Ophthalmic Lasers Part 2

Canaloplasty

  • microcatheter, placed in Schlemm’s canal to enlarge drainage canal

Tube shunt implant surgery

  • implanting shunt and aqueous drains through a valve into a filtering bleb

Enhancing fluid outflow: GATT, Kahook Tabectome, iStent (20% reduction)

Microtrabeculectomy (shunt fluid outside eye): XEN Gel stent, Preserflow

Excimer laser Trabeculotomy (ab interno) - MIGS

  • Characteristics (excimer)

    • short UV (193 um) cold laser

    • precision, no collateral tissue damage, nanosecond pulses

  • Method of action

    • enhances aqueous outflow (0.5 mm holes)

    • through TM including inner wall of schlemm’s canal

  • Indications: pts on max medical therapy, refractory POAG, long term lowering of IOP

    • can be performed with lensectomy

    • maintains integrity of TM and schlemm’s canal

  • Contraindications

    • narrow angles, iris neo

    • inadequate view of TM on gonio

    • advanced VF defects (scotoma within 10 degrees of fixation)

  • Procedure

    • 1.2 mm limbal incision made temporally + nasally

    • viscoelastic used to protect endothelium

    • excimer laser tip contacts TM and makes 8 spots (anterior trabecula), equally spaced at 500 um

Laser cyclophotocoagulation surgery

  • Methods: transscleral, transpupillary, endolaser (TTE)

  • Mean IOP dropped by 50.3 %

  • Indications:

    • later stage glaucoma (meds not effective), failure of other filtering surgeries, painful blind eye, alleviation of pain in neovascular glaucoma

  • Procedure

    • Nd:YAG laser with scleral endoscopic probe (50-80 micropulses, 0.5ms duration)

    • destruction of ciliary epithelium to REDUCE aqueous production

    • retrobulbar anesthesia: bupivicane, lidocaine

  • Complications

    • eye pain, photophobia

    • RD, hypotony, phthisis

    • loss of BCVA, macular edema, scleral thinning

    • inflammation

Anterior vitreolysis (aka laser floater removal)

Three P’s: photocoagulation, photodisruption, photoactivation

  1. Photocoagulation (Excimer laser)

    • laser absorbed by RPE (chromophore) and produces heat to denature proteins

    • thermal energy - coagulative necrosis

    • outer retinal layers more affected!

  2. Photodisruption (Femtosecond laser)

    • energy released in short time and small retinal area

    • acoustic wave disrupts tissue

  3. Photoactivation (PDT)

    • chemical

    • PDT uses IV-injected green dye called Vertporfin (chemically inert) but activated by light and destroys neovascular tissue

    • used for wet AMD

Types of lasers

  1. Focal laser treatments: macula edema due to focal retinal vessel leakage

  2. GRID laser treatments: macular edema due to DIFFUSE leakage

  3. panretinal laser treatment (PRP): treat PDR (uses ruby argon lasers) - 500 um sized

PanRetinal Photocoagulation

Grading of laser vascular coagulation (PRP)

  1. MINIMAL visible constriction of vessel

  2. total constriction and SPASM of vessel

  3. total constriction of vessel WITH coagulation of surrounding tissue

  4. total constriction, CHARRING vessel, COAGULATION of surrounding tissue

  • Complications

    • painful during/ immediately after t/x

    • inflammatory events

    • retinal architecture distorted

    • disrupts normal retinal connectivity

    • decreased VF (especially in periphery)

Pattern scanning laser (PASCAL)

  • Nd: YAG solid state laser (56 spots in 0.5 secs)

  • delivers multiple laser spots with shorter pulse duration in preset pattern

    • Less energy needed

    • less choroidal heating

    • less patient discomfort than classic PRP woohoo!

    • predetermined pattern helps to reduce retinal injury than just random firing of laser

Retinal detachment lasers

  • Causes/ risks of Retinal detachments

    • axial myopia

    • lattice degeneration (30% associated w/ rheg RD)

    • trauma

    • cataract surgery

    • PVD/ traction (10-20% risk)

    • idiopathic

  • Goals

    • generate firm chorio-retinal adhesion surrounding the retinal break

    • counter vitreoretinal traction

    • prevent liquefied vitreous from passing into subretinal space

  • Healing

    • 8 hours post op - RPE 50% weaker

    • 18 hours post op - RPE improved to 100%

    • 5 days post op*** - maximal strength achieved!!

  • Complications

    • laser hitting macula

    • choroidal effusion, angle closure glaucoma, ERM

    • Ant seg burns, hemorrhage, CNVM, new retinal breaks

  • Follow ups

    • BIO about 3 weeks after treatment

    • retreatment needed if: scarring incomplete, retinal break or subretinal fluid present