Selective laser trabeculoplasty (SLT) is associated with morphologic and cellular changes that disrupt endothelial cells in the corneoscleral trabecular meshwork, a study published in Clinical Ophthalmology shows.

This study evaluated SLT in corneoscleral rim explants from human eye donors collected by the eye bank in New Jersey and in discarded corneoscleral rims following corneal transplantation. All donor tissues (n=12) were obtained from individuals aged between 47 and 62 years with no history of ocular disease. All tissues underwent SLT with a protocol comprising laser settings (532 nm wavelength, 0.6-1.2 mJ/pulse, 3.0 nsec pulse, and 400 μm spot size). Treated segments were compared with untreated segments by light, transmission electron, scanning electron, and confocal microscopy to evaluate morphologic and cellular changes.

At days 1 and 7 after treatment, light microscopy detected mild disruption of the superficial trabecular beams. Deeper beams were unaffected and the wall of Schlemm’s canal and scleral stroma were intact. Cell nuclei remained preserved. The pattern of alterations did not differ between days 1 and 7.


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At days 2 and 7 after treatment, scanning electron microscopy found superficial damage of the trabecular beams. At higher magnification, the deeper corneoscleral trabecular meshwork and uveal meshwork appeared intact. There was no evidence of disruption to the surrounding collagen scaffold or bleb formation, indicating no coagulative damage.

Transmission electron microscopy at day 1 after treatment found that some uveal trabecular beams had lost their endothelial cell coverage. By day 7, extracellular pigment particles, cellular debris, and intracellular contents were observed.

DNA synthesis did not differ at day 2 after treatment compared with controls (mean, 0.250 vs 0.454 mitotic cells/100 μm z-stack; P =.305), however, by day 7 the treated eyes tended to have increased DNA synthesis (mean, 2.074 vs 1.537 mitotic cells/100 μm z-stack; P =.358), respectively. This trend was observed in 5 of the 9 treated samples.

This study may have been limited by using a lower maximum laser power setting than the reference SLT study (1.2 vs 2.0 mJ).

“SLT results in disruption of the endothelial cells of the corneoscleral and uveal trabecular meshwork as well as superficial ultrastructural changes to the trabecular meshwork anatomy,” the researchers explain. “There is a trend towards dynamic time-dependent alterations in nuclear division and/or cell proliferation that ultimately lead to the observed increased outflow facility and intraocular pressure reduction. The pathway is likely multifaceted involving changes at the nucleic acid level. The exact cascade of events remains to be fully elucidated.”

Disclosure: Multiple authors declared affiliations with industry. Please refer to the original article for a full list of disclosures.

Reference

Gupta M, Heo JY, Gong H, Cha E, Latina M, Rhee DJ. Morphologic and cellular changes induced by selective laser trabeculoplasty. Clin Ophthalmol. 2022;16:1383-1390. doi:10.2147/OPTH.S342787