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Abstract
To compare the histopathologic changes in the human trabecular meshwork (TM) after
argon laser trabeculoplasty (ALT) and selective laser trabeculoplasty (SLT) with a
Q-switched, frequency-doubled, neodymium:yttrium-aluminum-garnet laser.
Human "in vitro" experimental study. TISSUE AND CONTROLS: Eight human autopsy eyes
were obtained within 18 hours of death from persons aged 71 to 78 years.
The anterior segment of autopsy eyes was isolated, and one half of each trabecular
meshwork underwent SLT and the other half ALT. Specimens were evaluated with scanning
and transmission electron microscopy.
Structural changes in the TM were detected by scanning electron microscopy, and cellular
or intracellular changes were seen with transmission electron microscopy.
Evaluation of the TM after ALT revealed crater formation in the uveal meshwork at
the junction of the pigmented and nonpigmented TM. Coagulative damage was evident
at the base and along the edge of craters, with disruption of the collagen beams,
fibrinous exudate, lysis of endothelial cells, and nuclear and cytoplasmic debris.
Evaluation of the TM after SLT revealed no evidence of coagulative damage or disruption
of the corneoscleral or uveal trabecular beam structure. Minimal evidence of mechanical
damage was present after SLT, and the only ultrastructural evidence of laser tissue
interaction was cracking of intracytoplasmic pigment granules and disruption of trabecular
endothelial cells.
SLT applied "in vitro" to the TM of human eye bank eyes seemed to cause no coagulative
damage and less structural damage to the human TM when compared with ALT and, therefore,
may be a safer and more repeatable procedure.