Trabecular Meshwork Alteration and Intraocular Pressure Change Following Pulsed Infrared Laser Trabeculoplasty in Cats

Abstract

Abstract: : Purpose: To comparatively assess safety and variation in IOP of 2 pulsed near infrared (IR) lasers, Titanium:Sapphire (Ti–S) and Alexandrite (Alx) for laser trabeculoplasty versus conventional blue–green Argon laser trabeculoplasty (ALT) in an animal model. Methods: The left eyes of 15 healthy cats received a 180 degree laser trabeculoplasty treatment: 5 cats were treated with a Ti:S, 5 with an Alx and 5 with ALT. Laser energy was set for slight blanching of the treated trabecular meshwork (TM). One cat received a sham treatment. Preop, all animals underwent extensive ocular examination, including tonometry (Tonopen and pneumotonometry), pachymetry, gonioscopy, and slit–lamp examination. Exams were repeated at 1 hr, 1 day, 7 days, and weekly thereafter. 2 animals of each laser group were sacrificed after 4 weeks, the remaining after 12 weeks. SEM and LM histology were performed to evaluate potential alterations in the TM structure. Results: IOP at 1 hour, 1 day and 1 week post treatment was remarkably lower, irrespective of the laser source (1 week: Ti:S: – 21.6%; Alx: –16.6%; Argon: –18.5%). IOP at 3 weeks was significantly lower with IR laser trabeculoplasty compared to ALT. Following treatment with both IR lasers depigmentation in the area of the treated TM developed and could be detected postoperatively by gonioscopy. With time, depigmentation of the laser spots increased in size, some reaching confluence. ALT treated eyes displayed slight blanching of the treated tissue in the very early postoperative phase. Histology evaluation of ALT eyes showed focal scarring of the inner portion of the sclera adjacent to the TM. Those changes could not be found after IR laser treatment, although decrease in pigment density were observed in treated areas. With SEM no damage to the TM structure was detected after treatment with IR lasers. Conclusions: Ti:S and Alx laser trabeculoplasty were found to be effective to temporarily lower IOP in cats. The lasers selectively altered pigment containing cells, avoiding structural damage of the TM anatomy. CR: None Support: Florida Lions Eye Bank; Research to Prevent Blindness NY; Henri and Flore Lesieur Foundation; SOLX Boston; FWF Austrian Science Fund.

Keywords: trabecular meshwork • laser • intraocular pressure