Download Laser Therapy for Glaucoma

Laser and Surgical Therapy for Glaucoma
Joseph Sowka, OD, FAAO, Diplomate
Specific Laser- Tissue Interactions:
Photocoagulation:
 Laser is focused on pigmented tissue to be treated.
 Pigment (melanin) dependent
 Light is absorbed and converted into heat.
 When tissue is warmed by 10-20 degrees centigrade, photocoagulation occurs. Effects may
take hours to appreciate. Blood is coagulated and inflammation is produced which serves to
create desired scarring and adhesions (seal leakages).
 Tissue atrophy arises surrounding each photocoagulation scar (PRP)
 Photocoagulation warms collagen, stimulating it to contract. This changes the microanatomy
of the tissue (e.g. The trabecular meshwork in trabeculoplasty and the iris in iridoplasty)
 Argon and krypton lasers
Photovaporization:
 Dependent upon light absorption by pigment.
 Higher powered laser delivered in brief bursts with local temperature rises to 60-100 degrees
centigrade. This reduces tissue to CO2 and H2O and vapor is created
 The only time photovaporization is desirable is for thermal iridotomies
 In thermal laser photocoagulation, photovaporization is an undesirable side effect from over
treating with too much power.
 Argon and krypton lasers
Photodisruption:
 Non-pigment dependent
 Considered non-thermal.
 Involves the delivery of large amount of energy into very small focal spots in very brief
duration (nanoseconds to picoseconds).
 Done in the infrared spectrum.
 Instantaneous, highly localized temperature rise occurs (15,000 degrees centigrade).
 Heating is so quick that no outward dissipation occurs.
 Molecules and atoms are stripped of their electrons and ionization occurs.
 Photodisruption involves optical-breakdown. Light energy causes a tissue to be reduced to a
form of matter called plasma. This results in the generation of fluid forces described as
hemodynamic waves. Acoustic pulses (sound waves) are also produced. The forces
propagate outward in all directions (but especially back in the direction from which the laser
was shot). The propagating forces incise tissues.
 Coagulation does not occur.
 This is the basis for Nd:YAG capsulotomies and iridotomies.
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Complications Associated with Anterior Segment Laser Procedures:
 Elevation of IOP from intraocular inflammation
 Pre- and post-treatment with aqueous suppressers (apraclonidine, Alphagan, beta
blockers, CAI's) and steroids.
 Corneal burn
 Retinal detachment
 Intraocular hemorrhage
 Glaucomatous vision loss due to post procedure IOP rise.
Clinical Pearl: Complication rate is a factor of the total cumulative laser energy delivered
into the eye.
Laser Therapy for Open Angle Glaucoma:
Argon Laser Trabeculoplasty (ALT):
 Thermal laser alteration of the trabecular meshwork to increase aqueous outflow
 Indicated for:
 Pseudoexfoliative glaucoma
 Pigmentary glaucoma
 Primary open angle glaucoma
 Non-compliance with meds
 Inadequate medical control
 Not indicated for
 Angle recession glaucoma
 Developmental glaucoma
 Uveitic glaucoma
 Neovascular glaucoma
 Traumatic glaucoma
 ICE syndromes
 Steroid induced glaucoma
 Non-visible trabecular meshwork (but there are ways around this)
 Significant peripheral anterior synechia
 Corneal edema
 Anterior segment inflammation
 Non-pigmented trabecular meshwork
Pressure Lowering Effect of ALT:
 Etiology is truly unknown, but theories abound
A. Laser burns cause stretching of trabecular meshwork between the burns, which opens the
meshwork, pores and allows aqueous to flow better.
B. Laser burns attract phagocytes that clean up the debris within the meshwork and allows
aqueous to flow better.
C. Laser destroyed endothelial cells stimulate the production of new, more viable endothelial
cells.
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ALT will fail over time - ephemeral
Retreatment generally not beneficial
Selective Laser Trabeculoplasty (SLT)
 532 nm frequency doubled, Q-switched, Nd:YAG Laser
 Laser seems to stimulate the cells in the trabecular meshwork that have not been cleaning out
the debris and dividing into new cells.
 New cells are much more vigorous about cleaning out the meshwork.
 Wavelength that targets just the pigment in the trabecular meshwork. It provides the effect of
the argon laser with less injury to the inside of the eye.
 SLT & ALT are equivalent in their capacity to decrease the IOP in glaucoma patients
 Produces different effects at the treatment site
 ALT induces mechanical alterations, due to collateral thermal effects
 SLT induces no apparent tissue alterations, due to the lack of such thermal effects
 It is believed that SLT can be performed more than once, but this is unproven. Most will
only repeat one time.
 Lack of coagulative necrosis produced by SLT is related to the nanosecond duration of each
pulse and the selective targeting of melanin chromophores
 Application of SLT obliterated macrophages, leaving the non-pigmented lining TM cells
intact
Laser Therapy for Closed Angle Glaucoma:
Argon Laser Iridoplasty:
 Irido-retraction procedure
 Seen to be successful in breaking attack of acute angle closure
 Successful in phacomorphic glaucoma and plateau iris syndrome
 Long duration, low powered burns in circular pattern along far peripheral iris to scar iris and
cause iris to shrink and pull away from angle.
