Retinal image motion during deliberate fixation: implications to laser safety for long duration viewing

Area of Science:

• Ophthalmology
• Biophysics
• Optical Engineering

Background:

• Increasing accessibility of laser devices and light-emitting diode (LED) technology necessitates updated safety standards for prolonged light source viewing.
• Quantifying the impact of head and eye motion on retinal energy distribution is crucial for understanding potential hazards.

Purpose of the Study:

• To analyze retinal target motion resulting from head and eye movements during deliberate fixation tasks.
• To quantify the distribution and reduction of retinal radiant exposure under varying fixation conditions.

Main Methods:

• Volunteers performed deliberate fixation tasks on small visual targets (0.1 min of arc) with and without head/chin rest support.
• A Dual Purkinje Image Eyetracker recorded eye position during 100-second fixation trials.
• Retinal energy distribution and radiant exposure were analyzed based on measured eye and head movements.

Main Results:

• An elliptical retinal energy distribution was observed, oriented temporally/nasally, with a major axis 1.5 times the minor axis.
• The average half-maximum diameter of the major axis was 40 micrometers (fettered) and 107 micrometers (unfettered).
• Retinal radiant exposure at 100 seconds was reduced by factors of 10 (eye movement) and 30 (head and eye movement), remaining within the 200-micrometer foveal boundary.

Conclusions:

• Head and eye movements significantly reduce peak retinal radiant exposure over time.
• The observed retinal energy distribution, though elliptical, stays within safe foveal limits.
• Laser permissible exposure limits for continuous wave sources should incorporate adjustments for movement-induced radiant exposure reduction.