I hope someone may clarify to me a question regarding this paper:

Review of exposure limits and experimental data for corneal and lenticular damage from short pulsed UV and IR laser radiation. Schulmeister K, Sliney DH, Mellerio J, Lund DJ, Stuck BE, Zuclich JA. Journal of Laser Applications, Volume 20, Number 2, page 98-105

Figure 2 shows experimental photochemical threshold data points for exposure of monkey and rabbit corneas to incoherent radiation, as well as thresholds for exposure to short pulsed laser radiation (resulting from photochemical damage photokeratitis) together with the ICNIRP broadband exposure limit and the laser MPE for photochemical damage.

The text states:

"The thresholds refer to an endpoint of barely detectable increased haze observed with a slit lamp biomicrsoscope 24 h after exposure"

Reference 1: International Commission on Non-Ionizing Radiation Protection ICNIRP, “Guidelines on Limits for Laser Radiation of Wavelengths between 180 nm and 1000 um,” Health Phys. 71, 804–819 1996 states "Generally an order of magnitude factor between the ED-50 and the exposure limit was thought to provide an adequate margin of protection against significant or subjectively detectable acute injury".

From above mentioned figure 2, it seems the threshold for 355nm laser radiation is ~30-40J/cm2, whereas the MPE for laser radiation is 1J/cm2.

Further the article states that "as is typical of photochemical damage, the threshold for

corneal damage, expressed as radiant exposure J m−2, does not depend on the pulse duration or exposure duration over a very wide range from nanoseconds to thousands of

seconds".

I understand from this, that irradiating with 35J/cm2 will induce barely detectable increased haze observed with a slit lamp biomicrsoscope 24 h after exposure, and that irradiating below 1J/cm2 provides an adequate margin of protection against significant or subjectively detectable acute injury.

If 35J/cm2, I would expect that with 17.5J/cm2 the hazard for damage being very low, but MPE is far lower.

From the MPE of 1J/cm2 and the "order of magnitude" ICNIRP, I may interpret that 10J/cm2 already represents a risk.

How to reconcile these two values and, above all, below which exposure level may I be safe against corneal epithelium damage?