 ALT can be performed immediately afterwards, if necessary
Laser Peripheral Iridotomy (LPI): Indications:
 Angle closure with pupil block
 Create a communication between the anterior and posterior chambers to equalize the
pressure
 Relieve pupillary block
 Prophylaxis in narrow, occludable angles
Argon Laser LPI:
 Photocoagulation (long duration at low energy) extended to photovaporization (long duration
at high energy - burning of tissue)
 Unlikely to bleed
 Less likely to disrupt lens and vitreous
 Difficult (if not impossible) to penetrate iris
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Pigment dependent (contraindicated in blue irides)
More likely to close with time
Clinical Pearl: You cannot perform argon laser on a blue iris.
Nd:YAG Laser LPI:
 Photodisruption (short duration at high energy)- explosion of tissue
 More likely to bleed
 More likely to disrupt lens and vitreous
 Much easier to penetrate iris
 Less likely to close with time
 Pigment independent (can be used in blue irises)
Glaucoma Surgery -Trabeculectomy
 Also known as filtering surgery
 Creates a fistula through the trabecular meshwork and creates a communication between the
anterior chamber and the subconjunctival space. This creates another channel for aqueous to
exit the chamber. An iridectomy is also performed so that the iris doesn’t block and adhere
to the surgical filter.
 Aqueous bypasses the trabecular meshwork (which, in glaucoma, doesn’t process aqueous
properly) and rushes out to accumulate within the subconjunctival space. This creates a
“blister” on the conjunctiva (typically superior) called a “bleb”. The aqueous is then
absorbed by the conjunctival and episcleral vessels. The bleb should be elevated (not flat)
and avascular. A flat bleb indicates that the surgery is not working (likely from postoperative scarring). A vascularized bleb indicates that the site has become infected
(endophthalmitis) or inflamed (blebitis). Common complications of filtering surgery are flat
anterior chambers and hypotony (with possible choroidal effusion) due to over secretion or
poor wound closure. A common cause of failure is scarring of the filtering site.
Antimetabolites (mitomycin C and 5-Fluorouracil) are used in order to inhibit fibroblast
proliferation and reduce scarring so that the filter functions. However, they may work too
well in that no scarring occurs and the filter works too well with attendant hypotony and flat
chambers.
Anti-metabolites: Mitomycin C and 5-Fluorouracil
 Inhibit fibroblasts (prevents scarring after filtration surgery) - prevents closure of the
surgically created fistula due to scar formation. Used solely in filtration surgery.
 5-fluorouracil (5-FU): injected subconjunctivally during post-op.
 Mitomycin c: used intraoperatively in very controlled amounts. Problems:
 High degree of toxicity.
 Can work too well and prevent wound healing with resulting hypotony
 Most common anti-metabolite used today
 Extremely high rate of surgical complications
 These medications are only used surgically
 These medications create thin blebs with cellophane-like conjunctival membranes which are
prone to rupture, leakage, and endophthalmitis
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Considerations for Surgery
 Maximal medical therapy and progression
 Poor patient compliance with medications
 Failure or contraindication of LT
 Need for very low IOP
Signs of Surgical Failure
 Hypotony from wound leak
 Hypotony from over secretion
 Shallow anterior chamber with low IOP (sign of would leak or overfiltration)
 Residual elevated IOP
 Bleb encapsulation
 Localized, highly elevated, opalescent thick walled bleb with moderate to marked
vascular engorgement.
 IOP elevated
 Known as Tenon’s cyst
 Develops from proliferation of noncontractile collagen-producing fibroblasts – is
not the same as scarring and antimetabolites have no effect
 Over filtration
 Hypotony with a diffuse extensive bleb without wound leak
 Ciliochoroidal detachment
 Occurs due to imbalance between fluid pressure within the eye and the choroidal
vasculature. Hypotony yields transudation of fluids across the capillary walls of
the choroid to collect in the potential space between the uvea and sclera.
 Steroids and cycloplegics
 Posterior sclerotomy
 Cyclodialysis
 Ciliary body becomes disinserted from its attachment at the scleral spur
 Cycloplegics to reappose the tissues
Management of the Leaking Bleb
 Use of aqueous suppressants
 Reduces aqueous production and subsequently reduces the transconjunctival
filtration, which allows sealing of the wound
 Reduction in corticosteroids, if used
 Antibiotics
 Reduces risk of infection
 Aminoglycosides can cause allergic reactions with subsequent inflammation to
stimulate wound healing
 Large diameter soft contact lens
 Reduces lid movement across wound
 Simmons shell can be used, but much less comfortable
 Pressure patch
 Tamponades and encourages reepithelialization
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Cyanoacrylate tissue adhesive
Autologous blood
 Injected into subconjunctival space
 Raises IOP, improves vision, improves choroidal detachment
Chemical cauterization
 Produces irritation to induce inflammation and healing
Clinical Pearl: Following trabeculectomy, a shallow chamber and low IOP indicate
overfiltration or bleb leakage. However, a shallowing chamber and rising IOP
indicate malignant glaucoma.
Glaucoma Drainage Devices
 Molteno tube, Barvaelt tube, Krupin valve, Ahmed valve
 Tube is inserted into anterior chamber, which drains aqueous to a plate (made of
material that inhibits fibroblast attachment and scarring) buried beneath
conjunctiva
 Scarring less likely
 Indicated for high risk cases (uveitis, youth, previous trabeculectomy failure
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