Cat model for intraocular pressure reduction after transscleral Nd:YAG cyclophotocoagulation

Abstract

Transscleral neodymium:yttrium-aluminum-garnet (Nd:YAG) laser cyclophotocoagulation (TSNYC) is used to lower intraocular pressure (IOP) in glaucoma patients refractory to conventional medical and surgical therapy. Our study investigates the ability of TSNYC to lower IOP in normal cats. One eye of 13 cats was treated with non-contact TSNYC. Mean pretreatment IOP was 25 mm Hg (vs. 25.3 mm Hg in contralateral control eyes). Eyes received 80 laser applications over 360 degrees delivered at least 3 mm posterior to the limbus with maximum power (8 to 9 joules) and maximum retrofocus (3.6 mm). Eyes were retreated if IOP was not reduced below baseline after 2 weeks. By 4 weeks, IOP was decreased in all treated eyes by a mean of 29.2% and was maintained as long as 20 weeks (mean decrease 14.8%). IOP in 10 eyes was lowered after a single treatment session. Of these, 2 eyes had IOP spikes > 10 mm Hg prior to IOP reduction. Three cats required retreatment to maintain IOP reduction. All eyes developed transient (< 4 weeks) postoperative uveitis and 3 eyes developed rubeosis iridis which resolved with topical corticosteroids. Histologic examination (6 weeks post-treatment) showed focal disruption of the pigment epithelium and to a lesser degree the nonpigmented epithelium at the base of the ciliary body and in the valleys of the pars ciliaris. The epithelium at the apices of the ciliary processes appeared intact. Vascular engorgement was variably present. This study demonstrates that TSNYC lowers IOP in cats. This animal model will be useful for investigating mechanism(s) responsible for TSNYC-induced IOP reduction.

Effects of cyclophotocoagulation with a neodymium:yttrium-aluminum-garnet laser on corneal sensitivity, intraocular pressure, aqueous tear production, and corneal nerve morphology in eyes of dogs

“…Lower amounts of energy (< 100 J) have been associated with only transient reduction of IOP. 5,48 Because of variations among subjects, amounts of power, exposure times, and degree of scleral and uveal pigmentation, it is difficult to define an optimal treatment protocol. 5,48,49 In the study reported here, as expected, there was a significant decrease in IOP in treated eyes at most time points after laser treatment.…”

“…5,48 Because of variations among subjects, amounts of power, exposure times, and degree of scleral and uveal pigmentation, it is difficult to define an optimal treatment protocol. 5,48,49 In the study reported here, as expected, there was a significant decrease in IOP in treated eyes at most time points after laser treatment. The significant decrease in corneal sensitivity seen on all days after laser treatment documented that lower total energy delivery (eg, 100 J) is able to compromise corneal sensitivity.…”

Feline glaucoma—a comprehensive review

“…In addition, there appears to be marked inter‐individual variation in the location of the ciliary processes relative to the limbus in glaucomatous cats and bupthalmia may further enhance this variation. In one experimental study, cyclophotocoagulation with Nd:YAG laser led to a mean reduction in IOP of about 30% in normal cats 86 . However, the chronic nature of IOP elevation in most glaucomatous cats and variable degree of associated globe enlargement make it difficult to determine the most appropriate site for trans‐scleral laser or cryosurgical application based solely on knowledge of the anatomy of normal cats.…”

“…In one experimental study, cyclophotocoagulation with Nd:YAG laser led to a mean reduction in IOP of about 30% in normal cats. 86 However, the chronic nature of IOP elevation in most glaucomatous cats and variable degree of associated globe enlargement make it difficult to determine the most appropriate site for trans-scleral laser or cryosurgical application based solely on knowledge of the anatomy of normal cats. Pre-operative ultrasound biometry, as an aid to determining the location of the ciliary body in individual glaucomatous cats, could feasibly increase the success rate of surgical, cyclodestructive procedures.…”

Histologic effect of semiconductor diode laser transscleral cyclophotocoagulation on the normal equine eye

“…The goal of this procedure is the coagulation of the ciliary epithelium and stroma of the pars plicata where aqueous humor is produced, without causing marked architectural disruption and loss of anatomic integrity 19 . TSCP has been reported in dogs, 20–27 cats, 28,29 horses, 7,13,30 rabbits 31,32 and humans 33–38 . It is theorized that the reduction in IOP associated with TSCP is the result of destruction of the ciliary epithelium thereby reducing aqueous production 39,40 .…”