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S. J. Fudemberg, J. S. Myers, L. J. Katz; Trabecular Meshwork Tissue Examination With Scanning Electron Microscopy: A Comparison of Micropulse Diode Laser (MLT), Selective Laser (SLT), and Argon Laser (ALT) Trabeculoplasty in Human Cadaver Tissue. Invest. Ophthalmol. Vis. Sci. 2008;49(13):1236.
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© ARVO (1962-2015); The Authors (2016-present)
To compare the tissue effect of MLT with that of SLT and ALT in the trabecular meshwork of human donor corneoscleral rim tissue.
Three human donor corneoscleral rims remaining after use in keratoplasty at the Wills Eye Institute Surgery Center were collected, preserved in Optisol for less than 24 hours, and examined for the presence of trabecular meshwork (TM) with even 1-2+ pigmentation by slit lamp biomicroscopy. Rims were then marked into quarters with approximately 90 degrees of TM treated by ALT (50microns/0.8-1W/0.1s), SLT(400microns/1.2mJ/3ns), MLT (300microns/2W/200microseconds/15% duty cycle). The remaining TM was left as a control. Samples were fixed and prepared for scanning electron microscopy (SEM) using standard techniques.
During laser application, direct visualization revealed whitening of pigmented TM with each ALT spot, champagne bubbles with each SLT spot, and no visible changes with MLT. ALT created 60-70 micron craters in the trabecular meshwork with scrolling and whitening of tissue around each crater. Neither SLT nor MLT left identifiable changes of the TM with SEM.
ALT causes coagulative and structural damage of the TM evident on SEM. In contrast, SLT has been shown to cause no structural damage of the TM on SEM. However, cracking of pigment granules in the cytoplasm of pigmented TM cells has been demonstrated on transmission electron microscopy following SLT. By micropulsing a diode laser, thermal spread of laser energy is minimized and coagulative effects may be avoided. This study shows that, at the tested settings, SLT and MLT cause no evident morphologic change, including no coagulative damage, to the TM in human cadaver tissue.
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