Visible retinal lesions from ultrashort laser pulses in the primate eye

To evaluate the effects of ultrashort laser pulses of visible wavelengths on the retinas of rhesus monkey eyes and to perform threshold measurements for minimum visible lesions (MVLs) at pulsewidths from nanoseconds to femtoseconds.

Single laser pulses at visible wavelengths were placed within the macular area of live rhesus monkey eyes at varying pulse energies at five pulsewidths (4 ns, 60 ps, 3 ps, 600 fs, and 90 fs). The number of visible lesions was determined after 1 hour and 24 hours postexposure, and a probit analysis was performed for the dosage, causing 50% probability for damage (ED50) as well as the 95% fiducial intervals for ED50. Fluorescein angiography (FA) was performed, and hemorrhagic lesions were recorded as they became visible.

The ED50 threshold doses at the 1-hour reading, calculated from the measured data, decreased from 1.5 microJ at 4 ns to 0.60 microJ at 600 fs, but it increased to 1.18 microJ at 90 fs. At the 24-hour reading, the ED50 calculated doses decreased from 0.90 microJ at 4 ns down to 0.26 microJ at 600 fs, but it increased to 0.43 microJ at 90 fs. Fluorescein angiography visible lesion ED50 values were all higher than MVL values, showing that FA was not as sensitive in determining damage levels.

Laser pulses for pulsewidths between 4 ns and 90 fs are capable of producing visible lesions in monkey eyes with energies less than 1 microJ. Fluorescein angiography is not as sensitive in determining threshold levels as visually observing the retina through a fundus camera.