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Journal of the Optical Society of America A

Journal of the Optical Society of America A


  • Editor: Stephen A. Burns
  • Vol. 24, Iss. 5 — May. 1, 2007
  • pp: 1250–1265

Maximum permissible exposures for ocular safety (ANSI 2000), with emphasis on ophthalmic devices

François C. Delori, Robert H. Webb, and David H. Sliney  »View Author Affiliations

JOSA A, Vol. 24, Issue 5, pp. 1250-1265 (2007)

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After discussing the rationale and assumptions of the ANSI Z136.1-2000 Standard for protection of the human eye from laser exposure, we present the concise formulation of the exposure limits expressed as maximum permissible radiant exposure (in J cm 2 ) for light overfilling the pupil. We then translate the Standard to a form that is more practical for typical ophthalmic devices or in vision research situations, implementing the special qualifications of the Standard. The safety limits are then expressed as radiant power (watts) entering the pupil of the eye. Exposure by repetitive pulses is also addressed, as this is frequently employed in ophthalmic applications. Examples are given that will familiarize potential users with this format.

© 2007 Optical Society of America

OCIS Codes
(170.4460) Medical optics and biotechnology : Ophthalmic optics and devices
(330.3350) Vision, color, and visual optics : Vision - laser damage

Original Manuscript: August 10, 2006
Manuscript Accepted: September 26, 2006
Published: April 11, 2007

Virtual Issues
Vol. 2, Iss. 6 Virtual Journal for Biomedical Optics

François C. Delori, Robert H. Webb, and David H. Sliney, "Maximum permissible exposures for ocular safety (ANSI 2000), with emphasis on ophthalmic devices," J. Opt. Soc. Am. A 24, 1250-1265 (2007)

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  22. Class 1 lasers are those that cannot emit radiation in excess of the MP level for exposure durations longer than 2.7h(104s). There is no hazard. Class 2 lasers are those that cannot emit radiation in excess of the MP level (400-700nm) for exposure durations longer than 0.25s (aversion reflex). See ANSI Standard for complete classification.
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  39. The pupil factor P is not used explicitly in the Standard. For 400≥λ≥600nm and t≥0.7s, the pupil diameter is assumed to be 3mm, and the factor P is (7/3)2=5.44 (cell b; rounded down to 5.4 in the Standard). The Standard provides interpolations that we translated in Table (upper part): between 0.07s and 0.7s (cell a) and between 600 and 700nm (cell d). We added an interpolation for the combined interval 0.07≤t≤0.7s and 400≥λ≥600nm that was not covered in the Standard (cell c); P is then the product of the values in cells a and d, divided by 5.44.
  40. The discrepancy comes from reducing the source radiance from 100CBJcm−2sr−1 (ANSI Table 5b) to 20CBJcm−2sr−1 [ANSI Section 8.3(1)], and thus a factor of 5, to account for change in the pupil diameter instead of a factor 5.44 [ANSI Section 8.3(2)].
  41. Extrapolation of the MPΦ from cell 7 (Table ) toward shorter exposure durations intersects the MPΦ from cell 4a at a duration tex=2.75×10−3(CBα)1.33. The shortest value for tex occurs for CB=1(400<λ<450nm) and α=1.5mrad and equals 4.7ms.
  42. The IEC laser safety Standards defines CE differently from the ANSI Standard for large sources (CE,IEC=αmax/αmin for all α>αmax). The reason is that the IEC Standard emphasizes measurements and requires one to measure only the power or energy arriving within a cone angle of αmax; hence, CE is constant for larger angles. However, the ANSI Standard emphasizes calculations rather than measurements and therefore provides an ever-increasing CE for angles increasing beyond αmax.
  43. For a circular area with α≥αmax exposed with a radiant power Φtotal, the power Φin within a cone of angle αmax[Φin=(αmax/α)2Φtotal] is compared with the MPΦin calculated using CE=αmax/αmin. The factor CE is thus essentially replaced by (α/αmax)2(αmax/αmin)=(α2/αminαmax), identical to the value of CE for α≥αmax already incorporated into the Standard (Table II[a]). The method of "ignoring the power outside an αmax-cone" is identical to proper application of the current Standard for circular fields.
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