EFFECTS OF EXPOSURE

Exposure of the eyes to laser energy generally leads to two categories of effects.

1. Visual interference effects
2. Ocular injury (persistent anatomic or visual function abnormalities)

Incident with Temporary Visual Interference Effects

These effects are the result of wavelengths in the visible spectrum (400-700 nm). The wavelength or color of the source is associated with the degree of immediate visual function disruption following an exposure. This is because the human eyes spectral response to color varies across the visible spectrum. We see the color green much better than blue or red. Our response to color even varies with lighting conditions. The vision we use under well-lit, daytime conditions is called photopic vision and under low-light levels, nighttime conditions is called scotopic vision. For example, green light is capable of producing visual function disruption with less relative power than red light at similar distances. Effects include temporary flashblindness, afterimages, and glare. They also include startle, distraction, and disruption, effects that may not directly degrade vision but may have an effect on human performance. These effects are more pronounced when a person is exposed at night or in a dark environment.

Visual interference effects include:

1. Flash blindness - A visual interference effect that persists as an afterimage after the source of illumination has ceased.
2. Glare – An obscuration of an object in a person’s field of vision due to a bright light source located near the same line of sight.
3. Afterimage - A transient image that persists in one’s visual field after a bright source of illumination has been removed.
4. Startle – The involuntary reaction to an unexpected event that alters mental, physical, and visual activities and diverts selected attention away from the normal primary tasks of an individual. The startle response can be broken into four specific categories: Distraction, Disruption, Disorientation, and Operational Incapacitation.
   - Distraction – Momentary attention shift from primary tasks due to sudden exposure to a bright light source. This effect may not be readily identified by the Service member and should be asked specifically.
   - Disruption – Interference or interruption of critical tasks or task sequences that extend the shift of attention from primary tasks requiring selective attention.
   - Disorientation – Losing perspective in the relationship between the direction of travel and surroundings. Can include loss of both spatial orientation and situational awareness. Disorientation can occur simultaneously with distraction, disruption, and startle.
   - Operational Incapacitation – An individual’s loss of spatial orientation and loss of situational awareness in reference to the outside world. In the case of aviation, a pilot that becomes operationally incapacitated should immediately transfer control of their aircraft because they can no longer reliably discern or control the aircraft.

The natural aversion response to bright light sources limits exposure to visible wavelength lasers to about 0.25 seconds. Although exposure may be limited to a fraction of a second by your ability to blink or turn away from the offending light source it does not provide absolute protection from injury.

Incident with Suspected Ocular Injury

An ocular injury can result from any laser wavelength if sufficient power is delivered to the eye. The affected structure within the eye varies with wavelength. Lasers emitting in the far ultraviolet, UV-B and UV-C (180-315 nm), and far infrared, IR-B and IR-C (1400 nm – 1 mm), are absorbed by the cornea. Near ultraviolet, UV-A (315-400) wavelengths are absorbed by the lens of the eye. Visible (400-700 nm) and near infrared, IR-A (700-1400 nm) wavelengths are absorbed by the retina. The spectral region 400-1400 nm is commonly referred to as the retinal hazard region. Laser output power, or energy, is an important determinant for injury potential, as is the duration of the exposure and the exposed person’s location relative to the laser source exit aperture.

OPTICAL DEVICES

Vision enhancement devices, such as Night Vision Devices, provide an additional barrier between the laser and the eyes which can provide a degree of protection. However, they can be more sensitive to interference from intense light sources, both visible and non-visible wavelengths, especially compared to the unaided eye. This can cause difficulty with the device’s operation and significantly affect safety.

Optical scopes, or other devices with magnifying optics, may amplify or further focus the light source, leading to more energy delivered to the eye and increased risk of injury.