Problems With Determining Safe Limits

Since you have likely only received the standard single (1) pair of eyeballs and replacement isn't yet feasible (or covered by major health insurance plans!), trying to figure out if your laser is a hazard to vision by staring into its beam is a really really bad idea. Many factors can result in it being way to late before you discover that your vision has been harmed.
Note that even a wavelength considered eye-safe like 1,500 nm (1.5 um) is only safe in the sense that this light won't penetrate to the back of the eye and be focused on the retina. A high enough power density can still obliterate the cornea and/or lens!

There are a variety of problems with doing experiments to determine safe levels of optical radiation incident on the eye. Here are some:

• Subjects are generally not aware of any retinal damage until they notice that parts of the visual field of one eye are blind. The visual system does a good job of providing us with the illusion of perfect vision, in spite of deficits. There is little or no pain in most instances.
• There are individual differences in tolerance.
• Absorption of energy varies with wavelength.
• The blink reflex comes into play for visible sources.
  

Related Topics:

• You Only Received One Set of Eyeballs?
• Intensity of a 1 mW Laser versus the Sun
• Why a 1 mW Helium-Neon Laser Still Appears Bright a Mile Away
• Problems With Determining Safe Limits