Corneal Damage from Mid-Infrared Laser Radiation
Annual rept. 1 Apr 2003-31 Mar 2004
JOHNS HOPKINS UNIV LAUREL MD
Pagination or Media Count:
Corneal epithelial damage thresholds for exposures to sequences of pulses of 1.55 jim infrared radiation produced by an Er fiber laser were investigated. Thresholds were determined for sequences of 8 to 128 pulses at a repetition frequency of 10 Hz and 8 to 256 pulses at 20 Hz. The duration of the individual pulses was 0.025 sec and the 1e diameter of the laser beam was 0.1 cm. Threshold damage is correlated by an empirical power law of the form Hsub th CNexp -a, in which Hsub th is the threshold radiant exposure per pulse, and N is the number of pulses. The value of the exponent a is 0.32 for the 10 Hz exposures and 0.34 for the 20 Hz exposures. The constant C is 7.60 for the 10 Hz exposures and 5.99 for the 20 Hz exposures. Both values are greater than the estimated threshold for a single 0.025 sec pulse 4.90 Jsq cm. Thus the empirical power law breaks down for small numbers of pulses viz., N 8 where it overestimates the damage thresholds. An empirical critical temperature model also correlates the multiple-pulse injury thresholds.
- Anatomy and Physiology
- Medicine and Medical Research
- Lasers and Masers