Laser induced bubble formation in the retina.
OBJECTIVE
The immediate thermodynamic effects of absorption of a laser pulse in the retina are theoretically studied to understand underlying physical damage mechanisms at threshold fluences. Damage is most likely to occur at threshold levels in the retinal pigment epithelium due to the strong absorption by the melanosomes.


METHODS
The retinal pigment epithelium is modeled as an aqueous environment with absorption occurring at small spherical sites with absorption coefficients representative of melanosomes. For laser pulse durations of less than 10(-6) seconds, heat conduction is negligible during energy deposition and the resulting large energy density in the melanosomes will cause vaporization of the medium immediately surrounding a melanosome.


RESULTS
We developed expressions for calculating the size of bubbles produced as a function of pulse characteristics and melanosome properties. We show that for pulse durations between 10(-6) and 10(-9) seconds, bubble formation will occur for laser fluences that are smaller than those required to cause Arrhenius-type thermal damage.


CONCLUSIONS
Bubble formation is likely to be the mechanism of threshold damage to the retina for laser pulses durations in the time regime between 10(-6) and 10(-9) seconds.
Gerstman
B S
BS
Department of Physics, Florida International University, Miami 33199, USA.
Thompson
C R
CR
Jacques
S L
SL
Rogers
M E
ME
D000042:Absorption; D000388:Air; D000465:Algorithms; D004735:Energy Transfer; D006358:Hot Temperature / Q000009:adverse effects; D006801:Humans; D007834:Lasers / Q000009:adverse effects*; D008544:Melanocytes / Q000473:pathology; D008954:Models, Biological; D010857:Pigment Epithelium of Eye / Q000293:injuries / Q000473:pathology; D011312:Pressure; D012160:Retina / Q000293:injuries* / Q000473:pathology; D013816:Thermodynamics; D013997:Time Factors; D014835:Volatilization