Laser Surgery And Glaucoma Flashcards
Historically, how are lasers viewed for glaucoma
Drops until failure, then laser, then invasive surgery
Advantages of glaucoma drops
- choices
- effective
- familiar to patients and well received
Disadvantage of glaucoma drops
- compliance
- cost
- side effects
Glaucoma laser trial (GLT)
Timolol-ALT for newly diagnosed POAG
SLT/Med study
SLT is a variable first line treatment for POAG
UpToDate
We recommend pharmocologic laser therapy as first line treatment
Academy of ophthalmology and laser for glaucoma
Lasers can be considered as initial therapy in selected patients
OD role in laser surgery for glaucoma
- initial diagnosis
- intimate drops
- perform laser
- decision to refer for surgery (educate patient on expectations, outcomes)
Information for the referral for surgery
- max IOP
- IOP on current treatment
- current meds and any that were previously ineffective or not tolerated
- baseline and current VF
- baseline and correct OCT
- gonio findings
- eye surgery/injury history
Laser variables that’s influence interaction
- wavelength
- spot size
- pulse duration
Tissue variables that’s influence interaction
Transparency
Pigment
Laser variables
Wavelength
- varies by laser (YAG vs ARGON)
- determines which tissue is impacted
Spot size
-smaller=higher density
Pulse duration
-sometimes variable (argon); sometimes fixed (YAG)
Tissue variables
Transparency
-depends on wavelength
Pigment
- argon: pigment absorbed laser light and converted energy to heat
- more pigment=better absorption
Selective laser trabeculoplasty (SLT)
- wavelength output is 532nm green
- burn time is 3ns
Thermal relaxation time of SLT
Amount of time it takes melanin to convert light energy to heat
1micro second
SLT pulse duration is
3 nanoseconds
Thermal damage of SLT
No thermal damage, “cold laser”
What does SLT target
Intracellualr melanin
Effect on adjacent non melanin containg cells in SLT
No effect. “Selective”
Proposed mechanism of SLT
- targetcels activate cytokines, which activate macrophages
- macrophages clean area, decreasing outflow resistance
- no mechanical damage/scars (unlike ALT). Potentially repeatable
Trabeculoplasty recommendations
- POAG
- OHTN
- NTG
- pigment dispersion glaucoma
- PXG
Predicting SLT success
Looked at
-pre treatment IOP, current meds, phakic status, level of pigmentation, steroid use, age, gender
MIGS
Minimally invasive glaucoma surgery
-mild-mod glaucoma
Conventional surgery
More invasive
Moderate-sever glaucoma
What is MIGS
- minimal truama/disruption to normal anatomy
- Ab interno, micro incisional approach
- modest IOP reduction
- safe
- often combined with cataract surgery (and sometimes multiple MIGS prcoredures)
- rapid post op recovery
- first FDA approval in 2012
- now 15 different techniques
iStent
MIGS
- inserted from AC into schlemms canal. Creates channel from AC to schlemms
- increases aqueous outflow by bypassing the TM
Trabectome
- MIGS
- electrocautery device used to perform partial trabeculotomy
- TM and interior wall of schlemms canal are cauterized and eliminated
Endocyclophotocoagulation (ECP)
- MIGS
- a laser probe is used to destroy the anterior ciliary processes
Transscleral cyclophotocoagulation (CPC)
- MIGS
- laser energy is delivered at he limbus through the sclera and to the ciliary process
ECP and CPC both do what
Decrease aqueous production
Xen gel stent
- 6mm tube
- inserted from AC, through schlemms canal, into subconjunctival space
- creates a bleb
Difference between ALT and SLT
ALT has a longer burn time and causes burn damage to the TM. Not repeatable
SLT actually causes macrophages to come in and act like drane-o without burn damage. Repeatable
Incisional surgery
- more invasive than MIGS
- historically, the only surgical options
- tubes (aqueous tube shunt) and trabs (trabeculectomy)
Tube shunts
- divert aqueous humor to an external reservoir
- baerveldt vs Ahmed
- external incision through conjunctiva and tenons capsule
- implant is placed subconjunctivally with the tube entering the anteiror chamber
-otomy
Cutting into, putting a hole in
Ectomy
Removing tissue
Endo
Camera used for surgeon to see tissue
Cyclo
CB
Photo
Laser or light energy
Bleb
Between sclera and conjunctiva for aqueous to collect
Filtering blebs
Xen gel stent
Trabeculectomy
- the most establishes (oldest) of these procedures
- surgeon creates an opening into the AC from underneath a scleral flap
- aq flows into the subconjunctival space and creates a filtering bleb
- no tube is placed. Mitomycin C (MMC): antimetabolite; prevents fibrosis and grab failure
Tubes vs trabs
TVT study; similar IOP reduction
-trabs have higher failure rate (complications, need for more surgery, NLP vision)
Increasing usage of tubes over past 20 years
Post op care of MIGS
- similar to cataract surgery
- 1 day, 1 week, 1 month
- check for inflammation and infection
- judge IOP repsosne at 1 month. Consider reducing meds
Post op care of icisional surgery
The ideal bleb
- low lying
- minimal vascualrity
- IOP in teens
- well formed AC
- negative Seidel sign
Bleb complications
Hypotony
- IOP less than 5mmHg
- no visible bleb
Bleb leak
-positive Seidel test
Blebitis
- milky white bleb
- pain, blurry vision
- if AC and or vitreous involved-endopthalmitis
Tube complications
Same a bleb complications
Also diplopia
-tube plate is placed near EOMs
Micropulse diode laser trabeculoplasty(mDLT)
- delivers small, repetitive micropiulses rather than one continuous pulse
- cooling periods between micropulses reduces tissue damage
Annual low-power SLT for OHTN
- repeatedly yearly, regardless of IOP level
- followed 3-10 years
- mean treated IOP similar to transitional SLT
- fewer patients needed medications to control IOP vs traditional SLT
