Corneal vs Retinal Limits
Which part of the eye limits a laser exposure from 180 nm to 1 mm: the largest safe power under the ICNIRP 2013 retinal and corneal limits, the retinal image size and the cornea-to-retina gain.
Educational only — not compliance-grade
These pages implement the published exposure limits for the cases each one states, but they are educational tools: no laser safety officer has signed them off.
- Do not use these results alone for PPE selection, NHZ / NOHD approval, controlled-area sign-off, enclosure/interlock approval, or formal classification.
- Always verify against ANSI Z136.1, IEC 60825-1, your local procedures, and the responsible laser safety officer / CLSO.
Retina: max power
208 mW
Retina, thermal
Cornea / lens: max power
201 mW
Anterior eye (skin limit, 2 × in the IR)
Tissue at risk first
Cornea / lens
Anterior eye (skin limit, 2 × in the IR)
Retinal image diameter
25.5 µm
no smaller than 25.5 µm (α_min × 17 mm)
Retina / cornea irradiance gain
75356×
vs the corneal irradiance over 7 mm
Retinal irradiance at that power
4.07e+8 W/m²
before absorption in the eye
Which part of the eye limits the exposure, from the ICNIRP 2013 eye limits (Health Phys. 105:271, Tables 3, 5 and 8). From 400 to 1400 nm the cornea and lens pass the beam and the eye focuses it on the retina; ICNIRP puts the cornea-to-retina irradiance gain for a point source at about 100 000. Here the eye is a 17 mm lens that focuses a TEM₀₀ beam to 4λf/(πd), but never below 25.5 µm (α_min = 1.5 mrad), so the gain is (7 mm / image)², at most 7.5×10⁴. In the UV and from 1400 nm the cornea and lens absorb the beam and only the corneal limits apply. From 700 nm twice the skin limit also protects the cornea and lens (Table 5 note d; in the visible only for a large source); ICNIRP 2013 (p. 281) checks both limits from 1150 nm. Averaged, the anterior-segment limit binds only from about 1300 nm (for t ≥ 10 s; about 1360 nm for ns pulses) to 1400 nm, where C_C raises the retinal limit as water absorbs more. Each limit is a corneal exposure averaged over its aperture (7 mm retinal, 3.5 mm anterior, 1 → 3.5 mm corneal), except that a beam under 1 mm (1/e diameter) is held to its peak on the anterior segment and, below 0.35 s, on the cornea (ICNIRP Table 5 note c, Table 7 note b), so a narrow infrared beam can be anterior-limited well below 1300 nm. The max power is for this beam, staying within the limit at every duration up to t. Absorption in the ocular media is not modelled.
Largest power of this beam within the retinal and the corneal limits, 180 nm to 20 µm, for the chosen time. The lower curve governs.
Model and references
Textbook approximation. A standard approximation from the literature (for example paraxial, plane-wave or Gaussian-beam), valid within the range the page states. About the tiers
Limits: ICNIRP 2013, point source (exact). Retinal image: a 17 mm eye focusing a TEM₀₀ beam to 4λf/(πd), at least 25.5 µm (α_min); no absorption in the eye. Pulse trains not covered.
- ICNIRP (2013). Guidelines on limits of exposure to laser radiation of wavelengths between 180 nm and 1,000 µm. Health Phys. 105(3), 271–295. Tables 2, 3, 5 and 8. doi:10.1097/HP.0b013e3182983fd4
- Sliney, D. H. & Wolbarsht, M. L. (1980). Safety with Lasers and Other Optical Sources. Plenum, New York. The 17 mm reduced eye. doi:10.1007/978-1-4899-3596-0