
    "temperature increase",
    "thermal lesions",
    "interference effects",
    "polarization",
    "IEEE C95.1-2019",
    "ICNIRP 2020",
    "Active Denial"
  ],
  "suggested_hubs": [
    {
      "slug": "5g-policy",
      "weight": 0.35,
      "reason": "Focuses on mmWave (94–100 GHz) exposure and compares to IEEE/ICNIRP limits; relevant to mmWave safety discussions."
    },
    {
      "slug": "who-icnirp",
      "weight": 0.6,
      "reason": "Explicit discussion of ICNIRP (2020) and IEEE exposure/fluence limits for brief high-intensity mm-wave pulses."
    }
  ]
}

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AI-extracted fields are generated from the abstract and metadata and may be incomplete or incorrect. This material is for informational purposes and is not medical advice.

Identifiers and source

DOI: 10.1097/hp.0000000000001376
PubMed: 33760769

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